Disorders and Other Patterns of Inheritance Biology 1-2

Inherited Disorders In humans, many genetic disorders show complete dominance. In humans, many genetic disorders show complete dominance. Recessive disorders are caused by a recessive allele. Recessive disorders are caused by a recessive allele. Heterozygotes are carriers (have the recessive allele and can pass it on but do not show symptoms of the disorder). Heterozygotes are carriers (have the recessive allele and can pass it on but do not show symptoms of the disorder).

Inherited Disorders cont’d Dominant disorders are caused by a dominant allele. Dominant disorders are caused by a dominant allele. Both homozygous dominant and heterozygotes show the disorder. Both homozygous dominant and heterozygotes show the disorder. There are no carriers. There are no carriers.

Pedigrees A pedigree is a family tree tracing the history of a trait in a particular family. A pedigree is a family tree tracing the history of a trait in a particular family. Circle = female Circle = female Square = male Square = male Shaded= person with the trait. Shaded= person with the trait. Unshaded = either does not have the trait or is unknown. Unshaded = either does not have the trait or is unknown.

Incomplete Dominance Incomplete dominance-the heterozygote has an appearance that is an intermediate between the parents. Incomplete dominance-the heterozygote has an appearance that is an intermediate between the parents. The heterozygote produces a phenotype that is a blend of the other two phenotypes. The heterozygote produces a phenotype that is a blend of the other two phenotypes. Both alleles are dominant. Both alleles are dominant. Written as capital letters. Written as capital letters.

Codominance Codominance-both alleles are expressed fully in the heterozygote. Codominance-both alleles are expressed fully in the heterozygote. Both alleles show completely and fully. Both alleles show completely and fully. The heterozygote has both traits. The heterozygote has both traits. Both alleles are dominant. Both alleles are dominant. No recessive alleles. No recessive alleles. Both written as capitals. Both written as capitals.

Sex-Linked Traits Sex-linked traits are genes carried on the X or Y chromosomes. Sex-linked traits are genes carried on the X or Y chromosomes. Show more frequently in males than females. Show more frequently in males than females. Males have a single X chromosome. Males have a single X chromosome. Receive one copy of any gene on the X chromosome. Receive one copy of any gene on the X chromosome. Y chromosome has no equivalent gene. Y chromosome has no equivalent gene. Males show the gene on the X and cannot hide a recessive. Males show the gene on the X and cannot hide a recessive.

Sex-Linked cont’d Females have two Xs Females have two Xs A recessive on one X can be covered by a dominant on the other X. A recessive on one X can be covered by a dominant on the other X. Are written as X n X n or X n Y Are written as X n X n or X n Y n is letter of the trait. n is letter of the trait. Also includes traits that determine gender. Also includes traits that determine gender.