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Define Penetrance and Explain ?
Penetrance refers to the proportion of people with a particular genetic variant (or gene mutation) who exhibit signs and symptoms of a genetic disorder. If some people with the variant do not develop features of the disorder, the condition is said to have reduced (or incomplete) penetrance.
Difference Between Penetrance and Expressivity ?
| Penetrance | Expressivity |
|---|---|
| Penetrance is the percentage of individuals with a given phenotype, who exhibit the phenotype associated with that particular genotype | Expressivity is the extent of a given genotype, expressing at the phenotypic level. |
| Penetrance explains how often the gene is expressed. | Expressivity explains the extent of gene expression. |
| Penetrance is a quantitative measurement. | Expressivity is a qualitative measurement. |
| Penetrance explains whether the disease shows up. | Expressivity explains how a disease shows up. |
| Penetrance describes the expression of a single gene. | Expressivity describes the expression of a group of characters or a syndrome. |
| Incomplete penetrance is a phenomenon that makes genetic analysis more difficult. | Variable expressivity is a phenomenon that makes genetic analysis more difficult. |
| The expression of BRCA1 and BRCA2 genes develop cancers in some individuals but not in others as a result of penetrance. | The characteristics of Marfan syndrome widely vary among individuals as a result of expressivity. |
Difference Between Test Cross and Back Cross ?
| Test cross | Back cross |
|---|---|
| Breeding of the dominant phenotype with the homozygous recessive phenotype (parent) is known as a test cross. | The breeding of F1 generation with one of its parent plants is known as a back cross. |
| All test crosses are backcrosses. | A backcross can be said as a test cross if the parent is recessive. |
| The F1 hybrid is crossed with a recessive genotype. | An F1 hybrid is crossed with either homozygous dominant or heterozygous genotypes. |
| The test cross helps in the identification of the genotype of the dominant individual. | The back cross helps in the identification of the elite genotype by checking the segregation of genes at the time of gamete formation. |