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2.9 solve problems involving monohybrid crosses using Punnett squares or other appropriate techniques

solve problems involving monohybrid crosses using Punnett squares or other appropriate techniques

A monohybrid cross involves the inheritance of one characteristic. All problems apply Mendel’s basic laws of inheritance. The following is typical of a problem that uses Punnett squares to solve problems involving monohybrid crosses.

Worked example

In peas, the gene for the characteristic tall (T) is dominant over the gene for a short plant (t). If a homozygous tall plant (TT) is crossed with a heterozygous tall plant (Tt), what will be the possible phenotypes of the offspring?

A Punnett square is a diagrammatic method of indicating the possible offspring produced from a particular cross.

Punnett square

In the sample problem, a homozygous tall plant (TT) is crossed with a heterozygous tall plant (Tt), By filling in the squares, it is possible to work out all of the combinations that are likely to occur.

pun2

When you analyse the information in this case, you can predict that 100% of the offspring will be tall plants: 50% are homozygous tall (TT); 50% will be heterozygous tall plants (Tt).

Sample question

In gerbils, agouti (light brown) coat colour is dominant to black coat colour. If a gerbil, which is heterozygous for agouti coat-colour, is crossed with a black-coated mouse, what will be the possible coat colour of the offspring?

Answer

Here are some other useful sites that describe how to solve monohybrid crosses using Punnett squares or other appropriate techniques:

Examples of Punnett squares (external website) Access Excellence>

Mendel’s experiments (external website) Access Excellence

Mendel’s discoveries (external website) Bill Kendrick