Intro to genetics/ Prokaryotes/ Eukaryotes

Genetics

Science of genes and how traits are passed on from one generation to the next

Genes : sections of DNA found inside every human cell

Genetic disorder: happens when a gene(s) has a problem with its code causing health problems

Importance of study of genetics

1. Fundamental in understanding living organisms

2. Investigating biological processes (explains what makes individuals unique)

3. Identifying and treating genetic diseases

4. Understanding Hereditary and Evolution and Adaptation

5. Taxonomic classification

6. Bridge across all life sciences

Characteristics of prokaryotes

1. Lack nucleus

2. Nucleoid: store genetic info as single circular DNA molecules, floating within cytoplasm

3. Cell wall: extra layer of protection, helps maintain shape, prevents dehydration

4. Small size: allows quick entry and diffusion of ions and molecules to other parts of the cell while allowing fast removal of waste products out of the cell

5. Ribosome

6. Capsule: carbohydrate layer that surrounds the cell wall and helps the cell attach to surfaces

7. Flagella: tail like structures that allow the cell to move

8. Pili: surface appendage that aid in attachment and genetic exchange

Characteristics of Eukaryotes

1. Larger

2. Nucleus: houses the cells rod shaped chromosomes and directs protein synthesis.

3. Nuclear envelope: double membrane structure controls passage of ions, molecules ans RNA between nucleoplasm and cytoplasm.

4. Organelles: membrane bound like mitochondria, ER

5. Morphology: spheroid, ovoid, cuboidal, cylindrical and irregular (influenced by function, cytoskeleton organization, cytoplasm viscosity and rigidity of cell membrane/wall).

Prokaryotic cell division

Binary fission

1. DNA replication: single circular DNA chromosome of bacteria, found in nucleoid is replicates

2. Chromosome segregation: the two copies move to opposite ends of the cell

3. Cytokinesis: the cell divides into two genetically identical daughter cells

Eukaryote cell division

1. Mitosis: process by which a eukaryotic cell separates the chromosomes in its cell nucleus into two identical sets in two nuclei

2. Cytokinesis: physical process of cell division which divides the cytoplasm of a parental cell into 2 daughter cells

   Divided into 2 major phases: Interphase and the mitotic phase

Mitotic spindle

Apparatus that controls the movement of chromosomes during mitosis

Interphase

Cell grows and makes a copy of DNA. DNA replication occurs in the S phase with each chromosome becoming 2 sister chromatids. Centromere is duplicated, gives rise to mitotic spindle.

Mitotic phase

1. Prophase: nuclear membrane dissociated into vesicles. Nucleolus disappears. Centromeres move to opposite poles. Microtubules = spindle fibres extend pushing centromeres further apart. Sister chromatics coil more tightly with the aid of condensing proteins

2. Metaphase: metaphase plate, spindle Fibre arrange chromosomes along cell equator

3. Anaphase: sister chromatics separate at centromeres and are pulled to opposite poles by spindle fibers

4. Telophase: at opposite poles chromosomes decondense relaxing into chromatin configuration. Mitotic spindles are depolymerized into tubulin monomers that will assemble cytoskeleton components for each nuclear envelope

Origin and evolution of eukaryotic cells

Acquisition of membrane enclosed subcellular organelles through endosymbiosis I.e mitochondria

Development of nucleus and endomembrane system

2.7 bya

Endosymbiotic theory

Proposed that eukaryotic organelles originated from engulfing prokaryotic cells that formed a symbiotic relationship with the host cell

Evidence: presence of DNA in mitochondria and chloroplast similar to that of bacteria and the structural similarities between these organelles and prokaryotic cells

Inside out model

Suggests that an ancestral prokaryotic cell extruded membrane bound blebs beyond its cell wall leading to the development of the nucleus and other internal structures

Role of meiosis, fertilization and sex determination/uniparental inheritance

Meiosis: type of cell division play crucial role in reducing policy purging deleterious alleles and generating recombinant offspring

Fertilization: fusion of gametes, contributed to the reestablishment of the organelle haploif no. in eukaryotic cells

Sex determination & uniparental inheritance: of organelle genome were essential for the evolution of sexual reproduction and the transmission of genetic material

Inheritance

Process by which genetic information is passed down from parent to offspring

Genes

Basic unit of inheritance and they determine an organisms traits

Genetic transmission: occurs through the germ cells (sperms and egg cells)

Epigenetic inheritance

Transmission of certain epigenetic marks to offspring which can affect gene expression without changing the DNA sequence

Can be transmission through germ cells but mechanism isn’t fully understood yet

Principal of inheritance

1st proposed by Gregor Mendel in 1866

1. Fundamental theory of hereditary

2. Principal of segregation

3. Principal of independent

   Mendal found that paired pea traits were either dominant or recessive. When pure bred parents were cross bred:

   F1 = dominant traits (recessive hidden) and when left to self pollinate recessive traits appear

   Alleles of each gene segregate into individual reproductive cells during meiosis

   Genes located on different chromosomes will be inherited independently of each other (Principal of independent assortment)

Genes

Basic units of hereditary responsible for determining specific traits in an organism

Each can exist in different forms known as alleles (variant of a gene that can lead to different traits)

Mechanism of genetic transmission

Passing of genes from parents to offspring through germ cells

Process occurs during sexual reproduction and follows principles of hereditary, law of segregation and law of independent assortment.

However epigenetic inheritance is the transmission of certain epigenetic traits to offspring which can affect gene expression without changing the DNA sequence