Question

Complete dominance is absent in
A. Pisum sativum
B. Mirabilis jalapa
C. Lathyrus odoratus
D. Oenothera lamarckiana

Answer 1

Hint: Complete dominance is a type of dominance in which the dominant allele completely masks and does not allow the recessive allele to express its traits. Only the dominant allele is completely expressed and shows its traits. Mostly, it occurs in heterozygous conditions.

Complete answer:
The relationship between the alleles of a gene in which on the locus one allele is expressed over the other is called dominance. The dominant one is the first allele and the recessive one is the second allele. Mendelian inheritance is explained by the concept of dominance.

The effect of an allele that is dominant and is of a heterozygous genotype completely masks the effect of another allele. The allele that is masked is called the recessive allele. Generally, it is the condition in which the dominant gene completely masks the effect of the recessive gene in the heterozygous condition. Genotype ratios and phenotype ratios are important to proceed the complete dominance.
The phenotype of the heterozygote is indistinguishable from that of the dominant homozygotic process is best explained by complete dominance.

For example, the seed shape in peas. Peas can be round or wrinkled. In this case, three combinations of genotypes are probable: RR and rr are homozygous and Rr is heterozygous. Round peas are present in RR individuals, whereas wrinkled peas are present with rr individuals. In Rr individuals, the R allele is the dominant allele and thus it masks the effect of the r allele which is recessive, so these individuals also have round peas.

Whereas, in Mirabilis jalapa, incomplete dominance can be observed. Incomplete dominance is also known as partial dominance or semi-dominance. This type of dominance occurs when the phenotype of the heterozygous genotype is different from and often intermediate to the phenotypes of the homozygous genotypes.

Hence, the correct answer is option B.

Note: Monohybrid cross is the most important principle in which complete dominance occurs. Mendel has proposed three laws in genetic, namely;
a. Law of dominance.
b. Law of segregation and
c. Law of independent assortment.