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Genetic problems (20-21) Monohybrid crosses 1. In guinea pigs, a rough coat is dominant over smooth. If Pete, a cool, young homozygous rough coated guinea pig mates with Kris, an athletic, smooth coated guinea pig, what will be the phenotype(s) of their offspring? R

R

phenotypes

Genotypes RR

Rr

r

Rr 4/4 rough coat

4/4 Rr rr

Rr

r

Rr

2. Fred, a kind hearted homozygous black male guinea pig and Kate, a wonderful homozygous white female decided to start a family. Black is dominant to white. They have four children (F1 generation) . Two of their children mate (only acceptable for guinea pigs!!). Their children (F2 generation) are ¾ black and ¼ white. Assign letters for black and white, given the above information. B

B BB

b

b

B

Bb

B

Bb

BB

Bb F2

F1 b

bb

Bb

b

Bb

Bb

bb

3. Some of the black guinea pigs produced in the F2 generation in problem #2 are homozygous and some are heterozygous. Describe the cross you would use to determine whether a particular guinea pig was homozygous or heterozygous. B

B

BB

B

b

Bb

Bb

b

b

Bb

Bb

b

Bb

Bb

Bb

b

cross with the recessive

bb

bb

4. Speedy, a homozygous black rabbit and Slothra, a homozygous white rabbit decide it is time to grow up and become parents. If black is dominant, list the possible genotypes and phenotypes of their offspring. B b

B Bb

phenotype

Bb 4/4 black

b

Bb

genotype

Bb

4/4 Bb

5. In humans, dark eyes (brown, hazel or grey) are dominant over blue eyes. If a mysterious dark eyed man marries a carefree, blue eyed woman, what will be the phenotype of their children? B

B

b

Bb

bb

B

BB or Bb b

bb

b

Bb

Bb b

Bb

b

Bb

Bb

bb

pheno 2/4 brown, 2/4 blue

pheno 4/4 brown

6. In garden pea plants, round seed (R) is dominant over wrinkled seeds (r). A pea plant which is homozygous for round seed shape (RR) is crossed with another plant which is heterozygous for seed shapre (Rr). List the genotypes and phenotypes of the expected offspring. R

RR

R

R

RR

RR

r

Rr

Rr

pheno 4/4 round

geno 2/4 RR, 2/2Rr

Rr

7. In flying zebras, purple fur (P) is dominant to brown fur (p). If a zebra that is homozygous dominant for purple fur is crossed with a brown zebra, what proportion of their offspring will have purple fur? P PP

P pheno 4/4 purple

p

Pp

Geno 4/4 Pp

Pp

pp p

Pp

Pp

8. In longhorn butterflies, orange wings (O) are dominant to black wings (o). If an orangewinged heterozygous butterfly is crossed with a black-winged butterfly, what proportion of their offspring would be expected to have orange wings? O

o

Oo o

Oo

oo pheno 2/4 orange, 2/4 black

oo o

Oo

oo

geno 2/4 Oo, 2/4 oo

Dihybrid Genetic Crosses (20-21) 1. In watermelons, the genes for green color (G) is dominant over striped (g) and short shape (S) is dominant over long shape (s). If a plant with long, striped fruit is crossed with a plant which is heterozygous for the traits of color and shape. What are the genotypes for the two parent plants? What phenotypes would this cross produce?

2. In cattle the gene for polled (hornless) condition is dominant to the gene of having horns. Also, the gene for a spotted coat is recessive to the gene for a solid coat. The bull is purebred for polled and for solid coat color. The cow is a heterozygous for both polled and solid coat color. What are the genotypes and phenotypes for the offspring? H

H

S

HHSS

S

2/4 HH H

HH

2/4 SS S

HH

SS

SS

2/4 Hh HhSs

2/4 Ss s h

Hh

Hh

HHSS

HhSs

HHSs 4/16

Ss

HhSS

HHSs

pheno

genotype

HHSS 4/16

Ss

HhSs 4/16

HhSS 4/16

hornless and solid coat 4/16

3. In some dogs, the trait for barking is dominant over the trait for non-barking. Also, erect ears are dominant over drooping ears. The male is heterozygous for the barking trait and heterozygous for the trait of erect ears. The female is homozygous for drooping ears and heterozygous for barking. What will be the genotype and phenotype of the pups? B

b

E

e

BbEe B

BB

Bb e

Ee

ee

Bbee b

Bb

bb

1/4 BB

e

Ee

ee

2/4 Ee

2/4 Bb 1/4 bb 2/4 ee

BbEe 4/16 Barking with erect ears 6/16

Bbee 4/16 BBEe 2/16 16/16 BBee 2/16

Barking with Drooping ears 6/16

bbee 2/16 bbEe 2/16

Non-Barking with erect ears 4/16

Non-barking with drooping ears 4/16...