Atypical Meiosis and Genetic Screening

Mitosis and Meiosis? What is the difference? Somatic cells: any cell in a multicellular organism except a sperm or egg cell. Cells contain 46 chromosomes. Reproductive cells: cells that produce sex cells through the process of meiosis. Sperm and eggs cells- contain half of genetic information

What is Atypical Meiosis? if something goes wrong during meiosis in a reproductive cell, the resulting embryo is in serious trouble- all of its cells will be affected Nondisjunction is the failure to separate; an error that occurs when two homologous chromosomes move to the same pole during meiosis. What are homologous chromosomes?

Homologous: chromosomes of the same length, centromere position and staining pattern that’s posses genes for the same at corresponding loci. One homologous chromosome is inherited from the organisms father, the other from the mother. Disjunction: This means that in the resulting cells, one will have 24 chromosomes and the other will have 22 chromosomes. Which can result in a zygote having 47 or 45 chromosomes See pg 222

Some Disorders of non-disjunction are: Down Syndrome, Turner Syndrome, Klinefelter Syndrome Genetic Screening and Karyotypes In a technique called amniocentesis, a syringe is used to draw fluid from the sac that surrounds the fetus. This fluid is the amniotic fluid, which contains the cells from the fetus. By treating the cells with stains, the tiny chromosomes are made visible for microscopic examination. Pictures are taken and the chromosomes are arranged in a karyotype chart.

The karyotype compares number, size, and shape of homologous chromsomes This technique can be used to assess the “normalcy” of an individual’s chromosomes This whole process is called genetic screening. Ethical implications: Might diagnosing genetic disorders prior to birth lead to pregnancies being terminated? Some people fear this will lead to the selection of the sex.

Tell me more about this… Group Activity: You will get a number 1-8 and form a group of 4 with your peers (join a group and take a role if your are left out) Each group will have a question Each person in the group will have a role card Take a card and take on the responsibilities of that role Role Cards (at your table in an envelope): Lead Scientist: In addition to providing information, make sure every voice is heard, focus your group members. Data Collector: In addition to providing information, you compile group ideas, write on paper the data the reporter will present. Time keeper/ errand monitor: (lab assistant) In addition to providing information, you encourage the group to stay on task

Announce when time is halfway through and when time is nearly up Announce when time is halfway through and when time is nearly up. You also request help from peers or teacher when needed- find resources to solve your problem Presenter / Geneticist: In addition to providing knowledge, present the groups finished work to the class. You have 10 minutes to answer your question- then get ready to present in the class and take notes from the questions your peers answered. See pages 222- 227 in your text. Now lets number you 1-8, sit at designated tables.

Questions for groups 1-8 What do karyotypes show? What is your opinion of this procedure? Do you agree or disagree? What stage of mitosis would be best for preparing karyotypes? Why? Begin with a fetal cell and end with an organized karyotype. How are karyotypes prepared? What is nondisjunction? Explain how a human cell could have 47 chromosomes. Include a diagram if necessary. Provide a hypothesis that might explain why older women are much more likely to give birth to a child with Down Syndrome. Define and explain (chromosomes) the following disorders. Turner Syndrome, Klinefelter syndrome and Down Syndrome. Would the diagnosis of Turner syndrome in a single cell mean that every cell of the body contained 45 chromosomes? Explain your answer. Karyotyping can be used as a prenatal screening tool.  Is a baby guaranteed from genetic disorders if the chromosome configuration appears normal?  Explain.

Individual Activity Observe 3 karyotypes and answer the questions provided on the handout We will discuss answers after 10 minutes

Karyotype # 1

Karyotype # 2

Karyotype # 3