Patterns of Heredity Incomplete Dominance, Codominance and Sex-linked

Figure 14.2 Mendel tracked heritable characters for three generations

Genetics Vocabulary Incomplete Dominance - a form of intermediate inheritance in which one allele for a specific trait is not completely dominant over the other. If the trait is incomplete it will be stated in the problem. (Some people, like incomplete dominance, use superscripts or subscripts w/ diff letters)

Figure 14.9 Incomplete dominance in snapdragon color

Genetics Vocabulary Codominance - A condition in which both alleles of a gene pair in a heterozygote are fully expressed, with neither one being dominant or recessive to the other. If the trait is codominant it will be stated in the problem. ( When crossing codominant traits, use different capital letters) RR RW WW

Autosomes vs. Sex-chromosomes

Sex-linked traits Most human traits are inherited by passing autosomes – non-sex chromosomes – (just like peas) Sex-linked traits = inherited by passing sex- chromosomes. –Many human diseases including: Hemophilia & Color blindness

Designating Sex-Linked Traits X A = normal X a = the trait (a genetic disease or abnormality) Y = Y chromosome (males only) * X-linked traits are only on the X chromosome

GenotypePhenotype X A Normal female X A X a Normal female, also called a carrier X a Female with trait X A Y Normal male X a Y Male with trait

X-linked traits may also skip generations Males are affected more often than females because they only have one X chromosome

Sample problem Hemophilia is an X-linked disorder. If an affected father and a carrier mother have a boy, what is the probability that boy will have hemophilia?

What is the probability that boy will have hemophilia? Mother’s Genes XaX Xa Y XaXa XaX XaY XY Father’s Genes

Autosomal Dominant diseases Individuals have the trait if they have the dominant allele. –Ex: familial hypercholesterolemia –Huntington’s disease –Dwarfism –Neurofibromatosis –Colon cancer –Kidney disease –Etc.