Complex Patterns of Heredity Advanced Biology DNHS

Complex Inheritance Patterns Sometimes the laws and principles of genetics established by Gregor Mendel do not always explain the inheritance patterns seen in an organism.

Incomplete Dominance The heterozygous or hybrid individual will show an intermediate phenotype between the two homozygous individuals Example – Snap Dragons flower color red crossed with white = pink

R = red R’ = white R R R R’ RR’ RR R’ RR’ R RR’ R’ RR’ R’R’ RR’ RR’ R’ Genotype: All RR’ hybrid Genotype: ¼ RR; ½ RR’; ¼ R’R’ Phenotype: All pink Phenotype: ¼ red; ½ pink; ¼ white

Codominance The heterozygous individual will show the phenotypes of each of the homozygous individuals Example – chickens, black+white=checkered (black and white)

Multiple Alleles Situation wherein there exists more than two alleles for a specific trait. Example – Blood type in humans (A, B, O alleles)

Sex Linked Traits When a trait is seen in one sex more often than another due to a gene that is carried on one of the sex chromosomes Examples – eye color in fruit flies and hemophilia and color blindness in humans

Polygenic Inheritance When a trait is influenced by many genes Tends to be a wide range of phenotypic variation Examples: skin color, hair color, height in humans

Test Crosses A situation in which there is an individual of unknown genotype To determine the genotype you would cross it with a pure recessive individual

Pedigree A graphic genetic family tree that follows a trait through several generations

Aneuploidy A condition of having an abnormal chromosome number Example – Down’s Syndrome, Sex Chromosome Aneuploidies (Turner Syndrome)