Question

Two genes R and Y are located very close on the chromosomal linkage map of the maize plants. When RRYY and rryy genotypes are hybridized, the ${f}_{2}$ segregation will show:
(a) Segregation in the expected 9 : 3 : 3: 1 ratio (b) Segregation in 3 : 1 ratio (c) Higher number of parental types (d) Higher number of the recombinant types.

Answer 1

Linkage is the disposition of genes found within the chromosome to remain intact and transfer to the subsequent generation, Linkages assist in maintaining a newly improved variety, crossover, on the other hand, forms as a source of variations to supply new varieties.

Complete step by step answer:
When the linked genes are situated quite close, the probabilities of the crossover are highly reduced. Due to this, a large number of parental gametes are created and only some recombinant gametes are formed. This leads to a higher number of parental types in ${f}_{2}$ generation as compared to recombinants.
Since the R and Y genes are closely placed on the chromosome and show linkage; they will not assort independently and more parental types (RRYY and rryy) and fewer recombinants (Ry, rY) will be formed. Two pairs of genes showing independent assortment give 9 : 3: 3: 1 ration in ${f}_{2}$ progeny. Phenotypic ratio 3:1 is obtained for an allele of a gene showing segregation (monohybrid cross, the question is about dihybrid cross).
Additional information:
Independent assortment is the segregation of things for a trait independent of other factors throughout gamete formation followed by their irregular change in progeny thereby producing both parental and new combinations. The linkage is the tendency of closely placed genes on a chromosome to remain together during inheritance; it produces more parental combinations and less/no new combinations of the gene. Genes present together on a chromosome show linkage and do not follow independent assortment resulting in more parental types and fewer recombinants in the progeny.
So, the correct answer is '(c) Higher number of parental types'.
Note: Linkage was discovered by the British geneticist William Bateson, Edith Rebecca Saunders, and Reginald Punnett. Genes present together on a chromosome show linkage and do not follow independent assortment resulting in more parental types and fewer recombinants in the progeny. Linkage helps to stay the genes together within the same chromosome, whereas recombination is the process where DNA segments separate during crossover in meiosis.