Science Biology 🧬🧬🧬

• Law of Independent Assortment

  The distribution or assortment of one pair of factors is independent of the distribution of the other pair
• The law of independent assortment explains why traits are inherited independent of each other</b>
• The law applies to factors (or genes) that are found on separate chromosomes
• Since they are found on separate chromosomes, the segregation of one pair of factors is not affected by the segregation of the other pair
• Therefore, their distribution in the resulting gametes will be at random
• Meiosis I


  Alleles have segregated
• At fertilization, when the gametes formed during gametogenesis by RR and r plants unite, all the zygotes will have the genotype Rr
• All the F1 plants will have a genotype of Rr
• Heterozygous genotype


  An individual with contrasting alleles (a dominant and a recessive allele) for a particular character
• Rr individuals will still produce round seeds because of the presence of the dominant allele R
• Phenotype


  The expression of the genotype of an individual for a particular character
• During anaphase 1 of meiosis I the chromosome pairs separate and move to opposite poles
• A trait is governed by a pair of alleles, each allele is found in a chromosome of a chromosome pair
• When these chromosomes segregate during anaphase 1, the alleles they carry also segregate
• This becomes the chromosomal basis of Mendel's first law (the Law of Segregation)
• Dominant and recessive traits in Pisum sativum (Garden pea)

  • Seed shape: Round (dominant) / Wrinkled (recessive)
  • Seed color: Yellow (dominant) / Green (recessive)
  • Seed coat color: White (dominant) / Colored (recessive)
  • Pod shape: Inflated (dominant) / Constricted (recessive)
  • Pod color: Yellow (dominant) / Green (recessive)
  • Flower position: Axial (dominant) / Terminal (recessive)
  • Stem length: Tall (dominant) / Dwarf (recessive)
• Before Mendel, it was believed that all traits become blended when they mix, like red and blue paints mixing to give violet
• When Mendel crossed pure-breeding pea plants, the offspring did not produce blended or intermediate traits
• Mendel hypothesized that the factors (genes) for a trait segregate or separate during gamete formation
• This is now known as the Law of Segregation
• A pure-breeding, round-seeded pea plant has a genotype of RR, which are identical alleles
• A homozygous individual will produce gametes with identical alleles
• A homozygous dominant individual will produce round seeds, while a homozygous recessive individual will produce wrinkled seeds
• The nucleus is the control centre of the cell.
• Genes are made up of DNA.
• DNA contains genetic information passed from one generation to another.
• Genes are made up of DNA.
• Homozygous individuals have two copies of an allele (either both dominant or both recessive).
• Characters Studied


  • Seed shape
  • Seed color
  • Seed coat color
  • Pod shape
  • Pod color
  • Flower position
  • Stem length
• Mendel hypothesized that there was a factor in the plants which controlled the appearance of a trait. These factors are what we call genes today.
• Mendel hypothesized that traits were controlled by a pair of genes, now called alleles.
• Mendel noted that for each trait he studied, there is one that dominates the other.
• Dominant trait


  Trait that dominates or prevents the expression of the recessive trait
• Recessive trait


  Trait that is either prevented or hidden by the dominant trait
• Dominant and recessive traits are represented by a capital and a small letter, respectively.
• The offspring of the parental cross are called the first filial (F1) generation.
• The F1 generation are also called hybrids because they resulted from a cross between two pure-breeding plants with contrasting traits.
• Results of Mendel's crosses between pure-breeding pea plants

  • Seed shape
  • Seed color
  • Seed coat color
  • Pod shape
  • Pod color
  • Flower position
  • Stem length
• When the plants from the F1 generation were crossed with each other or self-pollinated, the offspring (F2 or second filial generation) were of two types.
• The ratio of round seeds to wrinkled seeds in the F2 generation was 2.96:1 or nearly 3:1.