4.3 Syllabus Points

1. 4.3 Syllabus Points Theoretical Genetics

2. Basic Vocab • Genetic Terms: • P = parental generation of a cross • F1 = the first generation after the parental (the results of the first cross) • F2 = a cross between F1 individuals yields F2

4. 4.3.1 More Basic Definitions • Genotype – the alleles of an organism as inherited from the parents • Phenotype – the characteristics of the organism due to the interaction of the genotype and the environment

6. 4.3.1 continued • Homozygous – having two identical alleles of a gene • Heterozygous – having two different alleles of a gene AA aa are homozygous Aa are heterozygous

7. 4.3.1 continued • Dominant allele – expressed phenotypically whether it is homozygous or heterozygous • Recessive allele – expressed phenotypically only in the homozygous state Capital letters are used to represent the dominant allele Lower case for the recessive Dominant allele always listed first

8. 4.3.1 continued • Codominant alleles – pairs of alleles that both affect the phenotype when present in the heterozygous state

9. 4.3.1 continued • Locus – the particular position of a gene on homologous chromosomes

10. 4.3.1 continued • Carrier – an individual that has one copy of a recessive gene that causes a genetic disease in individuals that are homozygous for the gene • Test cross – checking the genotype of an individual by crossing it with a known homozygous recessive B? X bb The percentage phenotype give answer

11. 4.3.2 • Determine genotypes and phenotypes using a punnett square.

12. Setting up the punnett square • The possible gametes of each individual are determined. • Each gamete will have one of the two alleles of the parent. • Generate a punnett square and write the alleles forparent 1on the left side of the Punnett square. • Place the alleles for parent 2 above the square • Fill the squares for each parent

14. Probability Rule of Multiplication • The odds of 2 or more independent events occurring together is the product of each independent event. • In a cross between pea plants that are heterozygous for flower color (Pp), what is the probability that the offspring will be homozygous recessive? • ½ x ½ = ¼

15. Rule of Addition • Probability that events that can occur in 2 or more different ways will occur, is the sum of the separate problems. • In a cross between pea plants that are heterozygous for flower color (Pp), what is the probability of the offspring being heterozygous? • ¼ + ¼ = ½

16. Law of Independent Assortment • The odds of two different traits occurring together in the same offspring is the product of each independent trait occurring in the offspring. • In which phase of meiosis does this event occur? • What assumption did Mendel make for this law to work?

17. 4.3.3 Multiple Alleles • Some traits have more than two alleles • Coat color in rabbits and cats • Drosophila wings • Human blood types

19. 4.3.5 Sex Chromosomes • Women – homozygous XX • Men – heterozygous XY • 23rd pair chromosomes • Dimorphic • SRY gene on Y determines Presence of male features

20. Gender • Mothers can only contribute X chromosome • Fathers can contribute either X or Y thus determine gender of child 50% chance boy, 50% chance girl for each fertilization event

22. Gender Not Just in Genes • Nile crocodiles sand temperature around the eggs during incubation affects gender - higher temperatures favor males • Turtles and lizards high temperatures favor females • Many fish are hermaphrodites and under certain environmental conditions will switch gender

23. 4.3.6 Gene distribution X and Y • http://www.ornl.gov/hgmis/posters/chromosome/chooser.shtml • X chromosome much larger than Y • Many genes found on X that are not present on Y

24. 4.3.7 Sex Linkage • Genes on X with no counterpart on Y are called sex linked genes • Often affect one gender more than another • Color Blindness and Hemophilia

27. 4.3.8 Hemophilia • Caused by mutant gene recessive • Encodes either clotting factor Vlll = h-A • Or clotting factor lX = h-B • Carried on X chromosome • Heterozygous will clot normally as their good copy of gene produces enough clotting factor • If only mutant gene copy present will suffer from excessive bleeding

28. 4.3.8 Color blindness • Red-green color blindness carried on X • Blue color sensitivity is carried on chromosome 7 and inherited as any autosomal gene

29. 4 Sex-Linked Traits:  1. Normal Color Vision: A: 29,  B: 45,  C: --,  D: 26  2. Red-Green Color-Blind: A: 70,  B: --,  C: 5,  D: --  3. Red Color-blind: A: 70,  B: --,  C: 5,  D: 6  4. Green Color-Blind: A: 70,  B: --,  C: 5,  D: 2

30. 4.3.9 .10 Female - Carrier • Females can be homozygous or heterozygous for sex- linked traits • Females with one or two dominant alleles for a sex linked trait will not exhibit the trait • Females that are heterozygous for sex-linked traits are called carriers • Only females can pass on sex-linked traits to their sons

31. Calico Cats • The calico cat is the result of multiple alleles on the X chromosome combines with X inactivation. • One allele causes orange fur and the other causes black fur. • The male cat will be either orange or black. • Only a heterozygous female will be calico with regions that are orange and regions that are black based on the X inactivation

32. Tortoise Shell Calico

33. 4.3.11 Punnett Squares • Predict genotype and phenotype using Punnett Squares for all of the inheritance patterns mentioned above

34. 4.3.12 Pedigrees • Deduce the genotype and phenotype of individuals in a pedigree chart