11.0     INTRODUCTION

GENETICS – It is the scientific study of genes, heredity, and genetic variation in living organisms.

HEREDITY – The transmission of genetic information from one generation to the next, determining the traits of an organism.

VARIATION – It is the morphological and physiological differences which occur within a species which could be hereditary or acquired from the environment.

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          11.1     BASIC CONCEPTS IN GENETICS

• Gene: They are the basic unit of inheritance, located in the chromosomes.
• Allele: Different forms of a gene that can exist at a specific locus on a chromosome.
• Genotype: The genetic makeup of an organism, represented by the alleles it possesses (e.g., AA, AS, SS).
• Phenotype: The observable physical and physiological traits of an organism, determined by its genotype and environmental factors.
• Incomplete Dominance: The phenotype of heterozygotes is intermediate between the phenotypes of the two homozygotes (e.g., red and white flowers producing pink flowers).
• Codominance: Both alleles in a heterozygote are fully expressed, resulting in a phenotype that shows both traits (e.g., AB blood type).
• Mutations: Change in the genetic make-up of an organism that can lead to new traits; can be beneficial, harmful, or neutral.
• Locus: The site for location of a gene in a chromosome.
• Sex-linked characters: Characteristics associated with the sex of an individual, the gene for the expression of the character is borne on the X- chromosomes e.g haemophilia, albinism, baldness, sickle cell anaemia, e.t c.
• Hybridization: The crossing of plants with contrasting characters; mono-hybridization involves the crossing of two pure traits while di-hybridization involves the crossing of two pairs of contrasting characters.
• Haploid: It is when an organism has one set of chromosomes in the gamete. It is represented by a small letter(n).
• Diploid: It is when an organism has two sets of chromosomes in the body cell. It is represented by (2n).
• Homozygous: An individual is said to be homozygous if it has two similar or identical genes for the same character e.g (TT) for tallness or (tt) shortness.
• Heterozygous: An individual is said to be Heterozygous if the two members of a pair of genes controlling a pair of contrasting characters are different e.g (Tt) for tallness or a plant with a Rr composition has a heterozygous red flower plant.

11.2     MENDELIAN GENETICS

Gregor Mendel, known as the father of genetics, conducted experiments with pea plants and established fundamental principles.

MENDEL’S FIRST LAW OF INHERITANCE – Law of Segregation: During gamete formation, the two alleles for a trait segregate from each other, so each gamete carries only one allele for each gene.

MENDEL’S SECOND LAW OF INHERITANCE – Law of Independent Assortment: Genes for different traits assort independently of one another during gamete formation, leading to genetic variation.

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          11.3     CHROMOSOMES AND DNA

• Chromosomes: Structures made of DNA and proteins that carry genetic information. Humans have 46 chromosomes (23 pairs).
• DNA (Deoxyribonucleic Acid): The molecule that carries genetic information, composed of nucleotides (adenine, thymine, cytosine, guanine), phosphate, deoxyribose.
• DNA Replication: The process by which DNA makes a copy of itself before cell division, ensuring genetic continuity.

PHENOTYPIC VARIATION – Phenotypic variation refers to observable differences in traits.

TYPES OF VARIATION

• Morphological variation /Continuous Variation: It refers to the noticeable physical appearance of the same species (e.g., height, skin colour) and are often influenced by multiple genes (polygenic inheritance).
• Physiological variation/ Discontinuous Variation: It refers to the differences in the ways individual of the same species behave or react to conditions in their environment(e.g., Ability to roll the tongue,fingerprints, e.t.c) and are often controlled by a single gene or a few genes.

11.4     APPLICATION OF VARIATIONS

• It is used in the Determination of paternity.
• It is used in the classification of the human race.
• It is useful in crime detection scenarios.