Meiosis Stages of Meiosis Review Comparison of Meiosis and Mitosis .
Meiosis
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Transcript of Meiosis
![Page 1: Meiosis](https://reader036.fdocuments.us/reader036/viewer/2022082818/56812c79550346895d91225f/html5/thumbnails/1.jpg)
Meiosis
• Gamete production, takes place in reproductive organs/parts in both plants and animals
• Gametes have half the number of chromosomes (haploid), so when they come together the zygote will be diploid
• If gametes weren’t haploid the offspring would have twice the correct number of chromosomes in every cell
• Corn plant has 20 chromosomes (10 pairs) in every somatic cell, so its gametes have 10 single chromosomes
• If it didn’t than the offspring would end up with 40 chromosomes (10 quads!)
• 20 + 20– 40 + 40
• 80 + 80– 160 + 160
» 320 the 5th generation would have 32 of each of the 10 chromosomes!!
![Page 2: Meiosis](https://reader036.fdocuments.us/reader036/viewer/2022082818/56812c79550346895d91225f/html5/thumbnails/2.jpg)
Meiosis, cont.• This is how the correct number of
chromosomes is maintained from generation to generation
• Called REDUCTION DIVISION— as cells divide, the number of chromosomes is reduced
• Consists of 2 successive nuclear and cell divisions
• Before Meiosis I, DNA replicates into fuzzy X’s
• Meiosis I— homologous chromosomes pair up and then separate into 2 cells
• Meiosis II—just like mitosis, but it happens to 2 cells simultaneously
• Chromosomes line up at the center and sister chromatids are pulled apart
• One “2n” (diploid) cell produces 4 “n” (haploid) cells
![Page 3: Meiosis](https://reader036.fdocuments.us/reader036/viewer/2022082818/56812c79550346895d91225f/html5/thumbnails/3.jpg)
Interesting occurrences during meiosis…..
• Crossing over—when homologous chromosomes exchange chromosome fragment
• Causes genetic recombination and provides genetic variation (good thing!)
• Happens during Prophase I, when chromosomes are coiling up and homologous chromosomes are pairing up
• Shown happening at both ends of chromosomes, but can happen at just one
• This is why you are not identical to your brothers/sisters
![Page 4: Meiosis](https://reader036.fdocuments.us/reader036/viewer/2022082818/56812c79550346895d91225f/html5/thumbnails/4.jpg)
Another interesting occurrence….• Nondisjunction—homologous chromosomes do not separate properly• Happens during Anaphase I or II• End result is two gametes end up with both chromatids (of that specific
chromosome) and the other 2 cells end up without a copy of that chromosome
• So if the gamete that has both of the chromatids is fertilized then that zygote will be trisomy for that chromosome
• If the gamete that is missing that chromosome is fertilized, it will be monosomy for that chromosome
• Relatively common-- 1 in 5 normal human pregnancies miscarry w/in the first 2 months due to the baby having too many or too few chromosomes