Non-Mendelian Genetics

1. Non-Mendelian Genetics

2. What color offspring would you get when you cross a pure (homozygous) red snapdragon with a pure white snapdragon?

3. Oddly Enough, Neither Red Nor White Snapdragon Flower Color is controlled by Incomplete Dominance and a new 3rd phenotype is seen.

4. How does Incomplete Dominance work?

5. Incomplete Dominance is a Blending Like Paint, the RED Pigment “MIXES” with the WHITE to create PINK-FLOWERED offspring

6. Incomplete Dominance can be seen in: • Horses ( Chestnut x Cremello  Palomino) • Snapdragons • Japanese Four O’ Clocks Many flowers exhibit incomplete dominance.

7. Allele Notation HOW DO YOU WRITE OUT THE GENOTYPE WHEN BOTH ALLELES ARE DOMINANT?

8. You Must Use Different Letters • Choose different letters to represent each form (In this case we’ll use “W” for the white allele and “R” for the Red allele). • Remember to always use CAPITAL letters. This is incomplete DOMINANCE. RR WW RW

9. So…The Cross Between Pure Snapdragons Looks Like This R R RW RW W RW RW W

10. You’ve Seen A Cross between Pure Snapdragons, now do the Punnet Square for a cross between two hybrids (heterozygotes). • What are the alleles of a heterozygous snapdragon? RW • What is the genotypic ratio? 1 RR : 2 RW : 1 WW • What is the phenotypic ratio? 1 Red : 2 Pink : 1 White

11. What kind of genetics do these organisms exhibit?

12. Codominance A cross between 2 tabbies (the heterozygotes) results in 1 black : 2 tabbies : 1 tan cat The same ratios as Incomplete Dominance occur: A ratio of 1:2:1 for both genotype and phenotypes of a monohybrid cross  Different Phenotype: The two original phenotypes are combined to give a SPOTTED or MULTICOLORED phenotype.

13. Notation for Codominance • Choose a letter to represent the gene. • Choose different letters to represent each of the alleles. • Take the letters representing the alleles and turn them into superscripts. • Combine the two. Remember to use capital letters.

14. Writing out the Genotype • We’re going to use C to represent Coat Color of a shorthorn cow. • Roan coat color is a combination of Red and White hair so we’ll use “R” to represent Red and “W” to represent white. • R  R and W  W • C + R  CR and C + W  CW • So a Red Cow would be CRCR , a white cow would be CWCW, and a roan cow would be CRCW

15. Codominance occurs in: • Shorthorn Cow (White + Red) • Blue Roosters (White + Black) • Human Blood Typing (AB) • Tabby Cats (Black and Tan Fur)

16. Let’s Practice Tabby cats exhibit codominance between tan and black fur. • Can Tan Cat be heterozygous? Why or Why not? • If you mate a tabby with a black cat, what is the phenotypic ratio of their offspring? • If the offspring of two cats are composed of 36 tabbies and 40 black cats, what are the parental phenotypes and genotypes?

17. Blood Typing • Human blood typing is an example of both Codominance and Multiple Alleles • What does Multiple Alleles Mean?

18. The Alleles • A and B blood types are coded for by the alleles:IA and IB respectively. These two alleles are CODOMINANT. • Blood type O is coded for by the allele i and is recessive to both IA and IB (notice the lower case letter).

19. Alleles and Their Blood Types

20. Let’s Practice • Could a man with AB blood have an AB child with a woman with type O blood? • If a child has type B blood, what are all the possible blood types for his/her parents? • A paternity test is being performed. The child has type A blood. The mother is type A. Potential Dad #1 has type B blood. Potential Dad #2 has type O blood. Who is the father? • Challenge: What two parents could produce the most diverse children as far as blood type is concerned?

21. Sickle-cell Disease -common in people of African descent -sickled allele causes hemoglobin to change and red blood cell forms a crescent shape – can’t carry oxygen well Codominance

22. Codominance • Genotypes: • BN BN: normal blood cells • BNBS: normal blood cells and sickled cells • BSBS: sickled blood cells

23. HOMEWORK Finish Bikini Bottom Genetics Packet

24. Sex-linked Traits • Traits (genes) located on the sex chromosomes • Sex chromosomes are X and Y • XX genotype for females • XY genotype for males • Many sex-linked traits carried on X chromosome

25. Sex-linked Traits fruit fly eye color XX chromosome - female Xy chromosome - male Example: Eye color in fruit flies Sex Chromosomes

26. Sex-linked Trait Problem Xr Xr XR Y • Example: Eye color in fruit flies • (red-eyed male) x (white-eyed female)XRY x XrXr • Remember: the Y chromosome in males does not carry traits. • RR = red eyed • Rr = red eyed • rr = white eyed • XY = male • XX = female

27. Sex-linked Trait Problem Xr Xr XR Y • Example: Eye color in fruit flies • (red-eyed male) x (white-eyed female)XRY x XrXr • Remember: the Y chromosome in males does not carry traits. • RR = red eyed • Rr = red eyed • rr = white eyed • XY = male • XX = female

28. Sex-linked Trait Solution: Xr Xr XR Xr XR Xr XR Y Xr Y Xr Y 50% red eyedfemale 50% white eyed male

29. Female Carriers

30. Question: Is it possible for a female carrier of hemophilia to have a daughter with hemophilia? XH Xh Xh XH Xh XhXh Y XH Y Xh Y

31. Epistasis When one gene hides the effects of another gene 2 genes determine coat color “E” gene can mask “B” gene

32. Epistasis Ee or EE= Can have dark pigment ee= can’t have dark pigment B = darker Dark pigment b = lighter Dark pigment

33. Dosage Compensation Females have 2 “doses” of X; Males only have 1 “dose” of X; To balance this difference one of the X chromosomes is inactivated or turned off X chromosome: Genes necessary For male/female Y chromosome: Genes necessary For male only

34. Chromosome inactivation: One X in each cell is randomly inactivated. Orange = cells where X chrom. with black allele is inactivated Black = cells where X chrom. With orange allele is inactivated Dosage Compensation

35. Barr bodies: • Inactivated X • chromosome forms • a condensed dark spot • in nucleus

36. Polygenic TraitsA trait that is controlled by more than one gene.

37. Polygenic Traits • So, instead of only 2 alleles contributing to a trait, there can be 4 or 6 or 8, etc. alleles contributing to a trait. • Skin color: the more dominant alleles for each gene, the darker the skin AABbCc = darker skin aaBbCc = lighter skin

39. Gene Linkage • Mendel studied genes on different chromosomes, so they assorted independently – many combinations • Genes located close together on the same chromosome are said to be linked – they get passed down to gametes together – don’t assort independently