Question

Calculate the percentage of pure line individuals from a cross between AaBbCcDdee $\times$aabbccddee
A. $50\mathrm{\%}$
B. $25\mathrm{\%}$
C. $12.5\mathrm{\%}$
D. $6.25\mathrm{\%}$

Answer 1

Hint: The monohybrid cross is made when the only single character needs to be determined. A dihybrid cross is made when two characters are studied together in an organism. To know the expected offspring produced from the cross Punnett square is made and the results are studied from it.

Complete answer:
The gametes when present in pure condition like ‘AA’ or ‘aa’ then they are said to be in homozygous dominant and homozygous recessive respectively. If they are present in ‘Aa’ condition then they are said to be in the heterozygous condition. The pure line individuals are those which have either the homozygous dominant gene or homozygous recessive gene.
There are five traits mentioned in the cross that needs to be done. So, let us take a single trait and perform a monohybrid cross to know the amount of pure line individuals being obtained from them.
Let us take Aa and aa;

	A	A
A	Aa	Aa
A	Aa	Aa

The highlighted part of the table shows the pure-line offspring that are obtained from the cross. So, out of four offspring, only two show the pure line. Similar results would be obtained from the cross made between Bb and bb, Cc and cc, and Dd and dd. But the cross of ee and ee would obtain all individuals as pure. The number of pure-line individuals is:
${\displaystyle \frac{2}{4}}\times {\displaystyle \frac{2}{4}}\times {\displaystyle \frac{2}{4}}\times {\displaystyle \frac{2}{4}}\times 1$=${\displaystyle \frac{16}{256}}$
This obtained amount when multiplied by 100, we obtain a percentage.
$\Rightarrow$ ${\displaystyle \frac{16}{256}}\times 100$= $6.25\mathrm{\%}$
So, the correct answer is $6.25\mathrm{\%}$,
So, the correct answer is “Option D”.

Note: Mendel knew about the dominant relationship that each allele possessed for each trait. But to determine any dependence of two traits on each other dihybrid cross was made. A Dihybrid cross is made for those organisms who have an identical hybrid of two traits.