Sunday, October 18, 2009

[Biology Form 5] Characteristics - Laws of Inheritance

Gregor Mendel is highly attributed for his work in genetics. The father of genetic studied the inheritance of characteristics from the common garden pea plant, Pisum sativum, and was credited with discovering the two basic laws of inheritance: the law of segregation and the law of independent assortment.
  1. All characteristics are controlled by pair of genes.

  2. a) A characteristic is a distinctive inherited feature. Three examples of characteristics in:
    • Plants - Height of plant, seed colour, seed shape.
    • Animals - Eye colour, height, colour of fur/skin.

    b) A trait is a variant for each characteristic. Two examples of traits in:
    • Plants - Yellow colour of seed, wrinkled seed shape.
    • Animals - Grey fur colour, green eyes.

  3. A gene is a specific segment of DNA.

  4. Two genes, each found on the same locus along a pair of homologous chromosomes, are needed to determine one characteristic.

  5. Each member of the pair of genes determining a particular characteristic is called an allele.

  6. A dominant allele is one which, when present, even singly, is strong enough to determine the phenotype. The two following conditions can allow a dominant allele to express itself in the phenotype.
    a) Homozygous dominant: two dominant alleles present.
    b) Heterozygous dominant: one dominant allele and one recessive allele present.

  7. A recessive allele can only determine a phenotype if it is present on both homologous chromosomes.

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