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Animation: A Simplified Cross of Two Characters in Humans

by Pearson
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Suppose two people who are heterozygous for widow's peak and freckles mate. Freckles and a widow's peak are both controlled by dominant alleles, so these heterozygous individuals show both traits. Would it be possible for this couple to have a child that had neither freckles nor a widow's peak? We can use a Punnett square to analyze a two-trait cross as long as the genes for the two traits are on different chromosomes. Keep in mind that during gamete formation, the alleles for a gene segregate and that genes for different traits that are located on different chromosomes will segregate independently of one another. Therefore, four possible allele combinations are produced in the gametes: dominant F dominant W, dominant F recessive w, recessive f dominant W, and recessive f recessive w. Each type of gamete has an equal chance of joining with any other type at fertilization. The relative numbers of phenotypes possible for the next generation are 9 freckled with widow's peak to 3 freckled with straight hairline to 3 no freckles with widow's peak to 1 no freckles with straight hairline. The expected phenotypic ratio is 9 to 3 to 3 to 1.
Suppose two people who are heterozygous for widow's peak and freckles mate. Freckles and a widow's peak are both controlled by dominant alleles, so these heterozygous individuals show both traits. Would it be possible for this couple to have a child that had neither freckles nor a widow's peak? We can use a Punnett square to analyze a two-trait cross as long as the genes for the two traits are on different chromosomes. Keep in mind that during gamete formation, the alleles for a gene segregate and that genes for different traits that are located on different chromosomes will segregate independently of one another. Therefore, four possible allele combinations are produced in the gametes: dominant F dominant W, dominant F recessive w, recessive f dominant W, and recessive f recessive w. Each type of gamete has an equal chance of joining with any other type at fertilization. The relative numbers of phenotypes possible for the next generation are 9 freckled with widow's peak to 3 freckled with straight hairline to 3 no freckles with widow's peak to 1 no freckles with straight hairline. The expected phenotypic ratio is 9 to 3 to 3 to 1.