Genotype — Science definition

Defined in 2 courses:

Where it is taught

In use

An organism's genotype is the pair of alleles it carries for a gene, written as two letters.

Inheritance, Probability & Punnett Squares

Genotype probabilities are 1/4, 1/2, 1/4; under complete dominance the phenotype expectation is 3/4 dominant and 1/4 recessive.

Mendelian Genetics

Questions using genotype

Problem 1

Which genotype is heterozygous at the fictional region?
  1. AA
  2. aa
  3. Aa
  4. A alone as a full diploid genotype
Answer and explanation

Aa

Aa contains two different versions at the studied region.

Problem 2

If B (brown) is dominant over b (white), an organism with genotype Bb will have which phenotype?
  1. A blend of brown and white
  2. It cannot be determined
  3. Brown
  4. White
Answer and explanation

Brown

One dominant B is enough to produce the brown phenotype, so Bb is brown.

Problem 3

In a hypothetical complete-dominance model, cross Aa with Aa. Find genotype probabilities. Explain the reasoning in your own words.
Answer and explanation

¼ AA, ½ Aa and ¼ aa; each offspring is a new probability event.

Each parent contributes A or a with probability one half.

The four equally likely combinations are AA, Aa, aA and aa.

Response criteria

  • Use the stated conditions.
  • Show the evidence or calculation.
  • Explain the conclusion and any stated limitation.

Problem 4

Under complete dominance, Aa×aa produces independent offspring with equal genotype probabilities. Find the expected aa count among 60 and the probability that the first three are all Aa.
Answer and explanation

Expected aa count is 60×1/2=30. The probability of three Aa outcomes is (1/2)³=1/8. Neither expectation forces a specific finite family outcome.

Expected aa count is 60×1/2=30. The probability of three Aa outcomes is (1/2)³=1/8. Neither expectation forces a specific finite family outcome.

Response criteria

  • Use the stated measurements or conditions, with correct units.
  • Connect the result to the biological mechanism or evidence relationship.
  • Identify the assumption, model limit or further evidence requested.

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