Biyo-Tek Günlüğüm…

Basic Principles of Genetics

Mendel's Studies of Traits

Many of your traits,including the color and shape of your eyes, the texture of your hair, and even your height and weight, resemble those of your parents.
The passing of traits from parents to offspring is called heredity

The scientific study of heredity began more than a century ago with the work of an Austrian monk named Gregor Johann Mendel.

Mendel was the first to develop rules that accurately predict patterns of heredity.

The patterns that Mendel discovered form the basis of genetics, the branch of biology that focuses on heredity.

The basic concepts of genetics should be learned to better understand Genetics.

The genetic code is carried by an amazing molecule called Deoxyribonucleic acid,or DNA.

A chromosome is a thread of DNA wrapped around certain proteins.

Certain parts of each DNA code for different characteristics. We call these bits of information as genes.

More about chromosomes:

There are totally 46 chromosomes in human body cells.

This total number of chromosomes is called as Diploid number and represented as 2n because chromosomes are found in pairs.

Eggs and sperms (gametes) have 23 chromosomes and this is called haploid number (n)

Each pair of chromosome in a diploid cell:

• are identical (means have the same genes)
• are called as homologous chromosomes

You can see a human karyotype above. (Picture of all sets of chromosomes)

Each trait is usually controlled by a pair of genes located on the homologous chromosomes. The alternative forms of genes for the same trait are called allele genes.

These two allele genes code for the same trait but structurally may not be the same. (Allele genes for the eye color, blue eye color gene and brown eye color gene)

Stronger allele gene which masks the effect of the other gene is called dominant gene.

Weaker allele gene is called recessive gene.

Genotype is the genetic composition of an individual (An individual's blue and brown eye color genes for eye color trait)

Phenotype is the outward appearance of an individual (Although the two different eye color genes individual has only brown eye color)

If the two alleles are the same we say that the individual is “homozygous” for that gene.

If they are different the individual is “heterozygous”.