Cell Reproduction

Includes Mitosis and Meiosis

reasons for cell division

reasons for cell division

• growth

• replace worn-out or damaged cells

• cells get too large to transfer materials

• reproduction (different type of division)

diploid

cell with 2 copies of each chromosome

2n-number

diploid

somatic/body cells

diploid

46 chromosomes in humans (23 pairs)

diploid

haploid

cell with 1 copy of each chromosome

n-number

haploid

gametes/sex cells/germ cells

haploid

23 chromosomes in humans

haploid

chromatin

tangled mass of unwound DNA present when a cell is not dividing

chromosome

condensed form of DNA present during cell division

homologous chromosomes

a pair of matching chromosomes (one from mom and one from dad)

autosomes

pairs of chromosomes that do not determine sex

sex chromosomes

pairs of chromosomes that determine sex

XX

female

XY

male

karyotype

a picture of the 46 chromosomes that are arranged in pairs according to shape, size, and banding

cell cycle

sequence of growth and development of a cell (a cells life cycle)

cytokinesis

division of the cytoplasm

mitosis

division of a somatic (body) cells nucleus

interphase

the time between cell divisions when a cell performs its regular functions

• chromatin present

• spindle begins to form

• centrioles duplicate

G1

growth 1, cell grows and makes proteins

S

synthesis, DNA (chromosomes) are replicated

G2

growth 2, cell grows and prepares for division

prophase

• chromatin coils into visible chromosomes

• nuclear envelope and nucleus appear

• centrioles move to the poles

• sister chromatids— (doubled chromosomes) are held together by centrioles

metaphase

chromosomes are pulled to the equator of the cell by spindle fibers

anaphase

• chromatid pairs are pulled apart by spindle fibers

• sister chromatids become daughter chromosomes as they move toward the poles

telophase

• two new cells start to form

• nuclear envelope and nucleus reform

• chromosomes unwind into chromatin

cytokinesis in animal cells

cleavage furrows forms and the cell pinches off

cytokinesis in plant cells

cell plate (new cell wall) forms between daughter cells

meiosis

type of division that forms gametes (sex cells)

• reduces the chromosomes number from diploid to haploid

• requires two sets of divisions

meiosis stage 1

first stage of meiosis which separates homologous chromosomes

major events in meiosis stage 1

• chromosomes replicate

• homologous chromosomes pair up

• crossing over occurs

• homologous chromosomes are pulled apart

• two haploid cells form

crossing over

exchange of genetic material between homologous chromosomes

genetic variation of gametes in meiosis stage 1

created by crossing over and independent assortment (how the chromosomes line up)

outcome of meiosis stage 1

produces 2 haploid cells

meiosis stage 2

the second stage of meiosis which separates sister chromatids

outcomes of meiosis stage 2

produces 4 haploid gametes

centromere

• holds the chromosomes together

• where the spindle attaches

centriole

builds and controls the spindle