5.1 Reproduction in living organisms
● ***Information controlling what offspring “look like” contained in DNA
○ This essential information divides so that some passed on to each of the cells
making up next generation
Asexual reproduction
● Doesn’t involve gametes
● Simply by dividing into two (particularly for microscopic organisms)
○ For unicellular organism (e.g.: bacterium, amoeba) - cell division =
(mitotic) reproduction
○ ***When the single (parent) cell divides, both daughter cells produced contain
a copy of ALL of the genes from the parent single cell
○ Cells/offspring produced by asexual reproduction are the result of division by
mitosis; so that offspring are genetically identical to parent
○ Only possible source of genetic variation is mutations which might occur
● A piece breaks off and is able to grow into a new individual (many
plants & animals)
○ Faster and more efficient than sexual reproduction (in the case of
plants/animals)
○ ***If parent organism is perfectly adapted to its current environment, then its
cloned offspring are also likely to be perfectly adapted
Sexual reproduction
● Involves gametes (配子) (sex cells), e.g.: eggs, sperms
● Gametes have half of DNA/chromosomes
○ For humans, we have 23 chromosomes in each gamete
● ***Fertilized egg: zygote (合子)
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● ***Information controlling what offspring “look like” contained in DNA
○ This essential information divides so that some passed on to each of the cells
making up next generation
Asexual reproduction
● Doesn’t involve gametes
● Simply by dividing into two (particularly for microscopic organisms)
○ For unicellular organism (e.g.: bacterium, amoeba) - cell division =
(mitotic) reproduction
○ ***When the single (parent) cell divides, both daughter cells produced contain
a copy of ALL of the genes from the parent single cell
○ Cells/offspring produced by asexual reproduction are the result of division by
mitosis; so that offspring are genetically identical to parent
○ Only possible source of genetic variation is mutations which might occur
● A piece breaks off and is able to grow into a new individual (many
plants & animals)
○ Faster and more efficient than sexual reproduction (in the case of
plants/animals)
○ ***If parent organism is perfectly adapted to its current environment, then its
cloned offspring are also likely to be perfectly adapted
Sexual reproduction
● Involves gametes (配子) (sex cells), e.g.: eggs, sperms
● Gametes have half of DNA/chromosomes
○ For humans, we have 23 chromosomes in each gamete
● ***Fertilized egg: zygote (合子)
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