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Genetics o The branch of biology that studies heredity and variation, especially the mechanisms of hereditary transmission of characteristics from parent to offspring.o positive charged o H1, H2A, H2B, H3, H4 Diverse group of proteins involved in various cellular processes, including gene regulation.The shape is ultimately determined by the specific function of the cell as follows: o Red blood cells (discoidal) o Nerve cells )stellate( o guard cells (Lenticular( 4-Structure A eukaryotic cell consists of the following components : A. Cell wall and plasma membrane B. Cytoplasm C. Nucleus Nucleus o The nucleus is centrally located and spherical cellular component which controls all the vital activities of the cytoplasm and carries the hereditary material the DNA in it. o The nucleus consists of the following three structures : 1-Nuclear envelope and nucleoplasm: Nuclear envelope comprises two nuclear membranes (an inner nuclear membrane and an outer nuclear membrane).

Genetics
• The branch of biology that studies heredity and
variation, especially the mechanisms of hereditary
transmission of characteristics from parent to
offspring.
Heredity
(Similarities)
❑Transmission of genetic characters from parent
to offspring
• DNA replication
• Repair of DNA
Variation
(differences)
❑Differences in the individuals of the same species
• Recombination
• Mutation
• The branch of biology that is concerned with the microscopic examination of cells, including
their structure, function, and formation.
Cytology
Cell
• The basic unit of organization or structure of all living matter.
• The general features of different types of eukaryotic cells which are as follows:
1-Cell Number
• unicellular organism
• multicellular organisms
2-Cell Size
• Eukaryotic cells(mostly ranging between 10 to 100 µm)
• prokaryotic cells (mostly ranging between 1 to 10 µm)
Largest animal cell is the egg of ostrich, having a diameter of 18 cm.
3-Cell Size
• The shape of the cell may be variable (Amoeba) or fixed.
The shape is ultimately determined by the specific function of the cell as
follows:
• Red blood cells (discoidal)
• Nerve cells )stellate(
• guard cells (Lenticular(
4-Structure
A eukaryotic cell consists of the following components :
A. Cell wall and plasma membrane
B. Cytoplasm
C. Nucleus
Nucleus
• The nucleus is centrally located and spherical cellular component which controls all the vital
activities of the cytoplasm and carries the hereditary material the DNA in it.
• The nucleus consists of the following three structures :
1-Nuclear envelope and nucleoplasm:
Nuclear envelope comprises two nuclear membranes (an inner nuclear membrane and an outer nuclear membrane). At
certain points, the nuclear envelope is interrupted by structures called pores or nucleopores which regulate exchange
between the nucleus and cytoplasm.
2- Nucleolus
Nucleus contains in its nucleoplasm a conspicuous, darkly stained, circular sub-organelle, called nucleolus. Nucleolus is
the site where ribosomes are manufactured.
3- chromosomes
Structure consisting of DNA and associated proteins that carries and transmits genetic information.
The number
of pairs of
chromosomes
varies among
organisms
organism No. Chromosome
Human 2n=46 , n=23
Horse 2n=64 , n=32
Fruit fly 2n=8 , n=4
Onion 2n=16 , n=8
Rice 2n=24 , n=12
Maize 2n=20 , n=10
Morphological
structure of
chromosomes
Chromosomes are classified
into four basic types:
1-Metacentric: The centromere is located
approximately in the middle, so the chromosome has
two arms of equal length.
2-Submetacentric: The centromere is displaced
toward one end, creating a long arm and a short arm.
3-Acrocentric: The centromere is near one end,
producing a long arm and a knob, or satellite, at the
other end.
4-Telocentric: The centromere is at or very near the
end of the chromosome.
chemical composition of chromosome
• Composed of thin chromatin thread called chromatin fibers.
chromatin
proteins DNA
Histones Non-Histones
Structural proteins that package and condense
DNA into chromatin.
• positive charged
• H1, H2A, H2B, H3, H4
Diverse group of proteins involved in various cellular
processes, including gene regulation.
• Negative charged
• Transcription factors, polymerases, helicases, and
many more.
NUCLEOSOME
• The basic unit of chromatin contains146
base pairs of DNA warped 1.75 times
around an octamer of eight histone
proteins (two copies each of H2A, H2B,
H3, and H4).
Chromatin
Euchromatin Heterochromatin
• Less condensed
• Euchromatin constitutes the majority of the
chromosomal material and is where most
transcription takes place
• Structure genes
• More condensed
Characterized by a general lack of transcription, the
absence of crossing over, and replication late in the S
phase
• Constitutive:
• It is fixed and form and function
• It does not reverse to euchromatin stage
• At the centromeres and telomeres; the Y chromosome
also consists largely of constitutive heterochromatin
• Facultative
• It has the faculty to return to the normal euchromatin
• The in active X chromosome is made up of facultative
heterochromatin
Karyotype
• A karyotype is the number of appearance of
chromosomes in the nucleus of a eukaryotic cell.
• It describe the number of chromosomes, and what
they look like under a light microscope.
• Attention is paid to their length and the position of the
centromere.
• The study of whole set of chromosomes.
• The study of chromosomal aberration and cellular
functions.