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3.3 Meiosis Adapted from: Taylor, S. (2010). Meiosis (Presentation). Science Video Resources. [Online] Wordpress. Retrieved from http://i-biology.net/ibdpbio/04-genetics-and-genetic- engineering/meiosis-inc-ahl/ https://www.youtube.com/watch?v=zjAdjY5Cl3g

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Meiosis is a reduction division of a diploid nucleus to produce four haploid nuclei.

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Cell division DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids. https://www.youtube.com/wa tch?v=vA8aMpHwYh0

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The halving of the chromosome number allows a sexual life cycle with fusion of gametes. 1. similarities between the life cycle of a moss and of a human include: both have haploid sperm and egg; both have an n stage; both have a 2n stage; both have mitosis, meiosis and fertilization; both have a zygote stage; 2. in humans the zygote gives rise to either male or female in individuals but in moss, the zygote gives rise to sporophyte; in moss sporophyte gives rise to spores whereas diploid human gives rise to gametes; eggs and sperm created by mitosis in moss but meiosis in humans; moss plant can give rise to male or female, but separate genders create gametes in humans; in moss, there is a gametophyte and a sporophyte but we dont have this in humans;

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Phases of meiosis https://www.youtube.com/watch?v=16enC385R0w Comparison between mitosis and meiosis: https://www.youtube.com/watch?v=rqPMp0U 0HOA https://www.youtube.com/watch?v=rqPMp0U 0HOA

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The early stages of meiosis involve pairing of homologous chromosomes and crossing over followed by condensation. Crossing over: random exchange of genes between homologous chromosomes. Orientation of pairs of homologous chromosomes prior to separation is random. Separation of pairs of homologous chromosomes in the first division of meiosis halves the chromosome number. This separation is known as disjunction: one chromosome from each bivalent moves to one of the poles and the other chromosome to the other pole.

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http://www.biology.iupui.edu/biocourses/N100/2k4ch9meiosisnotes.html

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Fusion of gametes from different parents promotes genetic variation. Crossing over and random orientation promotes genetic variation.

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Correct disjunction

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Non-disjunction can lead to changes in chromosome number In anaphase (I or II), a chromosome or pair of sister chromatids can be pulled to the wrong pole

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Karyograms are done using cells collected by chorionic villus sampling or amniocentesis, for pre-natal diagnosis of chromosome abnormalities.

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Do you want to see more? Check this videos: - Chorionic Villus Sampling http://video.about.com/pregnancy/Chorionic-Villus-Sampling.htm - Amniocentesis: http://www.medindia.net/animation/amniocentesis.asp Do you want to see more? Check this videos: - Chorionic Villus Sampling http://video.about.com/pregnancy/Chorionic-Villus-Sampling.htm - Amniocentesis: http://www.medindia.net/animation/amniocentesis.asp