12.2 Notes When Heredity Follows Different Rules

Other forms of dominance I. Complete dominance ex. II. Incomplete dominance ex. III. Codominance ex. IV. Multiple alleles ex. V. Polygenic inheritance ex.

Complete dominance--Inheritance controlled by either dominant or recessive alleles One completely hides the other Heterozygous and homozygous dominant have same phenotype Ex. Tt and TT = tall

However, not all traits are controlled by simple Mendelian principles of genetics

Incomplete dominance--heterozygous phenotype is in between the 2 homozygous phenotypes (neither allele is dominant)

With complete dominance Old way: if we crossed a red dominant and a white recessive flower Offspring would be red since dominant BUT….

WITH INCOMPLETE DOMINANCE RR= red flower WW (R’R’) = white RW (RR’) = pink flower R R R’ RR’ Cross red with white--The offspring are all pink because that color is in between 2 red and white

Red (RR) White (R’R’) Offspring: All pink flowers

Codominace--The phenotype of both homozygous phenotypes are expressed equally in the heterozygous phenotype

With complete dominance (old way) black dominant with white recessive = black offspring since black is dominant With incomplete dominance black with white = gray since gray is inbetween black and white BUT…

WITH CODOMINANCE BB = black chicken WW= white chicken BW = checkered B B W W BW Cross black with white chicken--The offspring are all black and white because that is a combination of both homozygous phenotypes

Multiple alleles--not all traits are only controlled by 2 alleles, some traits are controlled by many different alleles Ex. Mouse hair color is controlled by different alleles, black, brown, gray, albino, etc…

Polygenic inheritance--Trait that is controlled by 2 or more different genes Ex. skin color, height Ex. Blood pressure is controlled by genes for weight, cholesterol, kidney function, etc…

Review of other forms notes First step- always make key: yellow, blue dragons (figure out options for heterozygous) Cross blue and yellow (complete dom.) Cross blue and yellow (incomplete dom.) Cross blue and yellow (codominance)

Blood Type outline (day 2- stop here) I. An example of codominace and multiple alleles II. Alleles A= B= o= III. Chart IV. Universal donor/ recipient V. Rh factor PhenoGenoSurfacelikes A B AB O

Blood type An example of codominance in humans Example of multiple alleles, there are more than 2 alleles for this trait It is determined by the presence or absence of carbohydrates (antigens) on surface of blood cell Mixing incompatible blood types can cause cells to clump together and lead to death

Blood types alleles key I A = A I B = B i = o

Human Blood Types PhenotypeGenotypeBlood cell surface molecules Type AI A I A or I A iA antigens Type BI B I B or I B iB antigens Type ABIAIBIAIB A and B antigens Type OiiNo antigens

Watch teacher demo on board Determine blood types liked by other blood types

Alleles I A and I B –are codominant to each other Allele i –is recessive to I A and I B Type O blood—universal donor (has no antigens so anyone can receive it) Type AB blood—universal acceptor (has both A and B antigens so can take all blood types)

Cross parent with heterozygous A (I A i) blood with parent with heterozygous B blood (I B i) I A i IBIB i IAIBIAIB IBiIBi IAiIAiii Genotypic ratio 1 I A I B : 1 I A i : 1 I B i : 1 ii Phenotypic ratio (blood type) — 1 type AB : 1 type A : 1 type B : 1 type O

Rh Factor Describes the presence or absence of another protein on blood cells Rh Positive = have proteins Genotypes: Rh+/Rh+ or Rh+/Rh- Rh Negative = no proteins Genotype: Rh-/Rh-

Cross parent heterozygous for the Rh factor with another parent who does not have the Rh factor Rh+ Rh- Rh- Rh+/Rh- Rh-/Rh- Genotypic ratio 2 Rh+/Rh-: 2 Rh-/Rh- Rh+/Rh- Rh-/Rh- Phenotypic ratio 2 Rh+: 2 Rh-

Practice dihybrid cross Cross TtBb x TtBb Use FOIL method to set up square Remember rules of segregation and independent assortment! Genotypic and phenotypic ratios What is probability of having short + brown eyes?