Meiosis - Reproductive Cell Division Meiosis = cell division during which sex cells (gametes) are...
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Transcript of Meiosis - Reproductive Cell Division Meiosis = cell division during which sex cells (gametes) are...
Meiosis - Reproductive Cell Division• Meiosis = cell division during which sex cells
(gametes) are produced • Remember: sex cells contain half the number of
chromosomes as the body cells (haploid)• Male gametes = sperms (1n)
** n = # of chromosomes• Female gametes = eggs (1n)• Fertilization = uniting of male and female
gametes; resulting fertilized egg = zygote (2n)
1n (egg) + 1n (sperm) = 2n (offspring)
n=23egg
sperm n=23
2n=46zygote
Fertilization
Meiosis Cont.
• Occurs only in reproductive organs called gonads (testes or ovaries)
• Meiosis in males = spermatogenesis (gives rise to sperms)
• Meiosis in females = oogenesis (gives rise to eggs)
Karyotype = collection of all organism’s chromosomes
Overview of Meiosis
Homologouschromosomesseparate
Sister chromatidsseparate
Results of meiosis: 4 haploid cells are produced from one diploid cell
Haploid
Diploid
Meiosis I Meiosis II
Haploid
Prophase IMetaphase IAnaphase ITelophase I
Prophase IIMetaphase IIAnaphase IITelophase II
Meiosis I : homologous chromosomes separate
Prophase I(early)
(diploid)
Prophase I(late)
(diploid)
Metaphase I(diploid)
Anaphase I(diploid)
Telophase I(diploid)
Nucleus Spindlefibers
Nuclearenvelope
Meiosis II : sister chromatids separate
Prophase II(haploid)
Metaphase II(haploid)
Anaphase II(haploid)
Telophase II(haploid)
Four nonidentical
haploid daughter cells
Why do we have meiosis?
I. To make sperm and eggs
II. To make new combinations of genes (due to crossing over and independent assortment of chromosomes) which leads to variation within a species
Homologous chromosomes
Tetrad
Genetic variation
Tetrad
Random (independent) assortment
CELL DEATH
2 types of cell death:
• Orderly, genetically programmed cell death = apoptosis
• Cell death due to injury = necrosis
CELL AGING
• Geriatrics = branch of medicine dealing with medical problems of elderly
As we age:• Many vital functions slow down• Telomeres (DNA on tips of chromosomes) shorten• Glucose is added to proteins and contributes to
stiffening• Free radicals damage proteins, lipids, and DNA