Standard 7b Preknowledge
7b) Students know why alleles that are lethal in a homozygous individual may be carried in a heterozygote and thus maintained in a gene pool.
CALIFORNIA FRAMEWORKS SUMMARY:
Two types of allele pairings can occur in the genotype: homozygous (pairing two of the same alleles, whether dominant, codominant, or recessive) and heterozygous (pairing of two different alleles). Recessive lethal alleles (e.g., Tay-Sachs disease) will, by definition, cause the death of only the homozygous recessive individual. Healthy heterozygous individuals will also contribute the masked recessive gene to the population’s gene pool, allowing the gene to persist.