Understanding Sexual Reproduction and Mitosis in Genetics

1. Sexual Reproduction

2. Let’s Review!

3. Mitosis is: When a cell makes a copy of itself for: growth repair replacement

4. In mitosis: Mother cell with a full set Of chromosomes (diploid number; a.k.a. 2n) Two daughter cells With a full set of Chromosomes (diploid number; a.k.a 2n)

5. The Phases of Mitosis • Prophase • Metaphase • Anaphase • Telophase • Cytokinesis (you should ALL know these by heart by now!)

6. Mitosis Only body cells reproduce by mitosis (and some organisms too but we will talk about that later)

7. Chromosomes • Homologous chromosomes: the chromosomes that make a pair • They have the same length and same centromere position, and control the same inherited trait

9. Gametes • Sex cells that have half the # of chromosomes • Ensures that an organism has the same number of chromosomes from generation to generation • In humans, each gamete has 23 chromosomes • n = number of chromosomes in a gamete

10. Gametes • Haploid: n • Diploid: 2n (female n + male n) • When 2 human gametes combine through fertilization, 23 homologous chromosomes are formed

11. Meaning… Mom has 23 chromosomes Dad has 23 chromosomes You have 46 chromosomes

12. Meiosis • Process that creates gametes • Cell division that REDUCES the number of chromosomes • Occurs in reproductive structures • Mitosis maintains chromosome # • Meiosis reduces it by half by splitting homologous chromosomes • 2n  n • Meiosis I and II

13. Interphase • Replication of DNA • Protein synthesis

14. Meiosis I Prophase I: • Crossing over: chromosome segments are exchanged between homologous chromosomes • Centrioles move to opposite poles • Spindle fibers form and bind to sister chromatids at the centromere

15. Meiosis I • Metaphase I: Homologous chromosomes line up at center of cell • Anaphase I: Homologous chromosomes separate and pulled to opposite ends of cell, chromosome # is reduced from 2n to n • Telophase I: Chromosomes reach poles • Each pole contains only one chromosome of the original homologous chromosomes

17. Meiosis II • Prophase II: chromosomes condense • Metaphase II: HAPLOID number of chromosomes line up at the equator • Anaphase II: sister chromatids are pulled apart • Telophase II: chromosomes reach poles and nuclear membranes and nuclei form

18. Meiosis II • The chromosomes DO NOT replicate between I and II • End result is 4 haploid cells, each with n number of chromosomes

22. Sexual vs. Asexual Reproduction • Asexual • The organism inherits all of its chromosomes from one parent • Individual is genetically identical to its parent

23. Mendelian Genetics

24. Genetics • Genetics: the study of heredity • Heredity: the passing of traits from parent to offspring (INHERITANCE)

25. Father of Genetics • Gregor Mendel • Austrian Monk who experimented with garden peas in 1866 • Noticed certain traits seemed to be passed from one generation to another

26. Mendel • Mendel worked with peas • Peas self-fertilize • Noticed some varieties always made green seeds, and some always made yellow seeds • Mendel cross-pollinated the peas by hand

27. Peas • Parent Generation (P): 1st line of crosses • First Generation(F1): offspring of the parent generation • F2 Generation: second cross, using the F1 offspring

30. He concluded… • There must be TWO forms of a gene controlled by different factors • ALLELES: alternative form of a single gene • For example, the gene height • Tall or short

31. Alleles • Dominant: represented by a capital letter (T = tall • This is the trait that is seen • Recessive: represented by a lowercase letter (t = short) • This trait is not seen, it is masked by the dominant allele ~ it’s there, just hidden!

32. Dominance • If the dominant allele is present, it will show up • There must be 2 recessive alleles (one from each parent) in order to show up

33. Alleles • Since alleles are inherited from each parent, they can be the same or different • Homozygous: individual inherits 2 of the same allele • TT – homozygous dominant • tt – homozygous recessive • Heterozygous: individual inherits 2 different alleles, one dominant and one recessive • Tt • Since the dominant allele is present, it will show

34. So… • If presence of dimples is a recessive trait, and no dimples is dominant, what alleles would you see for – • An individual with dimples • An individual without dimples

35. Genotype & Phenotype • Genotype: organism’s allele pairs • Heterozygous, homozygous dominant, or homozygous recessive • Phenotype: observable appearance of genes

36. Putting it all Together… GENOTYPE (HETEROZYGOUS) Tt = Tall ALLELE ALLELE PHENOTYPE

37. Law of Segregation • Two alleles for a trait separate during meiosis • Each gamete will have a different allele • They will be reunited during fertilization

38. Punnett Square • Used to predict the possible offspring between two known genotypes • Monohybrid: crossing one trait at a time

39. Punnett Square Parent 2 – Pure Tall F1 Generation Parent 1- Pure Short

41. Tongue Rolling • Dominant Trait ~ T • 2 parents are heterozygous (Tt) for the trait • What possible phenotypes will their children have? T t Tt TT T Tongue roller Tongue roller tt Tt t Non-tongue roller Tongue roller

42. Law of Independent Assortment • When your body makes gametes (during meiosis), your gametes only get one copy of each gene • Whatever copy goes into the gamete is random; the inheritance of one gene does not influence the inheritance of another gene; they are independent • Every person with brown hair doesn’t have brown eyes • Some genes are inherited together (LINKED) because the genes are very close to each other on the chromosome. • people with red hair are also fair-skinned.