Meiosis and Mendel: Understanding Inheritance Patterns

1. UNIT 3 GENETICS

2. Chapter 6 Meiosis and Mendel

11. “hairy ears” (hypertrichosis)- due to holandric gene. (Y chromosome)-only occurs in males. Appears in all sons.

13. Polydactyly- having extra fingers

14. ‘Myths and Mutants’ Work with animals led to recognition of heritable traits in humans Stories of heritable deformities in humans appear in myths and legends (e.g. cyclops, giants, etc.) • 60 birth defects on Babylonian clay tablets (5000 years ago) • Knowledge of traits played role in shaping social customs and mores (e.g. choosing a wife/husband)

15. I. Chromosomes and Meiosis (6.1) A. You have many types of specialized cells in your body 1. Cells can be divided into two types a. Somatic Cells- body cells. Make up most of your body tissues and organs.

16. b. Germ Cells- cells in your reproductive organs, the ovaries and testes 1). Can develop into gametes (called sex cells)   2). Form egg and sperm cells

17. 2. Gametes have DNA that is passed to offspring in chromosomes

18. B. Each species has characteristic number of chromosomes per cell. 1. Chromosome number does not seem to be linked to complexity of organism. 2. Organisms differ from each other because of way genes are expressed, not because they have different genes.

19. II. You cells have autosomes and sex chromosomes A. Your body has 23 pairs of chromosomes 1. Each pair referred to as homologous pair 2. Homologous chromosomes are two chromosomes- one from father and one from mother

20. B. Autosomes- chromosome pairs 1-22 are called autosomes (are homologous)

21. C. Sex chromosomes- pair of chromosomes 1. Directly control development of sexual characteristics 2. Very different in humans (not homologous) a. X chromosome- female b. Y-chromosome- male Sex chromosomes

22. D. Body cells are diploid; gametes are haploid 1. sexual reproduction involves fusion of two gametes   a. results in genetic mixture of both parents b. Fusion of egg and sperm called fertilization c. Egg and sperm only have half usual number of chromosomes

23. 2. Diploid and Haploid cells   a. Body cells are diploid (two copies of each chromosome)   b. Gametes are haploid (have one copy of each chromosome) 

24. 3. Maintaining the correct number of chromosomes is important to survival of organisms

25. 3. Maintaining the correct number of chromosomes is important to survival of organisms  4. Germ cells (sex cells) undergo process of meiosis to form gametes a. diploid cell divides into haploid cell b. Sometimes called reduction division Haploid cells

26. II. Process of Meiosis (6.2) A. Cells go through two rounds of division in meiosis 1. Meiosis produces four haploid cells from one diploid cell 2. Process involves two rounds of cell division- Meiosis I and Meiosis II. 

27. B. Homologous Chromosomes and sister Chromatids 1. Need to distinguish between the two to understand meiosis 2. Homologous chromosomes- two separate chromosomes- one from mother, one from father. a. very similar to each other- same length and carry same genes

28.  b. Each half of duplicated chromosome is called a chromatid. (together called sister chromatids) 1). Homologous chromosomes divided in meiosis I 2). Sister chromatids not divided until meiosis II Sister chromotids

29. C. Meiosis I (first of two phases) 1. Occurs afterDNA has been replicated 2. Divides homologous chromosomes in four phases

30. D. Meiosis II (second of two phases) 1. Divides sister chromatids in four phases 2. DNA is not replicated between meiosis I and meiosis II 

31. E. Meiosis differs from mitosis in significant ways. 1. Meiosis has two cell divisions while mitosis has one. 2. In mitosis, homologous chromosomes never pair up 3. Meiosis results in haploid cells; mitosis results in diploid cells. 

32. F. Haploid cells develop into mature gametes 1. gametogenesis- production of mature gametes

33. 2. Differs between the sexes a. Males produce 4 equal sperm cells b. Females produce one large egg and smaller polar bodies that are eventually broken down

34. III. Mendel and Heredity (6.3) A. Mendel laid the groundwork for genetics 1. Traits are distinguishing characteristics that are inherited. 2. Genetics is the study of biological inheritance patterns and variation. 3. Gregor Mendel showed that traits are inherited as discrete units. 4. Many in Mendel’s day thought traits were blended. 

35. B. Mendel’s data revealed patterns of inheritance 1. Mendel studied plant variation in a monastery garden 2. Mendel made three key decisions in his experiments a. Control over breeding b. Use of purebred plants c. Observation of “either- or” traits (only appear two alternate forms)

36. 3. Experimental design a. Mendel chose pea plants because reproduce quickly and could control how they mate 

37. b. Crossed purebred white-flowered with purebred purple-flowered pea plants. 1). Called parental, or P generation 2). Resulting plants (first filial or F1 generation) all had purple flowers 

38. c. Allowed F1 generation to self-pollinate   1). Produced F2 generation that had both plants with purple and white flowers) 2). Trait for white had been “hidden”, it did not disappear. 

39. d. He began to observe patterns- Each cross yielded similar ratios in F2 generation (3/4 had purple, and 1/4 white)

40. 4. Mendel made three important conclusions   a. Traits are inherited as discrete units (explained why individual traits persisted without being blended or diluted over successive generations)

41. b. Two other key conclusions collectively called the law of segregation 1). Organisms inherit two copies of each gene, one from each parent 2). Organisms donate only one copy of each gene in their gametes (two copies of each gene segregate, or separate, during gamete formation

43. IV. Traits, Genes, and Alleles (6.4) A. The same gene can have many versions 1. gene- a “piece” of DNA that provides a set of instructions to a cell to make a certain protein.

44. Most genes exist in many forms (called alleles) • You have two alleles for each gene` 

45. 2. Homozygous- means two of same allele 3. Heterozygous- two different alleles 

46. B. Genes influence the development of traits 1. Genome- is all the organisms genetic material 2. Genotype- refers to genetic makeup of a specific set of genes 3. Phenotypes- physical characteristics of organism (wrinkled or round seeds)

47. C. Dominant and Recessive Alleles 1. Dominant alleles- allele that is expressed when two different alleles or two dominant alleles are present (use capital letter to represent)

48. 2. Recessive alleles- only expressed if have two copies of recessive present (use small-case letter to represent) 3. Homozygous dominant = TT 4. Heterozygous = Tt 5. Homozygous recessive = tt

49. D. Alleles and Phenotypes 1. Both homozygous dominant and heterozygous genotypes yield a dominant phenotype. 2. Most traits occur in a range and do notfollow simple dominant-recessive patterns

50. V. Traits and Probability (6.5) A. Punnett squares illustrate genetic crosses 1. Used to predict possible genotypes resulting from a cross a. Axes of grid represent possible gamete genotypes of each parents b. Boxes show genotypes of offspring c. Can determine ratio of genotypes in each generation