Question

In a given plant, red colour (R) of fruits is dominant over white fruit (r); and tallness (T) is dominant over dwarfism (t). If a plant with genotype RRTt is crossed with a plant of genotype rrtt, what will be the percentage of tall plants with red fruits in the next generation?
A. 100%
B. 75%
C. 50%
D. 25%

Answer 1

Hint: Genes are the hereditary determination characteristics in an organism. The genes are inheritable and are received from both the parents through the process of sexual reproduction. The genes make up the different sequences of the DNA and it produces the specific genotypes of the organism.

Complete step by step answer: The organism contains two pairs of alleles for a single trait. The allele that occurs and expresses itself phenotypically in the organism is known as dominance trait while the other trait that is unexpressed or hidden by the dominant character is known as recessive gene. Each organism receives a pair of genes from both the parents and exchange takes place during sexual production especially during the production of gametes.
This is shown as a tendency of DNA sequences that are close together on the chromosome. This process of expression and behaviour of genes was first described by Gregor Johann Mendel. His law of dominance explained that the dominant gene expresses itself and it masks the effects of the other gene. The gene which cannot expresses itself in the presence of the dominant gene is known as recessive gene.
In the given question, it is said that tallness (T) is dominant over dwarfism (t) and red colour (R) is dominant over white (r) fruit colour. So, the parents will be RRTt which is a red tall and rrtt which is a white dwarf. P1 or parent generation will be​ RRTt x rrtt. The gametes will be produced after the fertilization are RT, Rt, and rt.
The F1 generation will be two types of genotypes which are RrTt and Rrtt where RrTt is a tall plant, red fruit and Rrtt is dwarf plant, red fruit. The phenotypic ratio will be one tall plant and red fruit and one dwarf plant with red fruit.
Parent generation RRTt x rrtt


Gametes RT Rt rt


F1 generation RrTt Rrtt
So, it can be concluded that there are possibilities to produce tall plants with red fruits is 50% and the dwarf plant with red fruit is 50%.
Therefore, the correct option is option C.

Note: The expression of a gene in a chromosome occurs either in a dominant or recessive way. Dominant gene masks the effect of the other gene which is known as the recessive gene. The recessive gene can only express in the absence of the dominant gene. When in a condition, the parent phenotypes are RRTt and rrtt which after the fertilization produces in the F1 generation offspring with genotypes RrTt and Rrtt. So, the percentage of tall plants with red fruits in the next generation will be 50% .