suppose that an allele, d, of a sex-linked gene is recessive and lethal. A man marries a woman who is heterozygous for this gene. If the couple had many normal children, what would be the predicted sex ratio of these children?
Base your response on the number of predicted living children
- Genotypes of the parents
- Gene combination for the gametes of each parent
- A completed punnett square
- Genotype ratio of offspring (prediction)
- Phenotype ratio of offspring (prediction)
We do not do your homework for you. Although it might take more effort to do the work on your own, you will profit more from your effort. We will be happy to evaluate your work though.
To determine the predicted sex ratio of the couple's children, let's go through the steps:
1. Genotypes of the parents:
- The man's genotype is irrelevant in this case since we are focusing on a sex-linked gene. However, let's assume he does not carry the recessive allele "d" for the purposes of this question.
- The woman is heterozygous for the gene, meaning she has one dominant allele "D" and one recessive allele "d".
2. Gene combination for the gametes of each parent:
- The woman can produce two types of gametes: one with the "D" allele and one with the "d" allele.
- The man, assumed to not have the recessive allele "d," can only produce gametes with the dominant "D" allele.
3. Completed Punnett square:
Let's use "D" to represent the dominant allele and "d" for the recessive allele. The Punnett square for the cross between the woman and man would look like this:
| D | D |
---|-------|-------|
d | Dd | Dd |
---|-------|-------|
d | Dd | Dd |
As both parents only have the "D" allele, all offspring will receive the "D" allele.
4. Genotype ratio of offspring (prediction):
From the Punnett square, we can see that there are two genotypes possible for the offspring: "Dd" and "Dd".
The genotype ratio is 2 "Dd" : 2 "Dd" (or simply 1:1).
5. Phenotype ratio of offspring (prediction):
Since the recessive "d" allele is lethal, individuals with the genotype "Dd" will still be normal phenotypically.
Therefore, the phenotype ratio is also 2 normal : 2 normal (or 1:1).
In conclusion, based on this scenario, the predicted sex ratio and phenotype ratio of the couple's children would be equal, resulting in a 1:1 ratio of normal male to normal female offspring.