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 RWthat are pink
Codominance • Both alleles contribute to the phenotype • Heterozygous offspring express both alleles
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 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”
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)
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.