How can we explain inheritance patterns that do not follow simple Mendelian genetics? 1. Incomplete Dominance 2. Co-dominance 3. Multiple Alleles
A cross between organisms with two different phenotypes produces offspring with a THIRD phenotype that is a BLENDING of the parental traits - The alleles for the same gene cannot completely conceal the presence of the other
Example: In northeast Kansas there is a creature known as a wildcat. It comes in three colours: blue, red and purple. This trait is controlled by a single locus gene with incomplete dominance. A homozygous (B B B B ) individual is blue, a homozygous (B R B R ) individual is red, and a heterozygous (B B B R ) individual is purple. What would be the genotypes and phenotypes of the offspring if a blue wildcat were crossed with a red one?
BB BRBR BBBRBBBR BBBRBBBR BRBR BBBRBBBR BBBRBBBR GENTYPIC RATIO: 100 % B B B B PHENOTYPIC RATIO: 100% Purple
BB BRBR BBBRBBBR BBBRBBBR BRBR BBBRBBBR BBBRBBBR GENTYPIC RATIO: 100 % B B B B PHENOTYPIC RATIO: 100% Purple What are the ratios for the F 2 generation?
HUMAN DISEASE 1. FAMILIAL HYPERCHOLESTEROLEMIA - Prevents tissues from removing low-density lipoproteins (LDLs) from the blood causing high levels of cholesterol in the bloodstream - Mutation in the LDLR gene - Autosomal dominant - Homozygous dominant: 6x amount LDL in blood - Heterozygous: 2x amount LDL in blood - Homozygous recessive: unaffected
Example: Predict the phenotypic ratio of offspring when a white hair cow is crossed with a roan bull.
CWCW CWCW CRCR CRCWCRCW CRCWCRCW CWCW CWCWCWCW CWCWCWCW GENTYPIC RATIO: 1 C R C W : 1C W C W PHENOTYPIC RATIO: 1 White hair cow : 1 Roan hair bull
HUMAN DISEASE 1. SICKLE CELL ANEMIA - Results in mishaped red blood cells that do not transport oxygen efficiently because they cannot pass through small blood vessels - Genotypes: - Hb A Hb A = Normal - Hb S Hb S = Sickle Cell - Hb A Hb S = Some normal and some sickle cells (also resistant to malaria)
More than two alleles code for a specific trait - Any individual only has two alleles for each gene (one on each homologous chromosome) - Many DIFFERENT ALLELES for a gene can exist
HUMAN BLOOD GROUPS - A single gene determines a person’s ABO blood type - This gene determines what type of antigen protein (if any) is attached to the cell membrane of red blood cells - Antigen: molecule that stimulates the body’s immune system
BLOOD TYPEGENOTYPEANTIGEN PRESENT ANTIBODY PRESENT AI A I A or I A iAB BI B I B or I B iBA ABIAIBIAIB A and BNone OiiNoneA and B
Environmental conditions affect the expression of traits - Example: temperature affects the colouring on Himalayan rabbits
CONTINUOUS VARIATION: a range of variation in one trait resulting from the activity of many genes Ex: height, skin colour, POLYGENIC TRAITS: trait controlled by more than one gene (polygenes) Ex: skin colour