1. In cats, the sex-linked gene B determines black when homozygous, yellow when
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Question
1. In cats, the sex-linked gene B determines black when homozygous, yellow when homozygous recessive, and calico when heterozygous.
a) Determine the genotype of the following cats:
i. Yellow female cat
ii. Black female cat
iii. Calico female cat
iv. Yellow male cat
v. Black male cat
b) Explain why calico cats are almost always females.
c) Under what circumstances is it possible to have a calico male?
d) A calico mother has a litter of eight kittens. There are two yellow males, three black males, one yellow female and two calico females. What is the genotype of the father? Show your work.
e) A black cat fathered a litter consisting of two yellow and three calico offspring. What is the genotype of the mother? What are the sexes of the offspring in relation to each color (yellow and calico)? Show your work.
2. With Drosophila flies, eye color is an X-linked trait while leg length is an autosomal trait. For eye color, red (R) is dominant to white (r). For leg length, long legs (L) is dominant to stubby legs (l). A female fly that is heterozygous for red eyes and heterozygous for leg length is mated with a male fly with white eyes and stubby legs.
a) What is the genotype of the female fly?
b) What is the genotype of the male fly?
c) Create a Punnett square that gives rise to the F1 generation.
d) What is the probability (as a fraction) of the F1 offspring:
i. having red eyes and long legs?
ii. having white eyes and long legs?
iii. having stubby legs?
iv. being female with white eyes and stubby legs?
3. Flower position, stem length, and seed shape were three traits that Mendel studied. Each trait is controlled by an independently assorting gene and has dominant and recessive expression as follows:
TRAIT
DOMINANT
RECESSIVE
Flower position
Axial (A)
Terminal (a)
Stem length
Tall (T)
Dwarf (t)
Seed shape
Round (R)
Wrinkled (r)
As seen in the table, the alleles for each dominant and recessive trait is provided.
If a plant that is heterozygous for all three traits were allowed to self-fertilize, calculate the probability (as a fraction) of the following F1 offspring genotypes or phenotypes:
a) homozygous recessive for the three traits
b) heterozygous for the three traits
c) homozygous for axial and tall, heterozygous for seed shape
d) axial, tall, and wrinkled in phenotype
4. You cross together two organisms with genotypes X/x; Y/y; Z/z. Assuming independent assortment of these three genes, calculate the probability (as a fraction) of having offspring with the following genotypes (Show your work!):
a) X/X; y/y; Z/Z
b) x/x; Y/Y; z/z
c) X/x; Y/y; Z/z
d) x/x; y/y; Z/Z
5. Calculate the probability (as a fraction) that each of the following pairs of parents will produce the indicated F1 offspring (assume independent assortment of all gene pairs).
a) a/a; B/b; C/C x A/A; B/b; c/c ? A/a; B/b; C/c
b) A/a; B/b; C/c x A/a; B/b; C/c ? A/a; B/b; C/c
c) A/A; B/b; C/c x A/a; B/b; C/c ? A/A; b/b; C/C
d) A/A; B/B; C/C x a/a; b/b; c/c ? A/a; B/b; C/C
6. Labrador retriever dogs have three coat colors: black, brown and yellow. The color of the pigment deposited in the hairs is determined by a gene with two alleles (B or b). The B allele codes for black pigment and is dominant to the b allele which codes for brown. Another gene with two alleles (E or e) determines if the pigment created will be deposited into the hairs. If both copies (e/e) are recessive, no pigment will be deposited (regardless of which is produced), and the dog will be yellow.
a) What do you call the type of relationship that the E gene has with the B gene?
b) You cross together two Labradors with genotypes B/b; E/e.
i. What is the phenotype of the B/b; E/e genotype?
ii. Determine the phenotypic ratio for the F1 generation. Show your Punnett square!
c) What phenotypic ratios do you get if you cross the following types of Labradors (show your Punnett square as well):
i. B/B; E/E X B/B; E/e
ii. B/b; E/e X b/b; e/e
iii. b/b; E/E X B/B; e/e
Explanation / Answer
Answering completely the first question based on CHEGG rule:
a 1. XbXb -yellow female cat
II. Black female cat- XBXB
III. Calico female cat: XBXb
IV: Yellow male cat: XbY
b. For a cat to be calico in its color , the genotype of the sex linked gene should be heterozygous which is possible when both B and b are present on sex chromosome (XX) that correponds to a female.
c.For a male cat to have a calico pattern, they need to have three sex chromosomes: two Xs and a Y.This XXY combination will occur when there's an incomplete division of the male's XY chromosome pair during fertilization — andit happens rarely in cats. This is known as Klinefelter syndrome.
d. XbY (male) crossed with XBXb (female)
Progenies: XBXb- 2 calico females
XbXb- 1 yellow female
XBY- 3 black males
XbY- 2 yellow males
e. Black cat father genotype= XBY
Mother's genotype= XbXb
XBY crossed with XbXb
Progenies: XbY- 2 yellow (males)
XB Xb- 3 calicos (females)
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