Genetics Packet Practice Problems

Name: ______Date: ______

Genetics Packet Practice Problems

Part 1: A Dog Called Spot

Imagine this microscopic drama: a sperm cell from a male dog fertilizes an egg cell from the female dog. Each dog’s gamete contain 39 chromosomes and the zygote (which will eventually develop into a puppy) will have a total of 78 chromosomes, one set from the mother and one from the father.

Chromosome

From Mother

Chromosome

From Father

Two of the puppy’s chromosomes are shown above. It is a homologous pair because each chromosomes contains alleles (versions of a gene) that code for the same traits. One of the chromosomes in the pair came from the mother and one came from the father.

The only difference between the two is that one may have a dominant allele (capital letter) and the other a recessive allele (lower case) for a given trait. To have a dominant trait the puppy only needs to have one copy of the dominant allele. However, to have a recessive trait, they puppy must have both copies of the recessive allele.

Using the chromosomes above, the chart below, and your vocabulary list to answer the following questions.

TRAIT / DOMINANT / RECESSIVE
Hair Length / Short = L / Long = l
Hair Texture / Wiry = T / Silky = t
Hair Curliness / Curly = H / Straight = h
Coat Pattern / Spotted = A / Solid = a

1. What is the texture of the puppy’s coat? How do you know? Explain.

1. What is the texture of the father’s coat? How do you know? Explain.

1. What is the texture of the mother’s coat? How do you know? Explain.

1. What is the pattern of the puppy’s coat? How do you know? Explain.

1. Is the pattern of the puppy’s coat the same as pattern of the parent’s coat? How do you know? Explain.

1. Does either parent have curly hair? Which one(s)? How do you know? Explain.

1. List the traits for which the puppy is homozygous. Tell the genotype (letters) and the phenotype (the trait/appearance).

1. List the trait for which the puppy is heterozygous. Tell the genotype (letters) and the phenotype (trait).

1. Based on the information provided in this scenario, why can’t you completely describe the puppy’s parents even though you can accurately describe the puppy?

I. Dominant Recessive Traits

1. Cystic fibrosis (CF) is an inherited chronic disease that affects the lungs and digestive systems of about 30,000 children and adults in the United States. A defective gene causes the body to produce unusually thick, sticky mucus that clogs the lungs and leads to life-threatening lung infections and obstructs the pancreas. It is recessive trait, meaning you only show signs of the disease if you’ve inherited two recessive alleles from your parents.

Jennifer and Tim are a young married couple planning a family. Tim’s younger sister had CF and died before she finished high school. It is possible Tim carries the gene for CF. They have decided to have genetic tests before trying to conceive in order to determine whether they could have a child affected by the diseases. The couple received their test results and was devastated to find out that they are both carriers. Carriers are people who have one cystic fibrosis allele and one normal allele. They are not affected by the disease, but have a chance of giving it to their child.

Perform a Punnett Square below to predict the probability that Jen and Tim’s children will have CF. What is the probability that their child will have CF?

Note: Use ‘D’ for the healthy allele

since it is dominant over ‘d’ the

cystic fibrosis allele.

Write a sentence that answers the question from above. The first sentence has been done for you.

There is a 25% chance that their child will inherit Cystic Fibrosis

2. Huntington's Disease is a devastating, degenerative brain disorder for which there is, at present, no effective treatment or cure. Huntington’s slowly diminishes the affected individual's ability to walk, think, talk and reason. Eventually, the person with the disease becomes totally dependent upon others for his or her care. Signs of the disease don’t usually show up until age 30 or 40. However, Huntington’s disease is a dominant trait- which means you only need to inherit one copy of the allele to have the disease.

Sheila does not show any signs of having Huntington’s disease right now. Sheila’s father does have the disease, even though his mother does (grandma Lucy) does not have the disease. Sheila’s mother is healthy and does not have Huntington’s disease. What is Sheila’s probability of having the gene for Huntington’s and therefore developing the disease later in life?

Note: use ‘H’ for the Huntington’s allele &‘h’ = healthy allele.

Complete the chart below for Huntington’s disease and finish with a one sentence written response to the original question.

Genotype Ratio:

Phenotype Ratio:

Write a sentence that answers the question from above.

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3. Hypercholesterolemia is a disorder that causes excess cholesterol in the blood and heart disease. This disorder is caused by a dominant allele. If each of your parents had the disorder and had 12 children, how many of those children will not have the disorder? Hint: it is possible for these parents to have a child without the disorder. Show your work in the punnett square below. (assume both heterozygous)

Genotype Ratio:

Phenotype Ratio:

Write a sentence that answers the question from above.

4. Black hair is dominant to blonde hair. A man marries a woman and they have 24 kids; 18 of them have black hair and 6 have blonde hair. What is the genotype of the dad? Mom? What is the probability of these two individuals having a child heterozygous for black hair? Heterozygous for blonde hair?

Genotype Ratio:

Phenotype Ratio:

Sentence to answer questions: ______

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5. A woman who has freckles and black hair, had a father without freckles and had blonde hair. The woman marries a man who is heterozygous for freckles and black hair. What is the probability of having a child with freckles and blonde hair?

Sentence to answer questions: ______

______

II. Incomplete Dominance Traits

6. If traits are inherited through incomplete dominance, then they can be a blend of one another. For example, mixing a red rose and white rose makes a pink rose. Cross a pink rose and a white rose. What is the probability that the offspring will be heterozygous?

Write a sentence that answers the question from above.

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7. Human’s hair type is an example of Incomplete Dominance. If you have either of the two possible homozygous combinations for hair type, then you either have straight hair, or curly hair. If you are heterozygous then you have wavy hair.

Develop a punnett square problem for hair type where you have a genotypic ratio of 1:2:1. Then complete the problem.

Write a sentence that answers the question from above.

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III. Codominance

8. Codominance is just like incomplete dominance, except that the trait doesn’t show up like a blend. In incomplete dominance, a white chicken and a black chicken would make a gray one (WB), but in CODOMINANCE, a white chicken and a black chicken make a black and white spotted chicken (WB).

In your own words define the term codominance: ______

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9. Cross a white–and-black feathered chicken with another white-and-black feathered chicken? Draw the square. What’s the chance of getting a white-and-black chicken?

Write a sentence that answers the question from above.

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10.Horse hair color is codominant as well. White horses can breed with Red horses and make roan horses. Based off of your understanding of codominance, what would a roan horse look like?

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Perform a cross between a two roan horses. Draw the square. What is the probability that the offspring will be white?

Codominance: Blood Types

There are many different ways to classify blood types, but the most common blood type classification system is the ABO (said "A-B-O") system. There are four types of blood in the ABO system: A, B, AB, and O. These blood types refer to different versions of a carbohydrate molecules, complex sugars, which are present on the surface of red blood cells. People with Type A blood have Type A carbohydrate molecules, people with Type B blood have Type B carbohydrate molecules, and people with Type AB blood have both Type A and Type B carbohydrate molecules on their red blood cells. People with Type O blood do not have either the A or B carbohydrate molecules on their red blood cells.

The Type A and Type B carbohydrate molecules are called antigens because they can stimulate the body to produce an immune response, including antibodies. Antibodies are special proteins that travel in the blood and help our bodies to destroy viruses or bacteria that may have infected our bodies. Normally, our bodies do not make antibodies against any molecules that are part of our own bodies. For example, people with Type A blood do not make antibodies against the Type A (carbohydrate) antigen which is present on their red blood cells, but they do make antibodies against the Type B (carbohydrate) antigen.

Test your understanding of blood groups by completing the table below.

Blood Group / Antibodies in plasma for which blood type?
AB
A / B
B
O
/ Blood group A
If you belong to the blood group A, you have A (carbohydrates) antigens on the surface of your red blood cells and antibodies in your blood to fight off type B (carbohydrates) antigens.
/ Blood group B
If you belong to the blood group B, you have B (carbohydrates) antigens on the surface of your red blood cells and antibodies in your blood to fight off type A (carbohydrates) antigens.
/ Blood group AB
If you belong to the blood group AB, you have both A and B (carbohydrates) antigens on the surface of your red blood cells and no antibodies in your blood to fight off type A and B (carbohydrates) antigens.
/ Blood group O
If you belong to the blood group O, you have neither A nor B (carbohydrates) antigens on the surface of your red blood cells, but you have antibodies in your blood to fight off BOTH A and B (carbohydrates) antigens.
Rh factor / Possible genotypes
Rh+ / Rh+/Rh+
Rh+/Rh-
Rh- / Rh-/Rh-

What about the Rh factor?

The Rh factor genetic information is also inherited from our parents, but it is inherited independently of the ABO blood type alleles. There are 2 different alleles for the Rh factor known as Rh+ and Rh-. Like the ABO blood type RH+ will result in a Rh carbohydrate (antigen) located on the outside of the cell were a RH- will result in no carbohydrate (antigen).

Mother / Father / Child
Rh- / Rh+ / Rh+
Rh- / Rh- / Rh-

Someone who is "Rh positive" or "Rh+" has at least one Rh+ allele, but could have two. Their genotype could be either Rh+/Rh+ or Rh+/Rh-. Someone who Rh- has a genotype of Rh-/Rh-. Just like the ABO alleles, each biological parent donates one of their two Rh alleles to their child.

A mother who is Rh- can only pass an Rh- allele to her son or daughter. A father who is Rh+ could pass either an Rh+ or Rh- allele to his son or daughter. This couple could have Rh+ children (Rh- from mother and Rh+ from father) or Rh- children (Rh- from mother and Rh- from father).

Blood transfusions — who can receive blood from whom?

If you are given a blood transfusion that does not match your blood type, antibodies present in your blood will react with the antigens present on the donated red blood cells. For example, if a person who has Type A blood is given a Type B blood transfusion, then this person's anti-B antibodies will react with the Type B antigens on the donated red blood cells and cause a harmful reaction. This reaction can cause the donated red blood cells to burst and/or clump together and block blood vessels. This type of transfusion reaction is illustrated in the following drawing.

Transfusion reactions can be fatal. To prevent this from happening, doctors test whether a person's blood is compatible with the donated blood before they give a transfusion. The general principle is that a person can be harmed by donated blood if it has blood cells with an antigen that can react with the antibodies that the person has in his or her blood, since this will produce a transfusion reaction.

1. Test your understanding of blood groups by completing the table below.

Blood Group / Antigens on red blood cells / Antibodies in plasma / Can give
blood to / Can receive blood from
A+ / A & Rh+ / B / A+ and AB+ / A+/- and O+/-
A- / A / B & Rh+
B+ / B & Rh+
B- / B
AB+ / A and B & Rh+
AB- / A and B
O+ / Rh+
O- / None

1. Which blood type would you say could be called a universal receiver of any blood type?

1. Which blood type would you say could be called the universal donor to any blood type?

1. If a man who is blood type AB is in an accident and is in need of a blood transfusion, which parent or parent’s (Earnst - A, Denise - B, Michael - AB or Danielle - B) would be able to donate blood to this individual? Explain.

Genetics of Blood Types

Your blood type is established before you are born, by specific genesinherited from your parents. You receive one gene from your mother and one from your father. These two genes determine your blood type by causingthe presence or absence of the Type A and Type B antigen molecules on the red blood cells.

The blood type gene has three different versions or alleles: IA, IB, and i. i represents the allele for type O blood and is recessive. IA, IB represents the alleles for blood type A and B and they are both dominant. Since everybody has two copies of these genes, there are six possible combinations:

IAIA and IA i - both resulting in Type A blood,

IB IB and IB i- both resulting in Type B blood,

IAIB - resulting in Type AB blood,

i i - resulting in Type O blood.

These combinations are called genotypes, and they describe the genes you got from your parents.

Each biological parent gives one of their two ABO alleles to their child. For example, a mother who is blood type O has genotype ii and can only give an i allele to her son or daughter. A father who is blood type AB could give either an IA or a IB allele to his son or daughter. This couple could have children of either blood type A (i from mother and IA from father) or blood type B (i from mother and IB from father). This is illustrated in the Punnett square below.

Father
(Type AB)
Sperm / Mother
(Type O)
Eggs
i / i
IA / IAi / IAi
IB / IBi / IBi

14.If Michael Jr. grows up and marries a woman with blood type O, what is the probability of him and his wife having a child with blood type O? Let’s say that Michael Jr. is heterozygous for his blood type.

Write a sentence that answers the question from above.

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15.If a universal donor marries a universal receiver what is the probability of them having a child that is a universal donor or receiver?

Write a sentence that answers the question from above.

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16.A person that is heterozygous for blood type A marries a man that is homozygous dominant for blood type B. They both want to have children and really want to have a child that is a universal receiver. As a friend who knows about genetics explain to them if they can have a child that is a universal receiver and why they can or cannot.

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IV. Sex-Linked Traits

17. Hemophilia is a genetic disease in which the victim’s blood does not clot well, leading them to problems when they get cuts. They can easily lose too much blood, and even a bruise can lead to serious internal bleeding. Hemophilia is a Sex-Linked Recessive Disease. Cross a carrier female with a normal male. Fill in the chart, and answer the questions below.

Offspring’s Genotype / Offspring’s Phenotype (trait) / Percent of offspring
Male Hemophiliac
Normal Male
Female Hemophiliac
Normal Female

18. Muscular Dystrophy is a disease that causes people to lose function of their muscles, and can die from it. It is a Sex-linked Recessive trait. Cross a female who has MD with a normal male, then fill in the chart.

Offspring’s Genotype / Offspring’s Phenotype (trait) / Percent of offspring

19. Color Blindness is a sex-linked recessive trait. Cross a male who is color blind with a homozygous dominant female. What is the probability that the male offspring will be colorblind?

Sentence: ______

20. Hemophilia is a disease characterized by an individual whose blood does not clot properly. Hemophiliac’s blood takes a very long time to clot, and in many cases, hemophiliacs can die from internal or external bleeding. Hemophiliacs can take pills that contain “clotting factors”, which are proteins that plug up bleeds in your body. Hemophilia is a sex-linked recessive disorder. Roberta carries the gene for hemophilia, and marries Jim, who is a hemophiliac. Circle all of the statements that are true.

a. All of their children will be hemophiliacs

b. Half of their children of both sexes will be hemophiliacs (based on probability)

c. All of their female children will be hemophiliacs

d. Half of their female children will be carriers

e. 25% of their male children will be normal

V. Going further

After taking biology class, you realize that you want to pursue an education and career in biology. You study genetics and ecology in college, and wind up studying tree frogs in Peru. You discover a new species of tree frog, and name it Kelly’s Tree Frog, after the teacher who first influenced your decision to pursue a career in biology. You notice that the frogs are capable of having orange spots on their back and legs, or yellow spots on their back and legs. You are interested in the pattern of inheritance for spot color, so you start to track the parent frogs and their offspring. You follow a family of frogs, and find that the one parent has orange spots, and the other has yellow. After they breed, you are only able to find four of their offspring, three of which are yellow, and one of which is orange.