Gene Frequency and Zygotic Frequency and Forces Changing them | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Gene Frequency

Understanding Gene Frequency:

• Gene frequency refers to how common or rare a gene is within a population.
• It is the proportion of a gene's alleles present at specific loci on chromosomes.

Gene Frequency in Drosophila:

• Drosophila melanogaster, a commonly studied organism, has around 500 loci with known gene frequencies.
• The gene frequency is denoted by the letter 'q' conventionally.

Allelic Series:

• Allelic series involve different versions of a gene (alleles), such as A and a.
• In farm animals with longer generation intervals, gene frequencies can vary due to fewer offspring per delivery.

Total Number of Genes:

• Estimating the total number of genes is not a concern when discussing gene frequency.
• The gene frequency can range from 0 to 1, with allele 1-q representing the presence of the gene.

Zygotic Frequency

Understanding Genotypic Frequency:

• Definition: Genotypic frequency refers to the proportion or percentage of different genotypes within a group of individuals.
• Example: If there are two alleles, A₁ and A₂, at a certain locus A, the genotypes A₁A₁, A₁A₂, and A₂A₂ represent the genetic constitution of the group.

Zygotic Frequencies:

• Definition: Zygotic frequencies are genotype frequencies, indicating the proportion of each genotype in a population.
• Example: If 25% of individuals in a group have the genotype A₁A₁, the zygotic frequency of this genotype is 0.25 or 25%.
• It is essential that the sum of frequencies of all genotypes equals 1 or 100%.

Population Genetics:

• Definition: Population genetics involves studying genetic makeup and gene transmission within a breeding group across generations.
• Gene Frequencies: Gene frequencies represent the proportion or percentage of alleles at a specific locus within a population.
• Allele frequencies at a locus must sum up to 1 or 100%.

Forces Impacting Gene Frequency and Zygotic Frequency

Population Size:

• The size of a population influences genetic properties by affecting gene transmission between generations. Smaller populations experience greater sampling variation in gene frequencies compared to larger populations where this variation is minimal.

Differences in Fertility and Viability:

• Fertility and viability of individuals impact the genetic composition of the next generation. Variances in fertility among genotypes result in unequal contributions to gametes, altering gene frequencies. Similarly, disparities in survival rates among genotypes influence gene frequencies through selection processes.

Migration and Mutation:

• Changes in gene frequencies can occur due to immigration from other populations and gene mutations, both of which introduce new genetic variations into a population.

Mating System:

• The genotypes of offspring are determined by the pairing of gametes to form zygotes, which is influenced by the mating choices of parents. Genotype frequencies in the next generation are affected by the genotypes of mating pairs in the parent generation. It is crucial for mating pairs to not be genetically similar or closely related by ancestry to maintain genetic diversity within a population.