pedigree charts to determine possible genotypes

• A pedigree chart shows the family history of traits, such as heritable disorders. • An autosome is a chromosome that is not directly involved in sex determination. In humans there are 22 pairs of chromosomes. Defects in autosomal alleles can be categorized in various ways: · In a heterozygote, the autosomal dominant allele causes the disorder and masks the normal allele. · An autosomal recessive condition is expressed in the homozygous condition. • Sex-linked genes are located on the sex chromosomes, which are involved in sex determination. These genes are categorized in different ways: · X-linked dominant: In males or females, one abnormal allele on the X-chromosome causes the disorder. · X-linked recessive: Males with one abnormal allele express the trait, only homozygous females show the trait. · Y-linked: One abnormal allele on the Y chromosome causes the disorder.

- The pedigree on the left shows the occurrence of a heritable disorder among family members. Shaded blocks indicate presence of the disorder. - Review: Squares represent males and circles represent females. - Based on the pattern of inheritance, a number of mechanisms could explain the disorder. To determine what types of inheritance are possible, look at each type in turn and determine whether or not conflicting evidence is present. - Autosomal dominant: If the trait was inherited in this manner, the dominant “H” allele would cause the disorder and the normal phenotype would occur in a homozygous “hh” condition. The F1 male has the disease, but neither of the parents does. This pattern of inheritance is inconsistent with an autosomal dominant type of inheritance. - Autosomal recessive: If the disease was inherited in this manner, the homozygous condition “hh” would cause the disorder and “H-” individuals would be normal. No information conflicts with this mode of inheritance; therefore it is considered a possibility. - X-linked dominant: Individuals that are XH would have the disorder whereas Xh individuals are normal. The male in F1 shows the disorder and so should the mother in the P generation. This mode of inheritance is ruled out. - X-linked recessive: The disease will be present in the hemizygous condition in males (XhY) and homozygous females (XhXh). There is no information that is inconsistent with this type of inheritance; therefore, it is considered a possibility. - Y-linked: The disease should occur in all related males. The male in F1 has the disorder, but his father doesn’t. This possibility is ruled out.

Looking at the pedigree in the illustration, which of the following statements about the trait in question is incorrect?

- F1-5 and F1-6 have identical genotypes.

9.9.4 Pedigree Chart: Problem Review Flashcards by Irina Soloshenko

This is a private class.

You need a Pro account to access a Private class
I have an access code

To request access, contact Irina Soloshenko, and ask that they share the class directly with you, using the email address you use for your Brainscape account.

Brainscape's Knowledge GenomeTM

9.9.4 Pedigree Chart: Problem Review Flashcards

Brainscape's Knowledge Genome^TM