1. Topic 4.2.4 Non-disjunction leads to changes in chromosome number Non-disjunction = an unequal distribution of chromosomes in gametes because chromosomes don’t separate as expected during meiosis I or meiosis II In humans, this means an egg or sperm might have 24 instead of 23 chromosomes Failure of chromosomes to separate leads to aneuploidy (1 extra or 1 missing chromosome) Polyploidy = total non-disjunction (all homologous pairs fail to separate) 3n

2. Down’s Syndrome Non-disjunction of chromosome #21 = trisomy 21 which causes Down’s Syndrome Most common chromosomal anomaly and affects approximately 1 in 800 births Risk increases as the age of the mother increases Symptoms = heart problems, digestive system problems, varying levels of mental retardation

3. http://www.bing.com/videos/search?q=Down +Syndrome&view=detail&mid=51A25473C142 1700134D51A25473C1421700134D&first=0&F ORM=LKVR38#view=detail&mid=CDE875B19C 43971BF1F9CDE875B19C43971BF1F9 http://www.bing.com/videos/search?q=Down +Syndrome&view=detail&mid=51A25473C142 1700134D51A25473C1421700134D&first=0&F ORM=LKVR38#view=detail&mid=CDE875B19C 43971BF1F9CDE875B19C43971BF1F9

4. Topic 4.2.5 Karyotyping-chromosomes arranged in pairs Karyotyping is the process of finding the chromosomal characteristics of a cell. C’somes can be stained to show banding patterns C’somes paired according to size, banding patterns and location of the centromere

5. 4.2.6 Chorionic Villus Sampling and Amniocentesis for pre-natal diagnosis Down syndrome risk increases as mother’s age increases and genetics (relatives with Down syndrome) Two common pre-natal tests: – Chorionic villus sampling – amniocentesis

6. 4.2.6 (cont.) Human Embryonic Development: – Fertilization takes place in the oviduct – Zygote (fertilized egg) travels to the uterus and undergoes many divisions – When it arrives in the uterus it is a ball with inner cells and outer cells – The outer cells will come into contact with the mucus lining of the uterine wall and develop into chorionic villi – These cells will eventually become the placenta

7. 4.2.6 Chorionic Villus Sampling and Amniocentesis for pre-natal diagnosis http://www.youtube.com/watch?v=bZcGpjyOXt0 &feature=player_embedded http://www.youtube.com/watch?v=bZcGpjyOXt0 &feature=player_embedded http://www.youtube.com/watch?v=sxEf_ddmpZk &feature=player_embedded http://www.youtube.com/watch?v=sxEf_ddmpZk &feature=player_embedded

8. Chorionic Villus Sampling & Amniocentesis CVS: – Can be done at 11-12 weeks of pregnancy – Obtain cells from tissue that originally came from the zygote and a karyotype is made – Risks are very low < 1% Amniocentesis: – Performed around the 16 th week of pregnancy – Sample of amniotic fluid taken & karyotype is made – Risk is very low <.5%

9. Topic 4.2.7 Analyzing a Human Karyotype Analyze a karyotype to determine gender and the occurrence of non-disjunction Remember non-disjunction results in either one or three copies of a chromosome ACTIVITIES: 1.Biozone pages 143-148 Due Friday (beginning of class) 2.Human Karyotyping Analysis Lab (Tuesday & Wednesday-groups of 4 or 5) Period 1 - 5 groups of 4 and 2 groups of 5 Period 4 - 1 group of 4 and 2 groups of 5 Period 6 - 5 groups of 4 and 3 groups of 5