Question

In a classic experiment using pea shape, Mendel conducted two separate genetic crosses. In the first cross the parent plants were “true breeding” for pea shape; one had round peas ( R )and the other had wrinkled (r). The first cross produced a filial 1 generation of all round peas. In the second cross, Mendel bred plants from the filial 1 generation. This cross produced different results. Out of approximately 1000 plants, about 75% were round and 25% were wrinkled.

From these experiments, Mendel developed four hypotheses. They include all BUT
A one heritable factor may be dominant and mask the other factor.
B any organism that "shows" a heritable factor must be homozygous.
C an organism has two "heritable factors", now called genes, one from each parent.
D a sperm or egg carries only one heritable factor for each trait in the offspring.

Answer 1

B

Mendel did not propose that a visible trait must mean the organism is homozygous. He proposed dominance (A), two factors (alleles) per trait (C), and segregation of alleles into gametes (D). The F1 round peas were heterozygous (Rr), which produced the 3:1 ratio in the F2 when R and r segregated.