alleryStart learning →Why is the Punnett square abandoned for crosses involving four genes?
AThe square cannot show any recessive genotypes
BThe grid would need 256 boxes to be filled in
CThe product rule fails once four genes are used
DThe gametes stop assorting independently at four
Answer & Solution
Correct answer: B. The grid would need 256 boxes to be filled in
1. A heterozygote at four genes makes sixteen different gamete types.
2. Sixteen gamete types along the top and sixteen down the side give a grid of 256 boxes.
3. Entering each genotype by hand would be extremely cumbersome.
4. For more complex crosses the forked-line and probability methods are preferred instead.
5. Independent assortment and the product rule still hold, so the problem is practical rather than biological.
_Source: OpenStax Biology (1st ed., CC BY 4.0), Ch 12 "Mendel's Experiments and Heredity", section 12.3 Laws of Inheritance_
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