Some combinations of recessive alleles cause problems so severe that a fetus may cease to develop. Such lethal allele combinations appear to alter Mendelian ratios because Multiple Choice homozygotes for the lethal allele pass it on to half their offspring. homozygotes for the lethal allele do not appear as a progeny class. carriers do not constitute a progeny class. they do not show a 1:2:1 genotypic ratio.
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Some recessive alleles have such a detrimental effect that they are lethal when present in both chromosomes of a pair. Homozygous recessives cannot survive and die at some point during embryonic development. Suppose that the allele $r$ is lethal in the homozygous $r r$ condition. What genotypic ratios would you expect among the living offspring of the following crosses? a. $\quad R R \times R r$ b. $\quad \operatorname{Rr} \times R r$
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Why is the phenotypic ratio 2:1 the typical ratio for a lethal allele?
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Which of the following statements about the offspring of a cross between two carriers of a lethal recessive gene are true? Please select all that apply: Offspring genotypes follow a 2:1 ratio. The genotypes of the offspring follow the same Mendelian patterns as for crosses not involving lethal genes. Where the wild-type gene is dominant, all surviving offspring have the same phenotype. 50% of live offspring display the heterozygous phenotype.
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