Haploid gametes fuse at fertilization to restore diploid chromosome number in the zygote and combine alleles from two parents in inheritance problems.
Coverage 2018–2018 · Updated 16 Jul 2026
In the sexual life cycle common to eukaryotes, meiosis makes haploid gametes and fertilization fuses two gametes to form a diploid zygote.
Meiosis halves chromosome number from 2n to n. Fusion combines one maternal and one paternal set, restoring 2n without chromosome number doubling in every generation.
A diploid individual normally carries two copies of each autosomal gene, one on each homologous chromosome. Each gamete carries one copy, and the zygote receives two again.
A human sperm and ovum each contain 23 chromosomes; after nuclear fusion the zygote contains 46.
Fertilization combines two haploid sets; it does not copy one gamete or make the zygote genetically identical to either parent.
This objective is assessed through multiple choice, commonly using Identify.
Identify
Build the answer around this relationship: Gametes are haploid so fusion can restore the diploid number.
Representative question
For what reason do gametes contain only one allele of each gene?
To prevent inbreeding in a population
Haploid cells contain only one set of chromosomes
The two alleles of a gene are separated during mitosis
Crossing over will always produce one allele of a gene
Core D3.2 is secure when the student can move from allele rules into predictions and evidence: gametes form genotypes, genotypes can produce phenotypes, different dominance patterns need different notation, and pedigrees or plots require evidence-based interpretation.
Core inheritance exam questions reward disciplined reasoning. First identify the inheritance rule, then write the correct notation or evidence, then state the phenotype, ratio, or conclusion. This prevents the common mistake of writing definitions without solving the genetic problem.
