1. Genetics
Power point number 2

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

3. 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)

4. 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?

5. Practice
Practice Worksheet

6. 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

7. 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

8. 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

9. 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

10. 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

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

12. 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

13. 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.

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

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

16. 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