Genetics
Introduction to Genetics
Slide 1 – Introduction
Now that we understand how chromosomes are divided to produce egg and sperm, let’s begin
looking at genetics. The first branch of genetics we will study is Mendelian genetics. Mendelian
genetic is named for Gregor Mendel a monk who lived in the 1800’s. He worked during a time
when no one knew anything about chromosomes and DNA, but he was able to determine the
very basics of how traits are inherited. He did his work in the monastery garden on pea plants.
Interestingly he presented his work to the scientific community and they were unable at the time
to understand how important his work was. Mendel’s work was lost for almost 50 years.
Slide 2 – Dominant versus recessive
In order to understand Mendelian genetics, we need to define some terms. Traits can either be
recessive or dominant. Dominant traits mask or cover up other traits. If a dominant trait is
present, this is what we will see. In the common abbreviation used in inheritance, dominant
traits are represented with capital letters. Recessive traits are masked or covered up by dominant
traits. Recessive traits are presented by lower case letters.
Slide 3 – Mendel’s Principles
What did Mendel actually figure out from studying his pea plants? Fist he found out that
heredity is not blending; he found that traits come in either a recessive or dominant form.
Mendel also figured out that there are units of heredity. Today we know these units of heredity
as genes. He determined that every individual has a pair of these units for each trait. This means
that you have two copies of each gene for each trait. Remember the homologous chromosomes?
One came from your mother and one came from your father. Each has a gene for the same trait,
like eye color. What we know from Mendel’s work is that you have two copies, but they don’t
need to be identical. For example, your mother could have given you a gene for blue eyes, while
your father gave you a gene for brown eyes. Different forms of the gene are celled alleles.
During meiosis, the homologous chromosomes separate; therefore so do the alleles. Half of the
gametes produced by you would have the allele for blue eyes and the other half would have the
allele for brown eyes. This is why we say the egg and sperm are haploid. When the egg and
sperm come together a new diploid organism is formed.
Slide 4 – Alleles
Let’s review what an allele is. An allele is a form of a gene. Recessive alleles will be
represented by a lower case letter, while dominant alleles will be represented by a capital letter.
Slide 5 – Homozygous versus heterozygous
You have two alleles for each trait. You received one from your mother and one from your
father. If the two alleles you have are the same, you are homozygous. If the alleles are of the
dominant form, then you are homozygous dominant. If both your alleles are the recessive form,
then you are homozygous recessive. If you have one dominant allele and one recessive allele,
then you are heterozygous. The only time you can see a recessive trait is when the individual is
homozygous recessive, because there are no other traits to mask the recessive trait.
Slide 1 – Introduction
Now that we understand how chromosomes are divided to produce egg and sperm, let’s begin
looking at genetics. The first branch of genetics we will study is Mendelian genetics. Mendelian
genetic is named for Gregor Mendel a monk who lived in the 1800’s. He worked during a time
when no one knew anything about chromosomes and DNA, but he was able to determine the
very basics of how traits are inherited. He did his work in the monastery garden on pea plants.
Interestingly he presented his work to the scientific community and they were unable at the time
to understand how important his work was. Mendel’s work was lost for almost 50 years.
Slide 2 – Dominant versus recessive
In order to understand Mendelian genetics, we need to define some terms. Traits can either be
recessive or dominant. Dominant traits mask or cover up other traits. If a dominant trait is
present, this is what we will see. In the common abbreviation used in inheritance, dominant
traits are represented with capital letters. Recessive traits are masked or covered up by dominant
traits. Recessive traits are presented by lower case letters.
Slide 3 – Mendel’s Principles
What did Mendel actually figure out from studying his pea plants? Fist he found out that
heredity is not blending; he found that traits come in either a recessive or dominant form.
Mendel also figured out that there are units of heredity. Today we know these units of heredity
as genes. He determined that every individual has a pair of these units for each trait. This means
that you have two copies of each gene for each trait. Remember the homologous chromosomes?
One came from your mother and one came from your father. Each has a gene for the same trait,
like eye color. What we know from Mendel’s work is that you have two copies, but they don’t
need to be identical. For example, your mother could have given you a gene for blue eyes, while
your father gave you a gene for brown eyes. Different forms of the gene are celled alleles.
During meiosis, the homologous chromosomes separate; therefore so do the alleles. Half of the
gametes produced by you would have the allele for blue eyes and the other half would have the
allele for brown eyes. This is why we say the egg and sperm are haploid. When the egg and
sperm come together a new diploid organism is formed.
Slide 4 – Alleles
Let’s review what an allele is. An allele is a form of a gene. Recessive alleles will be
represented by a lower case letter, while dominant alleles will be represented by a capital letter.
Slide 5 – Homozygous versus heterozygous
You have two alleles for each trait. You received one from your mother and one from your
father. If the two alleles you have are the same, you are homozygous. If the alleles are of the
dominant form, then you are homozygous dominant. If both your alleles are the recessive form,
then you are homozygous recessive. If you have one dominant allele and one recessive allele,
then you are heterozygous. The only time you can see a recessive trait is when the individual is
homozygous recessive, because there are no other traits to mask the recessive trait.
Introduction to Genetics
Slide 6 – Genotype versus phenotype
Two more term that you need to know are genotype and phenotype. The genotype is the alleles
present in an individual. Unless you are homozygous recessive for a trait, you probably do not
know your genotype. The term heterozygous and homozygous refer to genotype.
The phenotype is what an individual looks like. For example, your phenotype would be whether
you have blue or brown eyes. If you have a dominant phenotype, you can either be homozygous
dominant or heterozygous.
Slide 7 – Check Your Understanding
Now that we have learned about genes and alleles, let’s check your knowledge of the subject.
The following slides will have a series of questions on the topic. Be sure to click “Submit” after
answering each question.
Slides 8 through 18 – Genes and Alleles Interactive Quiz
A non–graded assessment of your knowledge of genes and alleles.
Slide 19 – Punnet squares
Now that we have mastered terminology, let’s look at how we can determine the genotypes and
phenotypes of offspring. To determine the genotype and phenotype, we are going to use a device
called a Punnet square.
Slide 20 – Ear lobe attachment
Let’s see how to use a Punnett square by using an easily observable trait. The trait we will
observe is ear attachment. Unattached ear lobes are dominant to attached ear lobes; therefore
individuals with unattached ear lobes can have the genotype EE or Ee. Attached ear lobes have
the genotype ee.
Slide 31 – Punnett square
Let’s see what would happen if two people that are heterozygous for ear lobe attachment had
children. Both of the parents have the genotype Ee. This means that half of the mother’s eggs
would have the E allele and the other half would have the e allele. Half of the father’s sperm
would have the E allele and the other half would have the e allele.
Slide 22 – Punnett square
To make a punnett square we will place the possible alleles from the mother across the top of the
square and the possible alleles from the father along the left side of the square. Now it is like
cross multiplying.
Slide 23 – Punnett square
In the first square the mother contributes an E and the father contributes an E. The child has the
genotype EE.
Slide 24 – Punnett square
In the second square in the first row, the mother contributes an e, while the father contributes an
E, so the child has an Ee genotype.
Slide 6 – Genotype versus phenotype
Two more term that you need to know are genotype and phenotype. The genotype is the alleles
present in an individual. Unless you are homozygous recessive for a trait, you probably do not
know your genotype. The term heterozygous and homozygous refer to genotype.
The phenotype is what an individual looks like. For example, your phenotype would be whether
you have blue or brown eyes. If you have a dominant phenotype, you can either be homozygous
dominant or heterozygous.
Slide 7 – Check Your Understanding
Now that we have learned about genes and alleles, let’s check your knowledge of the subject.
The following slides will have a series of questions on the topic. Be sure to click “Submit” after
answering each question.
Slides 8 through 18 – Genes and Alleles Interactive Quiz
A non–graded assessment of your knowledge of genes and alleles.
Slide 19 – Punnet squares
Now that we have mastered terminology, let’s look at how we can determine the genotypes and
phenotypes of offspring. To determine the genotype and phenotype, we are going to use a device
called a Punnet square.
Slide 20 – Ear lobe attachment
Let’s see how to use a Punnett square by using an easily observable trait. The trait we will
observe is ear attachment. Unattached ear lobes are dominant to attached ear lobes; therefore
individuals with unattached ear lobes can have the genotype EE or Ee. Attached ear lobes have
the genotype ee.
Slide 31 – Punnett square
Let’s see what would happen if two people that are heterozygous for ear lobe attachment had
children. Both of the parents have the genotype Ee. This means that half of the mother’s eggs
would have the E allele and the other half would have the e allele. Half of the father’s sperm
would have the E allele and the other half would have the e allele.
Slide 22 – Punnett square
To make a punnett square we will place the possible alleles from the mother across the top of the
square and the possible alleles from the father along the left side of the square. Now it is like
cross multiplying.
Slide 23 – Punnett square
In the first square the mother contributes an E and the father contributes an E. The child has the
genotype EE.
Slide 24 – Punnett square
In the second square in the first row, the mother contributes an e, while the father contributes an
E, so the child has an Ee genotype.
Introduction to Genetics
Slide 25 – Punnett square
In the first square of the second row, the mother contributes an E, while the father contributes an
e, therefore the child has the genotype Ee.
Slide 26 – Punnett square
In the final square, each parent contributes an e, so the child has the genotype ee.
Slide 27 – Genetics Questions
From this punnet square, there are several questions that can be asked. I could ask what
percentage of the children have unattached ear lobes. The answer to this question would be 75%.
This is because three of the four boxes have least one dominant allele.
Slide 28 – Genetics Questions
I could also ask what percentage of the children are heterozygous. The answer to this question is
50%, since two of the four boxes have the genotype Ee.
Slide 29 – Genetics Questions
Another question that I could pose is the ratio of the dominant allele to the recessive allele. The
answer would be 3:1, since three of the boxes have a dominant allele and only one has recessive
alleles only.
Slide 30 – Genetics Questions
I could also ask what the ratio of homozygous dominant to heterozygous to homozygous
recessive. The answer to this question is 1:2:1. When doing genetics questions, be sure you are
doing what is being asked.
Slide 31 – Genotypic and phenotypic ratios
The discussion on the previous slide was about genotypic and phenotypic ratios. Phenotypic
ratios ask you to show the number of children that would have the dominant phenotype
compared to the number of children that would have the recessive phenotype. Genotypic ratios
ask you show the number of children who are homozygous dominant compared to the number of
children who are heterozygous compared to the number of children who are homozygous
recessive.
Slide 32 – Theoretical ratios
Looking at the ratios mentioned in the previous slides, does this mean that if a couple has four
children, they will see these ratios in their family? The answer is no. Each time the parents have
a child it is the luck of the draw as to which alleles will end up in the offspring. It is like tossing
a coin. You may have a streak where you have several heads in a row; however if you toss the
coin enough times you will end up with 50% heads and 50% tails. Punett squares show the
theoretical ratios that would occur if large numbers of individuals were born from a specific
pairing.
Slide 25 – Punnett square
In the first square of the second row, the mother contributes an E, while the father contributes an
e, therefore the child has the genotype Ee.
Slide 26 – Punnett square
In the final square, each parent contributes an e, so the child has the genotype ee.
Slide 27 – Genetics Questions
From this punnet square, there are several questions that can be asked. I could ask what
percentage of the children have unattached ear lobes. The answer to this question would be 75%.
This is because three of the four boxes have least one dominant allele.
Slide 28 – Genetics Questions
I could also ask what percentage of the children are heterozygous. The answer to this question is
50%, since two of the four boxes have the genotype Ee.
Slide 29 – Genetics Questions
Another question that I could pose is the ratio of the dominant allele to the recessive allele. The
answer would be 3:1, since three of the boxes have a dominant allele and only one has recessive
alleles only.
Slide 30 – Genetics Questions
I could also ask what the ratio of homozygous dominant to heterozygous to homozygous
recessive. The answer to this question is 1:2:1. When doing genetics questions, be sure you are
doing what is being asked.
Slide 31 – Genotypic and phenotypic ratios
The discussion on the previous slide was about genotypic and phenotypic ratios. Phenotypic
ratios ask you to show the number of children that would have the dominant phenotype
compared to the number of children that would have the recessive phenotype. Genotypic ratios
ask you show the number of children who are homozygous dominant compared to the number of
children who are heterozygous compared to the number of children who are homozygous
recessive.
Slide 32 – Theoretical ratios
Looking at the ratios mentioned in the previous slides, does this mean that if a couple has four
children, they will see these ratios in their family? The answer is no. Each time the parents have
a child it is the luck of the draw as to which alleles will end up in the offspring. It is like tossing
a coin. You may have a streak where you have several heads in a row; however if you toss the
coin enough times you will end up with 50% heads and 50% tails. Punett squares show the
theoretical ratios that would occur if large numbers of individuals were born from a specific
pairing.
Introduction to Genetics
Slide 33 – Recessive trait disorders
Recessive traits are traits that are inherited through a recessive allele. In order for an individual
to display a recessive trait, they must inherit a recessive allele from each of their parents. Some
diseases are inherited through recessive traits and can be very devastating. Among them are
Tay–Sachs disease, Cystic fibrosis, and Phenylketonuria (PKU). Individuals that inherit one
recessive allele for one of these diseases, but also inherit one dominant allele that mask the
recessive allele are known as carriers for the disease. If there is a history of one of these genetic
diseases in the family, an individual will often be testing to see if they are a carrier.
Slide 34 – Pedigrees
During genetic counseling it often becomes necessary to determine the family history through
the collection of a pedigree. In a pedigree, males are represented by squares, females by circles,
and individuals carrying a genetic disorder by shading. Looking at a pedigree can help
determine how a genetic disorder is transmitted through a family.
Slide 35 – Check Your Understanding
Now that we have learned about pedigrees, let’s check your knowledge of the subject. The
following slides will have a series of questions on the topic. Be sure to click “Submit” after
answering each question.
Slides 36 through 41 – Pedigrees Interactive Quiz
A non–graded assessment of your knowledge of pedigrees
Slide 42 – Dominant trait disorders
Dominant traits are those that are inherited by a dominant allele. People tend to think that
dominant traits are not harmful, but a few genetic disorders are caused by the presence of a
dominant trait. These include Marfan syndrome, hypercholesterolemia, Huntington’s disease,
and achrondroplasia. In order for an individual to inherit a dominant trait, one of their parents
must have has the trait. Both dominant and recessive traits in families can be traced using a
pedigree analysis.
Slide 43 – Check Your Understanding
Now that we have learned about Mendelian Genetics, let’s check your knowledge of the subject.
The following slides will have a series of questions on the topic. Be sure to click “Submit” after
answering each question.
Slides 44 through 53 –Genetics Problems Interactive Quiz
A non–graded assessment of your knowledge of working through genetics problems.
Slide 54 – Non–Mendelian inheritance
Not all traits are inherited in a simple Mendelian fashion. These traits are passed from one
generation to the next through non–mendelian inheritance. Some examples of non–Mendelian
inheritance include polygenic traits, incomplete dominance, multiple alleles, co–dominance, sex
linked traits, sex influenced traits, and environmental influenced traits. We will explore each of
these is further detail.
Slide 33 – Recessive trait disorders
Recessive traits are traits that are inherited through a recessive allele. In order for an individual
to display a recessive trait, they must inherit a recessive allele from each of their parents. Some
diseases are inherited through recessive traits and can be very devastating. Among them are
Tay–Sachs disease, Cystic fibrosis, and Phenylketonuria (PKU). Individuals that inherit one
recessive allele for one of these diseases, but also inherit one dominant allele that mask the
recessive allele are known as carriers for the disease. If there is a history of one of these genetic
diseases in the family, an individual will often be testing to see if they are a carrier.
Slide 34 – Pedigrees
During genetic counseling it often becomes necessary to determine the family history through
the collection of a pedigree. In a pedigree, males are represented by squares, females by circles,
and individuals carrying a genetic disorder by shading. Looking at a pedigree can help
determine how a genetic disorder is transmitted through a family.
Slide 35 – Check Your Understanding
Now that we have learned about pedigrees, let’s check your knowledge of the subject. The
following slides will have a series of questions on the topic. Be sure to click “Submit” after
answering each question.
Slides 36 through 41 – Pedigrees Interactive Quiz
A non–graded assessment of your knowledge of pedigrees
Slide 42 – Dominant trait disorders
Dominant traits are those that are inherited by a dominant allele. People tend to think that
dominant traits are not harmful, but a few genetic disorders are caused by the presence of a
dominant trait. These include Marfan syndrome, hypercholesterolemia, Huntington’s disease,
and achrondroplasia. In order for an individual to inherit a dominant trait, one of their parents
must have has the trait. Both dominant and recessive traits in families can be traced using a
pedigree analysis.
Slide 43 – Check Your Understanding
Now that we have learned about Mendelian Genetics, let’s check your knowledge of the subject.
The following slides will have a series of questions on the topic. Be sure to click “Submit” after
answering each question.
Slides 44 through 53 –Genetics Problems Interactive Quiz
A non–graded assessment of your knowledge of working through genetics problems.
Slide 54 – Non–Mendelian inheritance
Not all traits are inherited in a simple Mendelian fashion. These traits are passed from one
generation to the next through non–mendelian inheritance. Some examples of non–Mendelian
inheritance include polygenic traits, incomplete dominance, multiple alleles, co–dominance, sex
linked traits, sex influenced traits, and environmental influenced traits. We will explore each of
these is further detail.
Introduction to Genetics
Slide 55 – Incomplete dominance
One of Mendel’s rules was that heredity is not blending. However, there are some traits that do
show blending. These traits show incomplete dominance. As an example if you crossed a red
carnation with a white carnation, based on Mendel’s rules you would expect the offspring to be
red or white. This is not the case because the offspring would actually be pink. Because we see
blending this is an example of incomplete dominance. Another example of incomplete
dominance is the chocolate Labrador retriever, which results from a yellow Labrador crossed
white a black Labrador.
Slide 56 – Multiple alleles
Do you remember the blood types we discussed during the immune system portion of the
course? There were four different blood types, A, B, AB, and O. How is this possible if blood
type is on a single gene? According to Mendel’s rules there would only be three different
genotypes and two different phenotypes. This does not account for the four blood types seen in
human populations. The four blood types exist because there are three alleles in the population
for blood type, IA, IB, and i. Both IA and IB are dominant to i.
There are other human traits that are the result of multiple alleles. Another example is human
leukocyte antigen (HLA) alleles, which code for recognition proteins in the cell membranes of
body cells. These are important in the immune system and help cells distinguish between “self”
and “foreign”. Each HLA gene can have more than 30 different alleles. The multitude of HLA
alleles comes in to play when doctors are trying to find a suitable organ donor.
Slide 57 – Codominance
In addition to having three alleles, blood type is also unusual in that neither IA nor IB is dominant
to the other. In the blood type AB, the individual has the alleles IA and IB. Both of these alleles
make an antigen. IA make the A antigen and IB makes the B antigen. These individuals end up
with both genes making something that is seen in the phenotype of the individual. This is an
example of co–dominance. Co–dominance is different from incomplete dominance in that there
is no blending of the traits. Both the A antigen and the B antigen are being made.
Slide 58 – Blood type alleles
Let’s take a moment to look at the possible genotypes and phenotypes for blood type. If a person
has type A blood, they must have the IA allele. They might have another IA allele or they may
have the recessive i allele. A person with type B blood must have the IB allele. Their second
allele can either be another IB or a recessive i. A person with type O blood has the recessive trait
and must have two i alleles.
Slide 59 – Blood typing and paternity
Before current paternity testing methods using DNA, blood typing was the sole method of
determining paternity. This was not as accurate as today’s DNA testing. If two men had the
same blood type, there was no way to exclude either one of them. This method did not allow for
the proving of paternity, it only excluding individuals from paternity if a punnet square between
the mother and the individual in question could not produce a box with the child’s blood type.
Slide 55 – Incomplete dominance
One of Mendel’s rules was that heredity is not blending. However, there are some traits that do
show blending. These traits show incomplete dominance. As an example if you crossed a red
carnation with a white carnation, based on Mendel’s rules you would expect the offspring to be
red or white. This is not the case because the offspring would actually be pink. Because we see
blending this is an example of incomplete dominance. Another example of incomplete
dominance is the chocolate Labrador retriever, which results from a yellow Labrador crossed
white a black Labrador.
Slide 56 – Multiple alleles
Do you remember the blood types we discussed during the immune system portion of the
course? There were four different blood types, A, B, AB, and O. How is this possible if blood
type is on a single gene? According to Mendel’s rules there would only be three different
genotypes and two different phenotypes. This does not account for the four blood types seen in
human populations. The four blood types exist because there are three alleles in the population
for blood type, IA, IB, and i. Both IA and IB are dominant to i.
There are other human traits that are the result of multiple alleles. Another example is human
leukocyte antigen (HLA) alleles, which code for recognition proteins in the cell membranes of
body cells. These are important in the immune system and help cells distinguish between “self”
and “foreign”. Each HLA gene can have more than 30 different alleles. The multitude of HLA
alleles comes in to play when doctors are trying to find a suitable organ donor.
Slide 57 – Codominance
In addition to having three alleles, blood type is also unusual in that neither IA nor IB is dominant
to the other. In the blood type AB, the individual has the alleles IA and IB. Both of these alleles
make an antigen. IA make the A antigen and IB makes the B antigen. These individuals end up
with both genes making something that is seen in the phenotype of the individual. This is an
example of co–dominance. Co–dominance is different from incomplete dominance in that there
is no blending of the traits. Both the A antigen and the B antigen are being made.
Slide 58 – Blood type alleles
Let’s take a moment to look at the possible genotypes and phenotypes for blood type. If a person
has type A blood, they must have the IA allele. They might have another IA allele or they may
have the recessive i allele. A person with type B blood must have the IB allele. Their second
allele can either be another IB or a recessive i. A person with type O blood has the recessive trait
and must have two i alleles.
Slide 59 – Blood typing and paternity
Before current paternity testing methods using DNA, blood typing was the sole method of
determining paternity. This was not as accurate as today’s DNA testing. If two men had the
same blood type, there was no way to exclude either one of them. This method did not allow for
the proving of paternity, it only excluding individuals from paternity if a punnet square between
the mother and the individual in question could not produce a box with the child’s blood type.
Introduction to Genetics
Slide 60 – Sickle cell disease
Another example of co–dominance can be seen in sickle cell disease. There are two possible
alleles for hemoglobin, HbA and HbS. HbA is the normal allele. A person that is completely
normal has the genotype HbA HbA. An individual with sickle cell disease has two copies of the
HbS allele. Individuals that have sickle cell trait, also known as a carrier, have one HbA allele
and one HbS allele. To test for sickle cell trait, blood cells are placed under low oxygen. If some
of the cells sickle, the person has sickle cell trait. A person with sickle cell trait produced both
normal hemoglobin and sickled cell hemoglobin. It has been found that the presence of some
sickled cell hemoglobin protects individuals from a disease called malaria.
Slide 61 – Check Your Understanding
Now that we have learned about some types of Non–Mendelian Genetics, let’s check your
knowledge of the subject. The following slides will have a series of questions on the topic. Be
sure to click “Submit” after answering each question.
Slides 62 through 69 – Interactive Quiz
A non–graded assessment of your knowledge of Non–Mendelian Modes of Inheritance
.
Slide 70 – Polygenic traits
All of the traits that Mendel observed were inherited from a single gene. Today we know that
many traits are influenced by many genes. When a phenotype is the result of the influence of
many genes it is called a polygenic trait. Polygenic traits show a bell curve distribution of
phenotypes. Take skin color for example. If you look around at the people in your workplace,
you will notice that they all have different skin colors. Even within your own family, you will
notice these differences. There is an average skin color and most people are a few shades lighter
or darker than this average. Very few people have no skin colorations at all and very few people
have the maximum amount of skin color. The distribution of skin color is therefore bell shaped,
with most of the individuals falling around the average skin color.
Slide 71 – Environmental Influences
Other traits are influenced by the external environment. A good example of this is the Siamese
cat. Siamese cats produce more melanin in the parts of their body that are cooler; therefore
Siamese cats are darker on their nose, ears, tail, and feet. Areas that stay warmer do not produce
as much melanin and remain a lighter color.
Slide 72 – Sex influenced traits
Some traits that are not carried on the sex chromosomes are influenced by the hormones
produced by a certain sex. These are called sex influenced traits. These traits are found on the
autosomal chromosomes and are inherited in a normal Mendelian way, but they are only
expressed when certain hormones are present. Sex influenced traits include male pattern
baldness, and fraternal twins.
Slide 73 – Sex chromosomes
The X chromosome contains information that does not related to sexual characteristics; therefore
there are some traits that will be inherited on the X chromosome. Recall that females have two
copies of the X chromosome, while males only have one copy of the X chromosome. Males also
have a Y chromosome. Females are homozygous for their sex chromosomes, while males are
heterozygous for their sex chromosomes. Where do men get there X chromosomes? They
Slide 60 – Sickle cell disease
Another example of co–dominance can be seen in sickle cell disease. There are two possible
alleles for hemoglobin, HbA and HbS. HbA is the normal allele. A person that is completely
normal has the genotype HbA HbA. An individual with sickle cell disease has two copies of the
HbS allele. Individuals that have sickle cell trait, also known as a carrier, have one HbA allele
and one HbS allele. To test for sickle cell trait, blood cells are placed under low oxygen. If some
of the cells sickle, the person has sickle cell trait. A person with sickle cell trait produced both
normal hemoglobin and sickled cell hemoglobin. It has been found that the presence of some
sickled cell hemoglobin protects individuals from a disease called malaria.
Slide 61 – Check Your Understanding
Now that we have learned about some types of Non–Mendelian Genetics, let’s check your
knowledge of the subject. The following slides will have a series of questions on the topic. Be
sure to click “Submit” after answering each question.
Slides 62 through 69 – Interactive Quiz
A non–graded assessment of your knowledge of Non–Mendelian Modes of Inheritance
.
Slide 70 – Polygenic traits
All of the traits that Mendel observed were inherited from a single gene. Today we know that
many traits are influenced by many genes. When a phenotype is the result of the influence of
many genes it is called a polygenic trait. Polygenic traits show a bell curve distribution of
phenotypes. Take skin color for example. If you look around at the people in your workplace,
you will notice that they all have different skin colors. Even within your own family, you will
notice these differences. There is an average skin color and most people are a few shades lighter
or darker than this average. Very few people have no skin colorations at all and very few people
have the maximum amount of skin color. The distribution of skin color is therefore bell shaped,
with most of the individuals falling around the average skin color.
Slide 71 – Environmental Influences
Other traits are influenced by the external environment. A good example of this is the Siamese
cat. Siamese cats produce more melanin in the parts of their body that are cooler; therefore
Siamese cats are darker on their nose, ears, tail, and feet. Areas that stay warmer do not produce
as much melanin and remain a lighter color.
Slide 72 – Sex influenced traits
Some traits that are not carried on the sex chromosomes are influenced by the hormones
produced by a certain sex. These are called sex influenced traits. These traits are found on the
autosomal chromosomes and are inherited in a normal Mendelian way, but they are only
expressed when certain hormones are present. Sex influenced traits include male pattern
baldness, and fraternal twins.
Slide 73 – Sex chromosomes
The X chromosome contains information that does not related to sexual characteristics; therefore
there are some traits that will be inherited on the X chromosome. Recall that females have two
copies of the X chromosome, while males only have one copy of the X chromosome. Males also
have a Y chromosome. Females are homozygous for their sex chromosomes, while males are
heterozygous for their sex chromosomes. Where do men get there X chromosomes? They
Introduction to Genetics
inherit their X chromosome from their mother; they will inherit the Y chromosome from their
fathers.
Slide 74 – Sex chromosomes
Since males only have one copy of the X chromosome, if they get a chromosome with a certain
trait they are going to show that trait. Women have two copies of the X chromosome, so they
can mask a recessive trait just like in regular Mendelian genetics. These women are considered
carriers for these traits, since they do not display the trait but have the ability to pass it on.
Slide 75 – X–linked traits
Examples of X–linked traits are hemophilia and color blindness. Men are more likely to display
X–linked traits compared to females. For women to be color blind, they need to inherit two color
blind X chromosomes. Males will show color blindness with only one color blind X
chromosome. Since males get their X chromosome from their mothers, the mother of a color
blind male will have to be at least a carrier for the color blind trait. Males cannot be carriers for
an X–linked trait.
Slide 76 – Check Your Understanding
Now that we have learned about X–linked traits, let’s check your knowledge of the subject. The
following slides will have a series of questions on the topic. Be sure to click “Submit” after
answering each question.
Slides 77 through 86 – X–linked Traits Interactive Quiz
A non–graded assessment of your knowledge of X–linked traits.
Slide 87 – Y chromosome analysis
There are few examples of Y–linked traits. This is because the Y chromosome contains a small
amount of genetic information and the majority of that information encodes traits that relate to
being male. One example of a Y–linked trait is hairy pinna. Hairy pinna is the excessive growth
of hair on the external part of the ear.
The Y–chromosome can be used to trace human ancestry. The Y chromosome is passed from
father to son with no exchange of genetic information with any other chromosome. Because of
this, there is very little change in the DNA on the Y chromosome over many generations.
Individuals can trace paternal lines through the Y chromosome.
Slide 88 – mtDNA and Deep Ancestry
Is the nucleus the only place you find DNA in a cell. The answer is no. Recall the mitochondria
and in the case of plants the chloroplasts. These organelles are believed to have at one time been
free living organisms that developed a symbiotic relationship with the cell. A symbiotic
relationship is one in which both parties benefit. In the case of the mitochondria, the
mitochondria got a nice place to live inside the cell and access to food and nutrients from the
cell. In return, the cell got ATP energy from the mitochondria through the process of cell
respiration.
Mitochondria still have some of their own DNA. This DNA is inherited directly from your
mother, since all of the mitochondria you have came from the egg that was fertilized. There are
some traits on this DNA; however the big use of mitochondrial DNA is in determining maternal
inherit their X chromosome from their mother; they will inherit the Y chromosome from their
fathers.
Slide 74 – Sex chromosomes
Since males only have one copy of the X chromosome, if they get a chromosome with a certain
trait they are going to show that trait. Women have two copies of the X chromosome, so they
can mask a recessive trait just like in regular Mendelian genetics. These women are considered
carriers for these traits, since they do not display the trait but have the ability to pass it on.
Slide 75 – X–linked traits
Examples of X–linked traits are hemophilia and color blindness. Men are more likely to display
X–linked traits compared to females. For women to be color blind, they need to inherit two color
blind X chromosomes. Males will show color blindness with only one color blind X
chromosome. Since males get their X chromosome from their mothers, the mother of a color
blind male will have to be at least a carrier for the color blind trait. Males cannot be carriers for
an X–linked trait.
Slide 76 – Check Your Understanding
Now that we have learned about X–linked traits, let’s check your knowledge of the subject. The
following slides will have a series of questions on the topic. Be sure to click “Submit” after
answering each question.
Slides 77 through 86 – X–linked Traits Interactive Quiz
A non–graded assessment of your knowledge of X–linked traits.
Slide 87 – Y chromosome analysis
There are few examples of Y–linked traits. This is because the Y chromosome contains a small
amount of genetic information and the majority of that information encodes traits that relate to
being male. One example of a Y–linked trait is hairy pinna. Hairy pinna is the excessive growth
of hair on the external part of the ear.
The Y–chromosome can be used to trace human ancestry. The Y chromosome is passed from
father to son with no exchange of genetic information with any other chromosome. Because of
this, there is very little change in the DNA on the Y chromosome over many generations.
Individuals can trace paternal lines through the Y chromosome.
Slide 88 – mtDNA and Deep Ancestry
Is the nucleus the only place you find DNA in a cell. The answer is no. Recall the mitochondria
and in the case of plants the chloroplasts. These organelles are believed to have at one time been
free living organisms that developed a symbiotic relationship with the cell. A symbiotic
relationship is one in which both parties benefit. In the case of the mitochondria, the
mitochondria got a nice place to live inside the cell and access to food and nutrients from the
cell. In return, the cell got ATP energy from the mitochondria through the process of cell
respiration.
Mitochondria still have some of their own DNA. This DNA is inherited directly from your
mother, since all of the mitochondria you have came from the egg that was fertilized. There are
some traits on this DNA; however the big use of mitochondrial DNA is in determining maternal
Introduction to Genetics
relationships. Since your mitochondrial DNA came from your mother, all of those individuals
that you are related to maternally would have similar mitochondrial DNA. Just as Y
chromosomes can be used to trace paternal lines, mtDNA can be used to trace maternal lines.
The lineage that is traced with mtDNA is historical and has been used to trace human
populations to their origins approximately 200,000 years ago.
Slide 89 –mtDNA and Deep Ancestry
YouTube video
http://www.youtube.com/watch?v=kS5qREISS–Q
Slide 90 – Summary
This slide is a summary of all of the “Check Your Understanding” questions from this lecture.
Be sure to review the questions you answered incorrectly.
relationships. Since your mitochondrial DNA came from your mother, all of those individuals
that you are related to maternally would have similar mitochondrial DNA. Just as Y
chromosomes can be used to trace paternal lines, mtDNA can be used to trace maternal lines.
The lineage that is traced with mtDNA is historical and has been used to trace human
populations to their origins approximately 200,000 years ago.
Slide 89 –mtDNA and Deep Ancestry
YouTube video
http://www.youtube.com/watch?v=kS5qREISS–Q
Slide 90 – Summary
This slide is a summary of all of the “Check Your Understanding” questions from this lecture.
Be sure to review the questions you answered incorrectly.
Psychology Homework
Stuck with a homework question? Find quick answer to Accounting homeworks
Ask Psychology Tutors
Need help understanding a concept? Ask our Accounting tutors
Psychology Exams
Get access to our databanks of Discussion questions and Exam questions
How We Safeguard Your Tutor Quality
All tutors are required to have relevant training and expertise in their specific fields before they are hired. Only qualified and experienced tutors can join our team
All tutors must pass our lengthy tests and complete intensive interview and selection process before they are accepted in our team
Prior to assisting our clients, tutors must complete comprehensive trainings and seminars to ensure they can adequately perform their functions
Interested in becoming a tutor with Online Class Ready?
Share your knowledge and make money doing it
1. Be your own boss
2. Work from home
3. Set your own schedule
