Recombinants Show the Complexities of Genetic Crosses
- When crossing plants with different traits, some offspring display unexpected combinations not seen in either parent.
- These are recombinants.
- They arise due to:
- Independent Assortment: When genes are located on different chromosomes or far apart on the same chromosome.
- Crossing Over: When genes are linked (close together on the same chromosome), recombination occurs during meiosis through crossing over.
Definition
Recombinant
Recombinants are individuals with new combinations of alleles and traits, differing from their parents.
Independent Assortment Produces Predictable Ratios
- For unlinked genes, independent assortment ensures all allele combinations have an equal chance of appearing in gametes.
- This leads to predictable phenotypic ratios:
- A test cross involving heterozygous and homozygous recessive individuals typically produces a 1:1:1:1 ratio of offspring phenotypes.
- This outcome confirms the genes are unlinked.
Seed Shape and Color in Peas
- Parental Genotypes: RrYy×rryyRrYy \times rryyRrYy×rryy
- Predicted Ratios:
- Round yellow: RYRYRY (25%)
- Round green: RyRyRy (25%)
- Wrinkled yellow: rYrYrY (25%)
- Wrinkled green: ryryry (25%)
Linked Genes Deviate From Expected Ratios
- For linked genes, independent assortment does not occur because the genes are inherited together.
- However, crossing over during meiosis can create recombinants.
- Parental Types: More frequent.
