genetics advanced

Complete dominance

When one allele (A) completely masks the expression of the other allele (a), resulting in a dominant trait in the heterozygote and dominant homozygote with identical phenotypes.

Incomplete dominance

When the heterozygote shows a phenotype that is a blend or intermediate between the two homozygous traits, like mixing red and white paint to get pink.

Co-dominance

When both alleles in the heterozygote are fully expressed, leading to a phenotype where both traits are visibly present, such as blood type AB from the interaction of type A and type B alleles.

Lethal alleles

Alleles that cause death either before or at birth, resulting in miscarriage, with the heterozygous state sometimes showing a different phenotype.

Hemizygous

Refers to individuals, like human males with one X chromosome, who only have one allele for X-linked traits, making them susceptible to X-linked conditions.

Carrier

Typically seen in females, carriers are heterozygous for a recessive disease condition, like hemophilia, where they do not show symptoms but can pass the condition to their offspring.

Polygenic inheritance

Inheritance pattern where multiple genes contribute to a single phenotype, such as height influenced by over 180 genes.

Pedigrees

Charts showing the genetic history of a family over generations, with males represented by squares and females by circles, used to track the inheritance of traits.

Autosomal dominant

Inheritance pattern where the presence of one copy of the dominant allele leads to the trait's expression, seen in heterozygous parents with affected offspring.

Autosomal recessive

Inheritance pattern where two copies of the recessive allele are needed for the trait to be expressed, observed in unaffected parents having affected offspring due to both being carriers.

epidermis

gives skin its color (melanin)