1. Genetics
Genetics is the branch of biology that deals with
the study of heredity and variation.
Heredity ; the transmission of characters from
parents to offsprings.
Variation ;the differences between closely related
organisms.
Azhar Zeb M.Sc Zoology izhaar99@yahoo.conm
2. CHROMOSOMES AND GENES
CHROMOSOMES are known as hereditary vehicles because they transfer
characters from one generation to the next generation.
chromosome is an organized structure of DNA and protein that is found in the
nucleus of the cells.
Chromosomes are in pairs, one from each parent.
Genes are carried on the chromosomes.
Genes control the characteristics of living
Organisms.
Before a cell starts dividing, the chromosomes are duplicated.
This process produces sister chromatids. sister chromatids joined at the
centromere.
Azhar Zeb M.Sc Zoology izhaar99@yahoo.conm
3.
Eukaryotic chromosomes exist in four major types based on the position
of the centromere with equal arms.
Metacentric chromosome;centromere is present at the middle point.
Acrocentric;centromere located closer to one endwith unequal arms.
Telocentric;centromere located at the end of chromosome.
Submetacentric;chromosome having arms of unequal length.
Azhar Zeb M.Sc Zoology izhaar99@yahoo.conm
5.
Each species have a constant number of chromosomes
e.g humans have 46 chromosomes.
Any deletion or addition in this number results in
serious disorders like down,s syndrome etc.
The process of meiosis is responsible for maintaining a
constant number of chromosomes.
Homologous chromosomes ;Identical Chromosome
which forms pairs during meiosis in diploid organisms.
One of maternal origin (inherited from mother) the
other of paternal origin (inherited from father).
Azhar Zeb M.Sc Zoology izhaar99@yahoo.conm
6.
Genes
A gene is a segment of DNA on a chromosome thad
codes for a specific protein thus determines a
particular trait.
Genes are the units of inheritance and are linearly
arranged on chromosomes
Each gene transfers a particular trait e.g. skin colour
from parents to offsprings..
In 1903 walter sutton found that genes and
chromosomes behave in a parallel fashion.
Morgan work on drosophila confirmed that genes are
linearly arranged on chromosomes.
Azhar Zeb M.Sc Zoology izhaar99@yahoo.conm
7. Crossing over
Crossing over ;The exchange of segments between
homologous chromosomes during the diplotene stage
of meiosis.
During the early stages of meiosis similar
chromosomes forms pairs and exchange parts with
one another.
This exchange may occur in more than one place.
Crossing over produces chromosomes which are
different from parental chromosomes.
Vast genetic diversity is produced in a population as a
result of crossing over.
Azhar Zeb M.Sc Zoology izhaar99@yahoo.conm
