Tag: classical genetics

Questions Related to classical genetics

A polygenic trait is controlled by $3$ genes $A, B$ and $C$. In a cross $AaBbCc \times AaBbCc$, the phenotypic ratio of the offsprings was observed as
$1 : 6 : x : 20 : x : 6 : 1$ What is the possible value of $x$?

trihybrid cross classical genetics botany

  1. $3$

  2. $9$

  3. $15$

  4. $25$

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Correct Option: C
Explanation:

In polygenic inheritance, a particular trait is controlled by 3 different genes. The given problem is of polygenic inheritance. In this, phenotypic ratio is 1:6:15:20:15:6:1 instead of 27:9:9:9:3:3:3:1 in F$ _2$ generation. In the given example, the genotype of parents is AaBbCc and AaBbCc. They will produce gametes ABC, ABc, Abc, abc, aBC, aBc, abC, AbC. The phenotypic ratio will be 1:6:15:20:`15:6:1.

Thus, the correct answer is '15.'

Frequency of a perfect heterozygous cross between AABBCC and AaBbCc is

trihybrid cross classical genetics botany

  1. 1/8

  2. 2/8

  3. 3/8

  4. 4/8

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Correct Option: A
Explanation:

Genotype AABBCC can produce only one type of gamete, i.e., ABC. The frequency for production of ABC gamete is 1.
Genotype AaBbCc can produce 8 types of gametes, i.e., ABC, Abc, ABc, AbC, abc, aBC, aBc and abC.
The frequency of production of one of these gametes is 1/8.
According to the question, a perfect heterozygous cross will occur only when abc gamete from AaBbCc parent fertilises with ABC gamete from AABBCC parent.
Thus, the frequency for this = 1/8X1 = 1/8.

A typical dihybrid and trihybrid test-cross ratio are respectively:

trihybrid cross classical genetics botany

  1. $1:1$ and $1:1:1:1$

  2. $1:1:1:1:1:1:1:1$ and $1:1:1:1$

  3. $1:1:1:1$ and $1:1$

  4. $1:1:1:1$ and $1:1:1:1:1:1:1:1$

Show answer
Correct Option: D
Explanation:
Dihybrid Test ratio: $1:1:1:1$
Trihybrid Test ratio : $1:1:1:1:1:1:1:1$
Test cross $\Rightarrow F _1$ generation $X$ recessive parent 
for dihybrid test cross- $RrYy\times rryy$
for Trihybrid test cross- $yyrrtt\times YyRyTt$

Number of genotypes produced when individuals of genotype 'YyRrTt' are crossed with each other

trihybrid cross classical genetics botany

  1. 4

  2. 45

  3. 28

  4. 27.

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Correct Option: D
Explanation:

A trihybrid plant YyRrTt during fertilization produces 27 types of genotypes.

It is calculated as 3n , n= number of contrasting pairs of characters/traits.

In YyRrTt, 3 contrasting pairs of characters are present. So 33 = 27.

So, the correct option is ‘27’.

Trihybrid ratio is

trihybrid cross classical genetics botany

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

  2. 27 : 9 : 9 : 6 : 6 : 3 : 3 : 1

  3. 1 : 6 : 15 : 20 : 15 : 6 : 1

  4. 36 : 6 : 6 : 6 : 3 : 3 : 3 : 1.

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Correct Option: A
Explanation:

A cross is made between the two parents on the basis of 3 contrasting characters is called Trihybrid cross. Mendel conducted trihybrid cross by three characters height of the stem, form of seed, and colour of the cotyledons. In the F2 generation, he obtained, 27:9:9:9:3:3:3:1.

So, the correct option is ‘27:9:9:9:3:3:3:1’.

A plant of genotype AABbCC is selfed. Phenotypic ratio of $F _2$ generation would be

trihybrid cross classical genetics botany

  1. 1 : 1

  2. 9 : 3 : 3 : 1

  3. 3 : 1

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

Show answer
Correct Option: C
Explanation:

A plant with genotype AABbCC, is subjected to self pollination, in the F2 generation 3:1 ratio of progeny are formed, because the parent show only one pair of contrasting characters.

So, the correct option is ‘3:1’.

Number of phenotypes possible from AaBbCc $\times$ AaBbCc is

trihybrid cross classical genetics botany

  1. 16

  2. 12

  3. 8

  4. 4

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Correct Option: C
Explanation:

When a cross is made between AaBbCc with AaBbCc, in the next generation 8 types of phenotypes appear, because this cross involves 3 pairs of contrasting characters 2n, n means number of pairs of characters.

Here 3 pairs of characters are present, 23 = 8.

So, the correct option is ‘8’.

How many types of gametes will be produced by individuals of AABbcc genotype?

trihybrid cross classical genetics botany

  1. Two

  2. Four

  3. Six

  4. Nine

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Correct Option: A
Explanation:

The plant with genotype AABbcc produces only two types of namely ABc, Abc, because it shows one pair of contrasting characters.

So, the correct option is ‘Two’.

How many types of gametes are expected from the organism with genotype AA BB CC?

trihybrid cross classical genetics botany

  1. One

  2. Two

  3. Four

  4. Eight

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Correct Option: A
Explanation:

AABBCC is trihybrid homozygous organism. This organism at the time of fertilization produces only one type of gametes. They are ABC.

So, the correct option is ‘one’.

The trihybrid phenotypic ratio of $27:9:9:9:3:3:3:1$ is obtained because of.

trihybrid cross classical genetics botany

  1. Multiple alleles

  2. Interaction of genes

  3. Multiple factor inheritance

  4. Independent assortment of genes

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Correct Option: A