A woman expressing a dominant phenotype is heterozygous (Dd) for the gene.


What is the probability that two grandchildren of the woman who are first cousins to one another will each inherit the dominant allele?

Verified step by step guidance

1. Step 1: Understand the genetic makeup of the woman. She is heterozygous (Dd), meaning she has one dominant allele (D) and one recessive allele (d). Each of her children has a 50% chance of inheriting the dominant allele (D) and a 50% chance of inheriting the recessive allele (d).
2. Step 2: Determine the genetic makeup of the grandchildren. Since the grandchildren are first cousins, they inherit their alleles from different parents (the woman's children). Each parent has a 50% chance of passing on the dominant allele (D) to their child.
3. Step 3: Calculate the probability of one grandchild inheriting the dominant allele (D). This is a simple probability problem where the chance of inheriting the dominant allele from a heterozygous parent is 50%.
4. Step 4: Calculate the probability of the second grandchild (first cousin to the first grandchild) inheriting the dominant allele (D). Similarly, this is also a 50% chance since the second grandchild's parent is heterozygous.
5. Step 5: Combine the probabilities for both grandchildren inheriting the dominant allele. Since the events are independent (inheritance from one parent does not affect the other), multiply the probabilities: P(grandchild 1 inherits D) × P(grandchild 2 inherits D).

Key Concepts

Dominant and Recessive Alleles

In genetics, alleles are different forms of a gene. A dominant allele, represented by a capital letter (e.g., D), masks the effect of a recessive allele (e.g., d) when both are present. An individual with at least one dominant allele will express the dominant phenotype, while a recessive phenotype is only expressed when an individual has two recessive alleles.

Punnett Square

A Punnett square is a diagram used to predict the genetic outcomes of a cross between two individuals. It allows for the visualization of how alleles from each parent combine to produce offspring genotypes. By filling in the square with the possible gametes from each parent, one can easily determine the probabilities of inheriting specific alleles.

Inheritance Patterns in Family Trees

Understanding inheritance patterns is crucial for predicting the likelihood of traits being passed down through generations. In this scenario, the woman (Dd) can pass either the dominant (D) or recessive (d) allele to her children. The probability of her grandchildren inheriting the dominant allele depends on the genotypes of their parents, who are the children of the woman, and their own genetic contributions.