Patterns of Heredity Multiple Inheritance, Pedigrees and other “fun” genetic stuff...

Different Rules of Heredity Simple Mendelian inheritance is what you have already learned about Most inheritance patterns are not as simple as dominant and recessive

Different Rules of Heredity Other types of heredity: –incomplete dominance –codominance –multiple allelic inheritance –sex-linked inheritance –polygenic inheritance

Incomplete dominance The phenotype of the heterozygote is a blend of the two characteristics EXAMPLE: red snapdragon crossed with white snapdragon gives pink snapdragons

Codominance Both phenotypes are expressed at the same time EXAMPLE: Black chicken is crossed with a white chicken and all of the offspring are checkered (have both black and white feathers)

Suppose a father of blood type A and a mother of blood type B have a child of type O. What blood types are possible in their children?

Multiple alleles Traits that are controlled by more than one allele EXAMPLE: in rabbits, four different alleles control coat color (sometimes as many as 100 different alleles can control the same trait)

Sex-linked inheritance Traits controlled by genes that are located on the X chromosome This means that the male only needs to have the characteristic carried on the X chromosome for him to express it EXAMPLE: red eyes vs. white eyes in fruit flies: X R X R - red eyes X R X r - red eyes X r X r - white eyes X R Y- red eyes X r Y- white eyes

Polygenic Inheritence Trait is controlled by two or more genes EXAMPLE: If stem length was controlled by three alleles and each dominant allele gave the plant 2 cm gain in length, while the recessive allele gives 1 cm gain in length. –AABBCC- 12 cm long –AaBbCc- 9 cm long –aabbcc- 6 cm long

Environmental effects Sometimes the environment has a large effect on the expression of genes EXAMPLE: the arctic fox is white in cold and snowy weather and when the weather warms up, its coat turns brown to match the grass (grass is usually brown in the arctic!!)

Practical uses of genetics Testcrosses Breeding Pedigrees

Practical uses of genetics Testcrosses are used to determine an unknown genotype from a known genotype. EXAMPLE: cross a homozygous recessive individual with an unknown, results will tell you what the unknown individual is

Practical uses of genetics Pedigree- graphical representation of an individual’s family tree Carrier- heterozygous, but it has the dominant trait (is carrying the recessive trait)

Selective Breeding Producing organisms with the desired traits inbreeding- producing pure lines by mating closely related individuals –however, this causes a problem because this can bring out harmful, recessive traits that are usually hidden Hybrids- produced by crossing two varieties of plants that are closely related and that have desirable characteristics, and offspring are larger and stronger than the parents