Inheritance Patterns

Beyond Dominant and Recessive

Red and white are 2 possible coat colors in cattle A homozygous white bull is bred with a

homozygous red cow…

XTheir offspring looked like this…

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

Codominance

Codiminance

– 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

Codominance

Four O’clock flowers also come in red and white

A red four o’clock flower pollinated a white four o’clock flower…

XTheir offspring looked like this…

When neither allele is recessive nor dominant

The phenotype is a blending of the two alleles

Incomplete Dominance

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

cch ch

C

c

Genotype:

• Ccch- 25%

• Cch- 25%

• cchc- 25%

• chc- 25%

Phenotype:

• Dark Gray – 50%

• Light Gray- 25%

• Himalayan- 25%

Ccch

chc

Cch

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

i

i

Genotype

Phenotype

IA i 50%IB i 50%

A 50%

B 50%

IA i

IA i

IB i

IB i

Codominance/Multiple Allele Practice

  IA IB

IA IAIA IAIB

i IAi IBi

 Genotypes: IAIA 25%IAIB 25%IBi 25%IAi 25%

Phenotypes: type AB 25%type B 25%type A 50%

Cross a person with type AB blood with another person with heterozygous type A blood.- O (ii) is recessive to all

___IAIB____  X  ____IAi___

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.

• 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.

Polygenic Traits

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

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

Traits influenced by the environment.

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. Ineach pair, one smoked and tanned, but the other didn’t…can you guesswhich is which?