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OCR A Biology

Homo State Genetic Hetero Phenotype Cross Monogenic Rules

Monogenic inheritance concerns the inheritance of a single gene, following a defined process for genetic crosses using Punnett squares. Crosses between homozygous parents produce heterozygous offspring, while crosses between heterozygous parents yield offspring with a 25% chance of displaying the recessive trait.

Monogenic inheritance describes the inheritance pattern of a single gene. Genetic crosses follow specific steps: state parent phenotypes and genotypes, list gametes, use a Punnett square to show offspring genotypes, and determine offspring phenotypes. Crossing a homozygous dominant with a homozygous recessive parent yields all heterozygous offspring with the dominant phenotype. Crossing two heterozygous parents results in a 1:2:1 genotype ratio (25% homozygous dominant, 50% heterozygous, 25% homozygous recessive), leading to a 3:1 phenotype ratio.

Front Genetic cross - what is monogenic inheritence, rules of genetic crosses (using examples of homo and hetero crosses)
Back
  • monogenic inheritence is where inheritance of single gene shown
  • Rules of genetic cross
    • state phenotype of both parents
    • state genotype of both parents (e.g Aa)
    • state gametes of each parent (e.g A and a and circle them)
    • punnet square and state proportion of each genotype
    • state corresponding phenotype for all possible genotypes
  • Homozygous and heterozygous crosses
    • homo dominant and homo recessive form heterozygous offspring (100% has phenotype of dominant allele)

    • take 2 hetero offspring, and you get 25% homo dominant, 50% hetero and 25% homo recessive, so 25% chance of recessive trait being displayed

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