5. The maximum number of genotypes possible for gametes formed from a diploid cell of the genotype AaBBCcDd is _____.
Maximum Number of Gamete Genotypes from AaBBCcDd Explained
Introduction
Gamete formation is one of the most fundamental processes in genetics and occurs through meiosis. During meiosis, homologous chromosomes separate according to Mendel’s Law of Segregation, while different chromosome pairs assort independently according to the Law of Independent Assortment. These two principles generate genetic diversity by producing different combinations of alleles in the 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 loci do not contribute to genetic variation because both homologous chromosomes carry identical alleles. In contrast, each heterozygous locus doubles the number of possible gamete combinations. This relationship is represented by the simple and widely used formula 2n, where n is the number of heterozygous gene pairs.
Correct Answer
Correct Answer: 8
Detailed Explanation
The number of genetically different gametes depends on the number of heterozygous gene pairs present in the genotype.
The given genotype is:
Aa BBCc Dd
Now examine each locus individually.
| Gene | Genotype | Heterozygous? |
|---|---|---|
| A | Aa | Yes |
| B | BB | No |
| C | Cc | Yes |
| D | Dd | Yes |
There are:
Three heterozygous loci (Aa, Cc and Dd).
Therefore,
n = 3
Using the standard genetics formula:
Number of Gamete Types = 2n
= 23
= 8
Step-by-Step Calculation
Step 1: Count the Heterozygous Gene Pairs
Aa → Heterozygous ✔
BB → Homozygous ✘
Cc → Heterozygous ✔
Dd → Heterozygous ✔
Total heterozygous loci = 3
Step 2: Apply the Formula
Number of Gametes = 2n
= 23
= 8
Possible Gamete Genotypes
Since gene B is homozygous (BB), every gamete receives only the allele B. The variation comes only from genes A, C, and D.
| Gamete Number | Gamete Genotype |
|---|---|
| 1 | ABCD |
| 2 | ABCd |
| 3 | ABcD |
| 4 | ABcd |
| 5 | aBCD |
| 6 | aBCd |
| 7 | aBcD |
| 8 | aBcd |
Formula Used in Gamete Calculations
| Formula | Application |
|---|---|
| 2n | Maximum number of gamete genotypes |
| n | Number of heterozygous gene pairs |
Examples of Gamete Calculations
| Genotype | Heterozygous Loci | Gamete Types |
|---|---|---|
| AABBCC | 0 | 1 |
| AABbCC | 1 | 2 |
| AaBbCC | 2 | 4 |
| AaBBCcDd | 3 | 8 |
| AaBbCcDd | 4 | 16 |
Why Homozygous Genes Do Not Increase Gamete Diversity
Homozygous gene pairs contain identical alleles on both homologous chromosomes. During meiosis, regardless of which chromosome enters a gamete, the same allele is transmitted. Therefore, homozygous loci contribute only one possible allele to every gamete. In contrast, heterozygous loci contain two different alleles, allowing two possible allele combinations in the gametes and thereby doubling the total number of gamete types.
Biological Significance
The production of genetically distinct gametes is essential for maintaining genetic variation within populations. Independent assortment and segregation ensure that offspring inherit unique combinations of parental alleles, providing the raw material for natural selection and evolution. This diversity also reduces the probability of identical genotypes among siblings and increases adaptability in changing environments.
Final Answer
Given genotype:
Aa BBCc Dd
Number of heterozygous loci = 3
Maximum number of gamete genotypes:
23 = 8
Correct Answer: 8
