Genetics Power point number 2

Definitions Genotype – the genetic makeup of an organism Example: Bb or BB Phenotype – the physical trait that an organism develops Example: Brown eyes or blue eyes

Di-hybrid Crosses Used when 2 different traits are involved in the same cross Results in 16 possible offspring When the number of offspring are large enough, the phenotype ratio is 9:3:3:1 (DD : DR : RD : RR)

Di-hybrid Cross Example Example: Cross an individual heterozygous for brown hair and brown eyes with an individual recessive for blond hair and blue eyes. What possible offspring will result?

Practice Practice Worksheet

Codominance Both alleles contribute to the phenotype of the organism Occurs in chickens black and white feathers give a speckled black and white feathered chicken

Polygenic traits The exhibited trait is controlled by two or more genes Example: wide range of skin color in humans because it is controlled by more than 4 different genes

Incomplete Dominance When one allele is not completely dominant over another Example: Crossing a red and white 4 o’clock plant (Mirabilis) gives a pink flower

Sex linked traits Sex-Linked Genes Genes on the X and Y chromosome Called sex-linked because the X and Y determine sex of an individual 100 genetic disorders have been mapped to the X chromosome

Sex-Linked con’t Sex linked genetic disorders are more common among men b/c men only have one X. Recessive alleles on the X will be expressed in males

Sex-Linked con’t Genetic Disorders Colorblindness Hemophilia Duchenne Muscular Dystrophy Male Pattern Baldness

Sex Linked con’t Colorblindness About 1 in 10 men (most common red-green) About 1 in 100 women Sex-linked genes are passed from Fathers to daughters and then may show up in sons of those daughters

Sex-Linked Hemophilia Protein necessary for normal blood clotting is missing About 1 in 10,000 males People can bleed to death from minor cuts and may suffer internal bleeding from bumps or bruises.

Sex-linked con’t Duchenne Muscular Dystrophy Progressive weakening and loss of skeletal muscle Rarely live through early adulthood About 1 in 3000 males

Sex linked con’t Male Pattern Baldness Fathers give to daughters who are carriers Daughters pass trait to son

Sex Linked Trait Example Color Blind father crosses with a Homozygous dominant mother XcY and XCXC Color Blind father and heterozygous mother XcY and XCXc