2. Do you Know them ?
Do they look like
one to each other ?
3. Do you see any ways that these children are
similar to their parents or brothers and sisters?
4. Look around. Is anyone just like you?
You and everyone else are unique. No two
people are exactly alike, including identical
twins. However, many of your traits are
inherited.
People in a family may have things in
common. They can share traits.
Through heredity, living things inherit traits
from their parents. Traits are physical
characteristics. You resemble your parents
because you inherited your hair and skin
color, nose shape, height, and other traits
from them.
10. So,what is heredity ?
Heredity is the passing on of characteristics
from one generation to the next.
It is the reason why offspring look like their
parents. It also explains why cats always give
birth to kittens and never puppies.
The process of heredity occurs among all living
things including animals, plants, bacteria,
protists and fungi.
The study of heredity is called genetics and
scientists that study heredity are called
geneticists.
11. Heredity and Genetics
Your genes determine whether or not you
possess certain physical traits. Your genes
make you blue eyed or brown eyed, or have
brown or blond hair. These traits are highly
complex, and involve the interaction of many
genes.
12. Objective:
• The learner will realize that certain
characteristics are passed from parent to
offspring
13. What Exactly is a chromosome?
Chromosomes are the rod-
shaped, filamentous bodies present in the
nucleus, which become visible during cell
division.
They are the carriers of the gene or unit of
heredity.
Chromosome are not visible in active nucleus
due to their high water content, but are
clearly seen during cell division.
16. The size of the chromosomes in mitotic phase of animal
and plants sp generally varies between 0.5 µ and 32
µ in length, and between 0.2 µ and 3.0 µ in diameter.
The longest metaphase chromosomes found in Trillium -
32 µ.
The giant chromosomes found in diptera and they may
be as long as 300 µ and up to 10 µ in diameter.
In general, plants have longer chromosomes than animal
and species having lower chromosome numbers have
long chromosomes than those having higher
chromosome numbers
Among plants, dicots in general, have a higher number of
chromosome than monocots.
Chromosomes are longer in monocot than dicots.
17. • In order to understand chromosomes and their
function, we need to be able to discriminate among
different chromosomes.
• First, chromosomes differ greatly in size
• Between organisms the size difference can be over
100-fold, while within a sp, some chromosomes are
often 10 times as large as others.
• In a species Karyotype, a pictorial or photographic
representation of all the different chromosomes in a
cell of an individual, chromosomes are usually ordered
by size and numbered from largest to smallest.
18. • Chromosomes may differ in the position of the
Centromere, the place on the chromosome
where spindle fibers are attached during cell
division.
• In general, if the centromere is near the
middle, the chromosome is metacentric
• If the centromere is toward one end, the
chromosome is acrocentric or submetacentric
• If the centromere is very near the end, the
chromosome is telocentric.
19.
20. • The centromere divides the chromosome into
two arms, so that, for example, an acrocentric
chromosome has one short and one long arm,
• While, a metacentric chromosome has arms of
equal length.
• All house mouse chromosomes are
telocentric, while human chromosomes
include both metacentric and acrocentric, but
no telocentric.
22. Definitions of the gene
• The gene is to genetics what the atom is to
chemistry.
• The gene is the unit of genetic information
that controls a specific aspect of the
phenotype.
• The gene is the unit of genetic information
that specifies the synthesis of one
polypeptide.
23. How has the concept of a gene
developed in the minds of
geneticists?
24. Mendel (1866)
Inheritance is governed by “characters”
or “constant factors” that each controls
a phenotypic trait such as flower colour.
25. What is so special about chromosomes ?
1.They are huge:
One bp = 600 dalton, an average chromosome is 107 bp
long = 109- 1010 dalton !
(for comparison a protein of 3x105 is considered very big.
2. They contain a huge amount of non-
redundant information (it is not just a big
repetitive polymer but it has a unique sequence) .
3. There is only one such molecule in each
cell. (unlike any other molecule when lost it cannot be
re-synthesized from scratch or imported)
27. Genetic material of cells…
• GENES – units of genetic material that CODES
FOR A SPECIFIC TRAIT
• Called NUCLEIC ACIDS
• DNA is made up of repeating molecules
called NUCLEOTIDES
29. A HISTORY OF DNA
• Discovery of the DNA double helix
A. Frederick Griffith – Discovers that a factor in
diseased bacteria can transform harmless bacteria
into deadly bacteria (1928)
B. Rosalind Franklin - X-ray photo of DNA.
(1952)
C. Watson and Crick - described the
DNA molecule from Franklin’s X-ray.
(1953)
SEE p. 292-293
30. Watson & Crick proposed…
•DNA had specific pairing between the
nitrogen bases:
ADENINE – THYMINE
CYTOSINE - GUANINE
•DNA was made of 2 long stands of
nucleotides arranged in a specific way
called the “Complementary Rule”
34. Chargaff’s Rule
• Adenine must pair with Thymine
• Guanine must pair with Cytosine
• Their amounts in a given DNA molecule will be about
the same.
G CT A
36. Genetic Diversity…
• Different arrangements
of NUCLEOTIDES in a
nucleic acid (DNA)
provides the key to
DIVERSITY among living
organisms.
37. The Code of Life…
• The “code” of the chromosome is the SPECIFIC
ORDER that bases occur.
A T C G T A T G C G G…
38. DNA is wrapped tightly around histones
and coiled tightly to form chromosomes
See p. 297
39. DNA Replication
• DNA must be copied
• The DNA molecule produces 2
IDENTICAL new complementary
strands following the rules of base
pairing:
A-T, G-C
•Each strand of the
original DNA serves as a
template for the new
strand See p. 298
40. DNA Replication
• Semiconservative
Model:
1. Watson and Crick
showed: the two strands of
the parental molecule
separate, and each
functions as a template for
synthesis of a new
complementary strand.
. Parental DNA
DNA Template
New DNA
