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Meiosis vs. Mitosis Animation. 2 divisions daughter cells genetically different from parent produce 4 cells 2n 1n produces gametes crossing over!!. 1 division daughter cells genetically identical to parent produces 2 cells 2n 2n produce cells for growth & repair - PowerPoint PPT Presentation
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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
Meiosis
Stages of Meiosis Review
BioFlix Animation
Unique Features of Meiosis
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
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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gametes
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
Gametogenesis – sperm & egg production
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
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
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
•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.
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.
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.
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.
•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
•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
What if something goes wrong?
What happens then???
• nondisjunction - chromosomes do not segregate correctly during meiosis
• Incorrect chromosome #• Deletion• Duplication• Inversion• Translocation ** Extra chromosomes often means survival**
**Missing chromosomes often means DEATH**
• Monosomy - One less chromosome due to missing chromosome in gameteEx: Turner Syndrome
KARYOTYPE
• Trisomy - Gamete has an extra chromosome
•Ex: Trisomy 21 (Down Syndrome)
• Polyploidy - Complete EXTRA sets of chromosomes– almost ALWAYS lethal to animals
– plants can be healthier & larger
Genetic testing•Amniocentesis in 2nd trimester
▫sample of embryo cells▫stain & photograph chromosomes
•Analysis of karyotype
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