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Mendel and Meiosis

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Title: Mendel and Meiosis


1
Mendel and Meiosis
2
Mendels Laws of Heredity
  • Heredity passing on traits from parents to
    offspring
  • Gametes sex cells they have a haploid number
    of chromosomes they have only ½ as many
    chromosomes as normal cells or one copy of each
    gene

3
  • Fertilization when a male gamete unites with a
    female gamete
  • Zygote fertilized cell
  • Gene - chemical factors that determine traits
  • Alleles different forms of a gene

4
Mendels experiments
  • Pea plants are self-pollinating male and female
    parts in the same flower
  • Only studied one trait at a time and subjected
    his data to statistical analysis
  • First cross was between two purebreds or true
    breeding plants (tall x short)
  • All offspring were tall

5
Mendels experiments (cont)
  • The result was a hybrid with one allele for tall
    and one for short
  • Then, Mendel allowed the hybrids to
    self-pollinate (hybrid x hydbrid)
  • Second generation offspring were ¾ tall and ¼
    short

6
Rule of Unit Factors
  • each organism has two factors/alleles for each
    trait the two alleles are located on different
    copies of a chromosome, one from each parent

7
Rule of Dominance
  • in a hybrid where only one trait can be observed,
    that trait is said to be dominant over the trait
    that is not visible the other trait is said to
    be recessive

8
Law of Segregation
  • In sexually reproducing organisms, offspring have
    one gene from each parent, these are segregated
    in gamete (sex cell) formation

9
Law of Independent Assortment
  • genes for different traits are inherited
    independently of each other

10
Phenotypes and Genotypes
  • Phenotype physical appearance of a trait in an
    organism
  • Genotype gene/allele combination of an organism
  • Homozygous organism that has two of the same
    alleles for each trait
  • Heterozygous organism that has two different
    alleles for each trait

11
Crosses
  • Monohybrid cross Mendels first crosses
    studying one trait and its inheritance at a time
  • Dihybrid cross studies the relationship between
    the inheritance of 2 traits

12
Punnett Squares
  • Monohybrid cross (one trait) is a two by two grid
  • One parents genotype is listed at the top one
    allele per column
  • The other parents genotype is listed along the
    side one allele per row
  • Squares are filled in with one allele from one
    parent (top) and one from the other (side)

13
  • Dihybrid cross (two traits) is a four by four
    grid
  • Very similar to the monohybrid cross, but you
    must account for all possible gene combinations
    from parents

14
probability
  • chance that you will get one result over another
  • Punnett squares are a way to determine
    probability
  • the more data you have, the closer to the
    predicted probability your results should be

15
Meiosis
16
Genes and chromosomes
  • Diploid 2n - cell/organism that contains two of
    each type of chromosome (one copy from each
    parent)
  • Haploid n - cell (sex cell) that contains only
    one copy of each type of chromosome

17
  • Homologous chromosomes two chromosomes of the
    same type or a pair of similar chromosomes in a
    diploid cell
  • Meiosis process of cell division that reduces
    the number of chromosomes in a cell from diploid
    to haploid used for reproduction
  • sperm male gametes
  • egg female gametes

18
Meiosis I similar to mitosis
  • EXCEPT
  • In Prophase I, homologous chromosomes come
    together as tetrads
  • during metaphase I, tetrads line up along the
    center of the spindle
  • the tetrad is pulled apart during anaphase I, so
    the homologs are now separate from each other in
    two different cells

19
  • when tetrad are formed, crossing over may happen
    this basically means that homologous chromosomes
    could trade ends

20
Meiosis II
  • no chromosome replication before meiosis II
  • chromosomes line up along center of spindle in
    metaphase II
  • sister chromatids are pulled apart in anaphase II
  • result of both divisions together is 4 haploid
    cells

21
Genetic Recombination
  • Crossing over just refers to trading ends
    between homologous chromosomes during the tetrad
    grouping in prophase I and metaphase I
  • Also caused by the law of independent assortment
    different chromosomes will be segregated
    independently of one another

22
Nondisjunction
  • when chromosomes fail to separate properly during
    meiosis
  • Monosomy lacking a chromosome
  • Trisomy extra chromosome
  • Tetrasomy 2 extra chromosomes

23
Polyploidy
  • Organisms have more than 1 set of chromosomes
  • Rare in animals usually results in death or, in
    humans, mental retardation
  • Plants have a higher occurance rate can create a
    better or healthier plant, commercially or
    biologically

24
Gene Linkage and Maps
  • Genes on the same chromosome are said to be
    linked
  • If they are far apart on the chromosome, crossing
    over is more frequent
  • genes maps are charts of chromosomes with gene
    locations on them (ex. Human Genome Project)
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