Genetics Chapter 2 Mitosis and Meiosis

motor proteins

"molecular motors", use the energy generated by the hydrolysis of ATP, chromosome migration results from their activity, they shorten spindle fibers (removal of tubulin subunits)

cohesin

#3

nucleus

(eukaryotic cell), a membrane-bound structure that houses the genetic material, DNA, which is complexed with an array of acidic and basic proteins into thin fibers

prophase I

3 events characterize this initial stage in meiosis 1)chromatin present in interphase thickens and coils into visible chromosomes 2)members of each homologous pair of chromosomes pair up, undergoing synapsis 3)crossing over occurs between chromatids of synapsed homologs (divided up into 5 substages: leptonema, zygonema, pachynema, diplonema, and diakinesis)

cell cycle

3 major checkpoints

sister chromatids

DNA contained in each is genetically identical, held together by a multi- subunit protein complex called cohesin

G2/M checkpoint

DNA is monitored prior to the start of mitosis, if DNA replication is incomplete or any DNA damage is detected and has not been repaired, the cell cycle is arrested (between G2 and mitosis), chels for cell size, DNA replication

nucleoid

a long, circular DNA molecule is compacted into this unenclosed region, in bacteria

shugoshin

a unique protein family, protects cohesin from being degraded by separase at the centromeric regions; #6

daughter chromosome

after disjunction split chromosomes are referred to as this

anaphase II

after the shugoshin complex is degraded, the centromeres separate, then this stage is initiated, and the sister chromatids of each dyad are pulled to opposite poles

kinetochore

an assembly of multilayered plates of proteins associated with the centromere

plasma membrane

an outer covering that defines the cell boundary and delimits the cell from its immediate external environment

nondisjunction

and error in the disjunction of meiosis cells

chiasma (pl. chiasmata)

areas where chromatids are intertwined, thought to represent a point where nonsister chromatids have undergone genetic exchange through the process referred to above as crossing over

chloroplasts

associated with photosynthesis, the major energy-trapping process on Earth

cyclins

bind to kinases , activating them at appropriate times during the cell cycle

G2

by the end of this phase the volume of the cell has roughly doubled, DNA has been replicated, and mitosis (M) is initiated

middle lamella

cell plate becomes this

G0

cells either enter this phase or G1, those who enter in this phase remain viable and metabolically active but are not proliferative

metaphase

centromeres align on metaphase plate

anaphase

centromeres split and daughter chromosomes migrate to opposite poles, shortest stage of mitosis, disjunction takes place

nonsister chromatids

chromatids from maternal and paternal members of a homologous pair

prometaphase

chromosomes are clearly double structures; centrioles reach the opposite poles; spindle fibers form

zygonema (zygotene stage)

chromosomes continue to shorten and thicken during this stage, Homology (rough) search is complete by the end of this stage, synaptonemal complex forms, at the end of this stage paired homologs are referred to as bivalents

anaphase I

cohesin is degraded between sister chromatids, except at the centromere region, which is protected by a shugoshin complex, then one-half of each tetrad (a dyad) is pulled toward each pole of the dividing cell, at the completion of this stage, a series of dyads equal to the haploid number is present at each pole

genome

collectively, the genetic information contained in a haploid set of chromosomes constitutes this, includes copies of all genes as well as a large amount of noncoding DNA

dyad

composed of two sister chromatids joined at a common centromere

tetrad

consisting of four chromatids

centromere

constricted region in chromosome whose location establishes the general appearance of each chromosome

centrioles

cytoplasmic bodies, located in a specialized region called centrosome, associated with the organization of spindle fibers that function in mitosis and meiosis

cytokinesis

cytoplasmic division

telophase

daughter chromosomes arrive at the poles; cytokinesis commences, final stage of mitosis

prophase II

each dyad is composed of one pair of sister chromatids attached by the common centromeric region

synapse (synapsis)

early in meiosis, when chromosomes form pairs

histocompatibility antigens

elicit an immune response during tissue and organ transplants

meiosis II

essential if each gamete or spore is to receive only one chromatid from each original tetrad

M checkpoint

final checkpoint, during mitosis, both successful formation of the spindle fiber system and the attachment of spindle fibers to the kinetochores associated with the centromeres are monitored

diakinesis

final stage of prophase I, chromosomes pull farther apart, nonsister chromatids remain loosely associated at the chiasmata. as separation proceeds, the chiasmata move toward ends of the tetrad. this is terminalization *begins in diplonema but completed during this phase, nucleolus and nuclear envelope break down, the two centromeres of each tetrad attach to the recently formed spindle fibers, by the end centromeres of each tetrad are present on the metaphase plate of the cell, centrioles transition to poles of the cell

oogenesis

formation of ova (sing. ovum)

receptor molecules

found on surface of cells, these molecules act as recognition sites that transfer specific chemical signals across the cell membrane into the cell

tetrad

four-membered structure, contains two pairs of sister chromatids

locus

gene sites on chromosomes

chromatin

genetic material when cell division is not happening, uncoiled and a diffuse network within the nucleus

sex-determining chromosomes

important exception to the concept of homologous pairs of chromosomes, this pair is often not homologous in size, centromere placement, arm ratio, or genetic content

cytosol

in the cytoplasm, a nonparticulate, colloidal material, surrounds and encompasses the cellular organelles

biparental inheritance

inheritance from two parents

prokaryotic organisms

lack a nuclear envelope and membranous organelles

mitosis

leads to the production of two cells, each with the same number of chromosomes as the parent cell, in somatic cells

chromomeres

localized condensations that resemble beads on a string

q arm

longer arm of chromosome, generally shown below centromere

cytoskeleton

made of microtubules (tubulin) and microfilaments (actin), maintains cell shape, facilitates cell mobility, and anchors the various organelles

homologous chromosomes

members of each pair of chromosomes that exist in paris with regard to lengths and centromere placement

G1/S checkpoint

monitors the size of the cell has achieved since its previous mitosis and also evaluates the condition of the DNA (between G1 and S phase), checks for cell size, nutrients, growth factors, dna damage

glycocalyx, or cell coat

most animal cells have this covering over the plasma membrane, consists of of glycoproteins and polysaccharides, provides biochemical identity at the surface of the cell

cell division cycle mutations

mutations that exert an effect at one or another stage of the cell cycle.

kinases

normal products of many of the mutated genes , enzymes, can add phosphates to other proteins(phosphorylate other proteins), activated by cyclins, responsive to DNA damage as well or cell stress allowing them to regulate cell cycle progression

karyokinesis

nuclear division, genetic material is partitioned into daughter cell during this process

prophase

often, over half of mitosis is spent in this stage, break down of nuclear envelope occurs while chromatin coils up and condenses; centrioles divide and move apart

spindle fibers

on centrioles, play an important role in the movement of chromosomes as they separate during cell division, composed of arrays of microtubules consisting of polymers of the protein tubulin

monads

one chromosome each

endoplasmic reticulum (ER)

organelle, compartmentalizes the cytoplasm, greatly increasing the surface area available for biochemical synthesis

activated kinases

phosphorylate other target proteins that regulate the progress of the cell cycle

cell wall

plant cells has this in addition to the plasma membrane, major component: cellulose (a polysaccharide)

folded-fiber model

postulated by Ernest DuPraw

homology search

precedes and is essential to the initial pairings (alignment) of homologs,

nucleolus

present in nucleus, an amorphous component where ribosomal RNA (rRNA) is synthesized and where the initial stages of ribosomal assembly occur

pachynema (pachytene stage)

prior to this stage, chromosomes continue to coil and shorten,synapsis (intimate search) is over before this stage begins during- each homolog is now evident as a double structure, each bivalent has four chromatids, crossing over occurs here

spermatogenesis

production of a male gamete, takes place in the testes, begins with enlargement of an undifferentiated diploid germ cell called spermatogonium

Mitosis

prophase, prometaphase, metaphase, anaphase, and telophase

meiosis

reduces the genetic content and the number of chromosomes by precisely half (haploid), leads to production of sex cells :gametes or spores, in germline cells, introduces genetic variability to chromosome in a process called crossing over

telophase I

reveals a nuclear membrane forming around the dyads, if a sex cell enters this stage the chromosomes do not replicate

telophase II

reveals one member of each pair of homologous chromosomes present at each pole, each chromosome is now a monad, cytokinesis occurs

equational division

second division, during meiosis II, the number of centromeres remains equal, each dyad splits into two nomads

ribosome

serve as sites where genetic information contained in messenger RNA (mRNA) is translated into proteins

chromosome

serve as vehicles for transmitting genetic information, an organism's DNA is organized into these structures

p arm

short arm of a chromosome, generally shown above the centromere (p for petite)

zygote

single-celled fertilized egg

disjunction

sister chromatids of each chromosome, disjoin (separate) from one another. 1) shugoshin must be degraded, reversing its protective role 2)the cohesin complex holding the centromere region of each sister chromosome is then cleaved by separase 3)sister chromatids of each chromosome are pulled toward the opposite poles of the cell

synaptonemal complex

starts out as lateral elements, begin to form between homologs, the vehicle responsible for proper alignment during the pairings of homologs

reductional division

takes place in meiosis I, the number of centromeres, each representing one chromosome is reduced by one-half),components of each tetrad- representing the two homologs- separate, yielding two dyads

Diplonema (diplotene stage)

tetrad (two pairs of sister chromatids) is even more apparent, chiasma are present, pairs of sister chromatids now begin to separate but still remain attached at the chiasma

metaphase II

the centromeres are positioned on the equatorial plate

metaphase I

the chromosomes have maximally shortened and thickened, the terminal chiasmata of each tetrad are visible and appear to be the major factor holding the nonsister chromatids togethers together, each tetrad interacts with spindle fibers, facilitating its movement to the metaphase plate

interphase

the initial stage of the cell cycle, the interval between divisions, cell growth, intensive metabolic activity and normal function take place, most importantly- the replication of the DNA of each chromosome occurs (includes the G0/G1, S, and G2 phases) (chromosomes not visible during this phase)

leptonema (leptotene stage)

the interphase chromatin material begins to condense, and the chromosomes, though still extended, become visible.along each chromosome are chromomeres. homology search being during this phase

multicellular plants

the life cycle alternates between the sporophyte stage and the haploid gametophyte stage (alternation of generations)

karyotype

the number and visual appearance of the chromosomes in the cell nuclei of an organism or species, display where chromosomes have been photographed, cut out of the print, and matched up

nucleolus organizer region (NOR)

the portions of DNA that encode rRNA

cytoplasm

the remainder of the eukaryotic cell within the plasma membrane, excluding the nucleus, includes a variety of extranuclear cellular organelles

mitosis, meiosis

the two major processes that are involved in the genetic continuity of nucleated cells

spermatogonium

this cell grows to become a primary spermatocyte, which undergoes the first meitotic division , after it divides it becomes a secondary spermatocytes (contain a haploid number of dyads)

bivalent

two homologs

mitochondria

usually found in both types of cells (animal and plant) , the sites of the oxidative phases of cell respiration, these chemical reactions generate large amounts of the energy-rich molecule adenosine triphosphate (ATP)

S phase

within Interphase, towards the end, the period which DNA is replicated