In Mendel’s experiments, when an individual expresses a trait with the alleles ‘gg’, this genotype is classified as homozygous recessive.
To break it down, Mendel’s laws of inheritance detail how traits are passed down through generations via alleles. Alleles can be dominant or recessive, and they come in pairs. In this case, ‘g’ refers to a specific allele.
When we talk about homozygous genotypes, we mean that both alleles at a given locus are the same. In the case of ‘gg’, both alleles are the same (both are ‘g’), and since we are using lowercase letters to denote this particular allele, we know ‘g’ is recessive. This means that the trait associated with ‘g’ will only be expressed when the individual has two copies of the recessive allele, which is exactly what we see in ‘gg’.
In contrast, a homozygous dominant genotype would be represented as ‘GG’, where both alleles are dominant. A heterozygous genotype would be represented as ‘Gg’, where one allele is dominant (‘G’) and the other is recessive (‘g’). Therefore, since ‘gg’ contains two recessive alleles, it is correctly identified as homozygous recessive.