Sexual Reproduction and Genetics

1. Sexual Reproductionand Genetics • Chapter 10 http://main.uab.edu/cord/show.asp?durki=38593

2. Meiosis10.1

3. Chromosomes • Human body cells have 46 chromosomes. Each parent contributes 23 chromosomes resulting in 23 pairs. • The chromosomes that make up a pair (one chromosome from each parent) are called homologous chromosomes. • Homologous chromosomes have the same length and centromere position and they carry genes that control the same traits.

4. Chromosomes http://www.phschool.com/science/biology_place/labbench/lab3/homologs.html

5. Chromosome Number • To maintain the same chromosome number from generation to generation, organisms produce gametes. • Gametes: sex cells that have half the number of chromosomes. • The symbol n is used to represent the number of chromosomes in a gamete.

6. Chromosome Number • An organism with n number of chromosomes is called a haploid cell. • Fertilization: the process by which one haploid gamete combines with another haploid gamete. • As a result of fertilization the cell will now contain a total of 2n chromosomes (n from the female parent and n from the male parent). • An organism with 2n chromosomes is called a diploid cell.

7. Chromosome Number

8. Asexual vs Sexual Reproduction • Asexual Reproduction: only one parent, offspring identical to parent. • Sexual Reproduction: two parents combine their genetic material to produce offspring that are genetically different from both parents.

9. Mitosis vs Meiosis • Mitosis maintains the chromosome number. • Meiosis reduces the chromosome number by half.

10. Mitosis vs Meiosis

11. Meiosis • Meiosis: cell division resulting in a reduced number of chromosomes, gamete formation. • Occurs in the reproductive structures of organisms that reproduce sexually. • Involves two cell divisions called Meiosis I and Meiosis II.

12. Sexual Life Cycle

13. Meiosis I • Chromosome pairs replicate resulting in two haploid (n) daughter cells with duplicated chromosomes different from the sets in the original diploid (2n) cell. • Occurs in 4 stages: prophase I, metaphase I, anaphase I, and telophase I. • Begins with interphase, like in mitosis. Cells increase in size, produce RNA, synthesize proteins, and replicate DNA.

14. Meiosis I http://kenpitts.net/hbio/8cell_repro/meiosis_pics.htm

15. Meiosis I: Prophase I • Replicated chromosomes become visible. • Pairing of homologous chromosomes occurs, each chromosome consists of two chromatids. • Crossing over: chromosomal segments are exchanged between a pair of homologous chromosomes producing an exchange of genetic information. • Nuclear envelope breaks down and spindles form.

16. Meiosis I: Prophase I http://www.biology.iupui.edu/biocourses/N100/2k2ch9meiosis.html

17. Meiosis I: Metaphase I • Chromosome centromeres attach to the spindle fibers. • Homologous chromosomes line up at the equator.

18. Meiosis I: Metaphase I http://www.biology.iupui.edu/biocourses/N100/2k2ch9meiosis.html

19. Meiosis I: Anaphase I • Homologous chromosomes separate and move to the opposite poles of the cell. • Sister chromatids remain attached. • Each daughter cell will receive only one chromosome from each homologous pair.

20. Meiosis I: Anaphase I http://www.biology.iupui.edu/biocourses/N100/2k2ch9meiosis.html

21. Meiosis I: Telophase I • The spindles begin to break down. • Chromosomes uncoil and form two nuclei. • The cell divides.

22. Meiosis I: Telophase I http://www.phschool.com/science/biology_place/biocoach/meiosis/teloi.html

23. Meiosis II • Each of the two daughter cells from Meiosis I contains only one chromosome from each parental pair. • Each daughter cell from Meiosis I will undergo Meiosis II.

24. Meiosis II

25. Meiosis II: Prophase II • The chromosomes condense and the spindles form in each new cell. • The spindle fibers attach to the chromosomes.

26. Meiosis II: Prophase II http://www.phschool.com/science/biology_place/biocoach/meiosis/teloi.html

27. Meiosis II: Metaphase II • The centromeres of chromosomes line up randomly at the equator of each cell.

28. Meiosis II: Metaphase II http://www.phschool.com/science/biology_place/biocoach/meiosis/teloi.html

29. Meiosis II: Anaphase II • The centromeres split. • The sister chromatids separate and move to opposite poles.

30. Meiosis II: Telophase II • Four nuclei form around chromosomes. • The spindle fibers begin to break down. • The cell divides.

31. Anaphase II & TelophaseII http://www.biology.iupui.edu/biocourses/N100/2k2ch9meiosis.html

32. Meiosis http://www.daviddarling.info/encyclopedia/M/meiosis.html

33. Mendelian Genetics10.2

34. How Genetics Began • Inheritance: the passing of traits to the next generation. • Gregor Mendel: published findings on the method and mathematics of inheritance in garden pea plants. http://www.scienceclarified.com/scitech/Genetics/The-Age-of-Genetics.html

35. Why Pea Plants? • Pea plants are easy to grow and many are true-breeding which means they consistently produce offspring with only on form of a trait. • Pea plants usually reproduce by self-fertilization (male and female gametes in same flower). • Pea plants can easily be cross-pollinated by hand (transferring a male or female gamete in one flower to another flower).

36. Pea Plants http://www.exploringnature.org/db/detail.php?dbID=22&detID=54

37. The Inheritance of Traits • Mendel noticed certain varieties of garden pea plants produced specific forms of a trait, generation after generation. • Mendel performed cross pollination by transferring male gametes from the flower of a true-breeding green-seed plant to the female organs of a flower from a true-breeding yellow-seed plant. • Mendel called the green-seed plants and the yellow-seed plants the parent generation or P generation.

38. The Inheritance of Traits • When Mendel grew the seeds from the cross between the green-seed and yellow-seed plants, all of the offspring had yellow seeds. • The offspring of the P cross are called the first filial (F1) generation.

39. The Inheritance of Traits • Mendel then planted the F1 generation of yellow seeds to determine whether the green-seed trait was no longer present or if it was being masked. • The results of the second filial (F2) generation are as follows: 6022 were yellow and 2001 were green (a nearly perfect 3:1 ratio of yellow to green seeds).

40. Inheritance of Traits • Mendel studied seven different traits, including: seed or pea color, flower color, seed pod color, seed shape or texture, seed pod shape, stem length, and flower positions. • He found that the F1 generation plants from these crosses also showed a 3:1 ratio.

41. F1 and F2 Generations

42. Genes in Pairs • From his experiments, Mendel concluded that there must be two forms of the seed trait in the pea plants and that each was controlled by a factor. • Allele: an alternative form of a single gene passed from generation to generation. • The green-seed and yellow-seed are different forms of a single gene or alleles.

43. Genes in Pairs • Mendel called the form of the trait that appeared in the F1 generation dominant and the form that was masked recessive. • The yellow-seed was dominant and the green-seed was recessive.

44. Law of Dominance • If the allele for a trait is dominant it is represented by a capital letter. In Mendel’s case the yellow-seeds were dominant and therefore represented by a Y. • If the allele for a trait is recessive it is represented by a lowercase letter. Therefore the green-seeds in Mendel’s experiment would be represented by a y.

45. Law of Dominance • An organism with two of the same alleles for a particular trait is homozygous. • Homozygous yellow-seed plants would be YY and homozygous green-seed plants would be yy.

46. Law of Dominance • Heterozygous organisms have two different alleles for a trait. • In Mendel’s experiment a plant with an allele for yellow-seeds and green-seeds would be represented by Yy. • When an organism is heterozygous the dominant allele will be expressed.

47. Genotype and Phenotype • Genotype: an organism’s allele pairs. • The genotype of a plant with yellow seeds would be YY or Yy. • Phenotype: the observable characteristics or outward expression of allele pair. • The phenotype of pea plants with the genotype yy would be green seeds.

48. Genotype and Phenotype http://hthbio.blogspot.com/2011/02/february-7-2011-february-11-2011.html

49. Law of Segregation • Two alleles for each trait separate during meiosis and during fertilization two alleles for that trait unite. http://www.transtutors.com/homework-help/Biology/Heredity/mendel-experiment-of-monohybrid-ratio.aspx

50. Law of Independent Assortment • A random distribution of alleles occurs during gamete formation. • Genes on separate chromosomes separate independently during meiosis.