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
Slide 2
Meiosis is a reduction division of a diploid nucleus to produce
four haploid nuclei.
Slide 3
Cell division DNA is replicated before meiosis so that all
chromosomes consist of two sister chromatids.
https://www.youtube.com/wa tch?v=vA8aMpHwYh0
Slide 4
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;
Slide 5
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
Slide 6
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.
Fusion of gametes from different parents promotes genetic
variation. Crossing over and random orientation promotes genetic
variation.
Slide 11
Correct disjunction
Slide 12
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
Slide 13
Slide 14
Slide 15
Slide 16
Karyograms are done using cells collected by chorionic villus
sampling or amniocentesis, for pre-natal diagnosis of chromosome
abnormalities.
Slide 17
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