Biology 1001A Lecture Notes - Lecture 10: Sister Chromatids, Synaptonemal Complex, Prophase

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19 Nov 2012

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Lecture 10 lecture outcomes: reason why meiosis i is reductional and meiosis ii is equational in meiosis i, it is reductional because the chromosome number is reduced from diploid to haploid. Their sequences are very similar because they are homologous recombination enzymes make cuts on the backbone of the homologous chromosomes and pastes them on another chromosome. Cuts and pastes from non-sister chromatids this is really kinda like a mutation the switch is very precise, the same base pairs are cut and pastes. Usually no bases are lost or gains. Sexual recombination occurs all the time for males. Because it happens in prophase of meiosis. Females experience prophase of meiosis as a fetus, it gets past prophase and recombination and stops. They"ve already done sexual recombination but meiosis has not com- pletely finished. Meiosis will finish when eggs are fertilized: role of cohesin and synaptonemal complex. Cohesin is a protein that holds sister chromatids together.

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Determine if the following events occur during Mitosis, Meiosis I, Meiosis II, Mitosis and Meiosis, Mitosis and Meiosis I, or Mitosis and Meiosis II. (Answers may be used once, more than once or not at all. Be as accurate as possible with your answer.)

___ 1. The chromosome number is reduced by half.

___ 2. The amount of DNA in the cell is twice the amount of a normal diploid cell in G1.

___ 3. DNA is replicated during S phase.

___ 4. Homologous chromosomes separate.

___ 5. Sister chromatids separate.

___ 6. Chromosomes condense and align along the metaphase plate.

___ 7. Homologous chromosomes align and undergo crossing over.

___ 8. Has one round of division per round of DNA replication.

___ 9. The number of chromatids is equal to the number of chromosomes of a diploid cell in G1.

___ 10. Tetrads align on the metaphase plate.

a. Mitosis and Meiosis I only

b. Both Mitosis and Meiosis

c. Meiosis II only

d. Mitosis and Meiosis II only

e. Mitosis only

f. Meiosis I only

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-Complete the following sentences: metaphase of mitosis, prophase II of meiosis, crossing over, anaphase I of meiosis, variable, random fertilization, identical, random orientation, metaphase I of meiosis, prophase I of meiosis, metaphase II of meiosis, reduction division

Two processes that occur during meiosis produce genetically ____________ cells.

In a process called ____________ , paired homologous chromosomes align randomly at the cell equator. This occurs during this stage of cell division: ____________ .

In a process called ____________ , genetic material is exchanged between homologous chromosomes. This occurs during this stage of cell division: ____________ .

-Complete the following paragraph to describe nondisjunction and the resulting effects on chromosome number.

words: euploidy, primary nondisjunction, nomal, nondisjunction, secondary nondisjunction, homologous chromosomes, abnormal, trisomy, monosomy, sister chromatids, aneuploid

1.During meiosis I, ____________ separate and move towards opposite ends of the poles.

2.During meiosis II, ____________ separate and move towards opposite ends of the poles.

3.During meiosis I, if both members of a homologous pair go into the same daughter cell, ____________ is said to occur and no normal gametes are produced.

4.During meiosis II, if the sister chromatids fail to separate and both daughter chromosomes go into the same gamete, ____________ is said to occur. Half the gametes are aneuploid while the other half are euploid.

5.If an egg that contains 24 chromosomes instead of 23 chromosomes is fertilized by a normal sperm, ____________ is said to have occurred.

6.If an egg that contains 22 chromosomes instead of 23 chromosomes is fertilized by a normal sperm, ____________ is said to have occurred.

1). Explain the significance of the fact that gametes contain half of the chromosome complement of somatic cells. Tell me something about variation, if you have a sibling (if you don't imagine you do) - how is your sibling's genetic make-up similar and/or different from yours? What about your mom and dad?

2). Explain the terms reductional division and equational division. What is reduced or kept equal? To which nuclear divisions do these terms refer?

3). What is the diploid number (2n = ?) of an organism if it has
a) 12 chromosomes at Anaphase of Mitosis?
b) 12 chromosomes at Anaphase I of Meiosis?
c) 12 chromosomes at Anaphase II of Meiosis?

4). Compare/contrast Metaphase I of Meiosis with Metaphase of Mitosis.

5). What are the two mechanisms of variation in Meiosis, and during which stage(s) does each occur?

6). Draw a diagram of a bivalent and label the following parts: centromere, sister chromatids, non-sister chromatids, homologous chromosomes, chiasma.

7). A diploid cell has 1 pair of acrocentric chromosomes (Chromosome 1) and 1 pair of submetacentric chromosomes (Chromosome 2).
Â· Gene X is on Chromosome 1. Gene Y is on the short arm of Chromosome 2 and Gene Z is on the long arm of Chromosome 2.
Â· The maternal chromosomes have the X, y, z alleles, whereas the paternal chromosomes have the x, Y, Z alleles.
Draw these chromosomes, labeling ALL alleles, as they might appear in Metaphase I of Meiosis.

Biology 1001A Lecture Notes - Lecture 10: Sister Chromatids, Synaptonemal Complex, Prophase

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