Patterns of Inheritance

I: Mendel's laws Two factors called genes control each trait For each gene, organisms receive one allele (form) from each parent randomly. If an organism receives different alleles for the same trait, one allele is dominant over the other

II: Test crosses Monohybrid cross Breeding individuals to observe the inheritance of one trait Ex: Mendel’s round vs wrinkled peas Expected phenotypic ratio 3 dominant: 1 recessive

Test Crosses Continued… Dihybrid cross Breeding individuals to observe the inheritance of two separate traits Ex: Mendel’s cross for shape and color Expected phenotypic ratio: 9 dom dom: 3 dom rec: 3 rec dom: 1 rec rec

Practice time Assume the following: A = round head a = square head B = belly buttonb = no button If two parents are heterozygous for belly buttons what are the odds/percentages that their child will not have a belly button? ¼ or 25% If parent #1 is homozygous dominant for both traits and parent #2 is homozygous recessive for both traits what are the odds/percentages their child will have a round head but no belly button? 0/16 or 0%

III: Complex inheritance Incomplete Dominance: Blending of traits Heterozygotes, and homozygotes have different phenotypes

Continued… Co-dominance: Heterozygotes express both dominant phenotypes

Continued… Sex determination 23 rd chromosome=X or Y XX=femaleXY=male Sex linked traits: Genes for the traits located on the sex chromosome Ex: fruit fly eye color X R = RedX r = white Human color blindness

Continued… Polygenic: Poly=many gen=genes Multiple genes are responsible for the expression of the trait