Tag: classical genetics

Questions Related to classical genetics

A plant of F$ _{1}$-generation is having the genotype "AABbCC". On selfing of this plant, what is the phenotypic ratio in F$ _{2}$-generation?

trihybrid cross classical genetics botany

  1. 3 : 1

  2. 1 : 1

  3. 9 : 3 : 3 : 1

  4. 27 : 9 : 9 : 9 : 3 : 3 : 3 : 1

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Correct Option: A
Explanation:

It is given that the f$ _1$ generation is having genotype AABbCC. The gametes of these parents will contain ABC and AbC alleles. On selfing of this plant, the phenotypic ratio of F$ _2$ generation will be 3:1. Similarly, the genotypic ratio of the F$ _2$ generation will be 1:2:1 where one part will be AABBCC. 2 parts will be AABbCC and 1 part will be AAbbCC.

Thus, the correct answer is '3:1.'

What proportion of the offsprings obtained from cross $AABBCC \times AaBbCc$ will be completely heterozygous for all the genes segregated independently?

trihybrid cross classical genetics botany

  1. $1/8$

  2. $1/4$

  3. $1/2$

  4. $1/16$

Show answer
Correct Option: A
Explanation:

Since one parent is homozygous AABBCC  the genotype formed will be only 1 type i.e. ABC. The other parent is heterozygous for all genes. About 1/8th or 12.5% of total offspring will be heterozygous at all three-locus.


So the answer is '1/8'. 

Find out the number of plants produced with genoptype AabbCc out of 256 seeds collected from $F 2$ progennines of a trihybrid cross ______.

trihybrid cross classical genetics botany

  1. 32

  2. 16

  3. 12

  4. 8

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Correct Option: B

Frequency of recombinant plants in the $F _2$ generation of a trihybrid cross is?

trihybrid cross classical genetics botany

  1. $42.18\%$

  2. $96.8\%$

  3. $56.25\%$

  4. $43.75\%$

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Correct Option: A

The offspring of AA bb $\times$ aa BB is crossed with, aabb. The genotypic ratio of progeny will be

trihybrid cross classical genetics botany

  1. 9 : 3 : 3 : 1

  2. 1 : 2 : 1

  3. 1 : 1 : 1 : 1

  4. 4 : 1

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Correct Option: C
Explanation:

The cross is made between AAbb to aaBB. The progeny formed shows the genotype AaBb. This progeny is crossed with aabb. The genotypes of the progeny are 4 AaBb, 4Aabb, 4aaBb, 4aabb. The genotypic ratio is 1:1:1:1.

So, the correct option is ‘1:1:1:1’.

What percentage of offsprings would have the genotype AA Bb Cc in F2 generation of a trihybrid cross __________.

trihybrid cross classical genetics botany

  1. 12.5%

  2. 6.25%

  3. 25%

  4. 37.5%

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Correct Option: A

In humans, pointed eyebrows (B) are dominant over smooth eyebrows (b). Seemas father has pointed eyebrows, but she and her mother have smooth. What is the genotype of the father?

trihybrid cross classical genetics botany

  1. BB

  2. Bb

  3. bb

  4. BbBb

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Correct Option: B
Explanation:

Since pointed eyebrow (B) is dominant over smooth eyebrows (b). So, Seema can have smooth eyebrows only if her father is heterozygous for the dominant character. If her father has the genotype Bb and her mother is bb (smooth eyebrows) then her genotype will be either Bb (pointed) or bb(smooth eyebrows). If however, her father is homozygous for the trait the gamete being transferred from him will have the allele B and hence the progeny will only show the genotype Bb for pointed eyebrows. So, the correct option is 'Bb'.

On selfing a plant of ${F} _{1}$ generation with genotype "AABbCC", the genotypic ratio in ${F} _{2}$-generation will be

trihybrid cross classical genetics botany

  1. $1:2:1$

  2. $1:1$

  3. $9:3:3:1$

  4. $27:9:9:9:3:3:3:1$

Show answer
Correct Option: A
Explanation:

The possible gametes from the given genotype AABbCC are ABC and AbC.

The various possibilities of their their selfing would be :
1.  ABC × ABC = AABBCC
2. ABC × AbC = AABbCC
3. AbC × ABC = AABbCC
4. AbC × AbC = AAbbCC
It is evident from the above crosses that the genotypic ratio of F2 generation will be 1:2:1.
So, the correct option is '1:2:1'.

In $TtggRr \times TtGgRr$, the percentage of recessive individuals will be

trihybrid cross classical genetics botany

  1. 12

  2. 6

  3. 25

  4. 3

Show answer
Correct Option: D
Explanation:

In a trihybrid cross, there are 32 possible combinations of alleles in the Punnett square out of which only one of the 32 combinations is recessive

i.e.3.125%
So, the correct option is '3'.

In trihybrid, when all gene show complete linkage then what is the ratio of test cross?

trihybrid cross classical genetics botany

  1. 1 : 1 : 1 : 1 : 1 : 1 : 1 : 1

  2. 1 : 1

  3. 1 : 1 : 1 : 1

  4. 9 : 3 : 3 : 1

Show answer
Correct Option: B
Explanation:

A trihybrid cross is between two individuals that are heterozygous for three different traits. For example, RrYyCc x RrYyCc is a trihybrid cross where, 

RR = round, Rr = round, rr = wrinkled
YY = green, Yy = green, yy = yellow

CC = smooth, Cc = smooth, cc = constricted
The complete linkage is when genes are so closely associated that they are always trans­mitted together, and that does not undergo crossing over. 
So, in this case, the ratio of test cross for trihybrid with complete linkage will be 1:1. 
Thus, the correct answer is '1:1'.