AP Syllabus focus:
‘Mendel’s laws describe how alleles segregate and assort independently when genes are on different chromosomes.’
Mendel’s laws explain predictable inheritance patterns in sexually reproducing organisms. They connect observable trait ratios to the behavior of alleles during gamete formation, and they set the baseline expectations for unlinked genes.
Core ideas and vocabulary
Mendelian genetics links inheritance to paired hereditary units carried in gametes.
Allele: an alternative version of a gene found at the same locus on homologous chromosomes.
Practice Questions
FAQ
Segregation is about allele separation into gametes, whereas dominance is about expression in a heterozygote.
Mendel inferred segregation by showing that a “hidden” allele could reappear in later generations, indicating it was transmitted intact rather than blended.
An independently assorting unit is a chromosome pair whose orientation does not constrain another pair’s orientation.
In many contexts, $n$ is the haploid number of chromosome pairs, but structural changes (e.g., translocations) can reduce independence.
Usually they assort independently, but rare exceptions can occur if chromosome behaviour is non-random.
For example, meiotic drive mechanisms can bias transmission of particular chromosomes, altering expected gamete frequencies.
“Random” refers to the orientation of chromosome pairs being equally likely among possibilities.
Predictability comes from large numbers: across many meioses, frequencies approach expected probabilities even though each meiosis is uncertain.
You look for combinations of traits appearing in proportions consistent with independent transmission.
Evidence is strongest when recombinant combinations occur as frequently as parental combinations, rather than being underrepresented (which would suggest linkage).
