Lecture 2 Genetics Flashcards
Lecture 2 Genetics
In Eukaryotes, how does the transmission of genetic material occur?
Via chromosomes involving Mitosis and Meiosis
Meiosis leads to the production of _____. Mitosis leads to the production of ____
- Meiosis: Sex cells/Germ-line cells/ Gametes or Spores
- Mitosis: Two cells with the same number of chromosomes as parent cell (2n)
Define Chromatin
During non-divisional phases, chromosomes uncoil into a diffuse network within the nucleus
There are two main types of cells: Prokaryotic (bacteria and archaea) + Eukaryotic (protists, plants, fungi, and animals)
All cells share some common features such as:
- Plasma membrane
- DNA
- Ribosomes
Compare Karyokinesis and Cytokinesis. Also, which division is INDEPENDENT?
- Karyokinesis: Splitting in the nucleus
- Cytokinesis: Splitting of cytoplasm
- Mitochondrial division is independent
Define Plasma Membrane. Also, compare plants and bacterial plasma membranes.
- Surrounds all cells
- Delimits cells from the external environment
- Plants: Have plasma membrane and cell wall composed mainly of cellulose (polysaccharide)
- Bacteria: Peptidoglycan in their cell walls
Define Glycocalyx or Cell Coat
- “Sugar Coat”
- Covering on plasma membrane of animal cells
- Made of glycoproteins and polysaccharides
- Function: Biochemical identity at cell surface
What are Receptor Molecules?
- Found on the surface of cells
- Recognition sites that transfer specific chemical signals across the cell membrane into the cell
Explain the Nucleus
- Found in eukaryotes
- Membrane bound’
- Houses genetic material (DNA)
Explain the Nucleolus. Also, explain the Nucleolus Organizer Region
- Where ribosomal RNA (rRNA) is synthesized
- Nucleolus Organizer Region (NOR): DNA that encodes rRNA
Explain the Nucleoid
- Found in prokaryotes
- Not membrane bound
What organelles have 2 membranes?
- Nucleus
- E.R.
- Chloroplast
- Mitochondria
Cytoplasm includes what contents?
- Extra nuclear cellular organelles
- Cytosol
- Cytoskeleton
Define Cytosol
Cytosol: Soluble/liquid portion in the cytoplasm, also known as colloidal materials surrounding organelles
Define Cytoskeleton + its content
Cytoskeleton: Made of extensive system of tubules and filaments
- Microtubules: Made up of the protein tubulin
- Microfilaments: Derived from the protein actin
What do microtubules and microfilaments allow?
Allow movement of other molecules in the cytoplasm = Cytoplasmic Streaming
What is the function of the Endoplasmic Reticulum?
- Compartmentalizes cytoplasm
- Increases surface area for biochemical synthesis
What is the function of Smooth Endoplasmic Reticulum?
Site of fatty acid and phospholipid synthesis
What is the function of Rough Endoplasmic Reticulum?
- Site of protein synthesis
- “Rough” = Studded with ribosomes
What is the function of Mitochondria?
Site of oxidative phases of cell respiration, which generated ATP
What is the function of Chloroplast? Which organisms possess it?
- Site of photosynthesis
- Fixation of atmospheric CO2
- Found in Plants, Algae, and Protozoans
What is the function of centrioles? Where are they found + what are they made of?
- Function: Organize spindle fibers for movement of chromosomes during meiosis and mitosis
- Found in animal and plant cells
- Made of microtubules
In diploid organisms, chromosomes exist in _____ ______
Homologous Pairs
Define Homologous Chromosomes
- Similar, but NOT identical
- Carry genes for the same inherited characteristics
- May carry different versions of the same gene called alleles
Sister chromatids with centromere have two types of arms. Describe them
- Long arm = q arm
- Short arm = p arm “petite”
Explain Centromeres and the 4 different locations
- Constricted regions on chromosomes
- Location of centromere establishes appearance of chromosome
- Locations include: Metacentric, Submetacentric, Acrocentric, and Telocentric
What is a fun way to describe Kinetochores?
“Like screws” to which fibers attach which helps with how chromosomes will be pulled
Explain the # of chromosomes in Body cells. Also, what are some exceptions?
- Body cells also known as Somatic cells have homologous pairs of chromosomes
- Humans: 46 chromosomes (23 homologous pairs)
- Represents diploid number, 2n
- Exceptions: Many bacteria and viruses with one chromosome AKA Haploid
Define Karyotype
- Illustrates the physical appearance of the different pairs of homologous chromosomes
- The human mitotic chromosomes have been photographed, cut out of the print, and matched up.
Define Genome
- Total genetic information
- Genetic information in haploid set
_____ converts the diploid number (2n) of chromosomes to the haploid number (n)
Meiosis
Define Locus (Loci)
- Each site on homologous chromosomes containing identical gene sites along their lengths
What is Biparental Inheritance?
- Inheritance from two parents
- NOTE: Diploid organisms contain two copies of each gene
Define Alleles
Alternative forms of the same genes can exist
Explain Sex-determining chromosomes. Provide an example
- NOT homologous
- Behave as homologs in meiosis w/ Meiotic Recombination
- Ex.) X and Y chromosomes in humans
Define Zygote
Single-celled fertilized eggs of multicellular organisms
Define Karyokinesis
Genetic material partitioned to daughter cells during nuclear division
Define Cytokinesis
Cytoplasmic division
Describe the Cell Cycle
- Composed of interphase and mitosis
- Interphase includes the S phase (DNA synthesized here) and 2 gap phases (G1 and G2)
- G0: Point in G1 phase where cells are nondividing but in a metabolically active state “Quiescent aka quiet phase”
- NO DNA duplication in GAP phases
Define Interphase
Characterized by the absence of visible chromosomes
Define Prophase
- Centrioles divide, move, and establish poles
- Nuclear envelope breaks down
- Chromosomes condense and become visible
Define Prometaphase
- Period of chromosome movement to equatorial plane of cell
- Equatorial plane referred to as metaphase plate
- Centrioles reach poles
- Spindle fibers form
Define Metaphase
- Chromosome configuration following migration
- Centromeres align on metaphase plate
- Kinetochore microtubules have one end near the centrosome region and the other end anchored to the kinetochore
- Cohesin, Separase, and Shugoshin are also involved here. (defined in other flashcards)
Define Kinetochore
- Proteins associated with centromere
- Spindle fibers bind to kinetochore; chromosome migrate
Define Cohesin during Metaphase
Protein complex that holds sister chromatids together
Define Separase during Metaphase
Enzyme that degrades cohesin
Define Shugoshin during Metaphase
Protein that protects cohesin from being degraded by separase
Define Anaphase
- Disjunction
- Sister chromatids separate now called sister chromatids
- Migrate to opposite poles by shortening of spindle fibers
- Motor proteins or molecular motors use ATP
Define Telophase
- Uncoiling of the chromosomes
- Reformation of the nuclear envelope
- Spindle fibers disappear
- Nuclear envelope reforms
Define Cytokinesis
- Two new cells are produced
- Note: Plant cells have a cell plate that is synthesized and laid down across the metaphase plate which becomes the middle lamella
- Note: Animal cells have a constriction of the cytoplasm or cell furrow
- DO NOT FORGET that organelles such as the mitochondria also separate to form these daughter cells
Explain Cell Division Cycle (CDC) Mutations
- Enzymes called kinases
- Can add phosphates to other proteins to regulate the cell cycle
- Are “Master Control” molecules functioning in conjunction with cyclin proteins
- Cyclin = Gatekeeper for PMAT
What do the Cell cycle checkpoints do?
- Monitor mitosis for errors
During which phase of MITOSIS does a cell last the longest? Why?
Prophase (36 min) due to chromatin condensation with Histones
Explain what happens during each of the Checkpoints
- G1/S checkpoint: Undamaged DNA and correct size/resources for synthesis to occur
- G2/M checkpoint: Prevents mitosis until correct DNA for it to occur
- M checkpoint: Proper formation of spindles and kinetochore attachment
What occurs during Meiosis?
- Reduces amount of genetic material by half
- Produces haploid gametes or spores, each containing one member of a homologous pair of chromosomes
What produces the Variability in Meiosis?
Crossing Over in Prophase 1 of Meiosis where genetic exchange between members of homologous pairs of chromosomes
Classify Meiosis 1 and 2 by their divisions
- Meiosis1: Reductional division
- Meiosis 2: Equational division
When does DNA synthesis occur/not occur during Meiosis?
- Occurs during Interphase, before the beginning of Meiosis 1
- Does NOT occur again before Meiosis 2
When can Nondisjunction occur in Meiosis?
Can occur in Meiosis 1 or 2 because it usually occurs during the Anaphase stage. In Meiosis 1 it may occur to the Homologous chromosomes or in Meiosis 2 with the sister chromatids
Define Chiasma
Where recombination takes place between two non-sister chromatids of homologous chromosomes where genetic material is exchanged during the process of crossing over
What are the substages of Prophase 1? Define them!
- Leptonema: Chromosomes appear as long, single threads, unassociated with each other
- Zygonema: “Rough Pairing”, Synapsis, Each pair of homologous chromosomes is known as bivalent
- Pachynema: Each bivalent becomes shorter, thicker, and splits into two sister chromatids called tetrads. CROSSING OVER OCCURS HERE!
- Diplonema: Within tetrads, sister chromatids separate. Chiasma found here which is where chromatids are still intertwined
- Diakinesis: Nucleus and nuclear envelope break down. Centromeres attach to spindle fibers
Define Metaphase 1
- Chromosomes at maximum shortness
- Terminal chiasmata holding sister chromatids together
- Binding to spindle fibers moves chromatids to metaphase plate
Define Anaphase 1
- Cohesin is degraded between sister chromatids
- Homologous chromosomes separate
- Nondisjunction MAY occur
Define Telophase 1
- Two haploid cells result
- Nuclear membranes forms
- Nuclei enter interphase
Summary of Metaphase 1, Anaphase 1, and Telophase 1
- Homologous chromosomes separate and move toward the poles
- Sister chromatids remain attached at centromeres
- Duplicated chromosomes reach poles. Each pole now has haploid set of chromosomes
- Cytokinesis: Two haploid daughter cells are formed
- Nuclear envelope forms around chromosomes in some species
- NOTE: Meiosis significantly increases the level of genetic variation due to crossing over
Explain Meiosis 2
- Prophase 2: Each dyad is composed of one pair of sister chromatids attached by the common centromeric region
- Metaphase 2: The centromeres are positioned on the equatorial plate
- Anaphase 2: Sister chromatids are separated at the opposite poles
- Each haploid daughter cell from meiosis 2 has one member of each pair of homologous chromosomes
- Telophase 2: One member of each pair of homologous chromosomes present at each pole which is where each chromosome is now a MONAD
- Cytokinesis results in 4 haploid cells
Explain Spermatogenesis
- Primary spermatocyte undergoes meiosis 1, producing 2 secondary spermatocytes
- Spermatocytes undergo meiosis 2, producing a total of 4 haploid spermatids
_____ is CRITICAL to the successful sexual reproduction of ALL diploid organisms
Meiosis!!!!
- Mechanism by which diploid amount of genetic information is reduced to haploid
Explain Oogenesis
- Formation of Ova in the Ovaries
- 4 daughter cells do NOT receive equal cytoplasm
- Only 1 daughter cell receives cytoplasm (Primary Polar Body), which undergoes meiosis 1 and 2. This can develop into ovum
Briefly describe the Plant and Fungi Life Cycles
- Fungi: Haploid vegetative cells arise via meiosis - proliferative via mitotic cell division
- Plants: Life cycle alternates between diploid sporophyte stage and haploid gametophyte stage
