Incomplete Dominance and Codominance copyright cmassengale 1 Incomplete

Incomplete Dominance and Codominance copyright cmassengale 1

Incomplete Dominance F 1 hybrids have an appearance somewhat in between the phenotypes of the two parental varieties. Example: snapdragons (flower) red (RR) x white (rr) r r RR = red flower rr = white flower R R copyright cmassengale 2

Incomplete Dominance r r R Rr Rr produces the F 1 generation All Rr = pink (heterozygous pink) copyright cmassengale 3

Incomplete Dominance copyright cmassengale 4

Codominance Two alleles are expressed (multiple alleles) in heterozygous individuals. Example: blood type copyright cmassengale 5

There are four blood types Type A Type B Type AB Type O These types are named after different antigens, we will talk about that next. You say ‘What about positive/negative ? !!? !’ Like A- or O-…. . This is determined by the presence or absence of the D antigen (called Rh factor) but don’t worry about that. Rh comes from the discovery in Rhesus Monkeys… copyright cmassengale 6

Antigens are proteins on the outside of the cell that communicate with white blood cells (the immune system) Antigens are identifying markers to keep your body from attacking itself when there is an infection. There are two main types of antigens: A and B copyright cmassengale 7

Blood Types: How they are different copyright cmassengale 8

How do we get FOUR blood types from just two kinds of antigens (A and B)? copyright cmassengale 9

Codominance Two alleles are expressed (multiple alleles) in heterozygous individuals. Example: blood type: both A and B are dominant 1. 2. 3. 4. type A B AB O = = IAIA or IAi IBIB or IBi Look, codominance! I AI B ii (the only recessive one!) copyright cmassengale 10

Codominance Problem Example: homozygous male Type B (IBIB) x heterozygous female Type A (IAi) IB IB IA I AI B i I Bi copyright cmassengale 1/2 = IAIB 1/2 = IBi 11

Another Codominance Problem • Example: male Type O (ii) x female type AB (IAIB) i i IA I Ai IB I Bi copyright cmassengale 1/2 = IAi 1/2 = IBi 12

Codominance Question: If a boy has a blood type O and his sister has blood type AB, what are the genotypes and phenotypes of their parents? boy - type O (ii) AB (IAIB) X copyright cmassengale girl - type 13

Codominance Answer: IA IB i i I AI B ii Parents: genotypes = IAi and IBi phenotypes = A and B copyright cmassengale 14

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 copyright cmassengale 15

Sex-linked Traits Example: Eye color in fruit flies Sex Chromosomes fruit fly eye color XX chromosome - female Xy chromosome - male copyright cmassengale 16

Sex-linked Trait Problem Example: Eye color in fruit flies (red-eyed male) x (white-eyed female) X RY X r Remember: the Y chromosome in males does not carry eye color traits. RR = red eyed Rr = red eyed rr = white eyed XY = male XX = female XR Y Xr Xr copyright cmassengale 17

Sex-linked Trait Solution: XR Y Xr XR Xr Xr Y 50% red eyed female 50% white eyed male copyright cmassengale 18

Female Carriers copyright cmassengale 19

Genetic Practice Problems copyright cmassengale 20

Breed the P 1 generation tall (TT) x dwarf (tt) pea plants t t T T copyright cmassengale 21

Solution: tall (TT) vs. dwarf (tt) pea plants t t T Tt Tt produces the F 1 generation T Tt Tt All Tt = tall (heterozygous tall) copyright cmassengale 22

Breed the F 1 generation tall (Tt) vs. tall (Tt) pea plants T t copyright cmassengale 23

Solution: tall (Tt) x tall (Tt) pea plants T t T TT Tt tt produces the F 2 generation 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt 1: 2: 1 genotype 3: 1 phenotype copyright cmassengale 24