Meiosis vs. Mitosis Animation
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Transcript of Meiosis vs. Mitosis Animation
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Meiosis vs. MitosisAnimation
▫1 division▫daughter cells
genetically identical to parent
▫ produces 2 cells▫ 2n 2n
▫produce cells for growth & repair
▫NO crossing over
▫2 divisions▫daughter cells
genetically different from parent
▫produce 4 cells
▫2n 1n▫produces
gametes▫crossing
over!!
▫division▫Begins
with interphase
▫PMAT
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Meiosis
Stages of Meiosis Review
BioFlix Animation
Unique Features of Meiosis
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Crossing Over• Homologous Chromosomes
• Synapsis• Chiasma form• Cross over at matching
regions of nonsister chromatids
• genetic recombination increases variation!!!
• Process itself varies• Bacteria – asexual reproduction
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mitosiszygote
Putting it all together…
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egg
sperm
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meiosis 4623
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fertilizationdevelopment
meiosis fertilization mitosis + development
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4646 46
gametes
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An Intro to Animal Development
•Fundamental biological question: How does a single cell—the fertilized egg—develop into a multicellular individual?
•Development proceeds in ordered phases through organism’s life cycle:▫Gametogenesis▫Fertilization▫Cleavage▫Gastrulation▫Organogenesis
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Gametogenesis – sperm & egg production
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Oogenesis
MEIOSIS I
MEIOSIS II
first polar body
secondpolar body
ovum(haploid)
secondaryoocyte(haploid)
primaryoocyte(diploid)
germinal cell(diploid)
primary follicles
mature follicle withsecondary oocyte
ruptured follicle(ovulation)
corpus luteum
developingfollicle
fertilization
fallopian tube
after fertilization
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Egg Structure and Function• Relatively large & nonmotile
• Size largely due to nutrient storage, required for early embryonic development
• Quantity of nutrients varies across species
▫Relatively small mammalian egg supplies nutrients for early development ONLY embryos start to obtain nutrition through placenta shortly after fertilization
▫Egg-laying species form larger eggs yolk of the egg is embryo’s SOLE nutritional source prior to hatching
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SpermatogenesisEpididymis Testis
Coiledseminiferoustubules
Vas deferens
spermatozoa
spermatids(haploid)
secondaryspermatocytes(haploid)
primaryspermatocyte(diploid)
germ cell (diploid)
MEIOSIS II
MEIOSIS I
▫ continuous & prolific process
▫ 100-600 million sperm can be produced daily
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•Fertilization - haploid sperm and egg cells fuse to form diploid zygote (a fertilized egg).
•Certain conditions MUST be met before a zygote can form:▫Location: gametes in same place at same
time.▫Recognition: recognize & bind to each
other.▫Fusion!▫Trigger onset of development.
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Successful fertilization leads to development – how
do we become a person from 2 single cells? Do you
think the process is the same for all living things? Explain and describe your
vision of this process.
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Why Does Only One Sperm Enter the Egg?• Animals use different mechanisms to avoid
polyspermy - fertilization by more than one sperm
• Ex: sea urchins - fertilization stimulates creation of a physical barrier▫Ca2+-based signal is rapidly induced & propagated
throughout the egg, form a fertilization envelope keeps away additional sperm
• Ex: mammals - cortical granules release enzymes modify egg cell receptors prevent binding by additional sperm.
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Cleavage• Cleavage - set of rapid cell divisions in animal zygotes
immediately after fertilization.
▫ 1st step is embryogenesis - process that makes single-celled zygote into multicellular embryo.
▫ partitions egg cytoplasm without additional growth of the zygote.
▫ Cells created by cleavage divisions called blastomeres.
▫ Completed cleavage results in embryo consisting of mass of blastomere cells called a blastula.
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•Gastrulation - extensive & highly organized cell movements radically rearrange embryonic cells into structure called the gastrula.
▫results in formation of embryonic tissue layers (**tissue is integrated set of cells functioning as a unit)
▫most embryos have 3 primary tissue layers: ectoderm, mesoderm, and endoderm.
these tissues are called germ layers because they give rise to adult tissues and organs.
Gastrulation
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•Ectoderm - forms outer covering of adult body & nervous system
•Mesoderm - gives rise to muscle, most
internal organs, & connective tissues like bone & cartilage
•Endoderm - produces lining of digestive tract or gut, along with some associated organs
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What if something goes wrong?
What happens then???
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• nondisjunction - chromosomes do not segregate correctly during meiosis
• Incorrect chromosome #• Deletion• Duplication• Inversion• Translocation ** Extra chromosomes often means survival**
**Missing chromosomes often means DEATH**
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• Monosomy - One less chromosome due to missing chromosome in gameteEx: Turner Syndrome
KARYOTYPE
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• Trisomy - Gamete has an extra chromosome
•Ex: Trisomy 21 (Down Syndrome)
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• Polyploidy - Complete EXTRA sets of chromosomes– almost ALWAYS lethal to animals
– plants can be healthier & larger
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Genetic testing•Amniocentesis in 2nd trimester
▫sample of embryo cells▫stain & photograph chromosomes
•Analysis of karyotype
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Sex chromosomes abnormalities•Human development more tolerant of
wrong numbers in sex chromosomes
Results in variety of distinct syndromes
▫XXY = Klinefelter’s syndrome male ▫XXX = Trisomy X female▫XYY = Jacob’s syndrome male▫XO = Turner syndrome female