What does Mendel's Law of Segregation state?

• A. Alleles segregate during gamete formation; offspring inherit one allele from each parent; typical phenotypic and genotypic ratios for heterozygous crosses are 3:1 and 1:2:1, respectively.
• B. DNA is transcribed into RNA and translated into protein; replication is separate.
• C. Genes on the same chromosome never show recombination.
• D. Nonrandom mating affects allele frequencies.

Answer: (A)

Alleles separate into separate gametes during meiosis, so offspring inherit one allele from each parent. This means a parent that is heterozygous for a gene (Aa) can produce two kinds of gametes, carrying A or a, with equal probability. When fertilization occurs, the gametes unite randomly, giving offspring genotypes in a 1:2:1 ratio (AA:Aa:aa) and, if one allele is dominant, phenotypes in a 3:1 ratio (dominant:recessive). For example, crossing Aa with Aa yields four equally likely offspring: AA, Aa, Aa, and aa, which translates to three showing the dominant trait and one showing the recessive trait. This pattern is the essence of Mendel's Law of Segregation: each parent passes one allele per gene to the offspring, and the two alleles separate during gamete formation.

Other statements refer to different genetics concepts: the flow of genetic information (DNA to RNA to protein) is about gene expression, not inheritance; recombination among genes on the same chromosome can occur, so linked genes are not strictly non-recombinant; and nonrandom mating affects allele frequencies in populations, not the segregation of alleles during gamete formation.