Question

In a certain animal species, four alleles \(\left(a^{+}, a^{1}, a^{2}\right.\) and \(\left.a^{3}\right)\) have a locus on chromosome 1. Another series of alleles (b) \(b^{1}\) and \(b^{2}\) ) have their locus on chromosome 2. Theoretically, how many genotypes are possible with respect to these two allelic series?

Short answer

There are \(64\) theoretically possible genotypes with respect to these two allelic series.

Step-by-step solution

Determine the number of combinations in chromosome 1

In chromosome 1, there are four alleles: \(a^+, a^1, a^2\), and \(a^3\). Since chromosomes come in pairs, for each allele, there are 4 possible pairs of chromosomes. Hence, there are a total of \(4 \times 4 = 16\) possible genotype combinations in chromosome 1's locus. Step 2: Analyze the possible combinations of alleles in chromosome 2

Determine the number of combinations in chromosome 2

In chromosome 2, there are two alleles: \(b^1\) and \(b^2\). Again, since chromosomes come in pairs, for each allele, there are 2 possible pairs of chromosomes. Hence, there are a total of \(2 \times 2 = 4\) possible genotype combinations in chromosome 2's locus. Step 3: Combine the possible genotype combinations of chromosome 1 & chromosome 2

Determine the total number of possible genotypes

Now we need to find the total number of combinations with respect to these two allelic series using the basic counting principle. We can multiply the number of combinations in both loci, which are independent events. Total number of possible genotypes = (Possible combinations in chromosome 1) × (Possible combinations in chromosome 2) Total number of possible genotypes = \(16 \times 4 = 64\) Answer: There are \(64\) theoretically possible genotypes with respect to these two allelic series.

Key concepts

Alleles

Alleles are different forms of a gene that are located at the same position, or loci, on a chromosome. They contribute to the genetic diversity within a species by providing variations of traits. For instance, consider a specific gene that determines eye color. The different possible alleles for this gene might include blue, brown, or green. This leads to the expression of different eye colors among individuals.

• Each individual inherits two alleles for each gene: one from each parent.
• The combination of alleles determines the organism's trait.
• Alleles can be dominant or recessive. A dominant allele, if present, will mask the expression of a recessive allele.

Alleles are fundamental units in genetics. In the given exercise, the alleles \(a^{+}, a^{1}, a^{2}, \) and \(a^{3}\) on chromosome 1 and \(b^{1}\) and \(b^{2}\) on chromosome 2 play roles in determining possible genotype combinations. With these alleles, diverse genetic mixtures arise. This reflects in the multitude of genotypes that are possible.

Genotypes

A genotype is the set of alleles that an organism possesses for a particular gene or trait. It is the genetic blueprint of an individual organism, determining specific characteristics or traits through the expression of these alleles. In simple terms, a genotype refers to the genetic makeup of an organism.

• Genotypes may include homozygous (same alleles, like \(AA\) or \(aa\)) or heterozygous (different alleles, like \(Aa\)).
• The genotype contributes to the phenotype, which is the observable characteristic, though it is also influenced by environmental factors.
• A combination of different genotypes can lead to diverse traits in a population.

In the exercise, we calculated possible genotype combinations, or possibilities of genetic makeup, by considering all combinations of alleles on both chromosomes. The exercise demonstrated that with four alleles on one chromosome and two on the other, we can reach a total of 64 different genotype combinations.

Chromosomes

Chromosomes are long thread-like structures of DNA and protein that house genetic information. They are crucial in ensuring that DNA is accurately copied and distributed in the vast majority of cell divisions. Each species has its specific number of chromosomes. For humans, it's 23 pairs, or 46 in total.

• Chromosomes come in pairs – one from each biological parent.
• Each chromosome further consists of genes, which are specific sequences of nucleotides.
• Chromosomes are only visible under a microscope during cell division.

Consider their role in the given exercise: each chromosome hosts potentially different alleles, which can pair up to form different genotypes. Here, chromosome 1 contained alleles \(a^{+}, a^{1}, a^{2}, \) and \(a^{3}\). Meanwhile, chromosome 2 had \(b^{1}\) and \(b^{2}\). By forming different allele pairs for these chromosomes, we derive numerous genetic combinations leading to genetic variability. This variability is crucial for the survival and adaptability of a species.