2. 1 Unit Two Patterns of Inheritance Richards High School AP Biology The chromosomal basis of inheritance provides an understanding of the pattern of passage (transmission) of genes from parent to offspring.

3. 2 Basics of Genetics

4. Vocab Review Gene – location on DNA that carries heritable info Diploid – 2n – have pairs of genes on homologous chromosomes Mutation – change in DNA Allele – alternative form of a gene Hybrid – offspring that has 2 different alleles for a gene Homozygous – 2 identical alleles Heterozygous – 2 different alleles Genotype – genetic makeup of an organism Phenotype – physical appearance of an allele 3

5. Vocab Review Dominant – trait that masks the appearance of another trait  CAPITAL LETTER Recessive – the trait that is masked in a heterozygous offspring  lower case letter Homozygous dominant – pair of dominant alleles – AA Homozygous recessive – pair of recessive alleles – aa Heterozygous – one of each allele – Aa P – parent generation F 1 – 1 st generation offspring F 2 – 2 nd generation offspring 4

6. 5 Genotype vs. Phenotype Genotype = Genes/Alleles  AA Homozygous Dominant True-Breeding Purebred  Aa Heterozygous Hybrid “ Carrier ”  aa Homozygous Recessive True-Breeding Purebred Phenotype = Physical Traits

7. 6 Generations P Generation  Parental Generation F 1 Generation  First Generation Offspring  F stands for “ Filial ” F 2 Generation  Second Generation Offspring F 3, F 4, etc.

8. 7 Wild-Type vs. Mutant Alleles A wild-type allele is a gene ’ s most common form.  Usually but NOT always the dominant form. A mutant allele is a gene ’ s less common form.  Usually but NOT always the recessive form. Achondroplasia (dwarfism) is a dominant trait, but definitely NOT the wild-type allele in the human population. Most humans are homozygous recessive for the gene controlling achondroplasia.

9. 8 Monohybrid & Dihybrid Crosses

10. 9 Monohybrid Crosses Monohybrid = Parents differ in only one characteristic.  P Generation: True Breeding x True Breeding  F 1 Generation: All of the same phenotype.  F 2 Generation: Always close to a 3:1 ratio.

11. 10 Punnett Square Method

12. 11

13. Types of Inheritance Patterns Gregor Mendel’s Original Research:  Complete dominance – in a heterozygote, one allele completely covers another Too advanced for Mendel:  Traits don’t follow predicted ratios (can’t quantify) Incomplete dominance – alleles blend Codominance – both alleles expressed, but do not blend Multiple alleles – more than two alleles Polygenic – traits controlled by more than one gene Sex-linked – traits found on X chromosome 12

14. Monohybrid Review Tall plants are dominant to short plants. Cross two heterozygotes. What are the probabilities of various genotypes and phenotypes of the offspring? 13

15. Test Cross 14

16. 15 Mendel’s Laws

17. 16 Genes are Located on Chromosomes

18. 17 Law of Segregation Alleles are alternative forms of a gene.  Eye Color Gene  Blue & Brown Alleles For every gene, an offspring inherits one allele from each parent.  Eye Color Genotype  BB or Bb or bb Alleles in each pair segregate (separate) during gamete formation.  An egg or sperm cell contains only one allele per gene (B or b).  Maternal and paternal alleles combine in the offspring.  Increases variation in the offspring!

19. 18 Dihybrid Crosses Dihybrid = Parents differ in two characteristics.  P Generation: True Breeding x True Breeding  F 1 Generation: All of the same phenotype.  F 2 Generation: Always close to a 9:3:3:1 ratio.

20. Dihybrid Review Purple flowers are dominant to white and green seeds are dominant to yellow. Cross a homozygous purple and homozygous yellow plant with a plant that is heterozygous for both traits. How many offspring will be purple and yellow? 19

21. 20 Independent Assortment The inheritance pattern of one trait will not affect the inheritance pattern of another trait.

22. 21 Independent Assortment Occurs During Meiosis Each gamete receives a random mix of maternal & paternal chromosomes.

23. Mendel’s Law of Independent Assortment As meiosis ends, genes on pairs of homologous chromosomes have been sorted out for distribution into one gamete or another, independently of gene pairs on other chromosomes. 22

24. 23 Linked Genes Linkage is the tendency of genes located on the same chromosome to be transmitted together in inheritance. Example – Humans:  ~25,000 genes  23 chromosomal pairs  Many genes found on each chromosome! 12:1:1:2

25. 24 Linked Genes & Crossing Over Linkage can be disrupted by crossing over - the exchange of parts of homologous chromosomes.

26. 25 Linkage Mapping Crossing over is more likely between genes which are located further apart. This can be utilized to map the location of genes!

27. 26 Linkage Mapping in the Fruit Fly = 17 Map Units on the Chromosome

28. 27 Genetic Mapping Sample Problem Genes A, B, and C are all located on the same chromosome (linked genes) with the following crossover data: GenesCrossover % A – C 18% B – C 3% A – B 21% Gene A and Gene B must be the furthest apart. Gene B and Gene C must be the closest together. The gene order appears to be: A C B (or the reverse: B C A). The space between the genes is based on the crossover percentages, which are equivalent to "map units" on the chromosome. _____________________________________________ A C B

29. 28 Polygenic Inheritance

30. 29 Polygenic Inheritance Additive effect of two or more (many) genes on a single phenotypic characteristic. Most traits show continuous variation.

31. 30 Height is a Polygenic Trait with Continuous Variation

32. 31 Sex-Linked Inheritance

33. Human somatic cells contain 46 chromosomes (23 pairs):  44 Autosomes (Non-sex chromosomes)  2 Sex Chromosomes (XX or XY) Human gametes contain 23 chromosomes. 32

34. 33 Sex Determination in Humans XXXY

35. 34 Eye Color in Drosophila is X-Linked DominantRecessive

36. 35 The Y Chromosome Carries Few Genes It is essentially a “ blank. ”

37. 36 X-Linked Punnett Squares

38. 37 Y-Linked Traits? Possible, but very rare since there are so few genes on the Y chromosome. Inherited only from fathers to sons.

39. Sex-linked Review Red-green colorblindness is a recessive mutation found on the X-chromosome. Cross a female who is a carrier of colorblindness with a normal male. Why are X-linked disorders more common in males than females? 38

40. 39 Are You Red-Green Colorblind? You may have one form of red-green colorblindness if you see the numeral “ 7 ” instead of “ 29 ” in the left circle. You may have another form if you see a “ 3 ” instead of an “ 8 ” in the right circle.

41. 40 If You Were Colorblind… What red-green color blindness means, using ripe red cherries on a green- leafed tree as an example. In this case, the perception of blues and yellows is normal, but the affected individual has difficulty distinguishing red from green.

42. Sex-Limited Traits Genes that are present in both sexes (male and female) but only expressed in one gender.  Generally autosomal (not sex-linked).  Cause the two sexes to show different phenotypes.  Ex: Milk production (lactation) in females. Genes are carried in both males and females, but only females express them.  Ex: Male pattern baldness Two alleles: bald or non-bald In the presence of high testosterone, the bald allele has a stronger influence. 41

43. 42 Pedigree Analysis

44. 43 Constructing Pedigrees The following symbols are used to represent gender: = Female= Male = Gender Not Specified

45. 44 Constructing Pedigrees Colored symbols are often used to represent the trait being studied. Example: Deafness trait in humans… = Deaf Female = Hearing Female = Deaf Male = Hearing Male

46. Pedigree Analysis Pedigree for the trait: Widow’s Peak “Widow’s Peak”“No Widow’s Peak” “ Autosomal Dominant ” 45

47. Pedigree Analysis Pedigree for the trait: Attached Ear Lobes “Widow’s Peak” “Attached Ear Lobe”“Free Ear Lobe” “ Autosomal Recessive ” 46

48. 47 Autosomal Recessive Inheritance

49. 48 Autosomal Dominant Inheritance Dominant traits that affect survival tend to decrease in a population over time, but not always. Why???

50. 49 X-Linked Recessive Inheritance

51. 50 What is the Inheritance Pattern? “ Autosomal Recessive ”

52. 51 Changes in Chromosome Number Cells have one extra or one less chromosome than normal.  Typically results from nondisjunction.  Monosomy = Individual with one missing chromosome  Trisomy = Individual with one extra chromosome

53. Nondisjunction Failure of homologous chromosomes to separate during meiosis Result: Monosomy (missing a chromosome) Result: Trisomy (extra chromsome) Result: Lethal mutation (half of all miscarriages) 52

54. 53 Nondisjunction

55. 54 Down Syndrome (Trisomy 21)

56. 55 Non-Nuclear Inheritance

57. Chloroplasts and mitochondria contain DNA Randomly assorted to gametes and daughter cells Do not follow Mendelian rules Example: Mitochondria  mtDNA = mitochondrial DNA  Contains 16,000 base pairs or 39 genes  Circular DNA but multiple copies present  Make enzymes and materials used for cellular respiration  During fertilization, the sperm’s mtDNA is destroyed, so your mtDNA came from your mother (maternally inherited) 56