Monday, November 7, 2011

November 8, 2011

Today in class we first went over the the three types of ways a species can gain variety.
Ways to get Variety
  1. Independent Assortment- this is when each homologous chromosome pair is decided during metaphase 1 by chance. Each pair arranges itself independently of the other pair. This allows for much variety in the resulting gametes.
  2. Random fertilization- the random chance of which of the 8000 possible sperm will fertilize the egg
  3. Crossing Over- genetic recombination that occurs during prophase 1. It's when parts of the homologous chromatids exchange or switch.
  • homologous chromosome - (in drawings, they are the chromosome pairs that look like little X's next to each other) 2 chromosomes that match are the same in size , shape, and sequence of gemes
  • gametes-a haploid cell created as a result of meiosis (the four cells that we see at the end of meiosis diagrams are gametes
  • haploid cell- cell with half the number of chromosomes

Next in class we watched a meiosis movie that reinforced what we learned on Friday. We also added to our notes if the movie explained something differently about meiosis that helped us.
After this we did pages 14 an 15 in our unit packet and walked through the steps of meiosis with a partner unsing the materials we had in order to keep reinforcing what we had learned.
Finally we finished class by discussing finishing our note packet about the possible errors that could occur in meiosis.

Errors in Meiosis
1) Nondisjunction- this is when chromosomes do not separate during either Anaphase 1 or 2. This could happen with autosomes (in humans, there are 44) or sex chromosomes ( in humans there are two)
a. it is worse when chromosomes fail to separate during Meiosis 1 because all of the resulting gametes are affected.

Examples of effects of nondisjunction
a. Down Syndrome -when the 21st pair of chromosomes has an extra chromosome
b. Klinefelter syndrome- when boys have two x chromosomes and an y chromosome giving them 47 chromosomes. This syndrome gives males more female traits
c. Turner syndrome- when females have an x chromosome but lack a y chromosome giving them a total of 45 chromosomes.

2)Breakage of a Chromosome (pictures help)
a. deletion- when part of a chromosome is lost
(ex: original pattern of numbers: 1 2 3 4 5 6, duplicated pattern: 1 2 3 6
b. duplication- if a fragment is repeated and put into a homologous chromosome
(ex: original pattern of numbers: 1 2 3 4 5 6, duplicated pattern: 1 2 3 4 5 6 5 6
c. Inversion- fragment reattaches to original chromosome but in the wrong direction (ex: original pattern of numbers: 1 2 3 4 5 6, duplicated pattern: 1 2 5 4 3 6
d. Translocation- fragment that reattaches to a non homologous chromosome
deletion duplication inversion

Homework: Cut out page 21 and bring in the cut outs to class tomorrow, study
optional: cut out page of chromosomes according to the letter you were assigned
- letter b: page 31
- letter c: page 32
- letter d: page 35

Next Scribe: Yvette


  1. This is a really good post- it helped me understand the notes better in a more condensed form. However, you got your date wrong! It was Monday, Nov 7th, not 8th :) Good Job!

  2. all Yvette said and...
    I had a bit of a hard time visualizing what happens during the errors in meiosis. The diagrams, though, were perfectly simple enough to basically show what happens. Your examples with the numbers were also helpful alternative illustrations of the concepts. I <3 THE DIAGRAMS. (okay im finished now:)

  3. I was amazed by how detailed, but helpful your descriptions of meiosis were. I don't think I was really understanding the difference between it and mitosis until I saw the moving diagrams you had. They helped a lot!