Recombinants have allele combinations different from parental combinations because crossing over reshuffles linked genes during meiosis in inheritance problems in inheritance problems.
Coverage 2012–2022 · Updated 16 Jul 2026
A recombinant carries a new allele combination relative to the parental chromosome combinations, produced by crossing over for linked genes or reassortment for unlinked genes.
Cross an individual heterozygous at both loci with an individual homozygous recessive at both. The recessive parent contributes only ab, so each offspring genotype and phenotype reveals the gamete made by the heterozygote.
| Heterozygote gamete | Test-cross offspring genotype | Classification for AB/ab parent |
|---|---|---|
| AB | AaBb | Parental |
| ab | aabb | Parental |
| Ab | Aabb | Recombinant |
| aB | aaBb | Recombinant |
If parental classes greatly exceed recombinant classes, the loci are linked; approximately 1:1:1:1 supports an unlinked or effectively 50%-recombining model.
Identify parental combinations from the cross, not from which phenotype looks 'normal'. Recombination frequency cannot exceed 50%.
This objective is assessed through multiple choice, commonly using Deduce / Identify.
Deduce / Identify
Build the answer around this relationship: Recombinants differ from parental allele combinations.
Representative question
An individual is heterozygous for two linked genes .
To investigate the frequency of crossing over, a test cross is carried out between the individual and another that is homozygous recessive for both genes. What are the possible recombinants in the offspring of this cross?
and
and
and
and
HL D3.2 is secure when chromosome behaviour explains the ratios: segregation and independent assortment produce unlinked dihybrid expectations, gene loci explain linkage, recombinants reveal crossing over, and chi-squared decides whether observed counts fit the expected model.
HL inheritance transfer is about deciding whether the expected ratio should be Mendelian or linked, then testing the evidence. Start from meiosis and gene location, predict gametes or ratios, identify parental and recombinant classes, and use chi-squared when observed counts need a statistical conclusion.
