CYTOGEN U1

Genetics

• Genetics is the study of heredity and variation of inherited characteristics.
• Cytogenetics is a branch of genetics that studies the structure and function of cells, especially chromosomes.
• Genes are sets of characteristics inherited from parents found on chromosomes and contain DNA.
• Heredity is the transfer of character or traits from parents to offspring.
• Variations refer to the similarities and differences between the character or traits among individuals of the same species.
• Genetic variation occurs due to mutations, which are any heritable change in the DNA sequence.
• Alleles are alternative forms of a gene, and genotype refers to the set of alleles for a given trait carried by an organism.
• Phenotype refers to the observable features of an organism.

Early History of Genetics

• Aristotle (350 B.C.) proposed the concept of "humors."
• William Harvey (1600s) proposed epigenesis, which states that an organism develops from a fertilized egg through a series of developmental events.
• Preformationism, another concept, proposes that a fertilized egg contains a complete miniature adult called a homunculus.
• Matthias Schleiden and Theodore Schwann (1830) proposed the cell theory, which states that all organisms are composed of basic structural units called cells.
• Louis Pasteur (1830) proposed that living organisms are derived from pre-existing organisms and consist of cells.
• Charles Darwin (1859) proposed the theory of natural selection, which states that existing species arose by descent with modification from ancestral species.
• Alfred Russel Wallace and Gregor Johann Mendel (1866) contributed to the development of modern genetics.

The Chromosome Theory of Inheritance

• In most eukaryotes, each species has a characteristic number of chromosomes called the diploid number (2n).
• Homologous chromosomes exist in pairs in diploid cells.
• Mitosis is the process by which chromosomes are copied and distributed so that each daughter cell receives a diploid set of chromosomes.
• Meiosis is the process by which cells produced by meiosis receive only one chromosome from each pair, resulting in a haploid number (n) of chromosomes.

Implications of Genetics

• Genetics helps in understanding the causation of diseases.
• Genetics helps in understanding normal variation between individuals.
• Genetics has led to possible means of prevention of genetic disorders through genetic counseling and antenatal diagnosis.
• Genetics serves to solve legal problems, such as disputed parentage.

Cells

• The discovery of cells is attributed to Robert Hooke, who observed cork cells in 1665.
• The cell theory was proposed by Theodor Schwann and Matthias Schleiden in 1839, and later added to by Rudolf Virchow in 1858.
• The principles of cell theory include:
  • All living things are made of cells.
  • The smallest living unit of structure and function of all organisms is the cell.
  • All cells arise from preexisting cells.
• Characteristics of all cells include:
  • A surrounding membrane
  • Containing protoplasm
  • Organelles (structures for cell function)
  • A control center with DNA

Cell Types

• Prokaryotic cells lack a nucleus and membrane-enclosed organelles.
• Eukaryotic cells have a nucleus and membrane-enclosed organelles.
• Organelles perform specific functions for the cell, such as protein synthesis, energy production, and waste management.

Cell Membrane

• The cell membrane, also known as the plasmalemma, is a selective permeable barrier between the cytoplasm and external milieu.
• The cell membrane has various functions, including:
  • Maintaining structural integrity of the cell
  • Controlling movement of substances
  • Regulating cell-to-cell interactions
  • Establishing transport systems
  • Transducing extracellular physical and chemical signals into intracellular events
• The cell membrane is composed of a phospholipid bilayer with integral and peripheral proteins.

Organelles

• Ribosomes are small particles composed of proteins and ribosomal RNA that function in protein synthesis.
• Endoplasmic reticulum (ER) is a largest membranous system of the cell that participates in protein synthesis, lipid synthesis, and detoxification.
• Golgi apparatus is a complex of flattened, membrane-bound sacs that function in protein modification and sorting.
• Lysosomes are membrane-bound sacs that contain hydrolytic enzymes and aid in digesting macromolecules, phagocytosing microorganisms, and cell debris.
• Peroxisomes are small, membrane-bound organelles that contain oxidative enzymes and participate in the catabolism of long-chain fatty acids.

Chromosomes

• Chromatin is a complex of DNA and proteins that represents the relaxed, uncoiled chromosomes of the interphase nucleus.
• DNA is the cell's genetic material that resides in the nucleus in the form of chromosomes, which are clearly visible during cell division.
• Heterochromatin is DNA that is generally not very active, while euchromatin is generally more active.
• Satellite DNA is a type of heterochromatin that consists of long stretches of repeat sequences.

Chromosome Structure

• A chromosome consists of two chromatids, which are identical copies of DNA.
• The centromere is the central region where the two chromatids are joined together.
• Telomeres are the ends of the chromosome that protect the DNA from degradation.
• Chromosomes can be classified into four types based on the position of the centromere: telocentric, acrocentric, sub-metacentric, and metacentric.

Cell Division

• Meiosis is a crucial process in reproduction that reduces the number of chromosomes from 2n to 1n, ensuring genetic variability and diversity of the gene pool.

Reproduction

• Chromosomes come in pairs, with one of each type of chromosome taken from each parent.
• The inheritance of gender is determined by the X and Y chromosomes.
• A karyotype is a chart used to identify the chromosomal composition of an individual and detect chromosomal abnormalities.

Barr Body

• The Barr body is a feature seen only in female cells that have two X chromosomes, one of which gets inactivated.
• X chromosome inactivation is a process that ensures females, like males, have only one functional X chromosome per cell.

Genetics

• Genetics is the study of heredity and variation of inherited characteristics.
• Cytogenetics is a branch of genetics that studies the structure and function of cells, especially chromosomes.
• Genes are sets of characteristics inherited from parents found on chromosomes and contain DNA.
• Heredity is the transfer of character or traits from parents to offspring.
• Variations refer to the similarities and differences between the character or traits among individuals of the same species.
• Genetic variation occurs due to mutations, which are any heritable change in the DNA sequence.
• Alleles are alternative forms of a gene, and genotype refers to the set of alleles for a given trait carried by an organism.
• Phenotype refers to the observable features of an organism.

Early History of Genetics

• Aristotle (350 B.C.) proposed the concept of "humors."
• William Harvey (1600s) proposed epigenesis, which states that an organism develops from a fertilized egg through a series of developmental events.
• Preformationism, another concept, proposes that a fertilized egg contains a complete miniature adult called a homunculus.
• Matthias Schleiden and Theodore Schwann (1830) proposed the cell theory, which states that all organisms are composed of basic structural units called cells.
• Louis Pasteur (1830) proposed that living organisms are derived from pre-existing organisms and consist of cells.
• Charles Darwin (1859) proposed the theory of natural selection, which states that existing species arose by descent with modification from ancestral species.
• Alfred Russel Wallace and Gregor Johann Mendel (1866) contributed to the development of modern genetics.

The Chromosome Theory of Inheritance

• In most eukaryotes, each species has a characteristic number of chromosomes called the diploid number (2n).
• Homologous chromosomes exist in pairs in diploid cells.
• Mitosis is the process by which chromosomes are copied and distributed so that each daughter cell receives a diploid set of chromosomes.
• Meiosis is the process by which cells produced by meiosis receive only one chromosome from each pair, resulting in a haploid number (n) of chromosomes.

Implications of Genetics

• Genetics helps in understanding the causation of diseases.
• Genetics helps in understanding normal variation between individuals.
• Genetics has led to possible means of prevention of genetic disorders through genetic counseling and antenatal diagnosis.
• Genetics serves to solve legal problems, such as disputed parentage.

Cells

• The discovery of cells is attributed to Robert Hooke, who observed cork cells in 1665.
• The cell theory was proposed by Theodor Schwann and Matthias Schleiden in 1839, and later added to by Rudolf Virchow in 1858.
• The principles of cell theory include:
  • All living things are made of cells.
  • The smallest living unit of structure and function of all organisms is the cell.
  • All cells arise from preexisting cells.
• Characteristics of all cells include:
  • A surrounding membrane
  • Containing protoplasm
  • Organelles (structures for cell function)
  • A control center with DNA

Cell Types

• Prokaryotic cells lack a nucleus and membrane-enclosed organelles.
• Eukaryotic cells have a nucleus and membrane-enclosed organelles.
• Organelles perform specific functions for the cell, such as protein synthesis, energy production, and waste management.

Cell Membrane

• The cell membrane, also known as the plasmalemma, is a selective permeable barrier between the cytoplasm and external milieu.
• The cell membrane has various functions, including:
  • Maintaining structural integrity of the cell
  • Controlling movement of substances
  • Regulating cell-to-cell interactions
  • Establishing transport systems
  • Transducing extracellular physical and chemical signals into intracellular events
• The cell membrane is composed of a phospholipid bilayer with integral and peripheral proteins.

Organelles

• Ribosomes are small particles composed of proteins and ribosomal RNA that function in protein synthesis.
• Endoplasmic reticulum (ER) is a largest membranous system of the cell that participates in protein synthesis, lipid synthesis, and detoxification.
• Golgi apparatus is a complex of flattened, membrane-bound sacs that function in protein modification and sorting.
• Lysosomes are membrane-bound sacs that contain hydrolytic enzymes and aid in digesting macromolecules, phagocytosing microorganisms, and cell debris.
• Peroxisomes are small, membrane-bound organelles that contain oxidative enzymes and participate in the catabolism of long-chain fatty acids.

Chromosomes

• Chromatin is a complex of DNA and proteins that represents the relaxed, uncoiled chromosomes of the interphase nucleus.
• DNA is the cell's genetic material that resides in the nucleus in the form of chromosomes, which are clearly visible during cell division.
• Heterochromatin is DNA that is generally not very active, while euchromatin is generally more active.
• Satellite DNA is a type of heterochromatin that consists of long stretches of repeat sequences.

Chromosome Structure

• A chromosome consists of two chromatids, which are identical copies of DNA.
• The centromere is the central region where the two chromatids are joined together.
• Telomeres are the ends of the chromosome that protect the DNA from degradation.
• Chromosomes can be classified into four types based on the position of the centromere: telocentric, acrocentric, sub-metacentric, and metacentric.

Cell Division

• Meiosis is a crucial process in reproduction that reduces the number of chromosomes from 2n to 1n, ensuring genetic variability and diversity of the gene pool.

Reproduction

• Chromosomes come in pairs, with one of each type of chromosome taken from each parent.
• The inheritance of gender is determined by the X and Y chromosomes.
• A karyotype is a chart used to identify the chromosomal composition of an individual and detect chromosomal abnormalities.

Barr Body

• The Barr body is a feature seen only in female cells that have two X chromosomes, one of which gets inactivated.
• X chromosome inactivation is a process that ensures females, like males, have only one functional X chromosome per cell.

Genetics

• The study of heredity and variation of inherited characteristics
• Cytogenetics: concerned with the study of the structure and function of cells, especially chromosomes
• Key concepts:
  • Genes: sets of characteristics inherited from parents found on chromosomes and contain DNA
  • Heredity: the transfer of characteristics or traits from parents to offspring
  • Variations: similarities and differences between characteristics or traits among individuals of the same species
  • Genetic variation: differences in the DNA sequence of individuals
• Early history of genetics:
  • Aristotle (350 B.C.): concept of "humors"
  • William Harvey (1600s): epigenesis (development from fertilized egg)
  • Matthias Schleiden and Theodore Schwann (1830): cell theory
  • Louis Pasteur (1859): living organisms derived from pre-existing organisms
  • Charles Darwin (1859): theory of natural selection
  • Alfred Russell Wallace (1859): natural selection based on observation of population growth
  • Gregor Johann Mendel (1866): traits passed from generation to generation in pea plants

The Chromosome Theory of Inheritance

• Each species has a characteristic number of chromosomes (diploid number)
• Homologous chromosomes: chromosomes in diploid cells exist in pairs
• Mitosis: chromosomes are copied and distributed to each daughter cell
• Meiosis: cells produced by meiosis receive only one chromosome from each pair, resulting in haploid number of chromosomes
• Implications of genetics:
  • Understanding of disease causation
  • Understanding of normal variation between individuals
  • Possible means of prevention of genetic disorders through genetic counseling and antenatal diagnosis
  • Solving legal problems involving disputed parentage

Cells

• Discovery of cells: Robert Hooke (1632)
• Cell theory:
  • All living things are made of cells
  • The smallest living unit of structure and function of all organisms is the cell
  • All cells arise from pre-existing cells
• Characteristics of all cells:
  • Surrounding membrane
  • Contains protoplasm
  • Organelles
  • Control center with DNA
• Types of cells:
  • Prokaryotic cells: no nucleus, no membrane-bound organelles
  • Eukaryotic cells: nucleus, membrane-bound organelles

Organelles

• Cell components that perform specific functions
• Key organelles:
  • Cell membrane (plasmalemma): selective permeable barrier between cytoplasm and external environment
  • Glycocalyx: carbohydrate chain that coats cell surface
  • Ribosomes: small particles composed of proteins and ribosomal RNA, involved in protein synthesis
  • Endoplasmic reticulum: largest membranous system of the cell, involved in protein synthesis and transport
  • Golgi apparatus: composed of flattened, slightly curved membrane-bound cisternae, involved in protein modification and sorting
  • Lysosomes: contain hydrolytic enzymes, aid in digesting macromolecules and recycling cellular waste
  • Peroxisomes: contain oxidative enzymes, involved in oxidizing fatty acids and amino acids
  • Mitochondria: involved in oxidative phosphorylation and lipid synthesis
  • Cytoskeleton: composed of thin filaments, intermediate filaments, and microtubules, provides structural support and shape to the cell
  • Nucleus: control center of the cell, contains DNA, involved in RNA synthesis and protein synthesis

Chromosomes

• Chromatin: complex of DNA and proteins, represents the relaxed, uncoiled chromosomes of the interphase nucleus
• DNA: the cell's genetic material, resides in the nucleus in the form of chromosomes
• Heterochromatin vs euchromatin:
  • Heterochromatin: generally not very active, compact during interphase
  • Euchromatin: generally more active, not condensed during interphase
• Chromosome structure:
  • Chromosome arms: short arm and long arm
  • Centromere: central region where the two chromatids are joined together
  • Chromatid: each chromosome consists of two identical copies of DNA
  • Telomere: ends of the chromosome, protect the DNA from degradation
• Classification of chromosomes:
  • Telocentric chromosome: centromere located at the very end of the chromosome
  • Acrocentric chromosome: centromere located near one end, creating a very short arm (p arm) and a long arm (q arm)
  • Sub-metacentric chromosome: centromere located slightly off-center, resulting in one arm being somewhat shorter than the other
  • Metacentric chromosome: centromere located in the middle, resulting in arms of equal length

Cell Division

• Crucial results in meiosis:
  • Reduction in the number of chromosomes from 2n to 1n
  • Recombination of genes, ensuring genetic variability and diversity of the gene pool

Reproduction

• Chromosomes and reproduction:
  • Chromosomes come in pairs, one of the pair is maternal and the other is paternal
  • When parents make sex cells, the number of chromosomes must be halved
  • One of each type of chromosome is taken
• Inheritance of gender:
  • Mother is XX
  • Father is XY
• Karyotype:
  • Chart used to identify the chromosomal composition of an individual and to detect chromosomal abnormalities
  • Consists of 22 pairs of autosomal chromosomes (numbered 1 to 22) and one pair of sex chromosomes (labeled X and Y)

Barr Body

• Only structure found only in females:
  • Barr body: an inactivated X chromosome found in female cells
• X chromosome inactivation:
  • One of the two X chromosomes is randomly inactivated during early embryonic development
  • Inactivated X chromosome becomes the Barr body
• Occurrence: seen in cells with two X chromosomes (females), not in cells with one X and one Y chromosome (males)
• Appearance: visible as a dense, dark spot in the nucleus, often drumstick-like in certain cell types
• Function: X chromosome inactivation is a process to ensure that females, like males, have only one functional X chromosome per cell