monohybrid cross

• mendel performed experiments on the Pea plant
• scientific name of the pea plant is pisum sativum
• the reason he selected the pea plant is because:

  1. pea plant has many distinct contrasting traits
  2. it produces large number of seeds and completes life cycle in one season
  3. flowers show self pollination which means they are true breeding
  4. it is easy to cross pollinate the pea flowers
  5. the hybrids produced were fertile
• contrasting traits of the pea plant

  
• heterozygous = hybrid
• true breeding = homozygous
• homozygous = both alleles are same
• homozygous dominant = purebred
• phenotype - physical appearance
• genotype - genetic makeup
• monohybrid cross - only one trait being studied at a time
• homozygous recessive = purebred
• monohybrid cross = crossing two plants that differ by only one trait (one gene)
• heterozygous = different alleles
• recessive traits only appear when there are two copies of that gene (homozygous)
• dominant phenotypes always appear in the F1 generation
• incomplete dominance occurs when neither parent has a fully dominant or recessive phenotype, so their offspring will have an intermediate phenotype.
• F2 generation is where we see all possible genotypic combinations
• F1 generation = first filial generation, offspring from the parental generation
• Punnett square is used to predict genotypes and phenotypes of offspring
• How many types of gametes are possible from a diploid organism having genotype AaBBCC?

  only the heterozygous one is used to determine the number of gametes so, Aa will be used in the formula 2^n=2^1=2 so 2 gametes
• Law of dominance:

  1. every character is controlled by discreet units called factors
  2. factors occur in pairs
  3. in a pair of dissimilar factors the one which is expressed is dominant and the one which is not is recessive.
• law of segregation states that during gamete formation (meiosis) the two alleles separate into different cells so that every gamete receives only one copy of each gene
• Incomplete dominance occurs when neither factor is completely dominant or recessive over the other
• Codominance occurs when both alleles are equally expressed
• in the monohybrid cross mendel crossed a homozygous tall (TT)and homozygous dwarf plant(tt) which resulted in the F1 progeny phenotype as tall while the genotype was (Tt, heterozygous).
• then the F1 progeny was self pollinated to produce F2 generation in which the phenotype of was 3 tall plants and 1 short plant. out of which one was homozygous tall(TT) and 2 heterozygous tall(Tt) and one homozygous dwarf(tt).
• The phenotypic ratio of the monohybrid cross was 2:1 while the genotypic ratio was 1:2:1