sexual reproduction heredity genes heredity - passing down of characteristics (genes) alleles ...
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Sexual ReproductionHeredity - passing down of characteristics (genes)
Alleles- different forms of the same gene
Sexual ReproductionWhy sexual reproduction? shuffles alleles; new combinationsprovides genetic variation in species
MeiosisType of cell division One germ* cell makes 4 gametes (egg/sperm) with the # of chromosomes.
Occurs only in germ* cells of gonads testes /ovariesOccurs in flowers ovary and anther *Germ here doesnt mean bacteria. Its a term used for the type cells that gives rise to gametes in organisms.
While females are born with all the eggs they will ever have (around 400,000), only about 400 will ever mature and ovulate between puberty and menopause.
Matrue males produce about 100 million sperm each day.
Sperm surrounding an egg
This shows how only one single sperm gets to penetrate the egg, releasing its nucleus of 23 chromosomes to merge with the nucleus of the egg and its 23 chromosomes.
Homologous ChromosomesPair of chrom. similar in shape , size, and types of genes.Each locus (location of the gene) in same position on chrom.
Humans have 23 pairs of homologuesHousefly 6 prs Chicken 39 prs Apple 17 prsDog 39 prsCat 19 prs
This is a karyotype (an image of an organisms chromosomes)
This is a karyotype of a normal human male
Chromosome numbers:However many types of chrom. an organism has, that number is the n number of chrom. it has.
Body cellsEgg/Sperm cellsCalled:Somatic cellsGametesTerm for chrom. #Diploid (2 sets of chrom.)Haploid (1 set of chrom.)n number2n1nFor Humans:46 chrom.23 chrom.
AnimationMeiosis A animationMeiosis B animationMeiosis C animation
Prophase ILongest and most complex phase (90% of meiosis).DNA condenses into chromosomes.Synapsis - a process: when homologous chrom. come together, pair up, form a tetrad.
Prophase I - Synapsis Nonsister chromatids
Prophase I - Crossing OverCrossing over may occur in the tetrad: between nonsister chromatids, ends break and reattach
Crossing Over - Provides Variation variation
Metaphase IShortest phase; paired homologues align.INDEPENDENT ASSORTMENT occurs pairs of homologues line up independently of other pairs orientation toward the poles -- random. Adds variation.
Anaphase IHomologous chromosomes separate towards the poles (Tetrads separate)
Sister chromatids remain attached
Telophase IEach pole now has haploid set of chromosomes (however still doubled).Cytokinesis occurs: two haploid daughter cells formed.
Meiosis IINo interphase II ( no more DNA replication)Remember: Meiosis II is similar to mitosisProphase II / Metaphase IIAnaphase II
Telophase IISame as telophase in mitosis.Nuclei form.Cytokinesis occurs (2nd time).Four haploid daughter cells produced (chromosomes now back to single condition).gametes ~ sperm or egg; ovule or pollen grain
Gamete Formation in AnimalsDiff. bet. male and female gametes.
Male: spermatogenesis all 4 develop into sperm cells. Female: oogenesiscytokinesis is uneven. most cytoplasm goes to 1 of the 4 eggs (forms 1 large egg cell) 3 other cells are small polar bodies which die
Oogenesis2n = 46human germ cellin ovarydiploid (2n)n=23Still doubledn=23Still doubled
meiosis I232323Ovumn=23Polar Bodiesmeiosis II
Mitosis vs MeiosisMitosisBody (somatic cells)2 daughter cells made (identical)Each w/ same # & kind of chrom. as parent cell1 division process 1 cytokinesisNo synapsis or crossing overAre diploid (2n)MeiosisGerm cells of gonads4 gamete cells made (all different)Each w/ chrom. # as parent cell2 divisions2 cytokineses eventsSynapsis & crossing over occurs in Prophase 1Are haploid (n)
NondisjunctionWhen the tetrad (in Anaphase I) or the sister chromatids (in Anaphase II) do not separate, creating an abnormal # of chrom. to occur in the gametes.
Lethal most of the time
Karyotype normal male
Karyotype normal female
Downs SyndromeTrisomy 2147, XY, +21
The only trisomy survivable to adulthood