In humans and other organisms, cells can have one or two sets of chromosomes, depending on their type and function. Understanding the difference between haploid and diploid cells is essential for grasping how genetic information is inherited and how cell division works. This concept is crucial for topics like mitosis, meiosis, and sexual reproduction.

What does this mean? "Each homologous pair contains genes that control the same characteristics__, but they may not carry the same version of the gene (allele)."

Each pair of chromosomes carries genes that control the same traits, like eye colour or height. However, they don't always carry the same version of the gene.

For example, one chromosome might carry a gene for brown eyes, while the other might have a gene for blue eyes.

A haploid cell has one set of chromosomes.

• The letter n represents a haploid cell.
• In humans, haploid cells include sperm and egg cells, each with n = 23 chromosomes.
• Haploid cells are crucial for sexual reproduction, as they combine during fertilisation to form a diploid cell.

A diploid cell has two sets of chromosomes.

• 2n represents a diploid cell.
• In humans, most body (somatic) cells are diploid, with 2n = 46 chromosomes.
• Diploid cells ensure genetic information is inherited in pairs, one set from each parent.

A haploid cell has one set of chromosomes. (n) A diploid cell has two sets of chromosomes. (2n)

Note: In birds, butterflies, and moths, males have XX chromosomes, and females have XY chromosomes. This is the opposite of humans, where females are XX and males are XY.

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