This document provides an overview of genes and heredity. It defines heredity as the passing of traits from parents to offspring via genetic information. A gene is the basic unit of heredity that determines characteristics and is made up of DNA. DNA is found in the cell nucleus and mitochondria, takes the form of a double helix, and contains genetic code in the form of four chemical bases. Genes are packaged into thread-like chromosomes that are found in the nucleus, with humans having 46 total chromosomes in diploid cells. The genotype refers to an organism's full genetic makeup, while the phenotype describes observable traits influenced by both genes and environment. Gregor Mendel discovered the laws of inheritance through his experiments with

2. GENES AND HERIDITY
ASIF NAWAZ KHAN
Mpill(Microbiology)
AUST

3. CONTENTS
 WHAT IS HEREIDTY
 WHAT IS A GENE
 WHAT IS DNA
 LOCATION OF DNA
 WHAT IS CHROMOSOMES
 TYPES OF CHROMOSOMES
 GENOTYPE AND PHENOTYPE
 DOMINANT AND RECESSIVE GENES
 MENDEL’S LAWS OF INHERITANCE

4. WHAT IS HEREDITY?
 Heredity means the passing on of traits from parents to their offspring , the
offspring cells or organisms acquire the genetic information of their parents.
 EXAMPLES:
Eye colour
Ear lobes attached or detached

5. WHAT IS A GENE?
 A basic physical and functional unit of heredity which is
transferred from a parent to offspring and is held to determine
some characteristic of the offspring.
 Characteristics like:
Skin colour
Hair colour
Eye colour
 Genes are made up of DNA
 Humans have between 20,000 and 25,000 genes.
 Most genes are the same in all people, but a small number of
genes (less than 1 percent of the total) are slightly different
between people.
 These small differences contribute to each person’s unique
physical features.

6. WHAT IS DNA ? DNA, or deoxyribonucleic acid, is the hereditary material in humans and
almost all other organisms.
 DNA is a double-stranded helix, with the two strands connected by
hydrogen bonds.
 Nearly every cell in a person’s body has the same DNA.
 Most DNA is located in the cell nucleus (where it is called nuclear DNA),.
 But a small amount of DNA can also be found in the mitochondria (where it
is called mitochondrial DNA or mtDNA).
 The information in DNA is stored as a code made up of four chemical bases:
Adenine (A) ,Guanine (G)
Cytosine (C),Thymine (T)
 Human DNA consists of about 3 billion bases, and more than 99 percent of
those bases are the same in all people.
 American biologist James Watson and English physicist Francis Crick
discovered DNA in the 1950s.

7. LOCATION OF DNA

8. WHAT IS A CHOROMOSOMES?
 The DNA molecule is packaged into thread-like
structures called chromosomes.
 Each chromosome is made up of DNA tightly coiled
many times around proteins called histones that support
its structure.
 If we extract whole DNA from one person’s body it can
stretched to the sun not once but 600 times.
 Chromosomes are the highest organized structure of
DNA.
 Human contain 46 numbers of chromosomes.
 Two types of chromosomes.
Haploid
Diploid

9. TYPES OF CHROMOSOMES
 In males the chromosomes are XY.
 In females the chromosomes are XX
 Two types of chromosomes.
Haploid
Diploid
 Haploid cells have half the number of
chromosomes (n) - i.e. a haploid cell contains
only one complete set of chromosomes.
 Cells used in sexual reproduction, sperm and ova
(also known as Gametes).
 Diploid cells contain two complete sets (2n) of
chromosomes.

11. PHENOTYPE AND GENO TYPE
 PHENOTYPES:
The sum of an organism’s physical appearance is their
phenotype.
Environmental factors that may influence the
phenotype include nutrition,
temperature, humidity and stress.
 GENOTYPE:
The entire genetic makeup of an organism.
Genotype controls Phenotype but environmental
factors that may
influence the phenotype

12. DOMINANT AND RECESSIVES GENE
 DOMINANT GENES:
The genes which express themselves are dominant genes.
 RECESSIVE GENE:
The genes which is not expressed but still present in
body are called recessive genes.
Gene Gene

13. GREGOR MENDEL’s LAW OF INHERITANCE
 Gregor Mendel was known as Father of Modern
Genetics.
 Gregor Mendel, through his work on pea plants,
discovered the fundamental laws of inheritance.
 Mendel tracked the transfer of parental genes and
their appearance in the offspring as dominant or
recessive traits.
 GREGOR MENDEL GIVE 3 LAW’s OF
INERITANCE
1. The Law of Segregation
2. The Law of Independent Assortment
3. The Law of Dominance