Download Human genetic L.Saba Abood

Human genetic
GENETICS:
variation.
L.Saba Abood
It is the science that deals with the study of heredity and
came from the word gen, genetikos meaning generative and genesis meaning
beginning.
• HEREDITY: transmission of traits from parent to offspring.
• VARIATION: similarities and differences.
The genetic information of an individual is contained in the chromosomes.
Every human cell contains 23 pair of chromosomes.
One pair is called sex chromosomes Male: XY, Female: XX, other 22 pairs of
homologous chromosomes are called autosomes (each chromosome in pair are
identical to the other).
Different organisms have different numbers of chromosomes: human cells usually
have 46 chromosomes, dogs have 78 chromosomes, while kangaroos have only 12
chromosomes.
Chromosome:
It is a combination of two words, i.e., “Chroma”-means ‘colour’ and “Somes”means ‘body’.
it is the structural unit of genetic material, rod shaped, made up of sister
chromatids joined at the centromere.
Chromatid: is a single, linear double-strand DNA molecule and proteins called
histones.
Each complex of DNA with core histones is called a nucleosome, which is the
basic structural unit of chromatin.
Number of chromosomes
Diploid - two sets of chromosomes.(produced by mitosis)
Haploid - one set of chromosomes. (produced by meiosis)
Structure of Chromosomes
– Homologous chromosomes are identical pairs of chromosomes.
– One inherited from mother and one from father
– made up of sister chromatids joined at the centromere.
1
Human genetic
L.Saba Abood
DNA :
Deoxyribonucleic acid is a double helix formed by base pairs attached to a sugarphosphate backbone. consists of a ribose sugar with a “missing oxygen” (that’s
the de-oxy part), It is a polymer made of repeating subunits called nucleotides
DNA Structure
A nucleotide consists of three main components:
1. deoxyribose (a pentose sugar)
2. a nitrogen-containing base (there are four different ones)
3. phosphate group
The bases of DNA:
They are divided into two groups
1. Pyrimidines (Thymine and Cytosine)
2. Purines (Adenine and Guanine)
Nucleotides are linked together by covalent bonds called phosphodiester linkage
2
Human genetic
L.Saba Abood
DNA Double Helix and Hydrogen
Bonding
Made of two strands of nucleotides that
are joined together by hydrogen
bonding
Hydrogen bonding occurs as a result of
complimentary base pairing
• Adenine always pairs with thymine
because they form two H bonds with
each other
• Cytosine always pairs with guanine
because they form three hydrogen
bonds with each other
The Gene
is the basic physical and functional unit of heredity. Genes, which are made up of
DNA, act as instructions to make molecules called proteins.
Transcription :is the process by which DNA is copied (transcribed) to mRNA,
which carries the information needed for protein synthesis.
Translation : The mRNA formed in transcription is transported out of the
nucleus, into the cytoplasm, to the ribosome (the cell's protein synthesis factory).
The cell cycle
it’s a sequence of events in which the cell duplicates its contents and then divides
in two. This type of duplication and division is called Cell Cycle.
Cell cycle has two parts:
I.
II.
interphase (growth and preparation)
cell division
1. mitosis (nuclear division)
2. cytokinesis (cytoplasm division)
3
Human genetic
L.Saba Abood
I. interphase (growth and preparation)
Most of the cell cycle is spent in interphase this is the time when:
1.
2.
3.
4.
5.
6.
the organelles carry on their usually functions
the cell get ready to divide
it grow larger
the number of organelles doubles
amount of chromatin doubles
DNA synthesis occurs
interphase is divided into 3 stages:
1) G1 stage: the cell return to normal size and resumes its functions, and
doubles its organelles (e.g., mitochondria and ribosomes)
2) S stage include DNA synthesis: a copy is made of all DNA in the cell,
by untwisting and replication of DNA
3) G2 : the cell synthesizes the proteins needed for cell division.
** G for growth of the cell which happen through these stages
4
Human genetic
L.Saba Abood
II.cell division
A.
Mitosis (nuclear division)
B.
Cytokinesis (cytoplasm division)
A.
Mitosis:
it’s the division of the nucleus of the cell into two new nuclei.
Mitosis is divided into 4 stages:
1. Prophase:
• Chromosome condense
• Microtubles form
• The nuclear envelope breaks down
2. Metaphase: Chromosomes are pulled to
center of cell Line up along “metaphase
plate”
3. Anaphase:
• Centromeres divide
• Spindle fibers pull one set of
chromosomes to each pole
• Precise alignment is critical to
division
4. Telophase
• Nuclear envelope form around
chromosomes
• Chromosomes uncoil
B. Cytokinesis
• Division of the cytoplasm occurs
• 2 daughter cells are formed
• Each new cell has a complete set of chromosomes
• New cell begins interphase
Meiosis :
A division of the nucleus that reduces chromosome number by half.
Its occurs only in reproductive organs, ovaries and testes, purpose of
meiosis is to produce sperm and egg.
5
Human genetic
L.Saba Abood
• Meiosis involves 2 cell divisions
• Meiosis produces 4 cells from 1 parental cell
• Each of the 4 daughter cells has 23 individual chromosomes rather
than 23 pairs of chromosomes
• Meiosis reduces the chromosome number from diploid to haploid
• Meiosis, like mitosis, is preceded by chromosome duplication
• However, in meiosis the cell divides twice to form four daughter
cells
• There are two stages of meiosis: Meiosis I and Meiosis II with
• Only 1 replication
Meiosis I: ( reduces the chromosome number by one half)
four phases: Prophase I, Metaphase I, Anaphase I, Telophase I.
In Meiosis II : the daughter cells undergo a second division; much like
mitosis but NO ADDITIONAL REPLICATION OCCURS
Meiosis II resembles a mitotic division:
-prophase II: nuclear envelopes dissolve and spindle apparatus forms
-metaphase II: chromosomes align on metaphase plate
-anaphase II: sister chromatids are separated from each other
-telophase II: nuclear envelope re-forms; cytokinesis follows.
6
Human genetic
L.Saba Abood
7