Beyond Dominant and Recessive Inheritance Patterns Beyond Dominant and Recessive

X Their offspring looked like this… Red and white are 2 possible coat colors in cattle A homozygous white bull is bred with a homozygous red cow… X Their offspring looked like this…

Codominance Both alleles are expressed i.e. you can see both clearly/separately in the phenotype In the cow both the red color is present as well as the white

Codiminance

Codominance Blood types result from codominant alleles. IAIB shows this Because the blood types come from three different alleles in the human population, this trait is also considered a multiple allele trait

X Their offspring looked like this… Four O’clock flowers also come in red and white A red four o’clock flower pollinated a white four o’clock flower… X Their offspring looked like this…

Incomplete Dominance When neither allele is recessive nor dominant The phenotype is a blending of the two alleles

Multiple Alleles Genes with 3 or more alleles for a particular trait. Examples are the ABO blood types, fur color in animals Remember: each individual will only have two alleles for a trait (gene) but there are several alleles to choose from.

Multiple Alleles

Cross a light gray rabbit with a dark gray rabbit. cchch x Cc Genotype: Ccch- 25% Cch- 25% cchc- 25% chc- 25% Phenotype: Dark Gray – 50% Light Gray- 25% Himalayan- 25% cch C Ccch Cch c chc cchc

Multiple allele/Codominance Practice If the dad had type AB blood and the mom had type O blood, what would the offspring genotype & phenotype possibly be? IA IB Genotype i IA i IA i 50% IB i 50% IB i IA i IB i Phenotype A 50% B 50%

Codominance/Multiple Allele Practice Cross a person with type AB blood with another person with heterozygous type A blood. O (ii) is recessive to all ___IAIB____  X  ____IAi___  Genotypes: IAIA 25% IAIB 25% IBi 25% IAi 25% Phenotypes: type AB 25% type B 25% type A 50%   IA IB IAIA IAIB i IAi IBi

Polygenic Traits ‘Poly’ = many ‘genic’ = gene Traits are controlled by more than 1 gene Examples include human height, finger print pattern, hair color, eye color, and skin color

Polygenic Traits Eye color has a least 3 genes with complicated patterns of expression Chromosome 15 – BEY 2 Gene has brown and a blue allele Chromosome 15 – BEY 1 Gene has a brown allele Chromosome 19 – GEY gene has blue and a green allele These genes do not account for all eye color variations, such as changes in eye color over time, the continuous range of eye colors and patterns of colors in eyes. As a result, scientist hypothesize that still undiscovered genes affect eye color. Order of dominance: brown > green > blue.

Polygenic Traits An epistasis gene can interfere (block) other genes. In mice at least 5 different genes interact to produce the phenotype for fur color. 2 genes = general color 1 gene = affects shading 1 gene = have spots or not 1 gene = epistasis gene which overshadows all others A mouse that is homozygous for the white alleles that prevent the coloration of fur will be white, regardless of the other dominant phenotypes. NOT TO BE CONFUSED WITH COMPLETE ALBINISM!!! The epistasis gene only affected the coloration of hair not pigment.

The yellow coat color of labs is an epistasis gene that blocks the black and brown alleles.

Albinism is an example of how 1 epistasis gene blocks the production of pigments in skin, hair and eyes of animals and humans.

Traits influenced by the environment. Color of hydrangea flowers (blue in acidic soil, pink in basic soil) Color of arctic fox

Traits influenced by the environment. Characteristics of an organism are not determined solely by genes environmental factors play a role as well Climate, soil conditions, nutrition, availability of water, etc. Genes provide a plan for development, but how the plan unfolds also depends on the environment The sex of sea turtles depends on both genes and the environment Eggs in warmer temps = females Eggs in colder temps = males

Environmental Influence on Traits Identical Twin Studies Helps scientists separate genetic contributions from environmental contributions. Traits that appear frequently in identical twins are at least partially controlled by heredity. Traits expressed differently in identical twins are strongly influenced by environment The pics show identical twins. In each pair, one smoked and tanned, but the other didn’t…can you guess which is which?