6.2 DNA - Alleles

Gene

• segment of DNA that codes for particular type of protein

• Together, the inherited genes determine characteristics we develop

• Some traits determined by single gene (mice fur colour, red/ green colour blindness in humans)

• Most characteristics are determined by several different genes that interact with each other

  • height

    • Example of multiple forms of same protein

• Different versions of the same gene are called alleles

• As we have 2 copies of every gene from parents, we have 2 alleles of each gene

  • could be same, or different 2 alleles

    • if same allele, we would be homozygous for that allele

    • If different alleles, we would be heterozygous for that allele

Dominant / Recessive

• Dominant allele will always be expressed

• Recessive is only expressed if an individual is homozygous recessive (has 2 copies of recessive allele)

Homozygous / Heterozygous

Homozygous - having 2 identical alleles of a particular gene

Heterozygous - having 2 different alleles of a particular gene

Genotype / Phenotype

• Genotype is entire collection of alleles we have

  • Different individuals with different alleles have different genotypes & so different genetic material

• Phenotype is characteristics you get from genotype

  • If heterozygous individual & homozygous individual have same characteristic, they have same phenotype