You want to know whether the gene for hair color in cats is autosomal or sex-lin
ID: 30520 • Letter: Y
Question
You want to know whether the gene for hair color in cats is autosomal or sex-linked.
You should assume that:
A. Only one gene controls hair color in cats.
B. There are only 2 alleles of this gene:G for gray and g for white.
C.In the heterozygous condition, gray is dominant.
You are given a white female cat from a long line of white (only) cats and a gray male from a very long line of gray (only) males.
1) Outline the breeding experiment you would set up to determine how hair color gene is inherited.
2) What information does the F1 generation give you?
3) What further information do you get from the F2 generation results?
Explanation / Answer
Your parents are homozygous (they are from lines that breed true). The only way to answer this properly is to do both crosses.
Autosomal BB x bb, female produces B gametes, males b. F1 is all Bb and brown.
F1 cross is Bb X Bb, both parents produce B and b gametes. F2 is BB Bb bB bb. Genotype ratio 1:2:1, phenotype ratio 3:1 brown: blonde.
Sex-linked XBXB x XbY. Females produce XB gametes, males Xb and Y.
F1 females are XBXb brown, F1 males are XBY brown.
F1 cross XBXb x XBY. Females produce XB and Xb gametes, males XB and Y.
F2 females are XBXB or XBXb all brown. Males are XBY and XbY. Half brown and half blonde.
Questions 1: Cross the brown and blonde parents. Cross F1 males and females, score phenotypes in F2.
2. The F1 confirms that brown is the dominant allele, as all offspring are brown. It also confirms that the brown parent is homozygous, as if it had been heterozygous (Bb x bb or bY) you would have got some blonde offspring.
3. The F2 confirms whether it is autosomal or X-linked. For autosomal you will get a 3:1 ratio brown:blonde and it is the same for both sexes. If it is X-linked you will get all brown females and half brown, half blonde males.
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