genetic theory

Cards (114)

  • Gregor Mendel worked with
    pea plants
  • Gregor Mendel discovered
    • dominant and recessive traits
    • concept of gene (heritable factor)
    • formulation of law of inheritance
  • a character is a heritable feature of an individual
  • a trait is a variant form of a character (the phenotype)
  • law of segregation
    2 forms of a gene (alleles) present in each parent segregate independently
  • law of segregation formulated by
    monohybrid crosses
  • monohybrid cross is
    cross between 2 true breeding individuals differing in only one character
  • P generation is the true breeding parents
  • F1 generation are the first generation of hybrids
  • Mendel's observation

    f1 progeny resembled one of the parents
  • Mendel's observation
    • f1 progeny resembled one of the parents
    • f2 generation have both P generation traits
    • ratio in f2 was 3:1
  • heritable factor for the recessive trait had not been lost in the f1 generation, but masked by presence of factor for dominant trait
  • Mendel's model:
    • variation in inherited characteristics are die to the existence of alternative versions of genes (alleles)
    • organism inherits 2 alleles for each character
    • dominant allele always presents itself in the phenotype
    • alleles remain discrete
    • 2 alleles segregate (separate) during gamete formation
  • how to do a testcross?
    Crossing an individual with a homozygous recessive individual
    will determine the genotype of an individual with the dominant phenotype
  • Law of independent assortment
    each pair of alleles assorts independently of each other pair of alleles during gamete formation
  • how did the law of independent assortment occur?

    following the inheritance of 2 characters at the same time
    involves a dihybrid cross
  • results of f2 generation in dihybrid cross

    2 new phenotypes (recombinants)
    9:3:3:1 ratio
  • meiosis occurs in germ line
  • mitosis occurs in somatic cells
  • role of meiosis
    produce haploid gametes and introduce genetic variability
  • homologous pair are individual chromosomes that were inherited from different parents
  • homologous pair=homologues
  • homologous pair have different versions of genes at some of their loci
  • chromatid is 1 of 2 identical strands of a newly replicated chromosome
  • chromatid is different to pair of homologous chromosomes
  • sister chromatids are the 2 identical chromatids held together by _ following replication
    centromere
  • chromosome terminology
    labels:
    A) homologous pair
    B) sister chromatids
    C) centromere
  • Sutton observed:
    • chromosomes occur in pairs in somatic cells
    • chromosome pairs segregate equally into gametes
    • different chromosome pairs assort independently
  • chromosome theory of inheritance
    • genes are located at specific positions (AKA loci) on chromosomes
    • chromosomes undergo segregation and independent assortment
  • genes are units of heredity and determine traits
  • law of segregation explained by 

    each allele on different member of a homologous pair of chromosomes and moves to opposite poles in anaphase I
  • independent assortment of chromosomes means that there are 4 possible combinations of alleles at 2 loci
  • law of independent assortment happens because of 

    the arrangement of chromosomes at metaphase I is random
  • heterozygote is a cell/organism carrying 2 different alleles at a genetic locus
  • sources of genetic variability in sexual life cycles:
    • mutation
    • independent assortment
    • crossing over
    • random fertilisation
  • recombinant phenotype -> phenotype differs from either parent
  • recombinant phenotypes occur from
    independent assortment (for genes on different chromosomes) and crossing over (genes on the same chromosome)
  • when does crossing over occur?
    during pachytene phase of prophase I
  • how does crossing over happen?
    synapsis (pairing of homologous chromosomes)
    synaptonemal complex (zipper) holding homologous chromosomes together in tetrad
  • chiasma is the point which chromosomes make contact during crossing over