I used this document in my GCSE revision and it helped me to achieve a Grade 8 in my final biology GCSE exam (edexcel igcse board). These notes are made based on the CGP GCSE guide.
small section Of DNA
OM change in DNA
coiled up
DNA -
a chromosome
↳
usually has no effect
↳ can alter (or stop) the
humans 'Code' for a protein
generally have
protein produced
23 ↳ determines YOUR
pairs
characteristics ↳ leads to disorders
↳ 46 in total
↳ One from each of allele : usually passed on
your parents two CON more
alternative forms
Of
found in the nucleus
the same gene that
! thread-like
arise by mutation
O structures
↳ alleles:
Dominant :
always expressed (even if only one
the combination of alleles an
is present)
Genotype :
individual has
copy
Recessive : only expressed if there are a
the physical characteristics that are
alleles (
Phenotype :
observed in the individual
copies (no dominant
Homozygous : 2 of the same alleles of a
Mother particular gene
B b
2 different
Heterozygous :
alleles of a
2 genotypes particular gene
BB Bb (B Or b)
B
↳ 3
(BB
Phenotypes
or Bb ON bb)
base pairs:
A -
Ademine
complimentary base
T-Thymine
b Bb bl
complimentary base
C-cytosine G-Guanine
PAIR OF CHROMOSOMES
Meiosis:
Br . Bu
Homozygous malves the number of chromosomes in gametes
dominant
↳When two gametes fuse at fertilisation ,
the full
GENES
number of chromosomes is restored
Nr n
Heterozygous PROCESS :
1. DNA replicates to make copies of genetic information
+ r - p Homozygous
recessive . The
2 cell divides TWICE
. The
3 cell division forms < cels called gametes
MEIOSIS: MITOSIS: ↳ each With a single set of chromosomes (half the original) ,
23
original cell (receives
↳ all genetically different from each other different
IDIII IIIII combinations of chromosomes
DNA replication
=>
to
of
form two copies
each chromosome
=>
DIFFERENCES
mitosis : meiosis :
*** *** maintains chromosomes
Divison 1
number of malves the number of chromosomes
*
Y produces genetically identical cells
produces genetically different ceus
Divison 1 happens in
# ** body cels
happens in reproductive organs
I cen division
·
& # 2 cen division
Divison 2
- -
Produces 2 (daughter) Cells
Produces & (daughter) Cens
NID WI
*** SIMILARITIES
2 new cells body cells
- DNA replicates before cell division
↑
=
cels =
gametes
increase in number of sub-cellular structures . Mitochondria /ribosomes
e g
.
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