Hereditary Factors in Development

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

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

Chromosomes Shaffer, 4th edition, p. 83

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.

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

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

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

Female Chromosomes Shaffer, 4th edition, p. 83

Male Chromosomes Shaffer 4th

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.

Sex determination, cont’d Fathers determine child sex

Chromosomal Anomaly Sometimes when a gamete is formed an error takes place. Miscarriage (Spontaneous Abortion): 15-25% of known pregnancies result in miscarriage usually in the 10th to 12th week of pregnancy.

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.

Down’s Syndrome - Frequency Overall: 1 in 800 births. Maternal age Frequency 20 1 in 1900 25 1 in 1200 30 1 in 900 35 1 in 365 37 1 in 225 40 1 in 109 42 1 in 67 45 1 in 32 47 1 in 20 49 1 in 12

Prenatal Diagnosis Alpha-fetoprotein Test Ultrasound Amniocentesis Chorion Villus Sampling

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.

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.

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.

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.

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

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

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