Divide a clean sheet of paper into four quadrants and draw one pair of homologous chromosomes in each quadrant. Draw the chromosomes with two sister chromatids each. The four sets of homologous pairs are identical. Label one chromosome of each pair with alleles A₁ and A₂  and the other member of each pair with the alleles A₁ and A₂. You are to illustrate a single crossover between the homologs in each quadrant and list the parental and recombinant chromosomes, but you are to illustrate four different ways the crossover can occur by involving different chromatids in each illustration.

Key Concepts

Homologous Chromosomes

Homologous chromosomes are pairs of chromosomes in a diploid organism that have the same structure and gene sequence but may carry different alleles. Each parent contributes one chromosome to the pair, resulting in two homologs that are similar but not identical. Understanding homologous chromosomes is crucial for grasping genetic variation and inheritance patterns.

Sister Chromatids

Sister chromatids are identical copies of a single chromosome that are formed during DNA replication. They are joined together at a region called the centromere and are separated during cell division. Recognizing the role of sister chromatids is essential for understanding processes like meiosis and the formation of gametes, where genetic recombination occurs.

Crossover and Genetic Recombination

Crossover is a process during meiosis where homologous chromosomes exchange segments of genetic material, leading to genetic recombination. This exchange occurs between non-sister chromatids and increases genetic diversity in offspring. Illustrating different crossover events helps in understanding how variations arise in populations and the principles of inheritance.