Meiosis

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Meiosis
Meiosis results in haploid cells. monoploid
Chromosome division for production of sex cells.
( Sexual Reproduction cycle)
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Alternation of Generation

• Both diploid and haploid stages are multicellular.

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Meiosis in the sporophyte stage produces
spores.A spore can then divide mitotically to
produce the gametophyte stage.
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Alternation of Generation

• Sporophyte stage is a diploid or 2n stage
• Gametophyte stage is a monoploid or 1n stage.

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Synapsis and Crossing Over
Homologous chromosomes pair and cross over during
prophase I Results in greater genetic diversity
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Crossing over- Tetrad Formation

• Homologous chromosomes exchange genetic material
  in synapsis
• by a zipper-like protein forming a synaptonemal
  complex resulting in chiasmata.

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Homologous chromosomes

• Chromosomes that control the same trait, and are
  inherited from different parents.

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Crossing over

• During prophase of meiosis homologous pairs may
  exchange genetic material.

• TETRAD or synapsis

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• Homologous chromosomes separate in 1st division
• Sister chromatids separate during 2nd division

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New Genetic Combinations

• Recombination during fertilization brings
  together two sets of genetic instructions
• Meiosis-crossing over brings about new
  combinations
• Random genetic mutation can result in random
  genetic change

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Principles of Heredity

• The two homologous chromosomes segregate
  (separate) during gamete formation.
• Non-homologous chromosomes separate
  independently of one another

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Spermatogenesis-sperm creation

• Male gamete

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Oogenesis-Egg creation

• Female gamete

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Ovary Cross Section
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Oogenesis
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Testes- seminiferous tubules
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Spermatogenesis
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Fertilization and Polar Body extrusion
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Sexual Reproduction

• Combining the monoploid chromosomes of two
  individuals to make a new diploid organism

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zygote

• Fertilized egg or gamete

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Meiosis
N2
Crossing over
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tetrad

• Chromosome arrangement in prophase of meiosis-
  homologous pairs lie side by side in synapsis

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Telophase I , Prophase II , Metaphase II
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Anaphase II and Telophase II
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Nondisjunction

• Chromosomes fail to separate properly during
  meiosis.
• Age is a factor
• results in Downs Syndrome
• results in Turners Syndrome
• results in Klinefelters Syndrome

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Karyotype- a picture or arrangement of metaphase
chromosomes.
Can be taken from- amniocentesis
-chorionic vili biopsy Can be
taken from any cells captured in metaphase of
mitosis. Chromsomes are stained and photographed
and then arranged by pairs according to size and
banding patterns.
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Klinefelters Syndrome
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Cri du chat
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Turners Syndrome
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Pataus syndrome
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Principles of Heredity

• For each character, an organism
• inherits two alleles, one from
• each parent.

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Alternative versions of genes (alleles) account
for variations in a trait.
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Law of Dominance

• If alleles differ, then the dominant will be
  fully expressed over the recessive.

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Law of segregation

• The two alleles segregate
• (separate) during Meiosis
• or gamete formation.

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Law of independent assortment

• Alleles on different chromosomes
• segregate independently of one
• another

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Heredity

• How traits are passed on from one generation to
  another

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Trait

• An inherited characteristic

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Gene

• DNA that can make a protein.
• The chemical factor that determines a trait.

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• Homologous chromosomes have genes that control
  the same trait but come from different sexes

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Allele

• Different forms of a gene.
• Ex. dominant or recessive.

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allele

• An alternate form of a gene
• A a
• B b

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Dominant

• Allele that is expressed ( visible
  )over the recessive.

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dominant

• A gene which can express itself when in the
  presence of a recessive

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Recessive

• A gene that is unable to express itself when
  present with a dominant.

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Recessive

• A gene which is unable to express itself when
  with a dominant
• Can only be expressed when homozygous recessive

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Phenotype

• Physical characteristic or expression of a gene

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Phenotype

• The expression of a genotype, what is seen in the
  individual
• eye color
• hair color
• disease present

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Genotype

• The actual genes present.the genetic makeup

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Genotype

• Actual gene present
• Not visible
• AA, Aa, aa

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Genetic Recombination

• Parental genes come together in fertilization to
  reveal new pairings of genes.

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Genetic recombination

• Genes come together in a random fashion as
  chromosomes pair following fertilization

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True breeding

• Alleles are the same both dominant or both
  recessive.
• HOMOZYGOUS

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Homozygous

• Both alleles are the same either both dominant or
  both recessive

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Hybrids

• Offspring of parents with different traits or
  alleles
• HETEROZYGOUS

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Heterozygous

• Both of the alleles are different
• One dominant and one recessive

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Punnett Square

• Shows the various gene combinations between
  individuals.