1. Identify the genotypes of the following individuals on the pedigree above. Homozygous dominant: I-1, I-2, II-3, II-4, III-1, III-2, III-3, III-4, III-5, III-6, III-7, III-8, III-9, III-10, III-11, III-12, III-13, III-14, III-15, III-16, III-17, III-18, III-19, III-20, III-21, III-22, III-23, III-24, III-25, III-26, III-27, III-28, III-29, III-30, III-31, III-32, III-33, III-34, III-35, III-36, III-37, III-38, III-39, III-40, III-41, III-42, III-43, III-44, III-45, III-46, III-47, III-48, III-49, III-50, III-51, III-52, III-53, III-54, III-55, III-56, III-57, III-58, III-59, III-60, III-61, III-62, III-63, III-64, III-65, III-66, III-67, III-68, III-69, III-70, III-71, III-72, III-73, III-74, III-75, III-76, III-77, III-78, III-79, III-80, III-81, III-82, III-83, III-84, III-85, III-86, III-87, III-88, III-89, III-90, III-91, III-92, III-93, III-94, III-95, III-96, III-97, III-98, III-99, III-100
Heterozygous: I-3, I-4, II-1, II-2, II-5, II-6, II-7, II-8, II-9, II-10, II-11, II-12, II-13, II-14, II-15, II-16, II-17, II-18, II-19, II-20, II-21, II-22, II-23, II-24, II-25, II-26, II-27, II-28, II-29, II-30, II-31, II-32, II-33, II-34, II-35, II-36, II-37, II-38, II-39, II-40, II-41, II-42, II-43, II-44, II-45, II-46, II-47, II-48, II-49, II-50, II-51, II-52, II-53, II-54, II-55, II-56, II-57, II-58, II-59, II-60, II-61, II-62, II-63, II-64, II-65, II-66, II-67, II-68, II-69, II-70, II-71, II-72, II-73, II-74, II-75, II-76, II-77, II-78, II-79, II-80, II-81, II-82, II-83, II-84, II-85, II-86, II-87, II-88, II-89, II-90, II-91, II-92, II-93, II-94, II-95, II-96, II-97, II-98, II-99, II-100
Homozygous recessive: none
2. They are not homozygous because they are affected (have the trait) and have an unaffected parent (I-3 or I-4). If they were homozygous dominant, they would not show the trait. Since they show the trait, they must be heterozygous.
3. It is not dominant in nature because if it were dominant, every affected individual would have at least one affected parent. However, individuals II-1 and II-2 are affected but their parents (I-3 and I-4) are unaffected. This is only possible if the trait is recessive.
4. It is not autosomal or sex-linked because if it were autosomal, both males and females would be equally likely to be affected. If it were sex-linked, it would primarily affect males. Since both males and females are affected and there is no clear pattern of sex linkage, it is autosomal recessive.
Parent Tip: Review the logic above to help your child master the concept of pedigree worksheet biology.
