27. The total number of genetically different types of gametes that will be produced by a heterozygous plant carrying the genotypes AABbCc is.
Total Number of Genetically Different Gametes Produced by the Genotype AABbCc
Introduction
The formation of genetically different gametes is one of the most fundamental concepts in classical genetics. During meiosis, homologous chromosomes separate according to Mendel’s Law of Segregation, while different chromosome pairs assort independently according to Mendel’s Law of Independent Assortment. Together, these two principles generate genetic diversity among gametes.
The total number of genetically different gametes produced by an individual depends entirely on the number of heterozygous gene pairs present in its genotype. Homozygous genes do not contribute to gamete diversity because every gamete receives the same allele from those loci. In contrast, each heterozygous gene pair contributes two possible alleles to gametes, thereby doubling the number of possible gamete types.
To simplify such calculations, geneticists use the formula 2n, where n represents the number of heterozygous gene pairs. This simple yet powerful formula is frequently tested in competitive examinations because it assesses a student’s understanding of meiosis, segregation, and independent assortment.
Correct Answer
Correct Answer: 4
Detailed Explanation
The genotype given is:
AABbCc
Each gene pair should be examined individually.
| Gene Pair | Genotype | Heterozygous? |
|---|---|---|
| A | AA | No |
| B | Bb | Yes |
| C | Cc | Yes |
Only the gene pairs Bb and Cc are heterozygous.
Therefore,
Number of heterozygous gene pairs (n) = 2
The number of genetically different gametes is calculated using:
Number of Gametes = 2n
Substituting the value of n:
= 22
= 4
Step-by-Step Calculation
Step 1: Identify Homozygous and Heterozygous Gene Pairs
AA → Homozygous
Bb → Heterozygous
Cc → Heterozygous
Step 2: Count the Number of Heterozygous Gene Pairs
n = 2
Step 3: Apply the Formula
Number of Genetically Different Gametes = 2n
= 22
= 4
Possible Gametes Produced
Since gene A is homozygous (AA), every gamete receives the allele A.
The heterozygous genes B and C can segregate independently, producing the following gametes:
| Gamete Number | Gamete |
|---|---|
| 1 | ABC |
| 2 | ABc |
| 3 | AbC |
| 4 | Abc |
Thus, the plant produces four genetically distinct gametes.
Formula for Gamete Calculation
| Formula | Description |
|---|---|
| 2n | Number of genetically different gametes |
| n | Number of heterozygous gene pairs |
Examples Using the Formula
| Genotype | Heterozygous Gene Pairs | Number of Gametes |
|---|---|---|
| AA | 0 | 1 |
| Aa | 1 | 2 |
| AaBb | 2 | 4 |
| AaBbCc | 3 | 8 |
| AABbCc | 2 | 4 |
| AaBbCcDd | 4 | 16 |
Why Homozygous Genes Do Not Increase Gamete Diversity
A homozygous gene pair contains identical alleles. During meiosis, each gamete receives the same allele regardless of which homologous chromosome separates. Consequently, homozygous loci contribute only one possible allele to every gamete and therefore do not increase the total number of genetically different gametes.
Only heterozygous loci possess two alternative alleles that segregate during meiosis, doubling the number of possible gametes with each additional heterozygous gene pair.
Biological Significance
The production of genetically different gametes is one of the primary sources of genetic variation in sexually reproducing organisms. Independent assortment and segregation generate numerous allele combinations, increasing diversity among offspring. This genetic variation provides the raw material upon which natural selection acts, making meiosis a fundamental process in evolution, breeding programmes, and population genetics.
Final Answer
Given genotype:
AABbCc
Number of heterozygous gene pairs = 2
Number of genetically different gametes = 22 = 4
Possible gametes: ABC, ABc, AbC, Abc
Correct Answer: 4
