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


Draw a pedigree that illustrates the transmission of the dominant trait from the grandmother to two of her grandchildren who are first cousins.

Verified step by step guidance

1. Start by understanding the inheritance pattern of the dominant trait. Since the woman is heterozygous (Dd), she has one dominant allele (D) and one recessive allele (d). A dominant trait requires only one dominant allele to be expressed.
2. Draw the grandmother at the top of the pedigree. Label her as heterozygous (Dd) for the dominant trait. Indicate that she expresses the dominant phenotype.
3. Add the grandmother's children below her. Assume she has two children: one heterozygous (Dd) and one homozygous recessive (dd). This follows Mendelian inheritance, where each child has a 50% chance of inheriting the dominant allele (D) and a 50% chance of inheriting the recessive allele (d).
4. Extend the pedigree to include the grandchildren. Assume that the heterozygous child (Dd) has two children, one heterozygous (Dd) and one homozygous recessive (dd). The homozygous recessive child (dd) does not pass on the dominant trait to their offspring.
5. Label the grandchildren who are first cousins and express the dominant phenotype. These grandchildren must have inherited the dominant allele (D) from their heterozygous parent (Dd). Ensure the pedigree clearly shows the transmission of the dominant trait from the grandmother to these grandchildren.

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 in a heterozygous individual. This means that an individual with at least one dominant allele will express the dominant phenotype, while the recessive phenotype only appears in individuals with two recessive alleles.

Pedigree Analysis

A pedigree is a diagram that depicts the inheritance of traits across generations within a family. It uses standardized symbols to represent individuals and their relationships, allowing for the visualization of how a trait, such as a dominant phenotype, is passed from one generation to the next. Analyzing a pedigree helps in understanding the genetic connections and predicting the likelihood of traits in offspring.

Heterozygosity and Genotype

Heterozygosity refers to having two different alleles for a particular gene, such as Dd. The genotype of an individual determines their potential to pass on traits to their offspring. In the context of the question, the heterozygous woman can pass either the dominant allele (D) or the recessive allele (d) to her children, influencing the expression of the dominant trait in the next generation.