Posted: February 6th, 2023

Genetics Worksheets

Genetics Worksheets
Go to the website for Cold Spring Harbor Laboratory (link below) and view the animations needed to complete this exercise. Cold Spring Harbor was where DNA was discovered. http://www.dnaftb.org/1/
Animation 1 – Children resemble their parents
Work through the “Children resemble their parents” animation and answer the following questions-
1. Why did Mendel study pea plants? What made a good plant to study?

2. Pea plants have the ability to self-fertilize. Explain what this means, and explain the structures that allow the plants to perform this.

3. When Mendel started his experiments, he wanted to cross-fertilize two different plants. Describe the two parent plants, and how Mendel succeeded in completing cross-fertilization.

Animation 2: Genes come in pairs
Work through the “Genes come in pairs” animation and answer the following questions
1. What is meant by phenotype, and how many phenotypes did Mendel observe in the pea plants? Describe each one.

2. For each distinct phenotype, how many different versions of that trait were observed in the plants? Why is this significant?

3. Why was it important that Mendel used “purebred” strains of pea plants to begin his experiments?

4. Mendel reasoned that each trait is controlled by one “factor” that has two “versions”. What terms are now given to describe these concepts?

5. For example for examining seed color, Mendel started with purebred yellow and purebred green seeded plants. Describe what is meant by purebred.

6. What is a genotype?

7. What was the genotype of the purebred yellow and purebred green seeded plants?

Animation 3: Genes don’t blend

Work through the “Genes don’t blend” animation, and answer the following questions.

1. For each trait that Mendel studied, he set up a cross between the two pure-bred plants with opposing traits. What did he expect the resulting offspring would look like for the following crosses:

Puffed x Pinched = _________________________

Yellow seed x Green seed = __________________

Tall x Short = _____________________________

2. What do we call the offspring of two purebred parent plants?

3. To Mendel’s surprise, what were the actual results from the purebred crosses?
Puffed x Pinched = _________________________
Yellow seed x Green seed = __________________
Tall x Short = _____________________________
Side flower x Top flower = ___________________
Colored coat x White coat = __________________
Round x Wrinkled = ________________________
Green pod x Yellow pod = ___________________
4. After the experiments falsified his hypothesis, what was Mendel’s next task?

Animation 4: Some genes are dominant
Work through the “Some genes are dominant” animation and answer the following questions.
1. What did Mendel do to figure out why the hybrids were not a blend of the parent population?

2. What were the results seen in the second generation?

3. After performing many experiments, what did Mendel conclude from the second generation?

4. Fill in the blanks of the following sentence:
Pea color is controlled by one __________, which has a “green” form and a “yellow” form. Each form is called a(n) ______________.
5. What is meant by the term homozygous green and homozygous yellow? What notation was used to represent these plants?

6. What do the offspring of two purebred plants inherit from each parent?

7. What combinations of alleles do plants have that produce yellow seeds? What combinations of alleles do plants have to produce green seeds?

8. The hybrid offspring can also be described as being heterozygous. Explain what this means.

9. What were the 3 possible genotypes in the second generation? Describe their corresponding phenotypes.

10. What was Mendel able to prove about the dominant and recessive versions of genes (factors) that are present within pea plants?

11. How are dominant and recessive genes written or abbreviated in a genotype?

Can you tell by looking at the genotype of the individual if he/she is homozygous or heterozygous for that trait? Explain

Case Study:
Visit the link below and get a perspective on the importance of Mendelian genetics and its applications in real life: https://knowgenetics.org/
Click on Case Studies
Select any two of these topics “Ownership of Genetic Information” and “Should Genes be Patentable” and “When Informed Consent is Unclear” and “Genetic Discrimination”. After reading them, vote on those two. Insert a short 3-5 sentence paragraph here on each topic and why you chose to vote that way.

Topic 1 – vote – reasoning

Topic 2 – vote – reasoning

Part 2 – Punnett Square Problems
1. Define:
a. Gamete,
b. gene
c. allele
d. dominant allele
e. recessive allele
f. phenotype
g. genotype
h. homozygous
i. heterozygous
j. Test cross
k. Parental generation
l. Pure breed
m. Hybrid
n. Incomplete dominance
o. Co-dominance
p. Epistasis

From the following problems (#1-#21) select any five and solve them in full detail.
2. In cats, long hair is recessive to short hair. A true-breeding (homozygous) short-haired male is mated to a long-haired female. What will their kittens look like?

3. Two cats are mated. One of the parent cats is long-haired (recessive allele). The litter which results contains two short-haired and three long-haired kittens. What does the second parent look like, and what is its genotype?

4. Mr. and Mrs. Jones have six children. Three of them have attached earlobes (recessive) like their father, and the other three have free earlobes like their mother. What are the genotypes of Mr. and Mrs. Jones and of their numerous offspring?
5. Mr. and Mrs. Anderson both have tightly curled hair. (The hair form gene shows incomplete dominance. There are two alleles, curly and straight. The heterozygote has wavy hair.) The Andersons have a child with wavy hair. Mr. Anderson accuses Mrs. Anderson of being unfaithful to him. Is he necessarily justified? Why or why not?

6. In certain portions of the Jewish population, there is a genetic disease called Tay Sachs disease, which is fatal to infants within the first five years of life. This disease is caused by a recessive allele of a single gene. Why doesn’t the allele for Tay Sachs disease simply disappear? (Hint: if it is a recessive disease – what should be the genotype to show the disease? What happens when the individual does not have a recessive genotype?

7. If a pure-breeding (homozygous) black (dominant), long-haired (recessive) cat is mated to a pure-breeding Siamese, short-haired cat, and one of their male offspring is mated to one of their female offspring, what is the chance of producing a Siamese colored, short-haired kitten?

8. In a particular family, one parent has Type A blood, the other has Type B. They have four children. One has Type A, one has Type B, one has Type AB, and the last has Type O. What are the genotypes of the parents?

NOTE: The ABO blood type gene has three alleles. IA and IB are codominant; i (for Type O) is recessive to both.
9. It was suspected that two babies had been exchanged in a hospital. Mr. and Mrs. Jones received baby #1 and Mr. and Mrs. Simon received baby #2. Blood typing tests on the parents and the babies showed the following:
Mr. Jones: Type A Mr. Simon: Type AB
Mrs. Jones: Type O Mrs. Simons: Type O
Baby #1: Type A Baby #2 Type O
a. Were the babies switched? How do you know whether they were or they weren’t?

10. A curled ear in cats is caused by a mutated gene and has been developed into a breed, known as the American Curl. A cat with curled ears was mated with a cat with normal ears and all of the offspring have curled ears. Is this trait dominant or recessive? What is the genotype of the curled eared cat?

11. In horses chestnut (red) color is recessive to spotted. If a heterozygous spotted male is crossed to a chestnut female what is the genotypic and phenotypic ratio of the offspring. Show your work.

12. A man with type O blood marries a woman with Type AB blood. Among their children, what proportion would you expect to have blood types like one or the other of these parents? What proportion would have expect to have blood types different from both parents? Explain.

13. If two people who are both carriers for a genetically inherited fatal recessive disease decide to become parents, what will be the odds that their children will also be carriers?

14. If a woman is homozygous normal and her husband is heterozygous for a genetically inherited recessive disease and they decide to become parents, what is the probability that they will have a healthy child?

15. In tigers, a recessive allele causes an absence of fur pigmentation (a “white tiger”) and a cross-eyed condition. If two phenotypically normal tigers that are heterozygous at this locus were mated, what percentage of their offspring will be cross-eyed? What percentage will be white?

16. Two true breeding parents are crossed similar to Mendel’s P generation. A tall plant is crossed with a short plant. What is the expected outcome for the F1 generation?
a. all short
b. all tall
c. all medium height
d. half tall, half short

17. A dihybrid cross (AaBb x AaBb) will result in what offspring ratio?
a. 4:4:2:2
b. 1:3:1
c. 3:1
d. 9:3:3:1

18. In humans colorblindness (b) is an example of a sex-linked recessive trait. In this problem, a male with colorblindness marries a female who is not colorblind but carries the (b) allele. Using a Punnett square, determine the genotypic and phenotypic probabilities for their potential offspring.

19. About 80% of the human population can taste the chemical phenolthiocarbamide (PTC), while the other 20% can’t. This characteristic is governed by a single gene with two alleles, a tasting allele and a non-tasting allele. What does this statistic tell us about which allele (tasting or non-tasting) is dominant?

20. In man, assume that spotted skin (S) is dominant over non-spotted skin (s) and that wooly hair (W) is dominant over non-wooly hair (w). Cross a marriage between a heterozygous spotted, non-wooly man with a heterozygous wooly-haired, non-spotted woman. Give genotypic and phenotypic ratios of offspring.

21. In horses, black is dependent upon a dominant gene, B, and chestnut upon its recessive allele, b. The trotting gait is due to a dominant gene, T, the pacing gait to its recessive allele, t. If a homozygous black pacer is mated to a homozygous chestnut trotter, what will be the appearance of the F1 generation?

Sex linked traits: Answer all questions in this section
Background Information:
Sex-linked traits are those whose genes are found on the X chromosome but not on the Y chromosome. In humans the X chromosomes are much larger than the Y chromosome and contains thousands of more genes than the Y chromosome. For each of the genes that are exclusively on the X chromosomes, females, who are XX, would obviously have two alleles. Males, who are XY, would have only one allele. Thus females with one recessive allele and one dominant allele, for a gene that is unique to the X chromosome, will always display the dominant phenotype. However, a male with a recessive allele for a gene unique to the X chromosome will always exhibit that recessive trait because there is no other corresponding allele on the Y chromosome.
In humans, each of two different sex-linked genes has a defective recessive allele that causes a disease. The diseases are hemophilia and colorblindness. In hemophilia, the defective allele prevents the synthesis of a factor needed for blood clotting. In colorblindness, the defective allele prevents a person from seeing certain colors.
Use the information below to answer the following questions.
XH- X chromosome with normal dominant allele (no hemophilia)
Xh – X chromosome with recessive hemophilia allele
Y – Y chromosome (does not contain comparable gene)
XB – X chromosome with normal dominant allele (not colorblind)
Xb – X chromosome with recessive colorblind allele
Y -Y chromosome (does not contain comparable gene)

1. Ace my homework – Write the genotypes for the following phenotypes of red-green color blindness.
a. normal male _____________
b. normal female carrying no colorblind alleles (Homozygous) _____________
c. colorblind male _____________
d. normal female carrying the colorblind allele (Heterozygous) _____________
e. colorblind female _____________
2. XBXB x XbY

a. What proportion/percent of the male children are colorblind? _____________

b. What proportion/percent of the female children
are colorblind? _____________
3. XBXb x XBY

a. What proportion of the male children are colorblind? _____________
b. What proportion of the female children are colorblind? _____________
4. What is the probability that a colorblind woman who marries a man with normal vision will have a colorblind child? _____________

_____________ X _____________
5. A normal-sighted woman (whose father was colorblind) marries a colorblind man. _____________ X _____________

6. What is the probability that they will have a son who is colorblind? _____________
7. What is the probability that they will have a colorblind daughter? _____________

For the following Sex-Linked Punnett Squares:
H= normal blood clotting
h=hemophilia

8. XHXh crossed with XHY
What is the probability that any of their offspring will have hemophilia? _____________

1. A woman who is a carrier for hemophilia marries a hemophiliac man:

a. What proportion of the male children are
hemophiliacs? _____________

b. What proportion of the female children are
hemophiliacs? _____________
2. A phenotypically normal man marries a homozygous normal woman.

_____________ X _____________

a. What is the probability that any of their children
will be hemophiliacs? _____________
3. A phenotypically normal woman has phenotypically normal parents. However, she has a hemophiliac brother.
(Mom is carrier) (Dad) Brother

_____________ _____________ _____________

a. What are her chances of being a carrier for
hemophilia? _____________

Gregor Mendel chose to study pea plants because they have distinct and easily observable traits, are self-fertilizing, and have a short generation time.

Self-fertilization means that a pea plant can produce seeds without the need for pollination from another plant. This is facilitated by the structures called stamens and pistils, which allow the transfer of pollen from the male reproductive organ (stamen) to the female reproductive organ (pistil).

Mendel started his experiments by crossing two purebred plants with contrasting traits. To complete the cross-fertilization, he removed the stamens of one plant and manually transferred the pollen from the other plant to the pistil.

Phenotype refers to the physical appearance of an organism. Mendel observed seven phenotypes in pea plants: flower color, flower position, seed color, seed shape, pod color, pod shape, and plant height.

For each phenotype, Mendel observed two different versions. This is significant because it showed that the traits were not simply blending together but instead were being passed down as distinct traits.

Mendel used purebred strains of pea plants because he wanted to ensure that the traits being studied were true-breeding, meaning that the offspring of the plants would display the same traits as their parents.

The terms now used to describe Mendel’s concepts are gene and allele.

Purebred refers to an organism that always produces offspring with the same traits when it is self-fertilized or crossed with another purebred organism of the same trait.

Genotype refers to the genetic makeup of an organism, including all of its inherited genes.

The genotype of the purebred yellow and green seeded plants was homozygous, meaning that they had two identical alleles for the gene controlling seed color.

Puffed x Pinched = all offspring with puffed flowers
Yellow seed x Green seed = all offspring with yellow seeds
Tall x Short = all offspring with tall plants

The offspring of two purebred parent plants are called F1 hybrids.

Puffed x Pinched = all offspring with puffed flowers
Yellow seed x Green seed = all offspring with yellow seeds
Tall x Short = all offspring with tall plants
Side flower x Top flower = all offspring with side flowers
Colored coat x White coat = all offspring with colored coats
Round x Wrinkled = all offspring with round seeds
Green pod x Yellow pod = all offspring with green pods

Mendel’s next task was to figure out why the hybrids were not a blend of the parent population.

Mendel repeated the crosses, but this time allowed the F1 hybrids to self-fertilize or cross-fertilize with each other.

In the second generation, Mendel observed the appearance of both traits from the parent population.

Mendel concluded that the traits from the parent population were still present in the offspring but were masked by the dominant trait.

“Pea color is controlled by one gene, which has a “green” form and a “yellow” form. Each form is called a(n) allele.”

Homozygous green and homozygous yellow refer to plants that have two identical alleles for the gene controlling seed color. The notation used to represent these plants was YY for homozygous yellow and yy for homozygous green.

The offspring of two purebred plants inherit

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