Genetics

Incomplete Dominance• Where neither the dominant or recessive allele

is truly dominant over the other, both are dominant

Incomplete Dominance

• The heterozygote will “blend” the two traits into an intermediate third trait

• RED Flower x WHITE Flower ---> PINK Flower

Incomplete Dominance

• Because neither allele is dominant over the other, we use a large base letter indicating the character and a capital superscript showing trait CR CR for red flower

CW CW for white flowerOne allele from each parent is passed on. A

cross would produce CR CW which is pink phenotype.

• It’s important to know when you’re dealing with incomplete dominance*notice that the offspring is showing 3rd phenotype*notice that the trait in offspring is a blending of parental traits

Codominance

• Similar to incomplete dominance because it too creates a 3rd phenotype, different from parents.

• Parental traits don’t blend, instead the two traits appear together in a hybrid

red and white --> red & white spotted

• Here’s an example of a codominant flower showing both parental pink and white traits.

X

ROAN COW

Human Blood Types• Antigen- molecules that can trigger an immune response

• A carries A antigen • B carries B antigen• AB has both antigens• O carries neither antigenRh Factor; Rh+ carry this antigen, while Rh-

individuals don’t.• In transfusions, a new antigen cannot be

introduced into the body of recipient

How common is your blood type?

46.1%

38.8%

11.1%

3.9%

• Who can give you blood?

• People with TYPE O blood are called Universal Donors, because they can give blood to any blood type.

• People with TYPE AB blood are called Universal Recipients, because they can receive any blood type.

• Rh + Can receive + or -

• Rh - Can only receive -

Universal Recipient

Universal Donor

Polygenic Inheritance• When multiple genes affect a single

character, variation • Height, weight, eye color, skin color• Suppose ABC were 3 “TALL” alleles and abc

were 3 “short” alleles• Someone with genotype AABBCC would be

very tall, while someone with genotype AaBBCC would be slightly less tall

AB Ab aB ab

AB AABB AABb AaBB AaBb

Ab AABb AAbb AaBb Aabb

aB AaBB AaBb aaBB aaBb

ab AaBb Aabb aaBb aabb

AB: Dark Red plantsab: white plants

Wide RANGE of phenotypes

Environment Influence on Phenotype

• Sometimes an organisms phenotype depends on their environment regardless of genotype

• For example, hydrangea flowers of the same genotype range from blue-violet to pink, depending on soil acidity

An enzyme responsible for dark fur is only active at cooler temperatures like cat’s extremities

Gene Linkage

• Genes on separate chromosomes assort and separate independently from each other

• Genes located on SAME chromosome and close together (close gene-loci) tend to be inherited together. * Genetic linkage

• If genes are far apart, but on the same chromosome, crossing over could separate them

Sex-Linked Genes• Any gene located on an sex chromosome

is a sex-linked gene• In humans, most of these are on the X

chromosome (much bigger than Y)

Hemophilia: X-linked genetic RECESSIVE disorder

h H h

Mother is a carrier

h h HH H

hHH

H

FATHER IS A CARRIER

h HH

h H H

Red-green color blindness• X-linked color blind allele is recessive• Heterozygous females have normal vision• Males who get recessive allele in their only

X chromosome are affected.

• X-linked recessive disorders are more common in men than women

• Women need 2 recessive alleles on each of her X chromosomes to be affected

• Men only need 1 recessive allele on his only X chromosome to be affected