Autosomal inheritance in humans
Human matings, like those of experimental organisms, show many examples of the inheritance patterns described above. Because controlled experimental crosses cannot be made with humans, geneticists must resort to scrutinizing records in the hope that informative matings have been made by chance. Such a scrutiny of records of matings is called pedigree analysis. A member […]
X-linked Recessive Disorders
Let’s look at the pedigrees of disorders caused by rare recessive alleles of genes located on the X chromosome. Such pedigrees typically show the following features: Males are affected more 1. Many more males than females show the rare phenotype under study. The reason is that a female can inherit the genotype only if both […]
PEDIGREE ANALYSIS OF AUTOSOMAL DOMINANT DISORDERS
What pedigree patterns are expected from autosomal dominant disorders? Here the normal allele is recessive, and the abnormal allele is dominant. It may seem paradoxical that a rare disorder can be dominant, but remember that dominance and recessiveness are simply properties of how alleles act and are not defined in terms of how common they […]
Penetrance and expressivity
Many mutations show incomplete penetrance: not every individual with the genotype expresses the corresponding phenotype. Thus penetrance is defined as the percentage of individuals with a given allele who exhibit the phenotype associated wit many mutations show incomplete penetrance: not every individual with the genotype expresses the corresponding phenotype.Thus penetrance is defined as the percentage […]
Epistasis
It is the type of gene interaction in which one gene locus masks or modifies the phenotype of other gene locus In trying to find evidence of gene interaction, one approach is to look for cases of a type of gene interaction called epistasis. This word means “stand upon,” referring to the ability of a […]
Recessive Lethal Alleles
Many mutant alleles are capable of causing the death of an organism; such alleles are called lethal alleles. The human disease alleles provide examples. A gene whose mutations may be lethal is clearly an essential gene. The ability to determine whether a gene is essential is an important aid to research on experimental organisms, especially […]
Mendel’s law of Independent Assortment
Mendel began working with the pair of characters,those were seed shape and seed color. The cross in which two traits are studied at same time is dihybrid. As we know the monohybrid cross for seed color (Y/y x Y/y), which gave a progeny ratio of 3 yellow:1 green. The seed shape phenotypes were round (determined by allele R) and […]
Chromosomal theory of Inheritance
Historical development of the chromosome theory The theory and practice of genetics took a major step forward in the early part of the twentieth century with the development of the notion that the genes, as identified by Mendel, are parts of specific cellular structures, the chromosomes. This simple concept has become known as the chromosome […]
Mendel’s law segregation
Mendel’s model for the pea-color example, translated into modern terms, was as follows 1. A hereditary factor called a gene is necessary for producing pea color. 2. Each plant has a pair of this type of gene. 3. The gene comes in two forms called alleles. If the gene is phonetically called a “wye” gene, then the […]
Single Gene Inheritance
The genetic approach to understanding any biological property is to find the subset of genes in the genome that influence that property, a process sometimes referred to as gene discovery. After these genes have been identified, their cellular functions can be elucidated through further research. There are several different types of analytical approaches to gene discovery, but one […]