1. Chromosome Inheritance
Human Biology
Chapter 18

2. Sperm and Egg formation
Sperm & Egg are haploid cells.
One egg (oocyte) divides during Meiosis 1 into 2 cells. One cell receives most of the cytoplasm out of 2 eggs. The other is called a polar body. The larger oocyte or egg stops dividing at Metaphase II. It completes anaphase and telophase II when a sperm enters the egg in the oviduct.

3. Twins
Identical twins can form from an egg dividing again after fertilization.
Fraternal twins form when two eggs are fertilized by two sperm

4. Too many chromosomes
Nondisjunction- one pair doesn’t separate during anaphase I or II.
Monosomy- 1. Fatal for all but the X chromosome.
Trisomy- 3 chromatids
Most are fatal except on 21st
Down’s Syndrome
Bottom half of chromosome
Causes brain malformation
Increased purines in blood
Varies in intensity

5. Barr Body
Females function with just 1 X chromosome. Of 2 X chromosomes, 1 is inactive in females, called a Barr Body after its discoverer.
Extra Y chromosome called Jacob’s syndrome.
Y chromosome carries few genes

6. Breast cancer
BRCA1 gene is linked with breast and ovarian cancer. Produces protein that normally suppresses cancer cells and also is involved in inactivating one of the X chromosomes.

7. Turner Syndrome Female who lacks an X chromosome
Short, broad chest and folds of skin on the back of neck.
No puberty, no breasts, no periods
Normal intelligence

8. Poly X females XXX Tall and thin
Some delayed motor and language development

9. Jacob’s Syndrome
XYY male
Taller, acne, speech and reading problems

10. Kleinfelter’s syndrome
Male with XXy
Y gene has code for testes and penis
One in 650 males
Speech and language delays

11. Chromosome malformations
Caused by chemicals, viruses, radiation
Broken ends of chromosomes
Duplication of parts of chromosome
Switched parts (translocation)
Deleted parts of chromosome
Inverted parts of chromosome

12. Williams syndrome Chromosome 7 lost a tiny end piece
Look like pixies, turned up noses, wide mouth, small chin, large eyes
Excellent at music and speech
Need order in their life

13. Cri du chat (cry of the cat)
Chromosome 5 missing end piece
Small head, mentally retarded, facial abnormalities, glottis and larynx make cry like a cat

14. Translocation
Alagille syndrome
2 and 20 chromosome
9 and 22
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