1. Chromosomal Basis of Inheritance Chapter 3

2. Chromosomes and Cellular Reproduction

3. Eukaryote Chromosomes • Multiple linear chromosomes • Many have two of each type • Diploid zygote • Fusion of two haploid gametes • Called homologous chromosomes • Autosomes • Sex chromosomes

4. Eukaryote Chromosomes • Differ in size and morphology • Specific to each species • Centromere - constriction • Metacentric, submetacentric, acrocentric, telcentric • Karyotype – complete chromosome complement

5. Human Karyotype • Genes ID is chromosome # and loci band on that chromosome • Also p or q arm • BRCA1 is at 17q21

6. Mitosis • Cell reproduction includes growth, mitosis and cytokinesis • Cell cycle includes mitotic phase and interphase between division • Mitosis is a process for growth, repair, and asexual reproduction • Interphase: G1, S and G2

7. Interphase • G1- presynthesis • Cell prepares for DNA synthesis and chromosome replication • S – DNA synthesis and chromosome replication • G2- postsynthesis • Cell prepares for division

8. S Phase • During interphase chromosomes unwound • Chromosomes are replicated • Sister chromatids • Centromeres replicated but not separated • Become daughter chromosomes

9. Mitosis • Length of process varies • Continuous process • 4 Phases: • Prophase • Metaphase • Anaphase • Telophase

10. Prophase • Chromosomes coil • Spindle forms • Centriole in animals • Nuclear membrane breaks down • Nucleolus disappears • Kinetochore forms

11. Metaphase and Anaphase • Metaphase • Microtubules orient the chromosomes • Along plane of cell • Metaphase plate • Anaphase • Centromeres separate • Daughter chromosomes move toward poles

12. Telophase and Cytokinesis • Telophase • Chromosomes uncoil • Nuclear envelope forms • Spindle disappears • Nucleolus reforms • Cytokinesis • Separation of cytoplasm • Different in plants and animals

14. Meiosis • One replication, two divisions • Reduction in number of chromosomes • Occurs at certain points in a life cycle • Only in certain tissues • Makes gametes • Gametogenesis • Four haploid daughter cells

15. Meiosis I – Prophase I • Chromosomes have duplicated • 5 substages • Leptotene stage – chromosomes coil • Zygotene stage – homologous pairs align in synapsis • Synaptonemal complex - Aligns perfectly base pair to base pair • Telomeres move and align chromosomes • Pachytene stage – crossing-over takes place • Recombinant chromosome

16. Meiosis I – Prophase I • 5 substages • Diplotene stage – synaptonemal complex disassembles • Chiasma are formed • Diakinesis – nucleus and nuclear envelope disintegrate

17. Meiosis I – Metaphase I and Anaphase I • Metaphase I • Homologous pairs line up on plate • Spindle is completely formed • Kinetochores formed • Anaphase I • Homologous pairs separate • Move toward opposite poles • Chiasma separate • Sister chromosomes remain joined

18. Meiosis I – Telophase I • Nuclear envelope forms • Cytokinesis

19. Meiosis II • Similar to mitosis • Prophase II – chromosomes condense • Metaphase II – sister chromosomes line up • Anaphase II – sister chromatids toward poles • Telophase II – nuclear envelope reforms, chromosomes no longer visible

21. Gene Segregation in Meiosis • Results of meiosis • Haploid cells with half of the # of chromosomes • In independent assortment • Each pair of chromosomes sorts its maternal and paternal homologues into daughter cells independently of the other pairs • 2n-1 where n=# of chromosomes • Crossover increases variation

22. Meiosis vs Mitosis

23. Meiosis vs. Mitosis

24. Meiosis in Animals • Diploid for most of their life • Haploid gametes fuse to restore • Sexual reproduction • Gametes produced by spermatogenesis and oogenesis

25. Spermatogenesis • In the testes • 1° Spermatogonia • 2° Spermatogonia • 1° Spermatocytes • Go through Meiosis I • 2° Spermatocytes • Go through Meiosis II • Spermatids

26. Oogenesis • In the ovaries • 1° Oogonia • 2° Oogonia • 1° Oocytes • Go through Meiosis I and unequal cytokinesis • 2° Oocyte and first polar body • Go through Meiosis II • Ovum and 2nd polar body

27. Meiosis in Plants • Gametophyte and sporophyte stage • Alternation of generations • Flower is sexual structure • Can be bisexual or unisexual • Stamens and pistils • Pollen from anther • Ovule contains egg cells

28. Alternation of Generations • Multicellular gametophyte • Meiosis then mitosis BEFORE fertilization • Plants fungi and algae

29. Chromosome Theory of Inheritance

30. Chromosome Theory of Inheritance • Correlation between traits and separation of chromosomes in meiosis • First called inheritance factors genes • Chromosome # varies

31. Sex Chromosomes • Autosomes • Sex chromosomes – represented differently in the two sexes • When gametes are formed one sex chromosome goes to each • In humans male determines sex • Some animals have unpaired chromosomes

32. Sex Chromosomes • The X-O system • The Z-W system • Chromosome Number

33. Sex Chromosomes • Drosophila melanogaster • Heterogametic and homogametic sexes • Same size but different shape • Genes create characteristics of male and female

35. Sex Linkage • Sex chromosomes also carry genes, any gene located on the sex chromosome is called a sex-linked gene • Most are found on X chromosomes • Hemizygous • X-linked Allele Animation

36. Sex Linkage

37. Nondisjunction of Chromosomes • Homologous or sister chromosomes do not separate • Can involve either autosomes or sex • In sex chromosomes can lead to either 2 X chromosomes or no X chromosomes • X chromosome nondisjunction • Aneuploidy and polyploidy • Primary and secondary nondisjunction (XXY)

38. Nondisjunction of Chromosomes

39. Secondary Nondisjunction

40. Sex Chromosomes and Sex Determination

41. Genotypic Sex Determination • Sex chromosomes play a role in inheritance and sex determination • Placentals sex determined by Y • Y carries genes toward male sex determination • Testis-determining factor gene • Factor causes gonad tissue to become testes instead of ovaries

42. Sex Chromosome Nondisjunction • XO individuals – • Turner Syndrome • Genetically female • At puberty, develop poorly • XXY individuals • Klinefelter syndrome • Genetically male • Several variations XXY, XXXY, XXYY • Symptoms include underdeveloped testes, taller and some breast tissue

43. Turner Syndrome

44. Klinefelter Syndrome

45. Dosage Compensation with Sex Chromosomes • Cannot have an unequal dosage of genes from duplicate sex chromosomes • Can be lethal if they are not equal • Barr body • Condensed and inactive X chromosome • Has become lyonized • Only in females • X independently chosen from cell to cell • Epigenetic silencing of one chromosome

46. Barr Bodies

47. Genic Sex Determinations • Allelic differences determine sex • Mating types in yeast • a and α • Same morphologies, but mating only occurs between different type • Same in some basidiomycetes

48. Analysis of Sex-Linked Traits in Humans

49. X-Linked Recessive Inheritance • Trait resulting from recessive mutant allele • More than 100 traits • Hemophilia A • Blood lacks clotting factor • Queen Victoria • Carrier daughters son with hemophilia • Females must be homozygous to express