Meiosis and Mendel

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Meiosis and Mendel
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Quiz 1

• Name two stages of mitosis
• What does MPF stand for?
• What scientist gave us the genetic principle of
  independent assortment?
• What model genetic organism did Thomas Hunt
  Morgan use?
• True or False- Sister chromatids typically carry
  identical genetic information
• True of False- Homologous chromosomes typically
  carry identical genetic information

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Overview

• History of Inheritance
• Meiosis
• Mendelian Genetics

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History of Inheritance

• Blending Inheritance?
• Do chromosomes contain hereditary information?
• August Weismann
• Hypothesized that a chemical signal in the
  nucleus of the cell contained hereditary
  information
• How is hereditary material kept constant?

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Meiosis Summary

• produces 4 cells rather than one
• results in a reduction in the number of
  chromosomes per cell
• results in increased genetic variety by alignment
  of homologues and crossing over

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What types of cells undergo meiosis?

• Somatic Cells- undergo mitosis only
• diploid
• Germ Cells
• produce gametes
• haploid
• ovum from ovaries
• sperm in testes

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Parthenogenesis

• The development of an unfertilized egg into a
  fully-formed, new individual
• examples?
• Why bother with sex?

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Introduction to Genetic Terms

• Genotype
• Phenotype
• Heterozygous
• Homozygous
• Dominant
• Recessive
• Allele

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The Secret to Mendels Success

• true-breeding plants, discontinuous variation
• controlled crossings

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The Secret to Mendels Success

• analyzed large numbers of offspring, mathematical
  analysis
• simplified by observing one trait at a time
• analyzed large numbers of offspring

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Monohybrid Cross

• All of the F1 showed one of two traits
• Principle of Dominance
• If F1 self-pollinate, dominantrecessive 31 in
  F2
• Principle of Segregation

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More Evidence for Segregation

• Mendel performs a backcross

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Mendels Dihybrid Cross

• Factors controlling different traits are
  inherited independently of one another
• Principle of Independent Assortment

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Mendel and the Chromosomal Theory of Inheritance
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Chromosomal Theory of Inheritance

• Mendels determinants are found on chromosomes
  and the behavior of chromosomes during meiosis
  accounts for his principles

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Why Fruit Flies?

• two weeks to grow from eggs to adults
• one female lays hundreds of eggs
• easy to maintain
• structurally complex organism
• 4 pairs of chromosomes

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Sex and Chromosomes

• Autosomes
• Sex Chromosomes
• X and Y
• XX mammalian females
• XY in mammalian males

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Sex Linkage in Drosophila melanogaster Bolsters
Suttons Theory

• Crossed white-eyed male to red-eyed female, all
  F1 have red eyes
• Allowed F1 siblings to mate, 31
  red-eyedwhite-eyed
• Backcross confirms Morgans hypothesis

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Why is independent assortment not valid if two
genes are linked?
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Explaining Morgans Result

• Why are the genotypes of the parents
  over-represented in the offspring of the
  backcross?
• What about the exceptions?
• Linkage groups correspond to each pair of
  chromosomes

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Genetic Analysis in Humans