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| What is Genetics, Mendelian law of Inheritance |
What is Genetics?
Genetics is the study of genes and inherited characteristics that are passed from parent to offspring. It plays a fundamental role in understanding the blueprint of life.
As we all know Gregor Mendel founded inheritance law by studying on Pea plant. Mendel observed that genes in parents are passed to the offspring as dominant genes and recessive genes.
Mendelian Law of Inheritance:
Mendel studied the law of segregation and the independent assortment of pea plants depending on the shape of the pea plant round and wrinkled and the color of the pea plant yellow and green. When the four species were crossbreeding the resulting offspring comes in the ratio of 9:3:3:1. Most of the progeny of pea pants was round yellow which shows that certain traits are inherited from parents to offspring. Yellow was dominant over the green color trait. Round predominates wrinkled shape.
When crossbreeding yellow and green pea plants, the F1 generation shows the dominant trait, the yellow pea plant. In contrast, the F2 generation contains 3:1, which shows most of the progeny with the dominant trait, yellow color while one offspring contains a recessive trait, green color. This shows some traits are dominant while some are recessive.
Outcomes of Mendelian Law of Inheritance are:
Segregation Law:
Gene pair determines each trait
that is inherited. Each sex cell during fertilization receives one gene from its parent.
Independent Assortment Law:
The law states that different genes responsible for different traits are assorted independently so that inheriting one trait does not affect the inheritance of another trait. During gamete fusion, different genes are transferred from parents to the next generation leading to the random distribution of traits. Expectations of this law occur when genes are closely linked on the same chromosome.
Dominance Law:
It states that two different forms of allele variants will be expressed in the dominant form. Dominant Law states here that an allele whose traits are dominant over another allele is the dominant allele. Dominant characters appear in the F1 generation and recessive traits have appeared in the F2 generation.
Genetic Disorders
As we know, the Human genome comprises 3 billion base pairs of nucleotides comprising 46 chromosomes (22 pairs of autosomal chromosomes and 1 sex chromosome which determine the sex of a person). Genes are made up of nucleotides. The problem in DNA sequence causes changes in genes leading to mutation. Genetic disorders occur when there is a mutation in any one of the genes. Almost 6000 gene abnormalities have been known to be found, and many can cause serious problems. Genetic disorders could be hereditary, changes in a person's DNA, or due to environmental factors.
There are four significant kinds of genetic disorders:
Chromosomal Disorder
A person infected with this disorder has a deletion or gap in the chromosome region. Chromosome abnormalities are caused by duplicate chromosomes, a missing whole chromosome or a fragment of the chromosome, and problems with cell division. The chromosomal disorder occurs when the entire numbers of chromosomes are different from the actual phenotypic composition.
Aneuploidy is having an abnormally large number
of chromosomes. Karyotype consists of a whole set of 46 chromosomes. The addition of chromosomes, Removal of chromosomes, insertion, and translocation of chromosome
regions are caused due to structural chromosomal abnormality. Examples include Downs Syndrome, turner syndrome, and Klinefelter
disease.
Multi-factorial Disorder
This genetic disorder is caused by a variety of factors that are involved in gene mutation. Genetic, social, and environmental factors contribute to this disorder. Chemical exposure, nutrition, overdosage of drugs, and large consumption of cigarettes or alcohol are among them. Multiple mutations can cause the same disease with different levels of phenotypic appearances.
Phenotype
appearance may be affected by changes in various genes, patient surroundings,
and other factors. Genetic components can be influenced by changes in the behavior
of an infected person or environment. Examples are galactosemia, CFTR mutations in
children, type 2 diabetes, cancer, and obesity.
Single-genetic Disorder
This can be caused by the mutation of the DNA sequence in a single gene. They are called monogenetic disorders. Gene can be changed in a variety of ways. The misspelling of a single DNA sequence is the most frequent among them, the loss of a gene, and the addition of a single base pair sequence. The result of this mutation will change the protein product and its function.
This genetic disorder occurs due to the presence of a faulty gene. If an individual is autosomal dominant then the defective gene bought a single copy from one parent and if the person is carrying autosomal recessive
disorder then the defective gene came from both parents. Examples include cystic fibrosis, sickle cell
anemia, anemia, muscular dystrophy, hemophilia, and Huntington's syndrome.
Mitochondrial genetic Disorder
Changes in the DNA of mitochondria, and its components within the cell are the main cause of mitochondrial gene disease. When the chromosome and mitochondrial DNA are separated from the nucleus during cell division. During gamete formation, mitochondrial DNA is inherited from parents to offspring. Examples are optic atrophy and coenzyme Q12 deficiency.
Some of the examples of genetic disorders applied in clinical
research trials are:
Sickle Cell Disease:
Genetically hereditary red blood cell disease is
known as sickle cell disease. Hemoglobin found in red blood cells is an oxygen-carrying pigment. Normal red blood cells provide oxygen to every region of the body. Red blood cells with sickle cell disease have sickle-shaped red cells
that are oval in shape and could not provide blood flow, they hinder the flow of blood
to other parts of the body.
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| Example of Genetic Disorder |
Down’s Syndrome:
When the last pair of chromosome 21 adds extra
genetic information during cell division, it leads to a genetic disease known as
Down syndrome. It is common in children. A newborn has 46 chromosomes.
Chromosome 21 has an additional copy in babies infected with Down syndrome.
Anemia:
Anemia is a genetic condition found mostly in
children. The condition is associated with a lack of platelets, RBCs, and WBCs in the blood cell line.
SCID:
It is a rare disease known as severe combined immunodeficiency caused by an abnormality
in genes involved in growth. It affects immune cells that provide protection
against infection. SCID appears in babies at the time of birth, who get prone
to infections.
Ethical Considerations:
With the progress in genetic research come ethical considerations. Issues such as privacy, informed consent, genetic discrimination, and equitable access to genetic services and therapies need to be addressed to ensure the responsible application of genetic knowledge.
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