Question

One of the genes controlling coat colour in cats is located on the X chromosome. The Xy allele of this gene produces yellow/orange coat colour and the Xb allele produces black coat colour. Heterozygous females have black and orange patches and are called tortoiseshell or calico. A litter of kittens consists of two calico females, and three yellow females. There is only one possible combination of parental phenotypes that would give rise to such a litter.

Answer 1

a. Using a punnett square, determine the phenotypes and genotypes of the parents.
b. How would it be possible to have a male calico cat? Include the genotype in your answer.

Answer 2

I never knew in a punntt square I can determine 5 genotypes..

Answer 3

Female genotypes have two X sex chromosomes

Xy allele gene produces yellow/orange coat colour (XyXy)

Xb allele produces black coat colour (XbXb)

Heterozygous females (XyXb) = calico

two calico females thus two that are heterozygous with XbXy chromosome

and three XyXy chromosome kitties

Notice that these were all popped out at the same time by the same mate usually the punnet square is used to describe static populations as they go through generations.

So we have three options
the female is XyXb and the male is Xy
or
the female is XyXy and the male is Xb
or
the female is XbXb and the male is Xy

Answer 4

since the male contributes an X chromosome from his gamete and there are homologous Xy chromosomes we must assume the the chromosomes have to be

the female is XyXb and the male is Xy

Answer 5

does this make sense to you?

Answer 6

kind of. wait a minute.

Answer 7

Think about the haploid gametes combining

Answer 8

and remember we are dealing with only one generation here

Answer 9

"two calico females thus two that are heterozygous with XbXy chromosome and three XyXy chromosome kitties".. I don't understand.

So you mean: Two calico females, which means that there are two heterozygous: XbXY? And three yellow females: XYXY?

Answer 10

a male can be Xb?

Answer 11

Well each parent provides half of the genetic make up for the offspring. So if the male was Xb, the XYXY chromosome would not be possible

Answer 12

why can't a male have a gene instead of just an allele?

Answer 13

ohh, yup.

Answer 14

im pretty sure an allele and a gene is the same thing, an allele is just a term used to describe an alteration of a gene in a population of the same type of gene

Answer 15

at least that is the understand I have obtained from my previous bio course

Answer 16

oh. But like I guess why can't a male have XbXb instead of just Xb?

Answer 17

A male is XY so it can't have more than one X chromosome. I recommend memorizing this as it is elementary and important to know (so people dont think you are dumb which I'm not saying you are because I'm still learning pellet I should know by now :D)

Answer 18

ohh.. right, anda female is XX.

Answer 19

yup

Answer 20

anything else you need explaining? thanks for the question it was fun

Answer 21

but how will I know the possible combination of parental genotypes if there are a litter of kittens consisting of two calico females and three yellow females? 'Cause in a punnett square isn't it just like 4 genotypes I can know?

Answer 22

thank you by the way :)

Answer 23

Well we are dealing with one litter, a punnet square is used to show how alleles are distributed over generations. We are dealing with one generation, since we are we only need to look at the kitties genomes to know the parents genomes.

Since a male can only have one X chromosomes and when his diploid genome splits into two haploid genomes with only one set of chromosomes. The gamete (sperm cell) will either have an X or a Y chromosome.

With the female the egg can either be Xy or Xb

Thus for there to be XyXy chromosomes the male sperm cell has to have an Xy chromosome

Answer 24

Pf = female parent
Pm = Parent Male

K = kitties

Answer 25

Just think of this as a population of 2 cats lol

Answer 26

ohh.. I see your point now :P LOL, thank you! So the info about 'a litter of kittens consists of two calico females, and three yellow females' is for me to know their gene?

Answer 27

like whether they are heterozygous XyXb or homozygous XyXy or XbXb?

Answer 28

if we had 4 cats all doing the nasty then you would have a square like this