Non-Mendelian Genetics

1. Non-Mendelian Genetics When Heredity Follows Different Rules

2. Incomplete Dominance • Incomplete Dominance – the phenotype of heterozygous individuals is intermediate to the homozygotes • NEITHER allele is dominant over the other so they MIX together • Example: • Homozygous R snap-dragons are RED (RR) • Homozygous R’ snap-dragons are WHITE (R’R’) • A cross between these two parents will result in all heterozygous snap-dragons, which are PINK(RR’) • A cross between two pink heterozygotes results in a 1:2:1 ratio of phenotypes

3. Complex Genetics – Incomplete Dominance • The dominant allele is not completely dominant over the allele. • Result: a blend of the 2 forms of the trait. • R – red flower • R’ – white flower • RR – red • R’R’ – white • RR’ - pink!

4. RR R’R’ RR’ RR’ RR’ RR’

5. RR R R’ RR’ R RR’ RR R’R’ R’ (All pink) RR’ R’R’ P

6. Codominance • Codominance – BOTH alleles are dominant so BOTH phenotypes are present in heterozygous individuals • Alleles do NOT MIX; both are equally present • Example: • Homozygous B chickens are BLACK (BB) • Homozygous W chickens are WHITE (WW) • Heterozygous chickens are BLACK AND WHITE (BW) in a checkered pattern • A cross between two checkered heterozygous chickens results in a 1:2:1 ratio of phenotypes

7. Complex Genetics – Co-Dominance • There are 2 dominant alleles for the trait. • Result: Both show up equally. • Ex. B – black feathers • W – white feathers • BB – black feathered chicken • WW – white feathered chicken • BW – black & white checkered feathered chicken!

9. Both are dominant allels and will display in the offspring WW X BB=BW

10. BB B W BW B BW BB WW W (All checkered) BW WW P

11. Sex Determination • Humans have a diploid number of 46 chromosomes in 23 pairs • 22 of those pairs are called AUTOSOMES and are the same between males and females • The 23rd pair are the SEX CHROMOSOMES and are indicated by the letters X and Y • Males – XY • Females - XX Y = PENIS ! 50% The sperm (father) always determines the sex of the offspring

12. Sex Chromosomes

13. Y X Y X Sperm X X X X XX XY Egg XX XY

14. Sex-linked Inheritance • Sex-linked traits – traits which are controlled by a gene on the X chromosome • Inherited differently in males and females • The Y chromosome does not carry any genes to override the homologous gene on the X chromosome • Males have the trait more often because they don’t get a second X to override a recessive gene on the first X chromosome (males cannot be carriers) • Females still need TWO copies of the recessive gene to exhibit the recessive phenotype (females can be carriers) • Colorblindness • Hemophilia – bleeding disorder causing your blood not to clot properly

15. X-Linked Traits • The allele is attached to the X chromosome. • Can only be passed from Mother to son, Mother to daughter, or father to daughter.

17. X-linked genes means… • Girls can be normal or Carriers but Boys will be AFFECTED the most.

18. XH = normal vision Xh = colorblind Y = no genes Xh Xh XH XH Y Y XH XH x x Female Carrier Normal Male XH XH Y XH Normal Female Normal Male Xh Y XH Xh Female Carrier Colorblind Male

19. Hemophilia X-Linked Lacks clotting in the blood

20. Menkes Disease X-linked gene causes kinky hair and mental disorders