Variations of Inheritance Patterns Ch. 10.3

Objectives Describe intermediate inheritance Multiple alleles Understand polygenic inheritance Effect of environment on phenotypes

Variations of Inheritance Patterns With Mendel’s pea plants, alleles were quite simple: If a dominant allele present in genotype --> always present in phenotype If two recessive alleles present in genotype --> present in phenotype What about genes where NEITHER gene is dominant?

“Blue” Chickens? A black chicken and a white chicken can produce blue offspring in the F1 generation Neither black nor white allele is dominant But, this isn’t blending Both black and white phenotypes can reappear in F2 generation This is Intermediate Inheritance: offspring have phenotype that is intermediate between phenotypes of parents

P F1 F2 Make the Punnett squares of the F1 generation, then the F2 Since no dominant alleles, C is used for “color” and superscripts used for alleles. P CB CB CW CW F1 Make the Punnett squares of the F1 generation, then the F2 CB CW F2 CB CB CB CW CB CW CW CW

Multiple Alleles with Blood Types 4 options for blood types Each parent gives one allele --> 6 possible combinations Blood type AB represents codominance: A heterozygote expresses both traits Blood Type Possible Genotypes A AA or AO B BB or BO AB O OO

Antigens Antibodies Can give Blood to Can receive blood from AB Group Antigens Antibodies Can give Blood to Can receive blood from AB A and B None AB, A, B, O A B A & AB A & O B & AB B & O O A & B A bit more on blood types . . .

Polygenic Inheritance Intermediate Inheritance and codominance involve multiple alleles. It’s also possible for multiple genes to affect a character. This is polygenic inheritance: Polygenic inheritance: Two or more genes affect a single character Height and skin color are two examples Let’s look at height as an example . . .

Polygenic Inheritance Let’s assume 3 genes produce height in humans Assume inherited separately (like Mendel’s pea genes) A, B, & C are tall alleles X, Y, & Z are short alleles Parents each give 3 alleles each AABBCC would be a tall individual AXBBCC would be a little shorter AXBYCC would be even shorter, and so on . . . until XXYYZZ would be the shortest individual The potential combinations of alleles (and phenotypes) for a character increases with the # of genes that affect that character --> huge range in heights!

XXYYZZ AABBCC

Importance of Environment Genotype never changes, but leaves vary in size, shape, and color depending on wind and sunlight Enzyme responsible for black fur in Siamese cat is only active in cooler temperatures Identical twins with exact same genotype accumulate differences in phenotype due to different diets, activity level, exposure to sunlight, etc.