These notes cover the four chapters that fall under paper 2 under the caps syllabus. Namely meiosis evolution and genetics et cetera. This document also includes the figures mentioned in the textbook and where figures cannot be included it references the pages in the textbook to find the figures.
>at the
beginning ofcell division (mitosis & meiosis), the chromation network unwinds to form
seperate string-like structures called chromosomes
Each chromosome
->
is made ofa strand ofDNA which is
up large tightly wrapped by an outer
protein cover and DNA
i n turn is made
up
of
nucleotides
->
a short ofnucleotides ofa
sequence which carries the
genetic code for the
development particular
characteristic or trait is called a
gene
some ofthe ofnucleotides that
->
DNA
portions strand contain
DNA a
sequence are non-functional
non-coding
-
Chromosomes in Somatic Cells and Sex Cells
tach body
->
cell somatic cell of its chromosomes, as indicated in the table
distinctn umber of
every organism has
or own
↳
somatic cells:all the animal
cells in a
plant or body, besides the sex cells (cell thatb ecomes the orum) the chromosomes are
genetically equivalent
the
->
chromosomes are in humans there
arranged in
pairs eg. are 23
pairs
-there different ofchromosomes called autosomes and ofs ex
are 22
pairs I
pair chromosomes/gonosomes
the
->
autosomes are numbered as chromosome 1,2,3, ... 22, and there are two each
↳
the two chromosomes each identical to each other
making up pair are
in females,the
->
two sex chromosomes are also identical to each other and are refered to as XX chromosomes
->inmales, out ofthese is an X chromosome and the other a Y chromosome
:female humans have 44 + XX chromosomes
male humans have 44 + XY chromosomes
->
somatic cells have ofchromosomes, and
a
diploid (2n) number in humans that diploid/2n 46 chromosomes
=
sex ofhumans
haploid (n) number ofchromosomes, and in humans
tells/gametes
->
have
just 1 set of2 3 chromosomes, we
say that the sex
cells/gametes have a
haploid/n 23 =
one
->
member ofe ach is ofmaternal and the other is of
pair origin paternal origin
of
a
pair identical chromosomes, one ofmaternal and the other of
homologus pair of chomosomes
called
->
paternal origin, are a
->
justprior to cell division (after DNA
replication), the chromosomes
appear double, each being made up of being held together by
two chromatids a centromere
Meiosis
Introduction
from
parent cell-each ofthese 4 cells
->
miosis is the division ofone cell into four cells each ofwhich has is
half the chromosome number as the
genetically different each
Other
->
it
usually occurs during gametogenesis, a
process during which gametes are formed
,->
inplants meiosis occurs in the anther to
produce pollen grains and in the
ovary to
produce the cult
->
in humans meiosis occurs in the testes to
produce sperms and in the
ovary
to
produce an orum
->
in some lower
organisms, meiosis occurs
immediatly after fertilization
Importance in Maintainingthe Chromosome Number
as seen in the table above, each species has characteristic number ofchromosomes that has to be maintained from
->
a the next
generation
one to
->
meiosis allows for diploid cells in the to form haploid gametes known the effect
sex
organs as
halving
-
->
when two haploid gametes fuse, form known
they a
diploid zygote
as the
doubling effect
-
in this effectofmeiosis overcomes the effect offusion, thus
way, the halving doubling
->
maintaining a chromosome number from
generation
constant one
to the next this the life ofdifferent
can be
clearly by studying cycles organisms
-
seen
Meiosis and life cycles
Meiosis Gamete formation:
during
->
(ie. before Greene *ne(2)
including humans meiosis gametes
-
in most
plants and animals, takes
place when are formed
Male(2n)
Adut
fertilisationI
MEIOSIS:
->These therefore have half the chromosome number setofchromosomes (n)
gametes MITOSIS
or one
compared to the adult
it
->
the fusion of the
gametes
results in the
diploid chromosome number
being restored in the zygote Eagere
e
mitosis to multicellular adult
which
undergoes produce a
Meiosis after fertilisation:
filament (n)
in
alge (KingdomProtista) eg. Spirogyre, Rhizoens the adults
haploid
->
some and in some
fungi eg. are
Mitosis
giving rise haploid gametes, which fertilisation resultin diploid zygote Meiosis
to on
a
->
meiosis occurs in the
zygote or
zygospore (ie. after fertilization) to halve thechromosome number
female
Zygospore (2n) gamete (n) Male
ofchromosomes
gamete
zigite (n)
The Place ofMeiosis in the Moss and the fern
->
Sporophyte
alternation of
mosses and ferns show
generations whereby haploid gametophyte (gamete producing
an a (2n)
generation alternates with a
diploid sporophyte (spore producing) generation Mitosis
meiosis
->
the
haploid gametophyte produces haploid gametes by mitosis Spores (n)
zygote y
Species Lantigen
->
the diploid
sporophyte produces haploid spores by
meiosis
->
it's the
halving effect ofmeiosis that allows for such an alternation
, -
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↑ ↑
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s r g gene
Exteriors e
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1
↑ ↑ ↑ ↑ ↑
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