6.5 Difficult Predictions

You will be able to: 1.To comapre and contrast patterns of inheritance that do not follow Mendel’s laws 2.To explain how traits are influenced by the environment 3.Incomplete dominance, codominance, polygenic traits, multiple alleles, pleiotropy

Complete Dominance If the genotype of the offspring is homozygous dominant or heterozygous, they will show the dominant trait. If the offspring is homozygous recessive, then the offspring will show the recessive trait. In complete dominance, the offspring will show only one trait or the other.

Complete Dominance

Incomplete Dominance A heterozygous condition Both alleles at a gene locus are partially expressed Produces an intermediate phenotype.

Incomplete Dominance

Codominance The expression of more than one allele in the phenotype for a specific trait. Codominant alleles will be equally expressed in the phenotype. Thus the phenotype of a heterozygous offspring would show both the alleles present in the genotype.heterozygous

Codominance

Polygenic Traits One trait Controlled by more than one gene Eye color Skin color Hair color Height

Polygenic Eye Color Parent 1: Brown Eyes Genotype: bey2 Brown-blue, gey:blue-blue Parent 2: Blue Eyes Genotype: bey2: blue-blue, gey:blue-blue

bey2: gey: Brown blue blue blue Brown-blue blue-blue blue-blueblue-blue blue blue-blueblue-blue blue blue-blueblue-blue blue blue-blueblue-blue 50% probability of brown eyes 50% probability of blue eyes On average, about half the children of this cross will have brown eyes and the other will have blue eyes

bey2: gey: Brown blue Brown Green blue Greenblue Brown blue Brown-Brown blue-blue Brown-Brown Green-blue blue-Brown Green-blue blue-Brown blue-blue Brown Green Brown-Brown blue-Green Brown-Brown Green-Green blue-Brown Green-Green blue-Brown blue-Green blue Green Brown-blue blue-Green Brown-blue Green-Green blue-blue Green-Green blue-blue blue-Green blue Brown-blue blue-blue Brown-blue Green-blue blue-blue Green-blueblue-blue Parent 1: Brown Eyes, Genotype: bey2: Brown-blue, gey:Green-blue Parent 2: Brown Eyes, Genotype: bey2: Brown-blue, gey:Green-blue

Height GenotypeMalesFemales aabbcc5'0"4'7" Aabbcc (or aaBbcc etc.)5'3"4'10" AaBbcc etc.5'6"5'1" AaBbCc etc.5'9"5'4" AaBbCC etc.6'0"5'7" AaBBCC etc.6'3"5'10" AABBCC6'6"6'1"

AaBbCc X AaBbCc GenotypeMalesFemalesFrequency AABBCC6'6"6'1"1/64 AaBBCC etc.6'3"5'10"6/64 AaBbCC etc.6'0"5'7"15/64 AaBbCc etc.5'9"5'4"20/64 AaBbcc etc.5'6"5'1"15/64 Aabbcc etc.5'3"4'10"6/64 aabbcc5'0"4'7"1/64

Polygenic Inheritance Additive effects of 2+ genes on a single phenotypic characteristic Human skin color –Controlled by several genes –More alleles for dark ---> darker skin –More alleles for light ---> lighter skin –Continuum with many colors

Human Skin Color

Multiple Alleles One trait Has more than two alleles

Multiple Alleles Example Blood type There are 3 different alleles for blood type (A, B, & O). A is dominant to O. B is also dominant to O. A and B are both codominant.

Pleiotropy One gene Affects several traits

Pleiotropy Impact of a single gene on more than one characteristic Sickle-cell disease –Most common inherited illness among black people –RBCs are sickle-shaped –Can cause many problems RBCs: Sickle-cell disease Normal RBCs

Sickle-Cell Disease

Pleiotropy & Sickle-Cell Disease Codominant alleles Homozygous recessive: has disease Heterozygous: normal, some cells sickled Disease very common in Africa: why??? Heterozygotes more resistant to malaria than homozygous dominant individuals

Environmental Effects on Traits External environment (outside) Internal environment (inside an organism)

Climate The Himalayan Rabbit Body temperature affects expression of genes that code for fur color Normal = all white Cold = fur turns black

Temperature Western White Butterfly Wing colorations patterns Need body temperature to be 28 – 40 °C to be able to fly

Temperature Butterflies that are ready to fly in spring have darker wing colors Why? Average temperature is 27  C Dark colors absorb more heat Need more heat to fly

Flower Color Hydrangea flower color due to pH Pink or blue Due to soil acidity Blue – acidic soil Pink – neutral or basic

Social Japanese Goby Fish Change its sex back and forth in response to changes in social environment Do this to optimize their relationships. This sex change increases their reproductive capacity.

Sex Change

Diet Nutrition Poor nutrition leads to shorter humans