An organism is heterozygous for two genes. These two genes make up part of the same DNA molecule.
For one gene, E represents the dominant allele, e represents the recessive allele.
For the other gene, R represents the dominant allele, r represents the recessive allele.
Assuming there is no mutation, at the end of a mitotic division producing two cells which row(s) is/are possible?
A. row 6 only
B. rows 4 and 5 only
C. row 1 only
D. rows 2 and 3 only
E. rows 6 and 7 only
The correct answer is E.
What is mitosis ?
To answer this question, we need to know that mitosis is.
It is a type of cell division that begins with the duplication of the DNA.
Furthermore, the daughter cells are genetically similar to the mother cell : a gene A with the allele y is transmitted to the daughter cells.
Its purpose is to ensure cell multiplication for tissue repair or growth.
In other words, from a single diploid mother cell (2n), 2 diploid daughter cells (2n) are obtained.
A diploid cell has 2 complete sets of chromosomes, usually written as being a 2n cell, as opposed to a haploid cell, that only has 1 set of each chromosome, and written as a n cell.
What is heterozygous ?
To understand this concept, let’s take the same random gene A :
Because humans are diploid, they will have 2 alleles (versions) of the same gene
A is a gene that has 2 alleles : Ay and Az
Heterozygous is when the 2 alleles of a gene are different, which can be represented by (Ay/Az)
On the other hand, homozygous is when when the 2 alleles of a gene are similar, which can be represented by (Ay/Ay)
Now, let’s answer the question :
It is said that the organism is heterozygous for both genes, and that it goes into mitosis
There are 2 genes :
- one that has the alleles E and e
- on that has the alleles R and r
All mitotic progeny are genetically similar
From what we just said, we can say that the daughter cells will have 4 different allele combinations possible :
- E and R on one molecule
- e and r on the other
- E and r on one molecule
- e and R on one molecule