Penetrance is the fraction of carriers showing a phenotype; expressivity is how strongly it appears.
Incomplete penetrance means some people with a genotype show no phenotype (BRCA1 carriers have about 70 percent breast cancer risk by 80); variable expressivity means that those who show it differ in severity (neurofibromatosis). Modifier genes and the environment explain this.
Penetrance is the fraction of carriers showing a phenotype; expressivity is how strongly it appears.
Penetrance and Expressivity is one of the 54 topics in Genetics. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Monohybrid Cross, Genotype and Phenotype, Allele.
Polydactyly can appear with variable numbers of extra digits.
Work through the Beginner topics in Genetics first, such as Heredity, Gene, Allele, then return to Penetrance and Expressivity. Advanced topics assume the Intermediate vocabulary.
The closest topics to Penetrance and Expressivity are Monohybrid Cross, Genotype and Phenotype, Allele, Heritability. Comparing them side by side is a good way to see how the ideas connect.
Read the summary and the in-depth section, then use the quick check on the interactive lesson for Penetrance and Expressivity. To practise the whole of Genetics, use the Genetics quiz.
Penetrance and Expressivity: Penetrance is the fraction of carriers showing a phenotype; expressivity is how strongly it appears. Monohybrid Cross: A cross following one gene with two alleles, giving a 3:1 phenotype ratio in the F2 generation. Read both side by side and note what each one explains.
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Monohybrid Cross and explain the difference aloud. Finally, take the Genetics quiz and come back to this page for any question you miss.
A cross following one gene with two alleles, giving a 3:1 phenotype ratio in the F2 generation.
🧬 GeneticsGenotype is an organism's allele makeup; phenotype is its observable traits resulting from genes and environment.
🧬 GeneticsOne of the alternative versions of a gene found at the same position on a chromosome.
🧬 GeneticsThe proportion of phenotypic variation in a population attributable to genetic differences.
🧬 Genetics