each chromosome in this homologous pair possesses a different allele. Homologous chromosomes share the same gene sequence but may have slightly different alleles due to random chance. It’s possible that not all of the variations in these alleles affect function.
Homologous chromosomes align and recombine during meiosis. Individuals are created when sperm and egg fuse, creating gametes with different sets of alleles on each chromosome.
Homologous chromosomes are genetically identical and share a common, linear gene order. Homologous chromosomes may have different alleles, but the genes they’re linked to are always the same. During meiosis, homologous chromosomes replicate and form synapses in order to get ready for the first division. The homologous genes are in perfect alignment with one another. Linear pieces of genetic material between homologous chromosomes are traded at this stage (Figure).
Recombination, also known as crossover, is a frequent occurrence in genetics. When recombination occurs, the genes remain in their original order because they are aligned. Alleles from both parents are combined onto a single chromosome as a result of recombination. Multiple recombination events can take place along a single chromosome, leading to a massive rearrangement of alleles.
A pair of genes is said to be linked if they sit next to one another on the same chromosome and their alleles tend to travel through meiosis together. Consider a dihybrid cross in which the genes for flower color and plant height are located on adjacent chromosomes to illustrate. It stands to reason that when gametes are formed, the alleles for tall plants and red flowers will go together into one gamete, while the alleles for short plants and yellow flowers will go together into other gametes.
These are the genotypes that were passed down unaltered from the individual’s parents and are therefore referred to as the parental genotypes. It’s true that there won’t be any tall yellow gametes or short red gametes, but that’s because the genes are on the same chromosome. Using these gametes to generate a Punnett square reveals that the classical Mendelian prediction of a 9:3:3:1 outcome of a dihybrid cross is incorrect.