A certain type of plant is only tall when it has a heterozygous genotype. If two heterozygous plants are crossed, what is the probability their offspring will also be tall?
Correct answer: B. 50%
- A. 25%
- B. 50%
- C. 75%
- D. 1%
Explanation
If a certain type of plant is only tall when it has a heterozygous genotype, it suggests that the tall trait is dominant and the short trait is recessive. Let's use "T" to represent the dominant allele for tallness and "t" to represent the recessive allele for shortness. When two heterozygous plants (Tt x Tt) are crossed, each parent contributes one allele for tallness (T) and one allele for shortness (t). The possible genotypes of the offspring are: TT (tall), Tt (tall), Tt (tall, tt (short) Out of these four possible genotypes, three of them result in the tall phenotype (TT, Tt, Tt). Therefore, the probability that the offspring will be tall is 3 out of 4 possible outcomes. However, since this plant can only be tall if heterozygous, then 2/4 i.e., 50% of the offsprings will be tall.
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Mendel's laws explain segregation, independent assortment and the prediction of genetic ratios using alleles, genotypes and phenotypes. The chapter also covers linked genes, recombination and crossing over during meiosis, then applies pedigree reasoning to X-linked recessive traits, which show different inheritance patterns in males and females.
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