Multiple Alleles

1. Multiple alleles - for some traits there are more than two alleles in the species • Single individual cannot have more then two alleles for each trait (1 on each homologous chromosome) • Multiple alleles explains why there are four different blood types (A, B, AB, and O) Multiple Alleles

2. Multiple Alleles • Three alleles code for blood type (A, B, O) • O is the recessive allele • A & B are both dominant over O, but neither one is dominant over the other. • Which genetic relationship does this sound like?

3. Multiple Alleles • Use capital letter “I” to show a dominant allele • Use a lower case letter “i” to show the recessive allele • Superscript letters stand for each dominant allele • Six possible genotypes!

4. Blood Antigens • On the surface of red blood cells are chemical structures (proteins) calledantigens • Blood plasma contains antibodies- proteins that bind to/attack specific antigens

5. Blood Typing Blood also containsantibodies– proteins thatrecognize and bind to certain, specific antigens Blood TypeAntigens on RBCAntibodies Can Receive A A anti-B A, O B B anti-A B, O AB AB none A, B, AB, O O none both A & B O (Rh + blood) contains Rh antigen (Rh – blood) no Rh antigen

6. Why is it bad if you receive the wrong blood type? • If blood containing a specific antigen is mixed with blood containing the corresponding antibodies, the blood clots • Universal donor- (type O blood) no antigens (RBC) to be attacked • Universal recipient- (type AB) no antibodies to attack received blood

7. Blood Typing Human serum containing specific antibodies can be purchased Separately mix a drop of unknown blood sample with drop of each anti-serum Reaction between blood and anti-serum No reaction between blood and anti-serum

8. Blood Typing Example A sample of unknown blood is mixed with three anti-sera samples: Tube 1 (Anti-A): No reaction Tube 2 (Anti B): No reaction Tube 3 (Anti Rh): Cloudy reaction In terms of the A-B-O and Rh systems, what type blood is the sample?

9. Sex Chromosomes & Sex Determination • 1905 Wilson studied insects • In male, 1 homologous pair or chromosomes did not match • In female, all homologous chromosomes matched • Called the female sex chromosome the X chromosome & the unmatched male chromosome the Y (determine sex • All the other body chromosomes are called autosomes • Male Gametes (X & Y) Female (X & X)

10. Sex-linked traits- a trait that is controlled by a gene found on the sex chromosome. • Chance of showing trait is affected by the sex of the individual • Most determined by genes found on the X chromosome Sex-linked Traits

11. Sex-linked Genes • Morgan studied Drosophila melanogaster (fruitflies) • Surprised to see a white-eyed fly (it was male) • Mated white-eyed male with normal red-eyed female resulting in an F1 generation: all red eyes • Conclusion: red eyes is _________ over white • Mated members of F1 generation: Results: ¾ red eyes, ¼ white eyes • BUT all white eyes were male!! • Concluded that this trait is carried on a sex chromosome! (sex-linked) • Gene for red & white eye carried on the X chromosome… no corresponding allele on the Y chromosome

12. Sex-Linked Genes • Therefore, males get eye color from 1 gene…on the X chromosome from mom • For a female to have white eyes, must get two white alleles • Determine genotypes of crossing two individuals from the F1 fruitfly generation: Crossed male & heterozygous female with red eyes… Resulted in 3 red eye: 1 white eye (male=white) = red allele on X chromosome = white allele on X chromosome Y = male sex chromosome with no allele for eye color

13. Genotypes if F1 fruitfly generation

14. Color-blindness • Hemophilia • Duschenne muscular dystrophy Human Sex-linked Traits

16. Testcross • Testcross- the crossing of an individual of unknown genotype with an individual with a homozygous recessive individual to determine the unknown genotype. • Can determine the genotype of any individual Whose phenotype expresses the dominant trait.