Concept of Genetics form four full notes
Concept of Genetics
The concept of
Genetics
Explain the concept of the genetics
Genetics is a branch
of biology which deals with the study of heredity and variations in
organisms.
Heredity refers to the
transmission of genetic information from one generation to another. That is,
the passing on of features or characteristics from parents to offspring or
progeny. In humans, for example, features such as hair colour and body shape of
the parents can be passed on (inherited) to their children. In genetics, a
feature that can be inherited by the offspring from the parent is known as a
trait. Thus, features such as hair texture, hair colour, and skin colour are
all traits.
The hereditary
characteristics are passed on from parents to their offspring through distinct
units called genes. Genes are hereditary materials or factors, which determine
a specific characteristic or trait in an organism.
Variations are the
observable differences in organisms of the same species. Living things arise
from other living things of the same species through reproduction. However,
organisms show a great number of variations. No two organisms are exactly the
same. The variations may be due to mutations of genetic material (DNA) caused
by x-rays, gamma rays, ultra radiations or radioactive elements. Variations may
also occur during gamete formation and combination of gametes at fertilization.
Genetics, therefore,
attempts to explain either how organisms do resemble their parents in certain
features or differ from their parents in other features.
Test Yourself
Common terms used in
Genetics
State common terms used in genetics
In genetics, there are
several terms that are often used to describe different genetic features, variations
or phenomena. Defined below are some of the common terms used in genetics.
a.
F1 generation: The first filial generation arising from the
crossing of two pure breeds.
b.
F2 generation: The generation obtained by crossing
individuals of the F1 generation.
c.
Genotype: The genetic makeup or constitution of an organism, which is
responsible for certain physical traits.
d.
Phenotype: The outward appearance of an organism determined by a gene.
e.
Haploidy (n): Having one set of unpaired chromosomes in the nucleus.
f.
Diploidy (2n): Having two sets of homologous (similar)
chromosomes in the nucleus.
g.
Alleles: Different forms of the same gene occupying the same position
on a chromosome, for example T or t for height.
h.
Homozygosity: The state of possessing two identical forms (alleles) of a
particular gene, one inherited from each parent, for example tt, TT BB or bb.
i.
Heterozygosity: The state of possessing two different
alleles of a particular gene at one or more corresponding chromosomal loci, one
inherited from each parent, for example Tt or Bb.
j.
Dominance: A relationship between alleles of one gene, in which the
effect on phenotype of one allele masks the contribution of a second allele at
the same locus. The first allele is dominant and the second allele is recessive.
For example, in height, both TT and Tt express tallness. Here, the contribution
of “t” allele to the phenotype is masked by “T” allele.
k.
Recessiveness: A condition where an allele can only express
itself in a homozygous form, for example tt for dwarfness.
l.
Mutation: A sudden, random change in the genetic make up of a cell,
causing it and all cells derived from it to differ from normal cells.
m.
Mutagen: An agent capable of increasing the rate of mutation in an
organism, such as formaldehyde or nitrous acid.
n.
Selfing: Crossing offspring of the same pair of parents. For example,
the crossing of offspring of F1 generation to produce F2 (F1×F1 = F2) is called
selfing.
Test Yourself
Genetics Materials
The concept of
Genetics Materials
Explain the concept of genetics Materials
Hereditory
characteristics are passed from parents to their offspring through distinct
units called genes.There are a lot of genes in an organism’s body. Genes are
arranged in a linear manner, making chromosomes.
Chromosomes are thread
like structures found in the nuclei of all body cells. Gene is made up of
chemical substances called Nucleic acid.
There are two types of
nucleic acids found in cells, these are:
1.
Deoxyribonucleic acid (DNA)
2.
Ribonucleic acid (RNA)
These acids are made
up of building blocks called nucleotides. Each nucleotide consists of three
molecules linked together, that is a pentose sugar, phosphoric acid and organic
base.
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