1. Meiosis and Human Reproduction
SPERMATOGENESIS
OOGENESIS

2. Learning Targets “I Can . . .”
-State the number of chromosomes in a typical human being.
-Name the two sex chromosomes in a human female.
-Name the two sex chromosomes in a human male.
-Define “nondisjunction.”

3. Chromosomes

4. Review
1. Human cells are diploid, meaning there are 23 pairs of chromosomes for a total of 46.
2. Human sex cells are haploid. Each sex cell (gamete) has 23 chromosomes and only one copy of every gene.
Sperm (23) Egg (23) =
A new human (46) !

5. Review
3. Genes are located on chromosomes. The location where they are found on that chromosome is called a locus (pl. loci)
*Chromosome theory of heredity: Genes are located on the chromosomes and each gene occupies a specific place on a chromosome. A gene may exist in several forms called alleles, and each chromosome contains one allele for each gene.

6. Review
4. Genes are swapped between homologous chromosomes during prophase I of meiosis when chromosomes are paired as tetrads. This process is called crossing over

7. Sex Determination
1. Autosomes (22 pairs): chromosomes that are the same in males and females
2. Sex chromosomes (23rd pair): final “pair” of chromosomes that are different in males and females
a. Females are XX
b. Males are XY
3. Genes that are found on sex chromosomes are sex-linked.

8. Chromosome mutations: change in the number or structure of chromosomes
1. Inversion: a section of a chromosome is reversed in order
2. Translocation: non-homologous chromosomes swap regions
3. Deletion: part of a chromosome is removed
4. Duplication: region of a chromosome is doubled
5. Nondisjunction: chromosome pairs do not separate
during meiosis
*Many genetic disorders result from chromosome nondisjunction during meiosis (diagram, page 401)

9. Chromosome mutations: change in the number or structure of chromosomes

10. Chromosome mutations can be observed using a karyotype
1. Karyotype: the arrangement of homologous pairs of chromosomes
2. Common chromosomal defects
a. Down Syndrome (Trisomy 21)
b. Edwards Syndrome (Trisomy 18)
c. Patau Syndrome (Trisomy 13)
d. Turner Syndrome (X)
e. ______________ Syndrome (XXY)

11. Karyotype for a person with Down Syndrome
Extra chromosome at the 21st position
Characteristics facial features such as widely-spaced eyes, flat noses, and large tongues
Mild to severe mental retardation

12. Down Syndrome

13. Edwards Syndrome

14. Edwards Syndrome

15. Patau Syndrome

16. Patau Syndrome

17. Sex Chromosome Disorders

18. Turner Syndrome

19. Klinefelter Syndrome

20. References http://www.biologycorner.com/bio1/meiosis.html

21. References www6.district125.k12.il.us
www6.district125.k12.il.us