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Genetics with Mitosis and Meiosis

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Genetics with Mitosis and Meiosis

Postby 1fh2 » Tue Jan 29, 2013 1:23 am

hi i need major help with two questions please please!

1. i need to draw a diploid organism that has a chromosome complement of 2n=6 at mitosis anaphase, meiosis anaphase 1 and meiosis anaphase 2. On the diagram i need to LABEL on each chromosome to show one set of possible locations for all the alleles for an individual of genotype AaBb given that there is no crossing over in this organism and that the two genes involved asoort independently.

2. State Mendels law of independent assortment and explain why it applies to meiotic cell division but NOT apply to mitotic cell division . I also have to refer to the diagram that would be drawn with question 1.

Please please help me with these two questions as i am craming for a final and can not figure out the answers!!!!
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Postby wildfunguy » Sun Feb 03, 2013 11:45 pm

Fellow bio-online members, please correct me if I got anything wrong.

Anaphase (in any type of division) is after the genetic material has separated and is being pulled toward the ends of the cell.

The cell cycle:
M-phase (division)

Mitosis: Before S-phase, each chromosome consists of one strand of DNA. The DNA is copied during S-phase. So, after S-phase, each chromosome consists of two strands. When the DNA is coiled, the two strands are referred to as sister chromatids.
The sister chromatids are what make chromosomes X-shaped. However, a chromosome with only one chromatid will be just a line, not an X.
The sister chromatids are what separate during mitosis. So, to draw mitosis anaphase, you should draw 4n chromatids (2n on each side) being pulled away from each other.
Since the genetic material is not being separated, there should be an A, a, B, and b on each side of the cell.

Meiosis I is when the alleles separate, so you should only place one A or a and one B or b on each side of the dividing cell. The two forms of a gene are present on the two homologous chromosomes, and the homologous chromosomes are what separate.
During meiosis I, the chromosomes still have sister chromatids, so you will be drawing X-shaped chromosomes. Also, since homologous chromosomes are separating, the resultant cells are 1n cells. Thus, you should draw 1n X-shaped chromosomes on each side of the dividing cell.

After Meiosis I is complete, the resultant cells each do Meisosis II. Meiosis II is basically like mitosis in that sister chromatids are being split apart, but there are half as many chromosomes (one from each homologous pair). This one should be easy.

This was actually a bit confusing for me. I am going to type out an image to help me remember.

Organism genotype = AaBb

A <-> A
a <-> a
B <-> B
b <-> b

Meiosis I
AA <-> aa
BB <-> bb

Meiosis II
A <-> A
B <-> B

If you want to get a really good grade, make the chromosomes differ in length. Homologous chromosomes (and their chromatids) are roughly equal in length. So all chromosomes or chromatids containing the same gene should be equal in length.
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Postby wildfunguy » Mon Feb 04, 2013 12:06 am

Actually, I'm only certain that the DNA is replicated during interphase, not necessarily S-phase.
Interphase = G1 + S + G2

The law of independent assortment wouldn't apply to mitosis because the alleles aren't be separated (see above).
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