In guinea pigs short hair S,is dominant to long hair. A heterozygous guinea pig mated with a homozygous recessive pure breed. State the proportion of the geno type and the phenotype of the offspring
3:1
To determine the proportions of genotypes and phenotypes of the offspring in this genetic cross, we need to use the principles of Mendelian genetics.
Let's assign the following letters to represent the alleles for hair length:
- "S" for short hair (dominant allele)
- "s" for long hair (recessive allele)
Based on the given information, we know that the heterozygous guinea pig (Ss) is crossed with a homozygous recessive pure breed (ss).
Now let's analyze the possible genotypes and phenotypes of the offspring.
Possible genotypes:
- When the heterozygous guinea pig (Ss) is crossed with a homozygous recessive (ss), there are two potential genotypes for the offspring: Ss and ss.
Possible phenotypes:
- The genotype Ss results in a short-haired guinea pig because the "S" allele is dominant.
- The genotype ss results in a long-haired guinea pig because it requires two copies of the recessive "s" allele to have long hair.
Now, let's calculate the proportions:
Genotypic ratio:
- 50% of the offspring will have the genotype Ss (short hair).
- 50% of the offspring will have the genotype ss (long hair).
Phenotypic ratio:
- 50% of the offspring will have short hair.
- 50% of the offspring will have long hair.
Therefore, the proportions of the genotypes are 1:1 (Ss:ss) and the proportions of the phenotypes are also 1:1 (short hair:long hair).
To determine the proportion of genotypes and phenotypes in the offspring of a heterozygous guinea pig mated with a homozygous recessive pure breed, we need to use Punnett square analysis.
Let's use the following symbols:
- S: Dominant short hair allele
- s: Recessive long hair allele
The parent genotypes are as follows:
Heterozygous guinea pig (Ss)
Homozygous recessive pure breed (ss)
We can now create a Punnett square to determine the possible genotypes and phenotypes of the offspring:
| s | s |
---------------------
S | Ss | Ss |
s | ss | ss |
From the Punnett square, we can see that there are two possible genotypes in the offspring:
- Ss: Short hair genotype
- ss: Long hair genotype
The ratio of genotypes in the offspring is 2:2, or 1:1.
Regarding the phenotypes of the offspring:
- The genotypes SS and Ss both show the dominant short hair trait, so the phenotype will be short hair.
- The genotype ss shows the recessive long hair trait, so the phenotype will be long hair.
Therefore, the proportion of phenotypes in the offspring will be 2:2, or 1:1, with an equal number of guinea pigs displaying short hair and long hair.