Incomplete Dominance

Neither allele is dominant over the otherHeterozygous offspring have a phenotype that is somewhere between the two.

Incomplete Dominance

Incomplete Dominance Homozygous red parent: RR

crossed withHomozygous white parent: WW

RR x WW yields heterozygous offspring

RW that are pink

Incomplete Dominance

Codominance

Both alleles contribute to the phenotype

Heterozygous offspring express both alleles

Codominance

X

Codominance: A black chicken crossed with a white chicken results in a speckled chicken

CODOMINANCE: ABO BLOOD TYPES

Blood type depends on the presence or absence of certain carbohydrates on the surface of red blood cells

3 alleles are possible: IA IB i

ABO BLOOD TYPES IA and IB are codominant to each other

when they are paired.

i allele is recessive to both IA and IB

ABO Blood Groups

ABO Blood Groups

ABO Blood Types Blood typing is actually far more

complicated than “A”, “B”, and “O” ABO are the MAJOR antigens There are also MINOR antigens

Rh factor: “+” or “-”

ABO Blood Types

ABO Blood Types

ABO Blood Types

ABO Blood Types Why is it important to get the right

blood type when getting a transfusion? Transfusion Reactions

Immune system (antibodies) will attack cells that have an antigen that the body doesn’t recognize as “self”

Transfusion Reaction

Multiple Alleles

More than 2 possible alleles exist in a population

Multiple AllelesCoat color in rabbits: there are at least 4

different alleles C = full color (dominant to all other

alleles) c (ch) = chinchilla c (h) = himalayan c = albino (recessive to all other alleles)

Full color rabbit

Chinchilla rabbit: partial defect in pigmentation

Himalayan rabbit: color in only certain parts of body

Albino rabbit: no color; recessive to all other alleles

Polygenic Traits

Traits that are produced by the interaction of more than one different genes

Polygenic Inheritance For example: coat color in Labrador

retrievers is a result of interaction of 2 different genes.

Polygenic Inheritance

Example: comb shape in chickens is a result of interaction between 2 different genes.

X-Linked Inheritance Early 1900’s

Thomas Morgan’s fruit fly studies

X-Linked Inheritance

X-Linked Inheritance More than 300 human traits are X-

linked. Most common X-linked recessive

disorders: Hemophilia Red-green colorblindness Duchenne muscular dystrophy Adrenoleukodystrophy (seen in the

movie Lorenzo’s Oil)

BARR BODIES Barr body is found only in females It is a darkly staining area in the

nucleus of a cell that represents an inactivated X chromosome

One X chromosome is randomly inactivated

Barr Body

Barr Body

Do you see the Barr body?

Barr Body: X inactivation Calico cat

Generally all females Have one X chromosome coding for for

gold color, and one X chromosome coding for black color

Color pattern shows how one X chromosome in each cell is randomly inactivated

Calico Cat There have been instances of male

Calico cats found How could this happen?

Male Calico cat? HINT: Male calico cats are sterile

Male Calico cat? Answer: Male Calico cats have XXY

chromosome configuration A Klinefelter’s cat? Yup, it happens.