Class Recap: 4/8/11

Hi Class, today we went over changes in chromosome structure and how these structural changes come about and the consequences of these changes. ***For those of you who missed class today, homework is listed at the end of the post. You have three days from the time you return to school to hand in missing work.

VOCABULARY
inversion (paracentric or pericentric)
deletion
duplication
reciprocal translocation
non-reciprocal translocation
Robertsonian Translocation

Intro: We know from yesterday's lecture that changes in the number of chromosomes can have dire effects on an individual. Today in class we learned about the effects of changes in chromosome structure.Much like changes in chromosome number, changing the structure of a chromosome can also produce some nasty effects. In class, we talked about inversions, deletions, duplications, and translocations.

Chromosomal inversions are chromosome rearrangements in which a segment of a chromosome is reversed end to end. Inversions occurs when a single chromosome undergoes breakage and rearrangement within itself. There are two types of inversions: paracentric and pericentric.

Chromosomal deletions occur as a result of a mutation that causes a segment of a chromosome (and the information contained in that segment) to be lost. Two types of deletions are terminal deletions and interstitial deletions.

Chromosomal duplications occur when any segment of DNA that contains a gene is doubled. Some types of duplications include tandem duplications, reverse tandem duplications, and terminal tandem duplications (see page *** of your textbook for pictures).

Chromosomal translocations are caused by rearrangement of parts between non-homologous chromosomes. The three major types of translocations are: reciprocal translocations (mutual exchange of parts), non-reciprocal translocations (non-mutual exchange of parts), and Robertsonian translocations (two acrocentric chromosomes that fuse near the centromere region with loss of the short arms).

The following video will provide a review of these terms we just went over and allow you to have a better picture of each of these chromosomal structural changes.

***HOMEWORK***
-Worksheet on chromosomal abnormalities
-Do questions 2-8, 11-13, and 18 on page ***

Article Reflection Assignment: Fetal Genetic Testing

For your article reflection assignment, I want you to write a 200-250 word response to the article I will link to at the end of this post. In your reflection, you may give your own opinion on the article, bring up any questions that the article brings to your mind, critique the thought or reasoning of the author, or write about how this article ties into class material. Please turn this assignment in during class or e-mail it to me.

In addition to this written assignment, I would also like you to leave at least one question or comment you have about the article in the comments section of this blog post. Also, respond to each other's queries (in a civil matter) as well. I will also be commenting on your postings.

If you're having difficulties reading the article, please let me know. 

Link to Article

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.