GENETICS AND EVOLUTION
INHERITANCE AND VARIATION
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Question
[CLICK ON ANY CHOICE TO KNOW THE RIGHT ANSWER]
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Fertilisation is random
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Fertilisation is inaccurate
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Punnet squares are not reliable
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Different alleles appear during fertilisation
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Detailed explanation-1: -However, predicted phenotype ratios among offspring are not always achieved. This can be for a variety of reasons, for example the sample size being too small or the ratios based on fertilisation (which is a random process).
Detailed explanation-2: -In short, whenever two genes are linked because of their location on a chromosome, their alleles will not segregate independently during gamete formation. As a result, test crosses involving alleles of linked genes will yield phenotypic ratios that stray from the classic Mendelian ratios.
Detailed explanation-3: -The expected genotype ratio when two heterozygotes are crossed is 1 (homozygous dominant) : 2 (heterozygous) : 1 (homozygous recessive). When a phenotypic ratio of 2 : 1 is observed, there is probably a lethal allele.
Detailed explanation-4: -There are many possible explanations for deviations from expected ratios. Sometimes these deviations are due to sampling effects, in other words, the random selection of a non-representative subset of individuals for observation.