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23 Cards in this Set

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reproduction
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
mitosis-interphase
1. cell spends most of its life here
2. chromosomes as chromatin
3. chromosomes duplicated near end of interphase
mitosis-prophase
1. chromatin condenses--chromosomes become visible
2. centrosomes begin moving to poles
3. spindle fibers begin to appear
4. nuclear envelope begins to disappear
mitosis-metaphase
1. chromosomes align along equator
2. spindle fibers attach to chromosomes
mitosis-anaphase
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
overview
-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