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

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

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

4. Applying Your Knowledge
G1 phase
S phase
G2 phase
Meiosis I and II
When does chromosome duplication occur?
When do the cytoplasmic contents double?
When does chromosomal division occur? 2 1 4

5. Homologous Chromosome Pairs
Diploid cells have pairs of chromosomes
Each homologous chromosome pair is genetically matched so that the genes are arranged in the same order
Meiosis distributes members of each pair to separate nuclei
Figure: 11.UN06b
Title:
Formation of daughter chromosomes
Caption:
Humans have 1 pair of sex chromosomes and 22 pairs of autosomes

6. 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

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

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

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

10. Anaphase I and Telophase I of Meiosis 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

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

12. Anaphase II and Telophase II of Meiosis 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

13. Applying Your Knowledge
Prophase I
Metaphase I
Anaphase I
Metaphase II
Anaphase II
When do sister chromatids separate?
When does crossing-over occur?
When do homologous pairs line up at the cell equator? 5 1 2

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

15. Sex Determination
Sex Chromosomes: homologous chromosomes that differ in size and genetic composition between males and females
Human
Chromosome X Y
Size
Larger
Smaller
Genetic
Composition
Multiple
genes
unrelated
to gender
Very few genes
TDF region determines maleness

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

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

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

19. 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)

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

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

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

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

24. Applying Your Knowledge
Crossing-over
Nondisjunction
Autosomes
Sex chromosomes
Translocation
What is the name for the X and Y chromosomes?
Which one describes the failure of chromatids to separate in Anaphase II?
Which one involves exchange of material between nonsister chromatids? 4 2 1