What did Mendel's experiments show about blending inheritance?

Answer 1

Blending inheritance was one hypothesis for how traits were passed from one generation to the next. The idea was that if both parents had different traits for a particular character, then the offspring would exhibit a blend of the two traits. For example, if the character in question is flower petal color, and one parent had white flowers and the other had red flowers, the hypothesis of blending inheritance would predict the offspring would have pink flowers, a blend of the two parent traits. In fact, if you cross red and white flowered plants, you do get a pink flower. However, Mendel was able to show that the inheritance of flower color was particulate, not blending, by going one step further and crossing two pink flowered parents. He found the offspring had a ratio of 1:2:1 for red:pink:white, so the granparents' traits were reappearing. This "skipping of generations" was classically Mendelian: the alleles for red and white were both contained in the pink flowers, so that when they were crossed, they were able to be seen in the offspring. In this case, consider that red flowers have the genotype RR (homozygous for R allele), white flowers have the genotype WW (homozygous for the W allele), and pink flowers have the genotype RW (heterozygous), where R and W are two different alleles for flower color. When red (RR) and white (WW) are crossed, the offspring can only get the R allele from the red parent and the W allele from the white parent, so they are all heterozygous (RW), resulting in a pink color. When two pinks are crossed (RW x RW), then each parent can give either a red allele (R) or a white allele (W) to the offspring, resulting in the following equally likely possible combinations: RW, RR, WW, and WR. Since WR and RW are the same (pink), the expected ratio of offspring is 1 RR: 2 RW: 1 WW. This is considered an example of particulate inheritance, not blending inheritance, because the alleles (particles) are being preserved throughout the generations; it is simply the combinations of alleles that give the appearance of a blending inheritance mechanism when red and white are crossed to produce pink. In classical genetics, the first cross between red (RR) and white (WW) was considered the P (parental) generation. The hybrid offspring produced (RW) were considered the first filial generation (F1). Crossing two F1's shows that the inheritance is particulate, by looking at the 1:2:1 ratio in the F2 generation (1 red: 2 pink: 1 white). Mendel was able to deduce the theory of particulate inheritance by carefully following the generations from P to F1 to F2.