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2011-04-10 09:38:19
biology genetics

BSCI106 - Borgia, Lecture 8,
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  1. diploids
    two sets of chromosomes/genes
  2. homozygous genotypes
    • have two copies of the same allele
    • ex: AA
  3. heterozygous genotypes
    • have two different alleles
    • ex: Aa
  4. dominance
    the same phenotype can result from different genotypes (AA and Aa) that have one copy of the dominant allele (A)
  5. Gregor Mendel
    • “Father of genetics”
    • Discovered basic laws of eukaryote genetics by following traits from crosses of plants
    • People thought that he might’ve made up the data, but this was proven wrong
  6. Genetic Inheritance
    • It was known that both parents contribute traits
    • to offspring
    • Before Mendel’s time it was believed that the units of inheritance blended and could never be separated
  7. Mendel proposed that:
    • Units of inheritance (genes) are particulate
    • There are two copies (alleles) of each gene in every parent
    • One of those alleles is in each sperm or egg
  8. Mendel’s first law of segregation
    During gamete formation, one allele for a trait is present in egg or sperm (at a particular locus) and each allele has an equal chance of appearing in offspring
  9. Mendel’s Second Law of independent assortment
    From studies of the simultaneous inheritance of two characters, Mendel concluded that alleles of different genes (loci) assort independently
  10. Determining dominance
    • Mendel could determine if a plant with the dominant
    • phenotype was homozygous or heterozygous by backcrossing with the recessive
    • phenotype
  11. Mitosis
    producing genetically exact copies
  12. Meiosis
    producing genetically different haploid descendent cells
  13. prophase
    chromosomes condense and move towards the middle of the cell
  14. Metaphase
    chromosomes move to the equatorial plate, then centromeres holding the chromatid pairs together separate
  15. Anaphase
    each daughter chromosome migrates to its pole along the spindle fiber/microtubule track
  16. Telophase
    the chromosome becomes less condensed. The nuclear envelope and nucleolireform, there is cytokinesis (cell division) producing two identical cells
  17. Chiasma
    the point of contact between paired chromatids during meiosis, resulting in a cross-shaped configuration and representing the cytological manifestation of crossing over like the letter X
  18. crossing over
    • Occurs during prophase during meiosis 1
    • Crossing over allows for missing genes among homologous (parental) chromosomes
  19. Meiosis 1: the first division
    • Prophase 1 – homologous chromosomes pair (forming
    • a tetrad)
    • Chromatid segments are exchanged by crossing over (at chiasma)
    • New chromosomes are created
  20. Important Results of Crossing Over
    • Crossing over breaks up linked loci allowing
    • independent assortment within a chromosome
    • It also allows beneficial alleles on different homologs to be on the same chromosome
    • Crossing over allows the production of chromosomes without deleterious mutations
  21. Crossing Over in Meiosis I
    It’s a common process and it produces recombinant chromosomes that combine genes from the mother and father to form new chromosomes
  22. Meiosis II: The reduction division
    • The sister chromatids separate
    • No DNA replication precedes this second division
    • resulting in haploid daughter cells
    • In sperm production there are 4 daughter cells.
    • In egg production there is a single cell with polar bodies
  23. Meiosis I gives rise to two lines of cells that then go
    through Meiosis II. There is no duplication of DNA between these divisions
  24. Meiosis: two aspects to genetic recombination that areimportant in generating new sexual genotypes
    • 1)The random selection of maternally and
    • paternally derived homologs contributes to genetically variable daughter cells
    • 2) Crossing over produces novel (recombined)
    • chromosome types
  25. Meiotic errors – nondisjuction
    • Sometimes one member of a homologous pair of
    • chromosomes fails to separate and both go to the same pole
    • One gamete has an extra chromosome and another
    • is lacking that chromosome