Incomplete Dominance  Neither allele is dominant over the other  Heterozygous offspring have a phenotype that is somewhere between the two.

Incomplete Dominance

 Homozygous red parent: RR crossed with Homozygous 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: I A I B i

ABO BLOOD TYPES  I A and I B are codominant to each other when they are paired.  i allele is recessive to both I A and I B

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

 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 Alleles  Coat 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

 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

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.