1). Explain the significance of the fact that gametes contain half of the chromo
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Question
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).
· 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.
· 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.
Explanation / Answer
1. Human cells are diploid (2n = 46). During sexual reproduction, the chromosome number is halved they have to merge to form a diploid zygote i.e n + n =2n or 23 + 23 =46. If suppose the chromosome number is not halved in the gametes then in every generation chromosome number would be doubled and that is not possible. Hence it is a mandatory condition to reduce the number of chromosomes to half prior to gamete formation.
I have a sister who is quite similar to me in terms of facial and other bodily features but we are two very different people with so many behavioural and physiological differences. So like other siblings, our variations are due to genetic recombination and crossing over during meiosis that occurred during gamete unison of my parents. Every time meiosis divides the genes differently and so thus the variations arise. Also due to these variations, and similarities I am called as my mom`s girl and my elder sister is called as dad`s girl.
2. The first division, called meiosis I, is often referred to as reductional division since it reduces the genetic material from diploid to haploid. The second division or meiosis 2 is the equational division because it does not reduce chromosome numbers. However, it maintains the original ploidy level.
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