1. Chapter 11-3 Chromosomes & Human Heredity

2. Focus Questions: How are Karyotypes used to study genetic disorders? What is the role of Telomeres? How is Nondisjunction related to down syndrome and other abnormal conditions? What are the benefits and risks of fetal testing? 11-3: Chromosomes and Human Heredity 11-3: Chromosomes and Human Heredity

3. Karyotypes “snapshot” of chromosomes Used to screen for genetic abnormalities Homologous Chromosomes paired up in decreasing size Telomeres Protective Protein “cap” on end of Chromosomes 11-3: Chromosomes and Human Heredity 11-3: Chromosomes and Human Heredity

4. Chromosome Type Autosomes = the chromosomes that do not determine sex; 22 pairs Sex Chromosomes = the chromosomes that determine sex; 23 rd pair 11-3: Chromosomes and Human Heredity 11-3: Chromosomes and Human Heredity

5. Gamete Differences Eggs carry an X chromosome: Sperm carry an X or Y chromosome The larger X chromosome carries more than 2,300 genes Y chromosome main codes for sperm production 11-3: Chromosomes and Human Heredity 11-3: Chromosomes and Human Heredity

6. Nondisjunction Chromatids fail to separate properly in Anaphase II Resulting cells have incorrect # of chromosomes Can result with extra or missing chromosomes 3 or more chromosome pairs : Trisomy 1 chromosome : Monosomy 11-3: Chromosomes and Human Heredity 11-3: Chromosomes and Human Heredity

7. Nondisjunction in Autosomes: Down Syndrome Trisomy 21 = 3 copies of chromosome #21 1:1000 birthdays, 1/16 in mothers over 45 Edward Syndrome Trisomy 18 11-3: Chromosomes and Human Heredity 11-3: Chromosomes and Human Heredity

8. Nondisjunction in Sex Chromosomes Turner Syndrome Sex Chromosome = XO Female, do not develop secondary sex characteristics infertile, short (4’8 avg.) Klinefelter Syndrome XXY Male, tall, low fertility, small testes, facial hair sparse, breasts somewhat enlarged, possibly mild mental impairment 11-3: Chromosomes and Human Heredity 11-3: Chromosomes and Human Heredity

9. Fetal Testing Can screen for potential genetic disorders 1.Amniocentesis- cells are removed from amniotic fluid, cultured and analyzed 2.Chorionic villi sampling –(CVS)- cells are removed from the Chorion, can yield results as early as 9 th week 3.Fetoscopy – an endoscope uses pulsed sound waves to scan the uterus and visually examine the fetus