Definition
What is mendelian inheritance?
Mendelian inheritance describes how traits controlled by single genes are passed from one generation to the next, following rules first worked out by Gregor Mendel, a monk in Brno. From crosses of thousands of pea plants, published in 1866, Mendel showed that traits do not blend but are carried by separate units, now called genes, that come in pairs. His work was largely ignored until it was rediscovered in 1900.
Three principles sum up the pattern. Under dominance, one allele can hide the effect of another in a heterozygote. Under the law of segregation, the two alleles of a gene separate when gametes form, so each gamete gets just one. Under the law of independent assortment, alleles of different genes sort into gametes independently of each other. Both laws follow from how chromosomes behave in meiosis, and together they explain the 3:1 and 9:3:3:1 ratios that Punnett squares predict.
In human genetics, Mendelian conditions are those caused mainly by a single gene; they follow autosomal dominant, autosomal recessive or X-linked patterns in pedigrees. Linked genes, incomplete dominance and traits shaped by many genes all depart from Mendel's simple ratios.
Related
Terms that go with it
- Punnett squareA Punnett square is a grid used in genetics to predict the possible genotypes of offspring, and how likely each is, from the alleles of two parents.
- Dominant alleleA dominant allele is a version of a gene whose effect shows in the phenotype even when only one copy is present, masking a recessive allele.
- Recessive alleleA recessive allele is a version of a gene whose effect appears only when an organism has two copies, because a single dominant allele masks it.
- MeiosisMeiosis is a two-stage cell division that turns one diploid cell into four genetically different haploid cells, the precursors of eggs and sperm.
- Genetic linkageGenetic linkage is the tendency of genes that lie close together on the same chromosome to be inherited together rather than sorted independently.
- PedigreeA pedigree is a family tree chart that shows how a trait or genetic condition is passed down through the generations of a family.
Sources
Checked against
Written for biofideX in plain words, after checking these references:
- NHGRI Talking Glossary: Mendelian Inheritance
- OpenStax Biology 2e, 12.1 Mendel's Experiments and the Laws of Probability
- OpenStax Biology 2e, 12.3 Laws of Inheritance
- MedlinePlus Genetics: What are the different ways a genetic condition can be inherited?
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