Heredity

BY :SYAHRIANI

Do you Know them ?

Do they look like one to each other ?

Do you see any ways that these children are similar to their parents or brothers and sisters?

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.

Eye Color

Hair color

Hair Texture

Skin Color

Body Shape

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.

Heredity and GeneticsYour 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.

Objective:

• The learner will realize that certain characteristics are passed from parent to offspring

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.

Organism No. chromosomes

• Human 46• Chimpanzee 48• Dog 78• Horse 64• Chicken 78• Goldfish 94• Fruit fly 8• Mosquito 6• Sequoia 22• Round worm 2

Organism No. chromosomes

• Onion 16• Mold 16• Carrot 20• Tomato 24• Tobacco 48• Rice 24• Maize 20• Haploppus gracilis 4• Crepis capillaris 6

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.

• 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.

• 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.

• 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.

What is a gene?

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.

How has the concept of a gene developed in the minds of geneticists?

Mendel (1866)

Inheritance is governed by “characters” or “constant factors” that each controls a phenotypic trait such as flower colour.

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)

DNA(Deoxyribonucleic Acid)

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

DNA Nucleotide

OO=P-O O

Phosphate Group

NNitrogenous base (A, G, C, or T)

CH2

O

C1C4

C3 C2

5

Sugar(deoxyribose)

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

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”

DNA Double Helix

NitrogenousBase (A,T,G or C)

“Rungs of ladder”

“Legs of ladder”

Phosphate &Sugar Backbone

DNA Double Helix

P

P

P

O

O

O

1

23

4

5

5

3

3

5

P

P

PO

O

O

1

2 3

4

5

5

3

5

3

G C

T A

Nitrogenous Bases

• PURINES1. Adenine (A)

2. Guanine (G)

• PYRIMIDINES3. Thymine (T)

4. Cytosine (C) T or C

A or G

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

BASE-PAIRINGS

CG

H-bonds

T A

Genetic Diversity…• Different arrangements

of NUCLEOTIDES in a nucleic acid (DNA) provides the key to DIVERSITY among living organisms.

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…

DNA is wrapped tightly around histones and coiled tightly to form chromosomes

See p. 297

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

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