NonMendelian Genetics What color offspring would you get

Non-Mendelian Genetics

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

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

How does Incomplete Dominance work?

Incomplete Dominance is a Blending Like Paint, the RED Pigment “MIXES” with the WHITE to create PINKFLOWERED offspring

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

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

You Must Use Different Letters 1. 2. 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

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

You’ve Seen A Cross between Pure Snapdragons, now do the Punnet Square for a cross between two hybrids (heterozygotes). n n n 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

What kind of genetics do these organisms exhibit?

Codominance A cross between 2 tabbies (the 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. heterozygotes) results in 1 black : 2 tabbies : 1 tan cat

Notation for Codominance 1. 2. 3. 4. 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.

Writing out the Genotype 1. 2. 3. 4. 5. 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

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

Let’s Practice Tabby cats exhibit codominance between tan and black fur. 1. Can Tan Cat be heterozygous? Why or Why not? 2. If you mate a tabby with a black cat, what is the phenotypic ratio of their offspring? 3. If the offspring of two cats are composed of 36 tabbies and 40 black cats, what are the parental phenotypes and genotypes?

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

The Alleles n n 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).

Alleles and Their Blood Types ii IA IA IA i IB IB IB i IA IB O A B AB

Let’s Practice n n 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?

Codominance 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 Genotypes: BN BN: normal blood cells BNBS: normal blood cells and sickled cells BSBS: sickled blood cells

HOMEWORK Finish Bikini Bottom Genetics Packet

Sex-linked 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

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

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

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

Sex-linked Trait Solution: Xr XR XR Xr Y Xr XR Xr Xr Y 50% red eyed female 50% white eyed male

Female Carriers

Question: Is it possible for a female carrier of hemophilia to have a daughter with hemophilia? XH Xh X H X h Y XH Y Xh Y

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

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

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

Dosage Compensation 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

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

Polygenic Traits A trait that is controlled by more than one gene.

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 AABb. Cc = darker skin dominant alleles for aa. Bb. Cc = lighter skin each gene, the darker the skin

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