Meiosis and Sexual Life Cycles

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Meiosis and Sexual Life Cycles

• Chapter 13

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Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity

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Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity passing of genes from parents to
  offspring
• variation

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Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity passing of genes from parents to
  offspring
• variation inherited differences within a
  species
• DNA

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Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity passing of genes from parents to
  offspring
• variation inherited differences within a
  species
• DNA Nucleic acid polymer with bases A,C,T, and
  G
• genes

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Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity passing of genes from parents to
  offspring
• variation inherited differences within a
  species
• DNA Nucleic acid polymer with bases A,C,T, and
  G
• genes

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Reproduction

• Why do offspring closely resemble their parents
  and not unrelated individuals?
• Heredity passing of genes from parents to
  offspring
• variation inherited differences within a
  species
• DNA Nucleic acid polymer with bases A,C,T, and
  G
• genes units of heredity made of DNA found on
  the chromosomes

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Asexual Reproduction

• What occurs in asexual reproduction?
• Single individual is the parent which copies all
  of its genes into an identically cloned
  offspring.
• Limited variation with asexual reproduction.
• What nuclear division is involved in asexual
  reproduction?

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Sexual Reproduction

• In order for 2 parents to combine their genes
  into one offspring, what must their genetic
  contribution be?
• Each parent must contribute 1/2 of their genes to
  the offspring.
• How does the process ensure that the offspring
  receives the correct genes from each parent?

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Vocabulary of genetics and reproduction

• Somatic cell

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Vocabulary of genetics and reproduction

• Somatic cell any cell other than sperm or egg.
  Human somatic cells have 46 chromosomes
• karyotype

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Vocabulary of genetics and reproduction

• Somatic cell any cell other than sperm or egg.
  Human somatic cells have 46 chromosomes
• karyotype display of individuals somatic cell
  metaphase chromosomes.
• Homologous chromosomes

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Vocabulary of genetics and reproduction

• Somatic cell any cell other than sperm or egg.
  Human somatic cells have 46 chromosomes
• karyotype display of individuals somatic cell
  metaphase chromosomes.
• Homologous chromosomes chromosomes that have
  same centromere position, same genetic loci, and
  same length.
• How, then, are homologous chromosomes different
  from one another?

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• Homologous chromosomes have different alleles.
• Allele

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• Homologous chromosomes have different alleles.
• Allele expression of a gene
• autosome

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• Homologous chromosomes have different alleles.
• Allele expression of a gene
• autosome non-sex chromosome
• sex chromosome

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• Homologous chromosomes have different alleles.
• Allele expression of a gene
• autosome non-sex chromosome
• sex chromosome dissimilar chromosomes that
  determine an individuals sex.
• How many autosomes and how many sex chromosomes
  are there in a normal human?
• How many homologous pairs of chromosomes?

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• diploid

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• diploid condition in which cell contains 2 sets
  of chromosomes abbreviated 2n
• haploid

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• diploid condition in which cell contains 2 sets
  of chromosomes abbreviated 2n
• haploid condition in which cells contain 1 set
  ( no homologous pairs) of chromosomes
  abbreviated n
• gamete

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• diploid condition in which cell contains 2 sets
  of chromosomes abbreviated 2n
• haploid condition in which cells contain 1 set
  9 no homologous pairs) of chromosomes
  abbreviated n
• gamete haploid reproductive cells, human
  gametes have 23 chromosomes
• fertilization

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• diploid condition in which cell contains 2 sets
  of chromosomes abbreviated 2n
• haploid condition in which cells contain 1 set
  9 no homologous pairs) of chromosomes
  abbreviated n
• gamete haploid reproductive cells, human
  gametes have 23 chromosomes
• fertilization union of 2 gametes
• zygote

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• diploid condition in which cell contains 2 sets
  of chromosomes abbreviated 2n
• haploid condition in which cells contain 1 set
  9 no homologous pairs) of chromosomes
  abbreviated n
• gamete haploid reproductive cells, human
  gametes have 23 chromosomes
• fertilization union of 2 gametes
• zygote diploid cell that results from fusion of
  gametes
• What sort of nuclear division must occur to
  produce haploid gametes?

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Meiosis

• Must have a stage that results in the reduction
  of chromosome number.
• In meiosis the diploid parent cell produces
  haploid gametes

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Interphase I

• What happens in interphase I?
• Chromosomes replicate
• centriole pairs in animal cells also replicate
• In what way is interphase I from meiosis I
  different from interphase of mitosis?
• There is no difference.

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Prophase I

• Synapsis occurs.
• Homologous chromosomes come together as pairs
• chromosomes appear as tetrads with 4 attached
  sister chromatids
• chiasmata form, they are sites where homologous
  non-sister chromatids cross over.
• 90 of meiosis is spent in prophase I

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Metaphase I

• Tetrads align at metaphase plate
• each homologue is attached to kinetochore
  microtubules emerging from opposite poles, so
  that the 2 homologues are destined to separate
  during anaphase I

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Anaphase I

• Homologous chromosomes are moved to opposite
  poles by spindle apparatus
• sister chromatids remain attached at the
  centromeres
• How does this differ from anaphase of mitosis?

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Telophase I

• each pole has a haploid set of chromosomes
• cytokinesis occurs and daughter cells are formed.
• What is the chromosome number in each daughter
  cell?

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• What has been accomplished by the end of meiosis
  I?
• Homologous pairs of chromosomes have separated.
• Why isnt meiosis over, if haploid daughter cells
  have already been formed?
• We still need to separate sister chromatids!

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Genetic Variation

• What are the 3 ways that meiosis and sexual
  reproduction generate variety?
• Independent assortment
• Orientation of homologous pairs of chromosomes
  with regard to each-other is random (metaphase I)
  
• there is a 50/50 chance that a particular
  daughter cell will receive a paternal or maternal
  chromosome

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• There are 2n possible combinations of maternal
  and paternal chromosomes.
• In humans there are 223 possible different
  combinations or 8 million.
• Random fertilization has the random combining of
  egg and sperm. Each egg and sperm has one in 8
  million different possibilities. Thus the zygote
  can have one in 64 trillion possible diploid
  combinations.
• This number hasnt even accounted for crossing
  over, which has a random contribution to genetic
  variation!

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Genetic Variation in all organisms

• In asexually reproducing organisms, mutations are
  the primary source of genetic variation
• In sexually reproducing organisms meiosis
  accounts for most of the variation.

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Oogenesis vs. Spermatogenesis

• On board

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