Question

15. Two short haired guinea pigs are mated several times. Out of

100 offspring, 25 of them have long hair. What are the probable
genotypes of the parents?

Answer 1

The probable genotypes of two short-haired guinea pigs that produce 25 long-haired offspring out of 100 are both heterozygous (Ss) for the hair length gene. A Punnett square reveals a 3:1 phenotypic ratio, which aligns with the observed outcome.

Step-by-step explanation:

If two short-haired guinea pigs produce 100 offspring, with 25 of them having long hair, we can assume that long hair is a recessive trait. To use a Punnett square to predict the probable genotypes of the parents, we must look at the proportion of long-haired to short-haired offspring. Since 25 out of 100 offspring have long hair, and assuming long hair is recessive, we can infer that each parent must have one allele for long hair.

Thus, the probable genotypes of the two parents are both heterozygous for the hair length gene (Ss), where 'S' represents the dominant short hair allele and 's' the recessive long hair allele.

Using the Punnett Square:

• Parental genotypes: Ss x Ss
• Probable offspring genotypes: SS (short hair), Ss (short hair), sS (short hair), ss (long hair)
• Genotypic ratio: 1 SS : 2 Ss : 1 ss
• Phenotypic ratio: 3 short hair : 1 long hair

In this case, the offspring ratio closely fits with the expected 3:1 phenotypic ratio for a cross between two heterozygous individuals with a simple recessive trait for hair length.

Answer 2

Both heterozygous, with the trait for short hair being dom over the long hair

Step-by-step explanation:

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