2. Incomplete Dominance, Codominance, Multiple Alleles, and Sex-Linked Traits

3.  AG  Ag  aG  ag

4.  AG  Ag  Why are there only two possible combinations?

5.  What is the probability of producing an offspring with the genotype AAGg?  AA -> ½  Gg -> ½  ½ x ½ = ¼

6.  No, Mendel’s studies with peas applied to traits controlled by a single gene with two existing alleles where 1 allele is completely dominant to the other  This is not the case for MOST genes

7.  Incomplete Dominance  Codominance  Multiple Alleles  Sex-Linked Traits

9.  Heterozygotes show a “blending” or intermediate form of the homozygous forms that exist – No true dominant allele  F2 genotypic ratio is 1:2:1 (HH: Hh: hh)  Ex: Snap Dragons, Hypercholesterolemia

11.  Two dominant alleles exist  Heterozygotes express both alleles EQUALLY  Ex: Type AB Blood, Speckled Chickens, Roan Cattle, Sickle-cell Anemia

12.  More than two alleles exist for a particular gene, but every organism has only 2 of them  Ex: Blood Types (A B and O alleles)  A and B are codominant  A is dominant to O  B is dominant to O  O is recessive to A and B

14.  Genes located on the sex chromosomes, mainly X-chromosome  Males XY; Females XX  Males will show recessively inherited characteristics more often than females.  Ex: Hemophilia, colorblindness, white eyes in flies

15.  Genes are on sex chromosomes  as opposed to autosomal chromosomes  first discovered by T.H. Morgan at Columbia U.  Drosophila breeding  good genetic subject  prolific  2 week generations  4 pairs of chromosomes  XX=female, XY=male 1910 | 1933

16. autosomal chromosomes sex chromosomes

17. Huh! Sex matters?! F 2 generation 100% red-eye female 50% red-eye male 50% white eye male P X F 1 generation (hybrids) 100% red eye offspring true-breeding white-eye male true-breeding red-eye female

18. RRrr x rr R R Rr 100% red eyes Rr x Rr R r RR Rrrr Rr 3 red : 1 white Doesn’t work that way!

19.  In humans & other mammals, there are 2 sex chromosomes: X & Y  2 X chromosomes  develop as a female: XX  gene redundancy, like autosomal chromosomes  an X & Y chromosome  develop as a male: XY  no redundancy XY X X XX XY 50% female : 50% male XX

20. XRXRXRXR XrYXrY x XrXr Y XRXR 100% red eyes XRXR XRXrXRXr XRYXRY XRYXRYXRXrXRXr x XRXrXRXr XRYXRY XRXR Y XRXR XrXr XRXrXRXr XRYXRYXRXRXRXR XrYXrY 100% red females 50% red males; 50% white males BINGO!

21.  Y chromosome  few genes other than SRY  sex-determining region  master regulator for maleness  turns on genes for production of male hormones  X chromosome  other genes/traits beyond sex determination  mutations:  hemophilia  Duchenne muscular dystrophy  color-blindness

22.  Sex-linked  usually means “X-linked”  more than 60 diseases traced to genes on X chromosome

23. < 30 genes on Y chromosome Sex-determining Region Y ( SRY ) linked Channel Flipping ( FLP ) Catching & Throwing ( BLZ-1) Self confidence ( BLZ-2) note: not linked to ability gene Devotion to sports ( BUD-E) Addiction to death & destruction movies ( SAW-2) Scratching ( ITCH-E) Spitting ( P2E) Inability to express affection over phone ( ME-2) Selective hearing loss ( HUH) Total lack of recall for dates ( OOPS) Air guitar ( RIF)