Biology 3201 – Genetics Study Guide Part 1 Gillam Holy Heart Name:______________

1.) In mice grey coat (G) is dominant to white coat (g). Determine the genotype and phenotype ratios in each of the

following crosses.

a) Pure grey x pure white

b) Pure Grey x hybrid grey

c) Pure white x hybrid grey

d) Hybrid grey x hybrid grey

2.) Both a man and his wife are heterozygous for freckles. Freckles are dominant to no freckles. What is the chance

(probability) that their first child will have no freckles?

These questions you will have to work backwards

3.) Both you and your sister have attached ear lobes, yet your parents have unattached (free) ear lobes. Free

earlobes are dominant to attached ear lobes. What are the possible genotypes of you, your sister and your

parents

4.) A father has dimples, the mother has no dimples, and all of the children have dimples. Dimples are dominant

over no dimples. Give the probable genotypes of both parents and the children.

5.) In pea plants yellow seeds are dominant to green seeds. What are the most probable genotypes of the parents

which produce the following results. (hint total number of plants is important)

a) 280 yellow-seeded plants and 285 green seeded plants.

b) 350 green seeded plants

c) 338 yellow seeded plants

d) 375 yellow seeded plants and 125 green seeded plants

6.) Label the following genotypes as heterozygous, Homozygous, dominant, recessive, hybrid or purebreed? (some

may have more than one label)

Rr

YY

yy

RR

Rr

Yy

rr

7.) Genotype:

___________________________________________________________________________________________

_________________________________________________________________

Phenotype:

___________________________________________________________________________________________

_________________________________________________________________

8.) Mendel found that the allele for tallness in peas (T) is dominant to its allele for shortness. What is the

phenotypic ratios for each cross below?

a) Heterozygous self fertilized

b) Homozygous tall x heterozygous

c) Heterozygous x short

9. Two Drosophila (fruit flies) with normal wings are crossed. Among 123 offspring, 88 have

normal wings and 35 have dumpy wings.

a. What inheritance pattern is shown by the normal and dumpy wings?

b. What were the genotypes of the two parents?

c. c. If a dumpy winged female is crossed with her father, how many normal winged flies will be expected among 80

offspring?

10. Sniffles, a male mouse with a colored coat, was mated with Esmeralda, an alluring albino. The

resulting litter of 17 all had colored fur. The next time around, Esmerelda was mated with

Fluffy, who was the same color as Sniffles. Some of Esmerelda’s next litter were white.

a. What are the probable genotypes of Sniffles, Esmerelda and Fluffy?

b. If a male of the first litter were mated with a colored female of the second litter, what phenotypic ratio might be

expected among the offspring?

c. What would the expected results be if a male from the first litter were mated with an albino

female from the second litter?

Test Cross 1. In fruit flies, red eyes are dominant over sepia (brownish) eyes. Being the great genetic student that you are, you

happen to have a culture of pure red eye and pure sepia eye flies in your laboratory. While working in your lab late one night, a cute, fuzzy, and fantastically friendly, red eyed fruit fly came in for a crash landing on your banana. Wanting (naturally) to know more about your new friend, you decide to run a test-cross on your little, buzzing buddy.

a. Give the phenotypes of the flies in your test-cross:___________X___________

b. If all of the offspring turn out to be red-eyed (all 347 of them!!!) what would the genotypes of the flies used in your test-cross? (Use “R” and “r”)

___________X__________ Diagram the cross:

Genotypic ratio= _____________________

Phenotypic ratio=_____________________

c. If about 179 of the 347 show up with sepia eyes, what was the actual genotype of your new found friend? _______________

2. Let’s say you decide to make your living as a mink farmer. In mink, black fur is dominant over white fur. Since the market for black mink coats is higher than white mink, you (being the entrepreneur that you are) decide to only raise black mink. Everything is going well but the guy you bought your mink from seemed a little crooked! You want to make sure they are pure breeds so you run a test-cross.

a. Give the phenotypes of the mink in your test-cross:

____________X___________

b. In your first test-cross, 30 out of 60 offspring are black and the rest are white! No wonder you got such a good deal! What are the genotypes of the mink used in your test-cross? (Use “B” and “b”)

___________X__________ Diagram the cross:

Genotypic ratio=_______________

Phenotypic ratio=_______________

c. Was the black-furred mink you chose for your test-cross a pure breed? What is his genotype? ______________

Incomplete Dominance Crosses involving incomplete dominance Heterozygotes show a mix between the two dominant traits. 1. In Japanese four o'clock plants red (R) color is incompletely dominant over white (W) flowers, and the

heterozygous condition (RW) results in plants with pink flowers. For each of the following construct a punnett square and give the phenotypic ratios of the offspring.

a) a red plant and a white plant b) a red plant and a pink plant b) a white plant and a pink plant d) two pink plants

2. In some cats the gene for tail length shows incomplete dominance. Cats with long tails and cats with no tails are homozygous for their respective alleles. Cats with one long tail allele and one no tail allele have short tails. For each of the following construct a punnett square and give the phenotypic ratios of the offspring.

a) a long tail cat and a cat with no tail

b) a long tail cat and a short tail cat

c) a short tail cat and a cat with no tail

d) two short tail cats

Co-dominance 1. In some cattle the genes for brown hair and for white hair are co-dominant. Cattle with alleles for both

brown and white hair, have both brown and white hairs. This condition gives the cattle a reddish color, and is referred to as Roan. For each of the following crosses construct a punnett square and give the phenotypic ratios of the offspring.

a) a brown cow and a white bull

b) a brown cow and a roan bull

c) a white cow and a roan bull

d) a roan cow and a roan bull

Dihybrid Crosses NOTE — Show all steps and working in these genetic problems. 1. A. The long hair of Persian cats is recessive to the short hair of Siamese cats. The black coat of Persian cats is dominant to the tan coat of Siamese cats. If a pure black, long-haired Persian is mated to a pure tan, short haired Siamese, what will be the appearance of the F1 generation

B. If two of these F1 cats are mated, what is the probability of obtaining a long-haired, tan coat in the F2 generation?

2. Red fruit (R) is dominant to yellow fruit (r) in tomatoes. Tallness (T) is dominant to shortness (t) in these plants. What phenotype and genotype ratios would you predict for the offspring of parent plants, one of which is red homozygous and tall homozygous, and the other is red heterozygous and tall heterozygous.

3. Attached ear lobes are recessive to free ear lobes, and red hair is recessive to brown hair in humans. What phenotype and genotype ratios would be expected in children born to a couple of which the male is purebred red hair and heterozygous for free ear lobes, and the female is heterozygous for hair color and homozygous recessive for earlobes.

4. The position of the flower on the stem of the garden pea is governed by a pair of alleles. Flowers growing in the axils(upper angle between petiole of leaf and stem) are produced by the action of a dominant allele (A). Those growing only at the top of the stem are recessive allele (a). Coloured flowers are produced by the dominant allele (C), and white flowers by its recessive allele (c). A dihybrid plant with coloured flowers in the leaf axils is crossed with a pure strain of the same phenotypes. What genotypic and phenotypic ratios are expected in the F1 progeny?

5. Suppose we decide to study two different traits of an organism at once. By applying Mendel’s Laws of Dominance, Segregation and Independent assortment, Find the genotype and phenotype ratio of traits in the F2 offspring in Guinea Pigs in which Black fur is dominant to white fur ; Short fur is dominant to long fur; and Rough coat is dominant to smooth coat. The following three P1 generations are crossed.

Case 1 BBSS X bbss Case 2 BBRR X bbrr Case 3 SSRR X ssrr

How do the genotypic and phenotypic ratios compare in all three crosses above?

6. Tall tomato plants are produced by the action of a dominant allele T and dwarf plants by its recessive allele t . Hairy stems are produced by a dominant allele H and hairless stems by its recessive allele h. A heterozygous tall, and heterozygous hairy plant is crossed with a dwarf hairless tomato plant. Determine the genotypic and phenotypic ratio for this cross

7. Black coat colour in Cocker Spaniels is dominant, while red coat colour is recessive; solid pattern is dominant, while spotted pattern is recessive. A solid black male is mated to a solid red female and

produces a litter of six pups: two solid black, two solid red, one black and white, and one red and white. Determine the likely genotypes of the parents. (Show all workings)

Use the information below for problems 8-10. Humans: Normal skin pigment – Dominant Tongue roller - Dominant Albino – Recessive Non-tongue roller - Recessive Freckles – Dominant Black hair – Dominant No Freckles – Recessive Light hair - Recessive 8. A person is heterozygous for tongue-rolling and homozygous recessive for freckles. This person marries an

individual who is heterozygous for both tongue-rolling and freckles. State the phenotypic ratios of any possible children.

9. A father is heterozygous for black hair and heterozygous for tongue-rolling. The mother is light-haired and cannot roll her tongue. What is the probability of having a child with light hair who is a tongue-roller?

10. A man who is heterozygous for freckles and skin pigmentation marries a woman who is also heterozygous for

freckles and skin pigmentation. State the phenotypic ratios for any possible offspring.

Multiple Alleles Crosses involving multiple alleles Blood types are controlled by three alleles A, B, O. Refer to your notes and text for the genotypes and resultant phenotypes involving this trait, and answer each of the following questions. 1. A woman homozygous for blood type B marries a man that is heterozygous for blood type A.

State the possible phenotypic ratios of the offspring.

2. A man with blood type O marries a woman with blood type AB. State the possible phenotypic ratios of the offspring. 3. A type B woman whose mother was type O marries a type O man. What are the possible phenotypic ratios of their

offspring? 4. A type A woman whose father was type B marries a type B man whose mother was type A. What are the possible

phenotypes of their offspring?

5. What is the probability that a couple whose blood types are AB and O will have a type A child? 6. A couple has a child with type A blood. If one parent is type O, What are the possible phenotypes of the offspring? 7. If a man with blood type B, one of whose parents were Type O, marries a female with blood Type AB, what will be

the theoretical percentage of their children with blood type B? 8. Diagram a cross between a male with type AB blood and a female with type AB. Show the genotypes, phenotypes

and ratios for the F1 generation. 9. Two newborn babies were accidentally mixed up in the hospital, and there was a question of which baby belonged

to which parents. From the following blood types, determine which baby belongs to which parents. Baby 1 - Type O; Baby 2 - Type A Mrs. Brown - Type B; Mr. Brown - Type AB Mrs. Smith - Type B; Mr. Smith – B

10. A man of blood group B is being sued by a woman of blood group A for paternity. The woman’s child is blood type O.

A. Is this man possibly the father of the child?

B. If this man is actually the father of this child then specify the parent’s genotypes.

C. If it is impossible for this man to be the father of this child, specify the man’s genotype. D. If a man was blood group AB, could he be the father of a group O child? Explain.

Polygenic Inheritance The table below shows the gene pairs involved in determining eye colour. One pair codes for pigment in the front of the

iris and the other for pigment in the back of the iris.

1. If a man has grey-blue eyes and a woman has green eyes, use a Punnett square to determine which eye colour

phenotypes would be possible for children born to this couple.

2. If a man has brown eyes and a woman has dark blue eyes, use a Punnett square to determine which eye colour

phenotypes would be possible for children born to this couple.

Sex Linked Traits 1. A woman that is a carrier of hemophilia marries a hemophiliac man. What is the probability that their first child will

be a hemophiliac? 2. A hemophiliac woman has a mother who is phenotypically normal. What are the genotypes of her mother and her

father? 3. What is the probability that a color-blind women who marries a man who is color blind, will have a daughter who is

colorblind? 4. A phenotypically normal man who has a brother with M.D. marries a homozygous normal woman. What is the

probability that any of their children will have M.D 5. What is the probability that two parents with normal color vision will have colorblind sons and daughters if the

mother’s father is colorblind?