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like structures that form part of the chromatin network in the
↳ made
up of a strand of DNA wound around proteins called histones
dye very easily (chromosomes
↳ absorb coloured bodies) which visible
makes them
-
,
seen as individual threads cell
under a
microscope but are
only when is dividing
↳ a short
piece of DNA in a chromosome comprises a
gene ,
which is a
hereditary
Unit consisting of a
sequence of DNA that occupies a specific location on a
and determines in
chromosome a
particular characteristic an
organism
↳ when
as a thread (chromatin network )
a cell is not
dividing ,
the chromosomes appear
↳
When a cell divides ,
the chromatin network condenses ,
the threads shorten ,
thicken
and become visible as chromosomes
In somatic (
body) cells of diploid organisms :
Number of chromosomes in each cell is the same
-
'
Chromosomes are made of two sets; maternal and paternal chromosomes ,
therefore called
diploid cells 12h
For maternal chromosome
each paternal chromosome there is
matching forming
-
a a
same
homologous pair The .
chromosomes in the
pair are then size ,
shape and
carry genes for the
same hereditary characters ,
but
may carry
a different form of the characteristic
alternative forms of the are called alleles
gene
Chromosome number
↳ each
species has a specific number of chromosomes in its somatic cells ,
which is not
related to the size
complexity of the species
↳ with identical numbers, have similarities in the DNA
organisms may
,purpose is to separate the homologous In humans : diploid number -
46
pairs so each gamete will possess one
,
haploid number -
23
chromosome of each homologous pair
meiosis ( reduction division )
↳ cell division that
takes place in the reproductive
organs of plants and animals to
produce gametes
The reduced from kn ) in the cell to one
-
number of chromosomes is two sets parent
set ( n ) in each of the cells formed ( number of chromosomes is halved )
daughter
The normal number of chromosomes in cells is called the diploid number
'
The gametes l spores formed are called haploid have of chromosomes
they one set
-
as
( one chromosome from each homologous pair )
↳
when two haploid gamete fuse , the diploid number is restored ( male haploid gamete t
female haploid gamete =
diploid zygote)
↳
zygote divides by mitosis ,
every somatic cell contains the diploid number of chromosomes
↳ in
that reproduce the number of chromosomes is
organisms sexually ,
always an even
number because it consists of two sets of chromosomes ( one from each
gamete )
↳ without
meiosis the number of chromosomes would double with each
generation
where does meiosis take ?
place
↳ in animals testis and ovaries
it takes place in the reproductive organs ,
spermatogenesis formation of sperm
-
cells in testis
-
oogenesis formation of cells lov a in ovaries
-
egg
-
↳ in
plants it takes place in the formation of spores in sporangia
In seed plants
bearing
-
:
-
micro are the pollen sacs in the male anthers
sporangia
in the
megasporangia
.
are the ovules female ovaries
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