In a branch of biology known as Genetics. This subject deals with the inheritance, as well as the variation of characters from parents to offspring Inheritance is the process by which characters are passed on from parent to progeny. It is the basis of heredity The theory explained the results by describing two laws of inheritance that introduced the idea of recessive and dominant genes.
Mendelian inheritance
Gregor Johann Mendel (1822-1884) started his historical experiments of heredity on pea (Pisum sativum) plant. Mendel’s experiment involved 4 steps as selection, hybridisation, selfing and calculations.
Rediscovery of mendel’s laws (the birth of genetics)
- Carl Correns –Germany(Experiment on Maize)
- Hugo de vries (Holland) (Experiment on Evening primrose) He republished the Mendel results in 1901 in Flora magazine
3.Erich von tschermak -(Austria ) (Experiment on different flowering plants) the credit or discovery of mendelism goes to three scientists
Mendel’s Law of heredity/Inheritance/mendelism
1st Law –- law of dominance
2nd Law-Law of segregation
3rd Law of independent assortment
There are three types of patterns of Mendelian inheritance which are X – linked, autosomal recessive and autosomal dominant. In a general sense, inheritance means whatever we get from our parents.
Inherited traits
A child may inherit the shape of its nose from its father’s genes or its hair texture from its mother’s genes. So we can say that there are certain traits which a baby gets from its parents. Parents’ genes affect the characteristics and the traits of their children and this is what is called inherited traits.
Here are some traits which are inherited from parents
1) Fingerprints
2) Lips
3) Height
4) Dimples
5) Eye colour
6) Teeth structure
7) Infertility
8) Mental disorders
9) Heart problems
10) Hair type and colour
11) Huntington’s disease
12) HIV/AIDS
13) Left–handedness
14) Blood sugar(Diabetes)
15) Hashimoto’s disease and many more.
Types of Inheritance
There are four types of inheritance which are as follows –
- Codominance
- Complete dominance
- Incomplete dominance
- Sex-linked
Incomplete dominance
In Incomplete dominance, heterozygous offspring show their intermediate traits and every genotype will have its phenotype. It means that the ratio of genotype and phenotype will always be the same. In this type of trait, two genes of a particular trait integrate so that a new phenotype is created, and neither of them dominates the other. An example of incomplete dominance is flower colour of Mirabilis jalapa (4’o’ clock plant)
Complete dominance
In Complete dominance, wherever there will be a heterozygous genotype, there always will be a dominant phenotype as in this type of inheritance, dominant allele always wears the mask of the expression of the recessive allele. An example of Complete dominance is pea flower colour.
Patterns of inheritance
1) X – Linked Dominant
2) Autosomal Recessive
3) X – Linked Recessive
4) Mitochondrial
5) Autosomal Dominant
Mendel’s law / principles of Mendelian inheritance
There are three principles (laws) on which the Mendelian inheritance works –
1) The Law of Segregation – it is based on the fact that two alleles are placed in different gametes. Mendel stated it when he discovered that the second generation pea plants still pass on the traits of their grandparents; on this, he was surprised. In other words, Mendel found that in parents, alleles are separated to be passed to the offspring. And each child gets one allele from each parent.
2) The Law of Independent Assortment — It is a principle in genetics which states that the inheritance of 1 gene will not affect the other gene’s inheritance. Here Mendel found that a specific phenotypic ratio is present in the crossed pea plants and looked at 2 traits at a time by applying some maths and stats. And if genes don’t sort freely, the ratio will not be the same.
3) The Law of Dominance – where there are two alleles, then only one allele will be expressed and it will be dominant. After crossing two pea plants having different traits and having offsprings that look similar to each other or one parent, Mendel did this experiment to find whether an offspring is able to pass on the traits of the other parent ? and he found that some new offspring have the traits of other grandparents.
Non – Mendelian Inheritance
Sometimes some changes are shown in the human skin tone, which may range from very dark to very light or vice versa and with every gradation that is possible between them.
Keywords –
1) Phenotype – A Phenotype is a trait that is observable, such as eye colour, height, blood type etc, and genotype is the genetic contribution to the phenotype. Genotype determines most of the traits. There are three genotypes pp (homozygous recessive), Pp ( heterozygous), PP (homozygous dominant). These all three (pp, Pp, PP) have different genotypes. The last two have the same phenotype (purple) but the first one has white.
2) Huntington’s disease – it is a serious disorder transferred to a child from a mother. A slow breakdown of the nervous system is caused due to it. And the prevention is never to take toxins during pregnancy.Huntington’s disease caused by a single defective gene on chromosome 4
3) Hashimoto’s disease – it is passed on by the mother or someone in the family tree to the child. It happens when the immune system is attacked by the immune system. For example – if a child has thyroid issues, the child needs to be checked too.
4) Pleiotropy – it is a case in which a gene is affected by two or more phenotypic traits.
5) Codominance – it happens when two alleles for a gene are expressed equally in phenotype.
Conclusion
Gregor Mendel discovered the laws of Mendelian inheritance between 1865 and 1866. We have learnt about its meaning. Mendelian inheritance is based on three laws – the law of segregation, the law of dominance and the law of independent assortment. And also there are four types of inheritance – complete dominance, incomplete dominance, codominance and sex-linked.