1. Chromosomal Inheritance Chromosomal Division for Sperm and Egg Production Chromosomal Abnormalities

2. Human Life Cycle Nuclear division reducing the chromosome number, leading to sperm or eggs Diploid number of chromosomes, two full sets Haploid number of chromosomes, one full set Nuclear division retaining the original chromosome number

3. Cell Cycle With Meiosis G1 cytoplasm doubles, including organelles S chromosomes duplicate G2 synthesis of proteins and assembly of components for division cytokinesis Meiosis Interphase includes G1 = growth phase 1 S = synthesis phase S = synthesis phase G2 = growth phase 2 Interphase Meiosis II cytokinesis Meiosis I Meiosis includes two chromosomal divisions Meiosis I Meiosis II Cytokinesis = division of cytoplasmic contents

4. Homologous Chromosome Pairs Diploid cells have pairs of chromosomesDiploid cells have pairs of chromosomes Each homologous chromosome pair is genetically matched so that the genes are arranged in the same orderEach homologous chromosome pair is genetically matched so that the genes are arranged in the same order Meiosis distributes members of each pair to separate nucleiMeiosis distributes members of each pair to separate nuclei Humans have 1 pair of sex chromosomes and 22 pairs of autosomes

5. Outcome of Meiotic Divisions Diploid Human Cell with 46 chromosomes (23 pairs) Duplication of Cell Contents Meiosis I: Reduction Division Separation of Homologous Chromosomes into Different Nuclei 2 Genetically-Different Haploid Human Cells with 23 duplicated chromosomes Meiosis II: Equational Division Separation of Duplicated Chromosomes into Different Nuclei 4 Genetically-Different Haploid Human Cells with 23 chromosomes

6. Duplicated Chromosomes in Early Meiosis Homologous Chromosome Pair Association of four chromatids of a duplicated homologous chromosome pair Centromere = constricted region Duplicated chromosomes joined at their centromeres Nonsister Chromatids are joined to different centromeres

7. Prophase I of Meiosis I  Chromosomes thicken  Genetic exchange occurs between nonsister chromatids through crossing-over

8. Metaphase I of Meiosis I  Homologous pairs line up at the cell equator  Spindle fibers attached to centromeres cause chromosomal movement Spindle fiber

9. Anaphase I and Telophase I of Meiosis I Anaphase I  Members of homologous pair separate and are pulled to opposite poles of the cell Telophase I  Chromosomes reach opposite poles + cytokinesis Cytokinesis  Cytoplasm divides into two separate cells Daughter cells are haploid with duplicated chromosomes

10. Prophase II and Metaphase II of Meiosis II Prophase II  Chromosomes thicken Metaphase II  Chromosomes line up at cell equator

11. Anaphase II and Telophase II of Meiosis II Anaphase II  Sister Chromatids separate and move to opposite poles Telophase II  Chromosomes have reached opposite poles + cytokinesis Cytokinesis  Cytoplasm divides into separate cells Daughter cells are haploid and have genetic differences

12. Sperm formation Equal divisions of cytoplasmEqual divisions of cytoplasm Four functional products per meiosisFour functional products per meiosis Egg formation Unequal divisions of cytoplasmUnequal divisions of cytoplasm Small polar bodies formedSmall polar bodies formed One functional product per meiosisOne functional product per meiosis Fertilization occurs after Meiosis I and stimulates Meiosis II

13. Sex Determination Sex Chromosomes : homologous chromosomes that differ in size and genetic composition between males and females Sex Chromosomes : homologous chromosomes that differ in size and genetic composition between males and females HumanChromosomeXY SizeLargerSmaller GeneticCompositionMultiplegenesunrelated to gender Very few genes TDF region determines maleness

14. Chromosomal Number Abnormalities Arise by Nondisjunction = Failure of homologous chromosomes or chromatids to separate during meiosis Nondisjunction during Meiosis II Nondisjunction during Meiosis I

15. Human Autosomal Abnormality How can Down Syndrome occur? Eg. Egg with 2 copies of #21 (24 chromosomes) + Sperm with 1 copy of #21 (23 chromosomes) + Sperm with 1 copy of #21 (23 chromosomes) = Embryo with 3 copies of #21 (47 chromosomes) = Embryo with 3 copies of #21 (47 chromosomes) Down Syndrome Trisomy 21 Three copies of chromosome 21

16. Karyotype for Down Syndrome Eye fold Palm Crease Physical Features

17. Human Sex Chromosome Abnormality Turner Syndrome XO One copy of X No second sex chromosome How can Turner Syndrome occur? Eg. Egg with 0 copies of X (22 chromosomes) +Sperm with 1 copy of X (23 chromosomes) = Embryo with 1 copy of X (45 chromosomes)

18. Non-functional Ovaries From Adult Female with Turner’s Syndrome Normal uterus, tubes and ovaries and ovaries Karyotype for Turner’s Syndrome

19. Other Human Sex Chromosome Number Abnormalities Klinefelter Syndrome XXY Poly-X Females XXX Jacobs Syndrome XYY Sterile Male Fertile Female Fertile Male

20. Chromosome Structure Abnormalities Williams syndrome is caused by a deletion = loss of a chromosomal segment.

21. Chromosome Structure Abnormalities Alagille syndrome is caused by a translocation = movement of a chromosomal segment to another non-homologous chromosome.