Chapter 13 Meiosis And Sexual Life Cycles Flashcards
Meiosis
Reduction division. The diploid number of chromosomes is half. Each gamete has a haploid number of chromosomes (a single set). The homologous chromosome are separated during meiosis one
Before meiosis 1, one duplication of DNA is followed by two division
There’s no duplication of DNA between meiosis one and meiosis two
How many autosomal pairs of chromosomes do humans have?
Humans have 22 pairs of chromosomes numbered one through 22. The 23rd pair is called the sex chromosome. Only females have a homologous 23rd pair of sex chromosomes because they have both ‘x’
Males have nonhomologous pairs of sex chromosomes because he has an X and Y
Contrast the number of genes that the Y chromosome has to the X chromosome
There are about 78 genes on the Y chromosome compared to 1100 to 2000 on the X chromosome
Meiosis one
Meiosis one separates homologous pairs, the two cells are called haploid. But they have double the amount of DNA of gametes that arise from meiosis two as sister chromatids get separated during meiosis two (similar to mitosis).
These sister chromatins are not identical to one another in meosis because of crossover chromosomal exchange
Image of meiosis one and meiosis two
Meiosis one: AB+CD=AC+BD
Meiosis two: A+B+C+D
Recombinant chromosomes
This crossing over and exchange of DNA happens between sister chromatin of a homologous pair. In humans crossing over happens on average between two and three times for each chromosome. Crossing over is required for dyads to pair properly as a tetrad and move to metaphase plate. This ensures that each so that results from meiosis one gets one of the homologous chromatins as a pair.
Hallmark of meiosis one
Prophase one: homologous pairs have come together and are exchanging DNA. Metaphase one: homologous pairs as tetrad are lined up in center of spindle.
Anaphase one: homologous pairs separate and go to opposite sides of the cell. No longer tetrad now individual dyads.
Telophase one: cytokinesis. Two cells results in human males (two very unequal size-wise cells results from human female meiosis one)
Hallmark of meiosis two
Two cells will go through meiosis two for every one cell that started meiosis one. This looks more like mitosis. Very similar to mitosis in that sister chromatins go through metaphase plate together and separate in anaphase. Different because sister chromatins are not I
denticle
Prophase two, metaphase two, anaphase two and telophase 2.
At end of meiosis two in male there are four haploid gametes formed. Not identical to each other or to the south and you cheated meiosis
What causes variability in meiosis one?
The way chromosomes align at the metaphase plate in meiosis one produces variability. The homologous pairs (each in a pair) are not identical so their arrangement on the spindle is meaningful. The arrangement of all tetrad in meiosis one and all dyad in meiosis two determine which chromosomes are grouped together in the gamete
Nondisjuction: What happens if chromatins don’t properly separate during either meiosis one or meiosis two?
Meiosis one creates for bad cells, incorrect gametes. Meiosis two creates two incorrect cells and two correct cells.
If separation of chromatins doesn’t occur properly, cells can end up with too few are too many chromosomes. Aneuploidy results.
Aneploidy
Having a particular gene or chromosomal region present in extra or fewer copies then in the normal type
