The Basics of Genetics

Written by S. Khatiwada

Despite being the same species, all of us are born with different faces, and characteristics. Genetics plays a huge role in differentiating humans morphologically.

Genetics is the branch of biology that deals with the study of genes, genetic variation, and heredity in living organisms.

To understand genetics we need to begin by learning what chromosomes are.

A chromosome is a package of DNA with the genetic material of an organism. The genetic material is transferred and combined through sexual reproduction among two opposite sex.

Humans have 23 pairs of chromosomes (a total of 46 chromosomes). One set of chromosome pairs comes from the female parent, and the other set comes from the male parent.

Autosomes, a type of chromosome, function as the coding instructions for proteins which are used to create every cell, enzyme, tissue, bone, and organ within the body. Other chromosomes, the X and Y chromosomes, determine an embryo’s sex as male or female. They are called sex chromosomes. DNA is organized into structures called chromosomes within the cell nucleus.

What is DNA?

DNA is a double stranded molecule that makes up genes. It carries the genetic instructions used in the growth, development, functioning, and reproduction of all known living organisms. The structure of DNA was first proposed by James Watson and Francis Crick in 1953.

Genes are made up of DNA sequences. A gene consists of a long combination of four different nucleotide bases, which are the basic building blocks of DNA. The four types of bases are:

A (adenine)

C (cytosine)

G (guanine)

T (thymine)

A gene consists of two strands. Among the four bases, adenine pairs with thymine and cytosine pairs with guanine. The sequence of these bases determines the instructions in the DNA. For example; the sequence ATCGTT codes for blue eyes. Genes determine traits such as eye color, height, and susceptibility to certain diseases.

What are alleles ?

Different versions of a gene are called alleles. There are different alleles for the gene that determines blood type, resulting in blood types like A, B, AB, and O. The genes that are expressed is known as dominant gene and the gene which remains hidden or unexpressed is known as a recessive gene.

In1865, Mendel cross- pollinated pea plants based on their different features to make discoveries on how traits are inherited between generations. He choose a pea plant because they grow quickly, are easy to breed, and have a variety of traits, perfect for the experiment. He found that taller height is a dominant trait and shorter height is a recessive trait in pea plants.

Similarly, humans also have dominant and recessive character. For example:

1. Broad lips are dominant character and thin lips are a recessive character.

2. Unattached earlobes are dominant over attached earlobes.

3. Freckles show a dominant inheritance pattern.