Independent assortment is Mendel's second law: genes on different chromosomes (or far apart on one) are inherited independently. Which allele a gamete gets at one gene tells you nothing about which allele it gets at another. That is how a cross produces combinations neither parent had.
In practice
It is the reason breeders can combine traits. Cross a plant with dense resin but late flowering to an early plant with thin resin; if the genes involved are on different chromosomes, some F2 plants will be early and resinous. The expected two-gene F2 ratio is 9:3:3:1, so the wanted double combination may be only 1 in 16, or rarer if both traits are recessive.
Cannabis has 10 chromosome pairs, so many genes do assort independently. Genes close together on one chromosome do not: they tend to travel together, which is linkage.
Don't confuse with
- Segregation: separation of two alleles of one gene; assortment is about how different genes combine.
- Linkage: the exception, when genes sit near each other and are inherited as a block.
- Recombination: crossing over within a chromosome, which is what eventually breaks linkage.
A gene is a stretch of DNA that carries the instructions for one functional product, usually a protein such as an enzyme, and is the basic unit of inheritance.A chromosome is one long DNA molecule packaged with proteins that carries many genes; cannabis normally has 10 pairs, nine autosome pairs plus an X/Y sex pair.An allele is one version of a gene; a diploid cannabis plant carries two alleles at each locus, one from each parent, which may be the same or different.F2 is the second filial generation, made by crossing or selfing F1 plants; it shows the widest segregation, bringing back hidden recessives and new combinations.A recessive allele only shows its effect when a plant carries two copies of it; in a single copy it is masked by a dominant allele and carried silently.Linkage is the tendency of genes that sit close together on the same chromosome to be inherited together, rather than independently.Segregation is the separation of a plant's two alleles at each locus into different gametes, so offspring of a heterozygous parent vary in which allele they get.Mendelian inheritance is the pattern in which single genes pass from parents to offspring in predictable ratios, following Mendel's laws of segregation and independent assortment.A Punnett square is a grid that lists each parent's possible gametes along two sides to predict the expected genotype ratios among offspring of a cross.
