1. KEY CONCEPT - Section 1 Gametes have half the number of chromosomes that body cells have.

2. You have body cells and gametes. Body cells are also called somatic cells. Germ cells develop into gametes. –Germ cells are located in the ovaries and testes. –Gametes are sex cells: egg and sperm. –Gametes have DNA that can be passed to offspring. body cells sex cells (sperm) sex cells (egg)

3. Your body cells have 23 pairs of chromosomes. –Homologous pairs of chromosomes have the same structure. –For each homologous pair, one chromosome comes from each parent. Chromosome pairs 1-22 are autosomes. Sex chromosomes, X and Y, determine gender in mammals. Your cells have autosomes and sex chromosomes.

4. Body cells are diploid (2n) Gametes are haploid (1n) Fertilization between egg and sperm occurs in sexual reproduction. Diploid (2n) cells have two copies of every chromosome. –Body cells are diploid. –Half the chromosomes come from each parent.

5. Haploid (n) cells have one copy of every chromosome. –Gametes are haploid. –Gametes have 22 autosomes and 1 sex chromosome.

6. Chromosome number must be maintained in animals. Many plants have more than two copies of each chromosome. Mitosis and meiosis are types of nuclear division that make different types of cells. Mitosis makes more diploid cells.

7. Meiosis makes haploid cells from diploid cells. –Meiosis occurs in sex cells. –Meiosis produces gametes.

8. KEY CONCEPT –section 2 During meiosis, diploid cells undergo two cell divisions that result in haploid cells.

9. Cells go through two rounds of division in meiosis. Meiosis does two things: –reduces chromosome number –creates genetic diversity. Why are these things important?

10. Meiosis I and Meiosis II each have four phases, similar to those in mitosis. homologous chromosomes sister chromatids sister chromatids –Pairs of homologous chromosomes separate in meiosis I. –Homologous chromosomes are similar but not identical. –Sister chromatids divide in meiosis II. –Sister chromatids are copies of the same chromosome.

11. Meiosis I occurs after DNA has been replicated. Meiosis I divides homologous chromosomes in four phases.

13. Crossing over during meiosis increases genetic diversity. Crossing over is the exchange of chromosome segments between homologous chromosomes. –occurs during prophase I of meiosis I –results in new combinations of genes

15. Meiosis II divides sister chromatids in four phases. DNA is not replicated between meiosis I and meiosis II. Why not?

18. 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 unique, haploid cells; mitosis results in identical, diploid cells.

19. Haploid cells develop into mature gametes. Gametogenesis is the production of gametes. Gametogenesis differs between females and males. –Sperm become streamlined and mobile. –Sperm primarily contribute DNA to an embryo.

20. –Eggs contribute DNA, cytoplasm, and organelles to an embryo. –During meiosis, the egg gets most of the contents; the other cells form polar bodies –The body gets rid of polar bodies

21. Summary 1.What is the major difference between Metaphase I and Metaphase II? 2.What is the major difference between Anaphase I and Anaphase II? 3.List the key differences between meiosis I and II. 4.Why is an egg cell much larger than sperm?

22. KEY CONCEPT – Section 3 Mendel’s research showed that traits are inherited as discrete units.

23. Review terms before we begin… Zyg = pair Homo = same Hetero= different; other So how would you define the following words? Homozygous and Heterozygous So which are homozygous? heterozygous? Aa aa AA rrRRRr

24. Mendel laid the groundwork for genetics. Traits are distinguishing characteristics that are inherited. Genetics is the study of biological inheritance patterns and variation. Gregor Mendel showed that traits are inherited as discrete units. Many in Mendel’s day thought traits were blended.

25. Mendel’s data revealed patterns of inheritance. Mendel made three key decisions in his experiments. –use of purebred plants –control over breeding –observation of seven “either-or” traits For example, a gene that is coding for height may have contrasting traits: either tall or short

26. Mendel used pollen to fertilize selected pea plants. Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant. –P generation crossed to produce F 1 generation –interrupted the self-pollination process by removing male flower parts

27. Mendel allowed the resulting plants to self- pollinate. –Among the F 1 generation, all plants had purple flowers –F 1 plants are all heterozygous –Among the F 2 generation, some plants had purple flowers and some had white

28. Mendel observed patterns in the first and second generations of his crosses.

29. Mendel drew three important conclusions. 1. Traits are inherited as discrete units. –The last two are the Law of Segregation: 2. Organisms inherit two copies of each gene, one from each parent. 3. The two copies segregate during gamete formation. purplewhite

30. KEY CONCEPT – Section 4 Genes encode proteins that produce a diverse range of traits.

31. The same gene can have many versions. A gene is a piece of DNA that directs a cell to make a certain protein. Each gene has a locus, a specific position on a pair of homologous chromosomes.

32. An allele is any alternative form of a gene occurring at a specific locus on a chromosome. –Each parent donates one allele for every gene. –Homozygous describes two alleles that are the same at a specific locus. –Heterozygous describes two alleles that are different at a specific locus.

33. Genes influence the development of traits. All of an organism’s genetic material is called the genome. G enotype refers to the makeup of a specific set of g enes. P henotype is the p hysical expression of a trait. So which is the genotype? Phenotype?

34. Alleles can be represented using letters. –A dominant allele is expressed as a phenotype when at least one allele is dominant. –A recessive allele is expressed as a phenotype only when two copies are present. –Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters.

35. Both homozygous dominant and heterozygous genotypes yield a dominant phenotype. Most traits occur in a range and do not follow simple dominant- recessive patterns.

36. KEY CONCEPT – Section 5 The inheritance of traits follows the rules of probability.

37. Punnett squares illustrate genetic crosses. The Punnett square is a grid system for predicting all possible genotypes resulting from a cross. –The axes represent the possible gametes of each parent. –The boxes show the possible genotypes of the offspring. The Punnett square yields the ratio of possible genotypes and phenotypes.

38. A monohybrid cross involves one trait. Mono = One Monohybrid crosses examine the inheritance of only one specific trait. –homozygous dominant (two capital letters)-homozygous recessive (two lower case letters): all heterozygous genotypes What would all of these plants look like? What would their phenotype be?

39. Heterozygous-Heterozygous— Genotype = 1:2:1 homozygous dominant: heterozygous: homozygous recessive Phenotype = 3:1 dominant:recessive

40. heterozygous-homozygous recessive— –Genotype = 1:1 heterozygous:homozygous recessive; –Phenotype = 1:1 dominant:recessive

41. The Unknown What if you have an unknown genotype? A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype. You have brown eyes but that means you have two possible genotypes –BB or Bb –If you cross with someone with blue eyes and have a child with blue eyes, what must your genotype be?

42. A dihybrid cross involves two traits. Mendel’s dihybrid crosses with heterozygous plants yielded a 9:3:3:1 phenotypic ratio. Mendel’s dihybrid crosses led to his second law, the law of independent assortment. The law of independent assortment states that allele pairs separate independently of each other during meiosis.

43. Heredity patterns can be calculated with probability. Probability is the likelihood that something will happen. Probability predicts an average number of occurrences, not an exact number of occurrences. Probability = number of ways a specific event can occur number of total possible outcomes Probability applies to random events such as meiosis and fertilization.

44. Ch 7.1 KEY CONCEPT The chromosomes on which genes are located can affect the expression of traits.

45. Two copies of each autosomal gene affect phenotype. Mendel studied autosomal gene traits, like hair texture.

46. Mendel’s rules of inheritance apply to autosomal genetic disorders. –A heterozygote for a recessive disorder is a carrier. –Disorders caused by dominant alleles are uncommon. (dominant)

47. Males and females can differ in sex- linked traits. Genes on sex chromosomes are called sex-linked genes. –Y chromosome genes in mammals are responsible for male characteristics. –X chromosome genes in mammals affect many traits.

48. Male mammals have an XY genotype. –All of a male’s sex- linked genes are expressed. –Males have no second copies of sex-linked genes.

49. Think about it… Why are sex-linked disorders such as color-blindness more common in males than females?

50. Female mammals have an XX genotype. –Expression of sex-linked genes is similar to autosomal genes in females. –X chromosome inactivation randomly “turns off” one X chromosome.

51. Ch 7.2 KEY CONCEPT Phenotype is affected by many different factors.

52. In incomplete dominance, neither allele is completely dominant nor completely recessive. –Heterozygous phenotype is intermediate between the two homozygous phenotypes –Homozygous parental phenotypes not seen in F 1 offspring Phenotype can depend on interactions of alleles.

53. Codominant alleles will both be completely expressed. –Codominant alleles are neither dominant nor recessive. –The ABO blood types result from codominant alleles. Many genes have more than two alleles.

54. Many genes may interact to produce one trait. Polygenic traits are produced by two or more genes. Order of dominance: brown > green > blue.

55. An epistatic gene is a single gene that, if present, overrides all other genes –Example: Mouse fur and Albinism

56. The environment interacts with genotype. Phenotype is a combination of genotype and environment. The sex of sea turtles depends on both genes and the environment-eggs buried in warm climates = female; in cooler climates = male Height is an example of a phenotype strongly affected by the environment. How might environment cause a difference?

57. 1.(pg. 207) How do multiple alleles differ from polygenic traits? 2.Do identical twins have identical genes? Do they have identical fingerprints? Multiple alleles are traits influenced by several different versions of one gene; polygenic traits are influenced by multiple genes. Yes, but finger prints will vary because when in the womb, they touch the walls and the environment affects the ridges