Biology 30: Cell Division

Diploma Prep

define haploid

haploid (1n) refers to one set of chromosomes. this would provide only 1 chromosome of each type

ex. gametic cells

define diploid

diploid (2n) refers to 2 sets of chromosomes. a set of chromosomes from the mother and a set of chromosomes from the father, giving 2 of each type of chromosome

ex. somatic cells

define polyploid

polyploid refers to more than 2 sets of chromosomes. this would provide more than 2 chromosomes of each type from the 2 parents

define karyotype/karyogram

karyotype refers to the properties of the chromosomes in question: number, size and shape. karyogram refers to the image of matched chromosomes in order

what are homologous pairs?

chromosomes are organized as homologous pairs (groupings of alike chromosomes carrying the same genes), one from the mother and one from the father matched based on: length of chromosome, banding pattern, and location of centromere

define autosomes

autosomes are chromosomes numbered 1 to 22 on a karyogram

define sex chromosomes

sex chromosomes is the 23rd pair of chromosomes: the x (long) or y (short) chromosomes

xx = female

xy = male

define cell cycle

the cell cycle is the events during a cell’s lifespan up to and including its division

what are the two phases of the cell cycle?

the growth stage (interphase - 95%): non-dividing stage

the division phase (5%): dividing stage → division of the nucleus (mitosis or meiosis) and division of the cytoplasm (cytokinesis)

what is interphase?

interphase is the phase of the cell cycle in which a typical cell spends most of its life. during this phase, the cell copies its DNA in preparation for mitosis. interphase is the daily living or metabolic phase of the cell, in which the cell obtains nutrients and metabolizes them, grows, reads its DNA, and conducts other normal cell functions

what are three sub-stages of interphase?

G1 (gap/growth 1) phase: organelles replicate

S (synthesis) phase: DNA replicates as genetic material goes from SS chromatin to DS chromatin

G2 (gap/growth 2): other cell reactions (cell respiration, protein synthesis, cell growth)

what is the division stage subdivided into?

nuclear division (karyokinesis → mitosis or meiosis)

cytoplasmic division (cytokinesis → cleavage furrow or cell plate)

what the two types of cytokinesis?

cleavage furrow: method used for cells with no cell wall (animal cells)

cell plate : method used for cells with a cell wall (plant cell)

what is mitosis?

mitosis is the nuclear division of the cell nucleus to produce 2 daughter cells containing identical genetic make up to the parent cell. it is the formation of somatic cells for growth of tissues, repair of tissues, embryonic development, asexual reproduction

what is the result of mitosis?

1 parent cell (2n) → 2 identical daughter cells (2n)

this process maintains the chromosome number and the genetic material. in fact it can said that the cells are all clones of each other

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what are the four phases of mitosis?

prophase

metaphase

anaphase

telophase

what happens during prophase?

chromatin condenses into DS chromosomes

nuclear membrane and nucleolus dissolves/disappears

centrioles begin to migrate to opposite ends of the cell and create spindle fibers (microtubules that will help migrate/separate the chromosomes)

what happens during metaphase?

DS chromosomes align in single file along the metaphase plate (equator)

centromere attaches to the spindle fiber

anaphase

centromeres replicate forming SS chromosomes (DS 🡪SS)

SS chromosomes migrate to the poles (centrioles) with the help of re-coiling spindle fibers

what happens during telophase?

chromosomes at poles uncoil from SS chromosomes into SS chromatin

nuclear membrane and nucleolus reforms around each set of SS chromatin

when cytokinesis occur?

cytokinesis may start occurring as early as anaphase but usually starts occurring during telophase

the division of the nucleus (mitosis) and the division of the cytoplasm (cytokinesis) are separate events even though they may be occurring at the same time

what is asexual reproduction?

asexual reproduction is a method of producing offspring using mitosis

1 parent - mitosis → 2 offspring

what are advantages and disadvantages of asexual cell reproduction?

advantages: can re-populate very quickly and less complicated for only one parent is needed

disadvantages: all are clones, therefore no variation to distinguish them and an environmental condition that can kill one can kill all

what are some types of asexual reproduction?

binary fission: a single parent cell divides into two daughters cells

budding: parent cell produces bud and it gets detached, developing into new individuals

spore formation: reproduces by forming spores which under favorable conditions develop into new individuals

fragmentation: organism with filamentous body break into two or more fragment with each fragment growing into a new individual

regeneration: organism’s body breaks up into one or several part with each part developing into a new individual

vegetative reproduction: organism produces new individuals by a vegetative part of the plant

what is cloning?

a clone is the formation of multiple identical offspring from a single parent. cloning occurs if a single parent undergoes mitosis repeatedly to form many offspring

what is meiosis?

meiosis is the division of the cell nucleus to produce 4 gamete cells each containing unique genetic information. it is for gamete production for sexual reproduction (reproduction that results in genetic diversity in the offspring)

what occurs during meiosis?

1 parent cell (2n) → 4 unique gamete cells (1n)

this process reduces the chromosome number so that when the 2 gametes combine they can form an offspring with the correct chromosome number ( 1n egg + 1n sperm → 2n zygote)

this process also allows for variation of gametes so that offspring are born with unique characteristics; a species survival advantage

what are the two sets and eight phases of meiosis?

meiosis I (reduction division):

prophase I

metaphase I

anaphase I

telophase I

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meiosis II (separation of sister chromatids)

prophase II

metaphase II

anaphase II

telophase II

what happens during meiosis I?

reduction Division is the key purpose of meiosis I. this involves the reduction of chromosome number

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1 diploid cell with DS chromosome → 2 haploid cells with DS chromosomes

what happens during prophase one?

DS chromatin Supercoils into DS chromosomes.

homologous chromosomes pair up (synapsis) forming a tetrad

the non-sister chromatids tangle (crossing over)

the non-sister chromatids disentangle swapping genetic information (recombination)

nuclear membrane & nucleolus dissolve

spindle fibers form

define synapsis

a tetrad forms when 2 homologous chromosomes align

define crossing over

a chiasma forms when non-sister chromatids entangle

define recombination

recombination occurs when genetic information is exchanged between non-sister chromatids

what happens during metaphase I?

tetrads align along the equator

what happens during anaphase I?

the tetrad is destroyed when the DS chromosomes within the homologous pair separates

DS chromosomes migrate to the poles

what happens during telophase I?

DS Chromosomes travel to the poles

nuclear membrane and nucleolus reforms around each collection of chromosomes

each nuclei = 1n but the chromosomes remain DS

what is interkinesis?

there is no interphase between meiosis I and meiosis II, only interkinesis. interkinesis or interphase II is a period of rest that cells of some species enter during meiosis between meiosis I and meiosis II. no DNA replication occurs during interkinesis

DS Chromosomes uncoil into DS Chromatin

no S phase ( no DNA replication)

this means that the chromosome number remains 1n

what is the purpose of meiosis II?

separation of sister chromatids is the key purpose of

meiosis II. it is going from DS chromosomes to SS chromosomes

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2 haploid cells with DS chromosomes → 4 haploid cells with SS chromosomes

what happens in prophase II?

DS chromatids supercoil into DS chromosomes

nuclear membrane and nucleolus dissolve

spindle fibers form

what happens during metaphase II?

DS chromosomes align at the equator in single file

what happens during anaphase II?

centromeres replicate

DS chromosomes become SS chromosomes

SS chromosomes migrate to the poles

what happens during telophase II?

SS Chromosomes at poles uncoil into chromatin.

nuclear membrane and nucleolus reform

what is the result of meosis II?

cells are haploid (½ of parent cells genetic content)

contain 1 of each kind of chromosome

are gametes (sex cells)

define gametogenesis

Gametogenesis is an alternate name for meiosis

(genesis = to create, gameto = gametes)

define spermatogenesis

spermatogenesis refers to the process of meiosis to create sperm in the testes of males

define oogenesis

oogenesis refers to the process of meiosis to create eggs in the ovaries of females

what occurs during spermatogenesis?

spermatogenesis starts in the testes at puberty (\~age 14 years)

the specialized germ cells that initiate the process are called spermatogonia (2n). these cells under mitosis to form primary spermatocytes which initiate the process of meiosis

the ratio is for every 1 primary spermatocyte that initiates meiosis, 4 sperm will be produced

what occurs during oogensis?

oogenesis is initiated in the ovaries during fetal development with meiosis I, and then pauses until puberty when only one cell per month will proceed with part of meiosis II

if fertilization occurs, meiosis II be completed to form an ovum

specialized germinal cells that initiate the process are called oogonia (2n). these cells undergo mitosis to form primary oocytes which initiate the process of meiosis

during meiosis I and meiosis II there is an asymmetrical cytokinesis causing one cell (that will eventually become the ovum) to receive most of the cytoplasm. the cells deprived of cytoplasm are called polar bodies

the ratio is for every 1 primary oocyte that initiates meiosis, only 1 egg can potentially be produced and may be accompanied by 3 polar bodies

what is meant by meiosis “under arrest".”

in the human embryo, the thousand or so oogonia divide rapidly from the second to the seventh month of gestation to form roughly 7 million germ cells

after the seventh month of in-utero development, however, the number of germ cells drops. most oogonia die during this period, while the remaining oogonia enter the first meiotic division.

these latter cells, called the primary oocytes, progress through the first meiotic prophase until the at which point they are maintained until puberty. this is is the first “meiotic arrest”

with the onset of adolescence, groups of oocytes periodically resume meiosis but stop in metaphase II. this is the second “meiotic arrest”

rhus, in the human female, the first part of meiosis begins in the embryo, and the signal to resume meiosis is not given until roughly 12 years later

why is recombination important?

the chance swapping of genetic information amongst the homologous chromosomes during prophase I allows for endless possible gene combinations

what is random orientation?

random orientation indicates the way the chromosomes attach during metaphase I or metaphase II is completely random. either the maternal or the paternal chromosome can orient towards a given pole

what is independent assortment?

independent assortment pertains to the random separation of chromosome pairs in anaphase I and anaphase II. the way that the maternal and paternal chromosomes of one pair separate is independent of how the maternal and paternal chromosomes of a different pair separate. they act independently

what is non-disjunction?

non-Disjunction is abnormal migration during either anaphase I or anaphase II of meiosis. this abnormal migration can result in gametes being formed with too many or too few chromosomes

what are the two types of non-disjunction?

monosomy: only one chromosome of a certain kind exists instead of a homologous pair

trisomy: 3 chromosomes of a certain kind exist instead of a homologous pair

define alternation of generations

alternation of generations is the cycling between diploid and haploid phases in an organisms life cycle

what are some characteristics found in alternation of generations?

when there is reduction division = meiosis (2n → 1n or 4n → 2n

when there is a doubling of chromosome number = fertilization (1n → 2n or 2n → 4n)

when the chromosomes stay the same= mitosis (2n → 2n or 1n → 1n)

what is alternation of generations like in plants?

the diploid phase of the life cycle is called the sporophyte generation or the asexual phase. the haploid phase of the life cycle is called the gametophyte generation or the sexual phase