1 Answer | Add Yours
In a pedigree chart for autosomal dominance, since only one gene is necessary for the trait to appear in the phenotype, a person who has one or two of these genes would display the trait and therefore, in the pedigree chart, the male(square) or female(circle) would be shaded to indicate they inherited this gene. In autosomal recessive inheritance, two genes(one from each parent) are required for this trait to be displayed in a person's phenotype. Therefore, in a pedigree chart, if two parents were both carriers(with one dominant and one recessive gene) they would be half shaded. If their offspring inherited a recessive gene from each parent, they would be fully shaded and would display the recessive trait. For sex-linked inheritance, which is recessive, these are traits linked to the X chromosome and in females, if they have two X chromosomes without this gene, they are normal, if one X has the gene and one does not, they are a carrier (a circle that is half-shaded) and if both X's have this gene, they would have the trait( a fully shaded circle). Females usually are carriers of X linked traits and rarely have the disease phenotype. Males however, are hemizygous for the X chromosome. They get their X chromosome from their mother. A male with the sex-linked gene would be indicated bya fully shaded box and he would display the disease phenotype. A male who didn't inherit the sex-linked gene would be normal and the box would be unshaded. For sex-linked dominant inheritance, if the gene linked to the X chromosome is a dominant gene, then it would only take one gene for the trait to be displayed. Therefore, for females, if one or two of her X chromosomes has the dominant gene, she would display it and this would be indicated by a shaded circle. If both genes were recessive, she would not display it and this would be indicated by an unshaded circle. Males that inherit the dominant X linked gene would display it in their phenotype--indicated by a shaded box and males that inherit the recessive gene on their X chromosome would not display the trait in their phenotype, indicated by an unshaded box.
We’ve answered 319,814 questions. We can answer yours, too.Ask a question