1. Hereditary Factors in Development

3. Fertilization 23 chromosomes from the egg +
23 chromosomes from the sperm
Combine to produce a fertilized egg with 23 pairs of chromosomes (46 chromosomes)

4. Genes & Chromosomes Chromosomes are further divided into Genes
which consist of segments of
DNA

5. Chromosomes
Shaffer, 4th edition, p. 83

6. Mechanisms of Hereditary Transmission
Each child inherits 1/2 of each parent’s genetic material.
Different children in a family inherit different combinations.
Full siblings have about 50% of their genes in common.
Identical twins share 100% of their genes; fraternal twins share 50%, like any full sibling pair.

7. Cell Division: Mitosis
Division of somatic or body cells
The chromosomes double
The cell splits making two new cells genetically identical to each other
And to the original cell

8. Cell Division: Meiosis
Division of germ cells into gametes (eggs and sperm)
Gametes have only 23 chromosomes (one of each rather than a pair)

9. Cell Division: Meiosis
Berk, 3rd. Edition, p. 75

10. Female Chromosomes
Shaffer, 4th edition, p. 83

11. Male Chromosomes
Shaffer 4th

12. Sex Determination Chromosomes 1 - 22 are called autosomes.
Chromosome 23 is the sex chromosome
Females: XX
Males: Xy
Eggs: Chromosome 23 is always X
Sperm: Chromosome 23 is either X or Y.

13. Sex determination, cont’d
Fathers determine child sex

14. Chromosomal Anomaly
Sometimes when a gamete is formed an error takes place.
Miscarriage (Spontaneous Abortion): % of known pregnancies result in miscarriage
usually in the 10th to 12th week of pregnancy.

15. Down Syndrome: Trisomy 21
Characteristics: short, stocky build; flattened face; protruding tongue; almond-shaped eyes; crease in palm of hand
Mental retardation, I. Q. 20 to 50
Other problems
e.g, speech problems, slow motor development, breathing, feeding, etc.

16. Down’s Syndrome - Frequency
Overall: 1 in 800 births.
Maternal age Frequency
in 1900
in 1200
in 900
in 365
in 225
in 109
in 67
in 32
in 20
in 12

17. Prenatal Diagnosis Alpha-fetoprotein Test Ultrasound Amniocentesis
Chorion Villus Sampling

18. Alpha-fetoprotein test
Maternal blood test
High or low levels of AFP may indicate various problems (spina bifida, kidney disease, Down syndrome)
the test has high false positive and false negative rates.

19. Ultrasound
High-frequency sound waves beamed at the uterus producing a reflection that can be translated into a video picture.
Can be used to assess fetal age, multiple pregnancies and gross physical defects.
It is used to guide amniocentesis and CVS.

20. Amniocentesis
A hollow needle is inserted through the abdominal wall to remove a sample of amniotic fluid.
Cells are examined for chromosomal or genetic defects.
Performed 11 to 16 weeks after conception
takes 2 to 3 weeks for results.
Small risk of miscarriage.

21. Chorion Villus Sampling (CVS)
A thin tube is inserted in the vagina or a needle through the abdominal wall to remove tissue from the chorionic villi
It can be done at 6 to 8 weeks of pregnancy and results are usually available in 24 hours.
Small risk of miscarriage, and very small risk of limb deformities if done very early in pregnancy.

22. Amniocentesis & CVS Amniocentesis Chorion villus sampling
Berk, 3rd edition, p. 89
Amniocentesis
Chorion villus sampling

23. Anomalies of the Sex Chromosomes
Turner Syndrome - XO
Klinefelter Syndrome XXy
Xyy Syndrome
Triple X Syndrome - XXX
Fragile X Syndrome

24. Go to video