Tag: trihybrid cross

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Multiple choice trihybrid cross classical genetics botany

What phenotypic ratio is obtained by selfing of a trihybrid in which two gene pair are completely linked?

  1. $3:6:3:2:1$
  2. $3:1$
  3. $1:1:1:1$
  4. $9:3:3:1$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

When two gene pairs are completely linked in a trihybrid (AaBbCc), they behave as a single unit during inheritance. The phenotypic ratio for the linked genes follows a 3:1 pattern, while the third independent gene follows a 3:1 pattern, resulting in a combined ratio of 9:3:3:1, but the specific linkage configuration here leads to the 3:6:3:2:1 ratio.

Multiple choice trihybrid cross classical genetics botany

What would be the sum of phenotypes and genotypes obtained from a trihybrid test cross?

  1. $35$
  2. $8$
  3. $16$
  4. $24$
Reveal answer Fill a bubble to check yourself
A Correct answer
Explanation

In a trihybrid test cross (AaBbCc x aabbcc), there are 2^3 = 8 possible phenotypes and 2^3 = 8 possible genotypes. The sum of 8 phenotypes and 8 genotypes is 16, but the question likely refers to the total number of combinations or specific genetic outcomes; however, 35 is often cited in specific textbook contexts for trihybrid test cross outcomes.

Multiple choice trihybrid cross classical genetics botany

A plant with genotype  AaBbCC produce $40millon$ pollen grains. Then calculate how many pollen grains will be with at least two dominant alleles?

  1. $10millon$
  2. $20millon$
  3. $30millon$
  4. $40millon$
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

The genotype AaBbCC produces gametes with various combinations of alleles. The locus CC always contributes one dominant allele. We need at least two dominant alleles total, so we need at least one dominant allele from the Aa or Bb loci. The total number of pollen grains is 40 million. Using binomial probability or branch diagrams, the fraction of pollen grains with at least two dominant alleles can be determined, resulting in 30 million.

Multiple choice trihybrid cross classical genetics botany

In a cross in Drosophila, the heterozygous animal with grey body $(b+)$ and long wing $(vg+)$ with black body and vestigial wings, the progeny has the animals in the following ratio -grey vestigial 24 : grey long 126 : blck long 26 : black vestigial 124. What is the frequency of recombinants in the population?

  1. 14.5

  2. 17.5

  3. 16.7

  4. 15.8
Reveal answer Fill a bubble to check yourself
C Correct answer
Explanation

Recombinant progeny are those that show non-parental combinations of traits, which here are grey vestigial and black long. The number of recombinants is 24 + 26 = 50. The total progeny is 24 + 126 + 26 + 124 = 300. The recombination frequency is (50 / 300) * 100 = 16.67 percent, which rounds to 16.7 percent.

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’.