Patterns of Inheritance Phenotype is affected by many different factors!

1. Incomplete Dominance Blending of traits Neither allele is completely dominant or recessive

Incomplete Dominance Example: snapdragons (flower) red (RR) x white (rr) RR = red flower rr = white flower Rr = Pink

Co-dominance Both traits are present at the same time Example #1: Red flower + white flower = a flower that with both colors (such as white with red edges, etc.) Example #2: Blood types

Polygenic Traits “Many Genes” Traits produced by 2 or more genes Example: Human skin color is a result of 4 genes that react to produce a continuous range of colors Example: Human eye color is a result of at least 3 genes Scientists hypothesize that additional genes code for variations in color, pattern, and changes over time

Environmental Impacts on Phenotype Phenotype is more than just gene expression Example: Sea turtles Eggs that mature in warmer sand = females Eggs that mature in cooler sand = males

Sex Linked Traits A trait determined by a gene or genes carried on the X chromosome but not on the Y chromosome Example: Color Blindness, hemophilia, etc.

*If a son inherits an X chromosome with the hemophilia gene, the trait will be expressed and he will have the disorder. If a daughter inherits the mutated X chromosome, her normal X chromosome will compensate for the abnormal chromosome and the disease will not be expressed.

Mendel’s Laws

1. Law of Dominance When the dominant allele is present, it will mask the recessive trait

Example of Dominance R = red flower r = white flower Problem: Cross homozygous dominant with homozygous recessive   ___ ___ x ___ ___ What are the results? Phenotype: ____ % red, ____ %white Genotype: ____ % homozygous or heterozygous

2. Law of Segregation & Recombination A parent randomly passes on only one allele for each trait to each offspring. Just because your parents have certain traits, doesn’t mean you are guaranteed to have the same traits

Example of Segregation Problem: Cross two offspring from the 1st filial generation (both are heterozygous) ___ ___ x ___ ___ Results? Phenotype: _____% red, ____% white Phenotypic ratio: ___ red : ___ white Genotype: ___% homozygous dominant ___% homozygous recessive ___% heterozygous

3. Law of Independent Assortment The genes for different traits are inherited independently of each other. Ex. Seed color and flower color have no relation.

Example of Independent Assortment Requires the use of a dihybrid Cross: Dihybrid Cross – Examines the inheritance of 2 different traits The genes are on separate chromosomes, so the traits themselves are unrelated *Handout

RrYy vs. RrYy (Seed Shape vs. Texture) R=round, r=wrinkled, Y=yellow, y=green The 4 allele combinations possible in each gamete are used to label each axis

Phenotypes & Genotypes Round/Yellow: 9/16 Round/Green: 3/16 Wrinkled/Yellow: Wrinkled/Green: 1/16 Ratio - 9:3:3:1