(CIE A2 Biology) Ploidy + homologous chromosomes (based on SaveMyExams revision notes)

Diploid Cell

A cell that contains two complete sets of chromosomes, represented as 2n.

Haploid Cell

A cell that contains one complete set of chromosomes, represented as n.

Gametes

Haploid cells involved in sexual reproduction; for humans, the female egg and male sperm.

Reduction Division

The first cell division of meiosis that reduces the chromosome number from diploid to haploid.

Homologous Chromosomes

Chromosomes that have the same genes in the same positions, but may carry different alleles.

Zygote

A fertilized egg formed when the nuclei of two gametes fuse, containing a diploid number of chromosomes.

Chromosome Number in Humans

Humans have 46 chromosomes in diploid cells (23 pairs) and 23 in haploid cells.

Centromere Position

The specific location on a chromosome that holds sister chromatids together.

Alleles

Different forms of a gene that may exist at a specific locus on homologous chromosomes in a gene pair.

Meiosis

The process of cell division that produces haploid gametes from diploid cells.