NonMendelian Genetics 4 B Incomplete Codominance Multiple Alleles

Non-Mendelian Genetics 4 B Incomplete & Codominance Multiple Alleles

Non-Mendelian Genetics Stop for first section of notes Begin Incomplete and Codominance Notes Non-Mendelian

If red flower were dominant over white flower, what color would the F 1 generation be? Why are the offspring a different color from either parent?

When neither allele is dominant. Incomplete Dominance: -The heterozygous phenotype (i. e. Rr) is between the two homozygous phenotypes -Neither allele is dominant over another -Example: a red flower crosses with a white flower to Genotype RR (homozygous) make pink flower. rr (homozygous) Rr (heterozygous) Phenotype Red White Pink

Incomplete Dominance Practice Problem A species of mice are controlled by incomplete dominance. The two alleles are black (B) and white (W). The heterozygous genotype is expressed as gray fur. Give the phenotypes: BB: WW: BW:

Incomplete Dominance Practice Problem Cross a gray male mouse with a white female mouse. List the probabilities of having the following offspring phenotypes: Black: Gray: White:

How are these two phenotypes different? Incomplete dominance Neither allele is dominant (blended) Codominance Both alleles are dominant (mixed)

Codominance: Both alleles are clearly expressed in the phenotype of a heterozygous. Some chickens: Allele for black (B) and white (W) feathers are codominant. Heterozygous chickens are speckled with black and

Codominance Practice Problem A species of chickens are controlled by codominance. The two alleles are black (B) and white (W). The heterozygous genotype is expressed as black and white speckled chickens. Give the phenotypes: BB: WW: BW:

Codominance Practice Problem Cross a speckled male with a speckled female. List the probabilities of having the following offspring phenotypes: Black: White: Speckled:

Beyond Dominant and Recessive Alleles There are important exceptions to many of Mendel’s principles – Not all genes show simple patterns of inheritance – Majority of genes have more than 2 alleles – Many important traits are controlled by more than one gene

Multiple alleles: genes with more than two alleles We’ve been working with two alleles (R/r) Human Blood type has more than two alleles

Blood Types

Can the environment affect the exression of traits? Genes provide the blueprint for an organisms traits Environmental conditions can affect how that develops

Pontia occidentalis Western white butterfly Born in spring, wings are darker Born in summer, wings are lighter

Spring vs Summer

Why? If the butterflies are born in the spring, temps are colder. They use the darker colors (absorb heat) to maintain body temp If butterflies are born in the summer, temps are warmer, don’t need darker colors, have lighter colors to avoid overheating