MEIOSIS PART 3 IMPORTANCE OF MEIOSIS ABNORMAL MEIOSIS MITOSIS VS MEIOSIS For each section please read the exam guidelines first before going on to the content Learn all the content in this presentation ID: 931265
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Slide1
ASSET GRADE 12 REVISION 2020
MEIOSIS PART 3:
IMPORTANCE OF MEIOSIS, ABNORMAL MEIOSIS, MITOSIS VS MEIOSIS
For each section please read the
exam guidelines
first before going on to the content.
Learn all the content in this presentation
Slide2Exam guidelines
Slide3Importance of Meiosis (importance is the same as function or purpose or significance of Meiosis)
State the importance of meiosis with regard to each of the following:
Production of haploid gametes (refer to detail of gametogenesis
in Human Reproduction)
Halving of the chromosome number (diploid to haploid)
M
echanism
to keep a constant chromosome number in a species
Mechanism to introduce genetic variation through:
Crossing-over
R
andom
arrangement of chromosomes on the equator at Metaphase 1/I and Metaphase 2/II
Slide4Cell Division in humans: An Overview
Female
embryo
2N
Male
embryo
2N
Many mitotic
divisions
Somatic cell production
A double set of chromosomes
Embryo
2N
A single set of chromosomes
Egg
1N
Sperm
1N
Fertilization
Zygote
2N
Many mitotic
divisions
Somatic cell production
Adult
2N
Somatic cell production
Many mitotic
divisions
Many mitotic
divisions
Meiosis
Meiosis
Gamete production
Male
adult
2N
Female
adult
2N
Slide5Revise crossing over
Mechanism to introduce genetic variation through:
Crossing-over
Slide6Revise: The random arrangement of chromosomes at the equator Mechanism to introduce genetic variation through Random Arrangement
Slide7Abnormal Meiosis
State what is meant by non-disjunction
Non disjunction
is the failure of homologous chromosomes or sister chromatids to separate properly during anaphase in cell division
See following 2 slides which show normal separation of chromosomes during anaphase and non disjunction
There are three forms of nondisjunction:
failure of a pair of homologous chromosomes to separate in
meiosis
I,
failure of sister chromatids to separate during meiosis II, and failure of sister chromatids to separate during mitosis. State the consequences of non-disjunctionNondisjunction results in daughter cells with abnormal chromosome numbers (aneuploidy).
Slide8Normal Meiosis
Slide9Non- disjunction learn the definition
Slide10Describe how non-disjunction of chromosome pair 21 in humans may lead to the formation of an abnormal gamete with an extra copy of chromosome 21. Look at the last row of cells which are the gametes
Slide11Describe how the fusion between the abnormal gamete and a normal gamete may lead to Down Syndrome
Slide12Karyotype of a person with Trisomy 21 which is the cause of Down Syndrome
Slide13Some characteristics of a person with Down Syndrome
Small, oblique eyes
Flattened, nasal bridge
Open mouth Protruding tongue Broad neck
Small underdeveloped ears set low on head
Epicanthic fold
Slide14Mitosis vs MeiosisSimilarities
Both mitosis and meiosis are associated with cytokinesis. The end result of both are daughter cells produced from a parent cell.
The fundamental sequence of events in mitosis is the same as in meiosis (in meiosis it happens twice).
Both processes include the breakdown of the nuclear membrane, the separation of genetic material into two groups, followed by cell division and the reformation of the nuclear membrane in each cells
DNA replication must take place in interphase before both kinds of cell division
Slide15Mitosis vs Meiosis
Differences –
state or tabulate
Slide16From MTG