Class Material Recap for 4/7/2011

Hello Class! During today's lecture we began going over sections 16.1-16.2 (pgs. 565-572; 572-588) in your textbooks. We focused today on changes in chromosome number. This blog post will recap the information we went over in class today (this information will be spread over several class days and blog posts). ***If you were absent today, the homework is listed at the END of the post. You have three days from the day you return to school to turn in the homework.

VOCABULARY

aneuploidy

nondisjunction 

Intro:You may ask, why does it matter if our chromosome number or structure changes? Well, it matters a great deal! Let's take a sneak peek at what happens when the number of chromosomes in a person is altered...

Discussing Aneuploidy In the clip, we saw that Down Syndrome is a condition caused by a change in chromosome number. Instead of having only 2 copies of chromosome 21, many Down Syndrome individuals have 3 copies. This type of chromosomal abnormality is referred to as an aneuploidy. An aneuploidy occurs when a few chromosomes in a set are lost or gained.  

In addition to being an aneuploidy, Down Syndrome is also further classed as a trisomy (a specific aneuploidy), which gives it a chromosome number of 2n+1, which indicates that it has 2 complete sets of chromosomes and 1 extra copy of one chromosome (in this case, an extra copy of chromosome 21).

 Other kinds of aneuploidy include: Patau Syndrome, and Edward's Syndrome.

Aneuploidy of the sex chromosomes can also occur as a result of non-disjunction during meiosis, or the failure of homologs or sister chromatids to separate properly to opposite poles. Aneuploidy of the sex chromosomes can lead to XYY syndrome, Turner Syndrome, or Klinefelter's Syndrome. 

Here is an example and description of non-disjunction events.

 From this graphic, we see that non-disjunction can take place in either meiosis I or meiosis II. If it occurs during Meiosis I (figure A), then the chromosomes fail to separate into two cells during anaphase I and one cell receives 2 whole chromosomes instead of each cell receiving 1. As a result, the resulting 4 gametes either have no gametes or contain 1 whole chromosome. 

***HOMEWORK***

1a.) What is the aneuploidy associated with Patau Syndrome, Edward's Syndrome, Klinefelter's Syndrome, XYY syndrome, and Turner Syndrome?

1b.) What are the physical characteristics associated with each of these syndromes?

1c.) How do these syndromes demonstrate the seriousness of changes in chromosome number?

2a.) Suppose you were a geneticist and one of your friends confided in you that their teenage son was getting picked on by his peers because he was slender, had broader hips, and his voice hadn't changed. They ask you if you would examine him for any genetic abnormalities. Without any testing, can you infer what your friend's son might be suffering from? How do you know?

2b.) How do you think this abnormality occurred?

2c.) Please draw how you think the abnormality occurred.