The Discovery of Dominant and Recessive Genes by Gregor Mendel

Introduction: Genetics is the study of how genes and heredity combine to create traits in living organisms. Gregor Mendel disproved the theory that heredity comes only from parents. He discovered that there were dominant and recessive genes and his “Law of Dominance” has been used to selectively breed plants and animals for particular attributes. It has also been successfully adopted to identify the risk of passing down genetic diseases. Francis Galton took Mendel’s discoveries further by studying multifactoral inheritance and discovering ‘blending traits’, also known as continuous variation. With these traits, involvement of a wide range of genetic and environmental factors results in the creation of wide-ranging genotypes.

Inheritance: Genetic inheritance begins at the time of conception. Humans inherit 23 chromosomes (Fig 1) from each parent. Together they form 22 pairs of autosomal chromosomes and a pair of sex chromosomes (either XX if you are female, or XY if you are male). Homologous chromosomes have the same genes in the same positions, but may have different alleles (varieties) of those genes. There can be many alleles of a gene within a population, but an individual within that population only has two copies, and can be homozygous (both copies the same) or heterozygous (the two copies are different) for any given gene. Chromosomes hold the genes inherited from parents. A gene is a location on a chromosome. Alleles are different options for the same gene. For example, there may be a specific gene for eye colour - meaning a location on the chromosome at which eye colour is specified. Whichever allele (for green eyes, blue eyes, brown eyes) gets placed in that location will determine the specific colour of the eyes.

Dom...

... middle of paper ...

...onto to any offspring. The phenotypic ratio is used to reveal an inheritance pattern. If the pattern is known, then the type of inheritance can often be determined. Figure 6 reveals the outcome of breeding guinea pigs carrying dominant phenotypes for black, short hair and recessive brown, long hair. A 9:3:3:1 ratio is typical for a dihybrid cross between two heterozygous individuals.

Conclusion: Inheritance is the means by which certain traits are passed down from one generation to the next. By applying Mendel’s law of dominance it is possible to choose genetic traits in parents to produce offspring that carries the desired trait. It is also beneficial in determining the likelihood of passing down genetic diseases from one generation to the next. However environmental factors and mutations can increase or decrease the probability of inheriting particular genes.