Mendelian Exceptions & Sex- linked Genetics Objective: E4 - Predict possible outcomes of non-Mendelian inheritance & explain how sex is determined

Mendelian Exceptions - Not all genes show simple patterns of dominant and recessive alleles Because the majority of traits are controlled by more than one gene/alleles

Codominance Cases in which both alleles are expressed White cow x Brown cow = Speckled (white and brown) cow

Incomplete dominance  Neither allele is dominant Red flower x White flower = Pink flower

In a certain cactus, prickly spines can be two pronged or one pronged. If a true breeding (homozygous) one-pronged cactus is crossed with a true breeding two-pronged cactus, the F1 generation has a mixture of spines, some are two- pronged, some are one-pronged. Is this an example of codominance or incomplete dominance? codominance Practice Problems

In snapdragons, the combined expression of both alleles for flower color produces a new phenotype that is pink. This illustrates incomplete dominance. The Punnett square above shows that both the white and red snapdragons are homozygous. Which of the following would be the correct product from a cross between two heterozygous pink snapdragons? [VA05 EOC] A 1 red, 2 pink, 1 white B 2 red, 2 white C 2 red, 1 pink, 1 white D 1 red, 1 pink, 2 white

Sex-linked Genetics

Section 12.2 Summary – pages Sex Determination If you are female, your 23 rd pair of chromosomes are homologous, XX. If you are male, your 23 rd pair of chromosomes XY, look different. XX = Female YX XY = Male XX Female XY Male X X X Y XX Female XY Male XX Female XY Male The male determines the sex of the offspring. X X

Section 12.2 Summary – pages Traits controlled by genes located on sex chromosomes are called sex-linked traits. The alleles for sex-linked traits are written as superscripts of the X or Y chromosomes. Sex-linked Inheritance

Sex Linked Traits When genes are located on the X chromosome, females receive two alleles for these genes, but males only receive one. In males, the genotype is automatically known. Colorblind male - X b Y (recessive) Normal male - X B Y (dominate). A female can be: X B X B - normal X B X b - carrier X b X b - colorblind

The following shows a cross between a normal man and a woman who is a carrier. The mother always passes sex-linked traits on to her son because he got the X from his mom & the Y from his dad.