Genetics

• Monohybrid cross


  Involves a single parent, organisms heterozygous for one character being studied
• Dihybrid cross


  Involves two parents, organisms heterozygous for two characters being studied
• Monohybrid cross results in a 9:3:3:1 ratio, dihybrid cross gives a 3:1 ratio
• Gregor Mendel's most significant conclusion

  Traits are inherited in discrete units and are not the result of "blending"
• An individual with genotype AaBbCCDdEE can produce 8 unique gametes through independent assortment
• Independent assortment


  The behavior of two or more genes relative to one another
• Mendel's law of independent assortment is accounted for by the alignment of pairs of homologous chromosomes along the middle of the cell during meiosis I
• Mendel's law of segregation is accounted for by anaphase I of meiosis
• A sexually reproducing animal with genotype HhTt can produce gametes with genotype HT
• Mendel's explanation for traits disappearing in F1 and reappearing in F2

  Traits can be dominant or recessive, and the recessive traits were "hidden" by the dominant ones in the F1
• Mendel's observation of the segregation of alleles in gamete formation has its basis in anaphase I of meiosis
• Mendel's law of independent assortment has its basis in the alignment of pairs of homologous chromosomes along the middle of the cell during meiosis I
• Punnett square showing genotypes and phenotypes in an F2 generation

  • 1, 2, 3, 4
• An organism with 4 alleles for a single gene can produce 4 different types of gametes
• Reason all F1 offspring in Mendel's pea crosses looked like one parental variety


  One allele was dominant
• The green allele for seed color in peas is recessive to the yellow allele
• The probability that the first child of two carriers of the recessive albinism trait will have albinism is 1/4
• If one parent is homozygous recessive for albinism and the other is heterozygous, the probability of having an albino child is 1/2
• Albinism is a recessive trait, black coat color in guinea pigs is dominant
• When gray-seeded pea plants are crossed, the expected F2 ratio is 3 gray : 1 white
• Heterozygous


  Having two different alleles for a particular gene
• Homozygous dominant


  Having two copies of the dominant allele for a particular gene
• Homozygous recessive


  Having two copies of the recessive allele for a particular gene
• Black guinea pig crossed with albino guinea pig


  • Produced 12 black offspring
• Albinism


  Recessive trait
• Black


  Dominant trait
• When the albino was crossed with a second black animal, six blacks and six albinos were obtained
• Gray seed color in peas is dominant to white
• Mendel's experiments with gray and white pea seeds

  1. Plants with gray seeds crossed among themselves

  2. Progeny: 302 gray and 98 white
• Genotype of parents


  Gg × Gg
• When Mendel crossed yellow-seeded and green-seeded pea plants, all the offspring were yellow-seeded
• When he took these F1 yellow-seeded plants and crossed them to green-seeded plants, the expected genotypic ratio was 1:1
• Black fur in mice

  Dominant to brown fur
• Short tails in mice

  Dominant to long tails
• The fraction of progeny of crosses BbTt × BBtt expected to have black fur and long tails is 1/2
• In pea plants, the tall phenotype is dominant to the dwarf phenotype
• If a heterozygous pea plant is crossed with a homozygous tall pea plant, the probability that the offspring will be dwarf in size is 0
• The probability of producing the genotype AABBCC in a cross of individuals who both possess the genotype AaBbCc is 1/64
• Given the genotypes AABBCc × AabbCc, the proportion of the progeny expected to phenotypically resemble the first parent with the genotype AABBCc is 3/4
• Addition rule of probability


  The probability that either one of two independent events will occur