Observing Patterns in Inherited Traits

1. Observing Patterns in Inherited Traits Chapter 7

2. Skin Color

5. Terms Used in Modern Genetics • Heredity- characteristics passing from parents to offspring through genes • Genes • Each gene has a specific locuson a chromosome • Heterozygous (Aa or Bb) • Homomzygous (AA or BB)

6. Gregor Mendel

8. Genetics • An allele is dominant if its effect masks the effect of a recessive allele paired with it

11. Mendel’s Law of Segregation • Only one of the 2 alleles gets put into each gamete

12. homozygous dominant parent homozygous recessive parent Segregation of Alleles at a Gene Locus (chromosomes duplicated before meiosis) meiosis I meiosis II (gametes) (gametes) fertilization produces heterozygous offspring Fig. 11-5, p. 172

13. genotype phenotype

14. Construction of a Punnett Square • Punnett square

21. Dihybrid Experiments • Tests for dominance relationships between alleles at 2 loci • AABB x aabb • F2 phenotype ratio is 9:3:3:1 (four different phenotypes) • inheritance of one trait does not affect inheritance of the other

22. Independent Assortment at Meiosis One of two possible alignments The only other possible alignment A A a a A A a a b B b B b b B B a a A A A A a a b b b b B B B B a B A A B b a a b b A A b B a B AB ab Ab aB Fig. 11-8, p. 174

23. Mendel’s Dihybrid Experiments

24. parent plant homozygous for purple flowers and long stems parent plant homozygous for white flowers and short stems P generation A Meiosis in homozygous individuals results in one kind of gamete. aabb AABB B A cross between plants homozygous for two different traits yields one possible combination of gametes: x ab AB Fig. 11-9a, p. 175

25. AaBb AaBb AaBb All F1 offspring are AaBb, with purple flowers and tall stems. F1 generation C Meiosis in AaBb dihybrid plants results in four kinds of gametes: Ab ab AB aB F2 generation These gametes can meet up in one of 16 possible wayswhen the dihybrids are crossed (AaBb X AaBb): Fig. 11-9b, p. 175

26. aB Ab ab AB AB AABB AABb AaBB AaBb AABb AAbb AaBb Aabb Ab aB aaBB AaBB AaBb aaBb AaBb Aabb aaBb aabb ab D Out of 16 possible genetic outcomes of this dihybrid cross, 9 will result in plants that are purple-flowered and tall; 3, purple-flowered and short; 3, white-flowered and tall; and 1, white-flowered and short. The ratio of phenotypes of this dihybrid cross is 9:3:3:1. Fig. 11-9c, p. 175

27. Mendel’s Law of Independent Assortment • Mendel’s law ofindependent assortment • Genes are sorted into gametes independently of other genes • Exception: Genes that have loci very close to one another on a chromosome tend to stay together during meiosis

28. Codominance in ABO Blood Types • Codominance • Two nonidentical alleles of a gene are both fully expressed in heterozygotes, so neither is dominant or recessive • Multiple allele systems • Genes with three or more alleles in a population • Example: ABO blood types

29. Codominance in ABO Blood Types

30. Incomplete Dominance • Incomplete dominance • One allele is not fully dominant over its partner • The heterozygote’s phenotype is somewhere between the two homozygotes, resulting in a 1:2:1 phenotype ratio in F2 offspring

31. Fig. 11-11b, p. 176

32. Epistasis • Epistasis • Two or more gene products influence a trait • Typically, one gene product suppresses the effect of another • Example: Coat color in dogs • Alleles B and b designate colors (black or brown) • Two recessive alleles ee suppress color

33. Epistasis in Coat Colors

34. Pleiotropy • Pleiotropy • One gene product influences two or more traits • Example: Some tall, thin athletes have Marfan syndrome, a potentially fatal genetic disorder

35. Linkage and Crossing Over • Linkage group • All genes on one chromosome • Linked genes are very close together; crossing over rarely occurs between them so they often separate together

36. Genes and the Environment • Expression of some genes is affected by environmental factors such as temperature, altitude, or chemical exposure • The result may be variation in traits

37. Effects of Temperature on Gene Expression • Enzyme tyrosinase, works at low temperatures

38. Complex Variations in Traits • Individuals of most species vary in some of their shared traits • Many traits (such as eye color) show a continuous range of variation