BIOL1115: Lab 6 - Mitosis and Meiosis

what two major activities does the cell cycle consists of?

interphase and cell division

what does interphase make up?

about 90% of the cell cycle

what is interphase comprised of?

- G1 (gap 1) phase

- S Phase (DNA Synthesis)

- G2 (gap 2) phase

what happens during the three subphases of interphase?

the cell grows and manufactures organelles, including those required for cell division such as centrosome and centrioles

what happens during S phase of interphase?

the replication of DNA occurs, in preparation for cell division

what does cell division consists of?

both mitosis and cytokinesis

what is mitosis?

the process by which a nucleus divides to produce two daughter nuclei identical in genetic material

what is mitosis accompanied by?

cytokinesis

what is cytokinesis?

the division of the cytoplasm which completes the separation into two new cells

what is mitosis and cytokinesis responsible for?

growth and repair in multicellular organisms, and reproduction in single-celled organisms

where does cell division occur primarily in plants?

apical meristem, at the tip of shoots and roots and in the cambium

what is the diploid number of onion root tips (allium)?

2n = 16

what is the cambium?

a region of actively dividing cells. it can produce new plant tissue for lateral growth (ie. to increase in diametre)

what does the cambium together with the apical meristem make up?

the meristematic tissue

what is the nuclear membrane?

separates the nucleus from the cytoplasm

what is chromatin?

threadlike mass of genetic material, consisting of DNA and histone proteins, that is present in the nucleus of a nondividing or interphase cell

what is the nucleoli?

site of ribosome synthesis

what happens to chromosomes during S-phase of interphase?

the chromosomes duplicate themselves into two sister chromatids

why is duplication necessary prior to cell division?

so each daughter cells can receive an identical and complete set of chromosomes during cell division

what are the four stages of mitosis? grrrrrrrrrr

- prophase

- metaphase

- anaphase

- telophase

what occurs during prophase of mitosis?

- chromatin condenses into visible chromosomes called chromatids

- sister chromatids are held together at the centromere

- spindle forms

- nuclear membrane fragments

- nucleoli disappear

what occurs during metaphase of mitosis?

- chromosomes line up at the metaphase plate

- chromosomes are attached to the spindle fibres at the centromeres

what occurs during anaphase of mitosis?

sister chromatids are separated and pulled towards opposite poles

what occurs during telophase of mitosis?

- chromosomes reach poles

- nuclear membrane reforms

- spindles disappear

what occurs during cytokinesis IN ANIMALS?

cleavage furrow forms to divide the cell and its cytoplasm into two daughter cells

what occurs during cytokinesis IN PLANTS?

cell plate forms which eventually fuses with the cell membrane to divide the cell into two daughter cells

how do chromosomes exist in in all eukaryotic organisms?

in pairs called homologous pairs

what are homologous chromosomes?

the same length, the centromere is in the same position, and they possess genes for the same traits

where do homologous chromosomes come from in all sexually reproducing organisms?

one is inherited from the father and one from the mother

what are the two members of the pair of chromosomes called?

homologues

what is having both homologues present in the same cell called?

diploid or 2n

what do animal cells contain that are rarely found in plants?

centrioles, which are formed from protein microtubules

what happens to centrioles?

separate during early prophase and microtubules appear to radiate out from them forming the spindle and two star-like asters

when does cytokinesis begin in animal cells?

with the formation of a cleavage furrow in the equatorial region. this indentation in the membrane deepens progressively as a ring of microfilaments surrounding the equatorial plate contracts, eventually resulting in the formation of two new cells

how does the process of cytokinesis in animal cells differ from that in plant cells?

cleavage furrow forms in animal cells as the cell membrane pinches inward, a cell plate forms from the golgi vesicles and develops into a new cell wall

where does mitosis take place in plants?

apical meristems

where does mitosis occur animals?

somatic cells

what is the significance of mitosis to the organism?

it allows growth, tissue repair, and replacement of damaged or dead cells while maintaining genetic stability

where is sexual reproduction found in?

plants, animals, fungi, and protists

what does reproduction involve?

fertilization (the fusion of two parental cells or gametes) and results in new gene combinations

what does the new gene combination do?

increase diversity within a population, an important evolutionary advantage

how are gametes produced in animals?

when a cell undergoes meoisis

what does division through meiosis do?

reduces the number of chromosomes found in cell by half, resulting in haploid (n) products from the division of a diploid cell

how many stages does meiosis have?

2

what happens during meiosis I?

carefully matches up the pairs of homologous chromosomes in a diploid cell in a process called synapsis and then pulls them apart to produce two haploid cells

what is the result after the two stages of meiosis?

four haploid daughter cells

what occurs during prophase I of meiosis?

- each chromosome consists of two chromatids held together at the centromeres

- homologous chromosomes pair in a process called synapsis. paired chromosomes coil around each other. during this time, crossing-over occurs and results in the exchange of genetic material between homologues

- the spindle microtubule form and attach to the centromere of the short, thick chromosome; the nucleoli and nuclear membrane disappear

what occurs during metaphase I of meiosis?

homologous pairs are moved to the centre of the cell by the microtubules with their centromeres on either side of the equatorial plane

what occurs during anaphase I of meiosis?

the homologous pairs are pulled apart and each homologue, consisting of sister chromatids, is then moved to opposite poles.

- each individual chromosome still consists of 2 sister chromatids

what is reductional division?

the total number of chromosomes in each cell is reduced by half

what occurs during telophase I of meiosis?

- the chromosomes of the two daughter nuclei are grouped at opposite poles

- the chromosomes uncoil and pass into interkinesis.

what occurs during interkinesis?

- no DNA replication occurs

- cytokinesis may or may not take place

- each daughter nucleus is now haploid even though each chromosome is composed of a pair of sister chromatids

what is the second meiotic division?

an equational division

what is an equational division?

the total number of chromosomes per cell does not change with cell division

what does meiosis II end with?

the production of four haploid cells

without considering cross-over, how many different end products can be produced in meiosis II?

2^n where n is the number of homologous chromosome pairs

without considering crossing-over, how many different kinds of gametes are formed in an animal with 3 pairs o f homologous chromosomes?

2^3 = 8

how many different types of gametes can be produced in a man with 23 pairs of chromosomes?

8,388,608

what is the significance of meiosis?

meiosis reduces chromosomes number from diploid to haploid and generates genetic variation

what are the haploid gametes called in animals?

eggs and sperm

what is the production of sperm called?

spermatogenesis

where does spermatogenesis occur?

within the seminiferous tubules of the testes

what does spermatogenesis produce?

four haploid sperm cells

what is the production of an egg called?

oogenesis

where does oogenesis occur?

ovaries

what does oogenesis produce?

a single haploid egg and three polar bodies

when does the egg get released from the follicle?

during ovulation

what is a mature follicle?

the final-stage follicle that releases the egg during ovulation

what is the difference between spermatogenesis and oogenesis in terms of end products?

- spermatogenesis: produces 4 functional sperm cells

- oogenesis: produces 1 functional egg and 3 nonfunctional polar bodies

how does meiosis occur in plants?

meiosis and fertilization alternate (as they do in all sexually reproducing organisms), but these events are widely separated in a life cycle known as the alternation of generations

what is the alternation of generations?

a life cycle that alternates between a haploid (n) gametophyte and a diploid (2n) sporophyte

what does plant meiosis produce?

haploid spores

what is the process of spore production called?

sporogenesis

what happens to the spores that get produced?

they grow directly into a haploid plant which, when mature, makes gametes by mitosis

what happens when the gametes fuse in plants?

it produces a diploid zygote, which grows into a diploid plant

what is the diploid, spore-producing plant called?

the sporophyte

what is the haploid gamete-producing plant called?

the gametophyte

where does meoisis occur in ferns?

in specialized spore containers generally found on the underside of leaves, called sporangia

how are sporangia organized?

into clusters, called sori (singular sorus)

what do fern spores grow into when they germinate?

haploid gametophytes

what is the gamete-producing structure that produce eggs in plants called?

archegonia

what is the gamete-producing structure that produce sperm in plants called?

antheridia

what is the difference between the size and shape of the gametophyte and sporophyte plants?

gametophyte plants are much smaller and simpler in structure compared to sporophyte plants. sporophytes are the larger, dominant generation with roots, stems, and leaves, while gametophytes are small and leaf-like

how do fern sperm differ from animal sperm?

- fern sperm are multi-flagellated and are coiled/spiral shaped, whereas animal sperm have one flagellum

- fern sperm require water to swim to the egg

what type of cell division produced haploid plant gametes? how does this compare to animal gametogenesis?

mitosis produces gametes in plants. whereas animals produces gametes through meiosis. in plants, meiosis produces spores

if the sporophyte has a total chromosome number of 24, how many

chromosomes will be present in the spore? what is the chromosome number of the gametophyte? of the unfertilized egg?

- chromosomes in the spore: 12 (spores are haploid, produced by meiosis)

- chromosome number of the gametophyte: 12 (gametophyte grows from the spore, remains haploid)

- chromosome number of the unfertilized egg: 12 (eggs are haploid gametes)

how does sperm travel to the the egg in plants?

sperm from one plant usually swims to the egg of another plant. it then travels down the neck of the archegonium to reach the egg at its base. the sperm is aided in its journey by chemical attractants released by the egg

what is the genetic advantage of exchanging gametes between two different fern plants?

it increases genetic diversity by combining genes from two parents, making offspring more adaptable to environmental changes and reducing the risk of harmful mutations

what is the disadvantage of fern fertilization?

fern sperm requires water to swim to the egg, making ferns dependent on moist environments and limiting where reproduction can occur

what happens once the egg is fertilized in fern fertilization?

the resulting zygote begins to divide and differentiate into a young sporophyte. initially, the sporophyte is dependent on the parent gametophyte but soon grows into an independent plant