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23 Cards in this Set

  • Front
  • Back
one of characteristics of living things.
production of new organisms or cells from pre-existing ones
-occurs through cell division
chromosomes (4)
a. consist of DNA and histone proteins
b. found in the cell nucleus
c. small segments of DNA=genes
chromosomes (cont'd)
must undergo duplication
a. two sister chromatids
b. held together by a centromere
2 modes of reproduction
1. asexual reproduction--mitosis
2. sexual reproduction--meiosis
1. cell spends most of its life here
2. chromosomes as chromatin
3. chromosomes duplicated near end of interphase
1. chromatin condenses--chromosomes become visible
2. centrosomes begin moving to poles
3. spindle fibers begin to appear
4. nuclear envelope begins to disappear
1. chromosomes align along equator
2. spindle fibers attach to chromosomes
1. centromeres divide -- chromatids become daughter chromosomes
2. daughter chromosomes begin moving to opposite poles
mitosis-telophase and cytokinesis
1. nuclear envelopes start to re-appear
2. chromosomes go back to chromatin
3. cytokinesis occurs--the cleavage furrow
major functions of mitosis
1. growth and repair in multicellular organisms
2. asexual reproduction
a. binary fission -- eg amoebas
b. budding -- eg yeasts
c. vegetative reproduction in plants -- stolons and rhizomes
sexual reproduction
1. cells have a diploid (2N) number
2. diploid number for humans (46)
3. chromosomes exist as homologous pairs
4. sex chromosomes--pair that determines sex
5. autosomes- chromosomes not involved in sex determination
-diploid zygote formed by fusion of gametes (fertilization)
-two diploid parents produce gametes
-gametes are haploid (1N)
-gametes are produced in germ tissue (gonads)
-gametes produced by meiosis
overview of meiosis
-consists of 2 nuclear divisions (meiosis I, II)
-first division reduces the number of chromosomes to the haploid condition
-second division is mitosis
-end result is 4 haploid cells
meiosis I-interphase I
1. just like mitosis
2. chromosomes duplicated near end
meiosis I-prophase I
1. homologous chromosomes form tetrads
2. crossing-over occurs--homologous chromosomes exchange part
meiosis I- metaphase I
1. tetrads align along cell equator
2. spindle fibers attached to centromeres
meiosis I-anaphase I
1. disjunction--tetrads separate and move towards opposite poles
2. here's where chromosome number is reduced to the haploid number
meiosis I- telophase I
1. cytokinesis
2. 2 haploid daughter cells
meiosis II
1. basically mitosis
2. results in 4 haploid daughter cells
meiosis in humans (males)
germ cells in gonads are capable of meiosis
-spermatogenesis in males
1. occurs in testis cells--spermatocytes
2. 4 haploid daughter cells produced
3. daughter cells develop intom otile gametes called spermatozoa
meiosis in humans (females)
called oogenesis
1. occurs in cells in the ovary -- oocytes
2. 4 haploid daughter cells produced
3. 1 daughter cell develops into a gamete called ovum (egg)
4. 3 daughter cells become small, non functional polar bodies
importance of meiosis
-haploid gametes keep diploid number the same from one generation to next
-crossing over is a source of genetic variation
bad meiosis
sometimes mistakes occur during
-these errors can result in gametes and zygotes with wrong number of chromosomes