Tag: classical genetics

Quizzes (7) Questions (110)

Questions Related to classical genetics

Multiple choice trihybrid cross classical genetics botany

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 $x$?

  1. $3$
  2. $9$
  3. $15$
  4. $25$
Reveal answer Fill a bubble to check yourself
C Correct answer
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.'

Multiple choice trihybrid cross classical genetics botany

Frequency of a perfect heterozygous cross between AABBCC and AaBbCc is

  1. 1/8

  2. 2/8

  3. 3/8

  4. 4/8
Reveal answer Fill a bubble to check yourself
A Correct answer
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.

Multiple choice trihybrid cross classical genetics botany

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

  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 $1:1:1:1:1:1:1:1$
Reveal answer Fill a bubble to check yourself
D Correct answer
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- $yyrrtt\times YyRyTt$
Multiple choice trihybrid cross classical genetics botany

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

  1. 4

  2. 45

  3. 28

  4. 27.
Reveal answer Fill a bubble to check yourself
D Correct answer
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’.

Multiple choice trihybrid cross classical genetics botany

Trihybrid ratio is

  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.
Reveal answer Fill a bubble to check yourself
A Correct answer
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’.

Multiple choice trihybrid cross classical genetics botany

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

  1. 1 : 1

  2. 9 : 3 : 3 : 1

  3. 3 : 1

  4. 27 : 9 : 9 : 9 : 3 : 3 : 3 : 1
Reveal answer Fill a bubble to check yourself
C Correct answer
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’.

Multiple choice trihybrid cross classical genetics botany

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

  1. 16

  2. 12

  3. 8

  4. 4
Reveal answer Fill a bubble to check yourself
C Correct answer
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’.

Multiple choice trihybrid cross classical genetics botany

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

  1. Two

  2. Four

  3. Six

  4. Nine
Reveal answer Fill a bubble to check yourself
A Correct answer
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’.

Multiple choice trihybrid cross classical genetics botany

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

  1. One

  2. Two

  3. Four

  4. Eight
Reveal answer Fill a bubble to check yourself
A Correct answer
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’.

Multiple choice trihybrid cross classical genetics botany

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

  1. Multiple alleles

  2. Interaction of genes

  3. Multiple factor inheritance

  4. Independent assortment of genes
Reveal answer Fill a bubble to check yourself
D Correct answer
Explanation

The phenotypic ratio of 27:9:9:9:3:3:3:1 is the classic F2 trihybrid phenotypic ratio expected under Mendel's Law of Independent Assortment when three gene loci segregate independently, each with complete dominance.