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Summary AQA A-Level Biology – Genetic Information, Variation and Relationships Between Organisms (Unit 4) – Complete Revision Notes

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These notes cover AQA A-Level Biology topic “Genetic Information, Variation and Relationships Between Organisms,” including DNA structure, protein synthesis, mutations, meiosis, genetic diversity, biodiversity, classification, and species concepts. The document explains inheritance patterns, genetic variation, natural selection, and evolutionary relationships in detail. It is organised as comprehensive revision material aligned with the AQA specification and suitable for exam preparation.

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,genes, triplet code, DNA, chromosomes
Gene section DNA that contain coded info bases making polypeptides &
of .
as
specific sequences of for
functional RNACERNA & RNA)
polypeptidechain proteins enzymesallchemical
code reatinas
CalungOrAminoacidsequence
·
=


genes


·
locus location of gene on the DNA molecule


codon sequence 3 consecutive nucleotides (triplets) that code amino acid
of for a
specific
·
exons
coding introns non-coding
·




The Genetic Code
-must be min 3 bases that code each amino acid
of .




for

onmino and regular ou
bases DNA
· each haveown code = codes inadequate
must its on




,




Features The Genetic Code
of
triplets
- 64 possible some amino acids coded
for by 2-6 triplets degenerate code =




triplet always read in one direction along DNA strand
starto DNA sequence =


always Methionine Triplet
m
if
not part of final polypeptide ,
later removed
stop codes 3 introns ends tide chain
a b pe abc def
=




code is non-overlapping (EG :
,


code is universal same
for
all
organisms (few minor exceptions -
indirect evidence
for
evolution

-


in
Eukaryotes DNA wound around histones forms chromosomes
,
-


-




chromosomes only visible when cell dividing otherwise dispersed throughout nucleus
,
↳ seen two chromatids (give identical DNA molecules) joined by centromere doe to DNA replication
as


This DNA is held together by histones highly coiled in DNA- histone complex before a
,


being further coiled & pacted into chromosome one condensed DNA strand as


↳ each (locus) along the DNA molecule
gene occupies specific position
a




Homologous Chromosomes
Homologous Pairs
sexually reproduced organisms
are a result of the maternal chromosomes & paternal
chromosomes coming together
·
total no .
=


diploid (EG : humans 46)
·

always same 2 chromosomes that carry same genes ,
but not necessarily same allele


-




During meiosis
, halving no .




of
chromosomes each daughter cell recieves one chromosome from
each homologus pair Frecieves chromosome from each homologous per
Alleles
Allele alternate each gene exists 2 Cor more
form of gene ,
an a in

·
each individual inherits one allele from each parent may be I

same or
different (due to change in base
sequence Amino acid sequence
-
mutation)

, structure of RNA
Genome complete set
of genes
in an
organism
Cincl . Mitochondria & chloroplasts
Proteome full range of proteins produced by the genome
sometimes called complete proteome
·




r
proteome here proteins produced by
F

type cell under certain set conditions
a
given of
a
of


protein synthesis the cytoplasm sections of DNA code transcribed onto RNA
-




since occurs in are
,




mRNA
messenger
RNA , transfers DNA code
from
nucleus to cytoplasm as small enough to leave through nuclear pores
o

long strand in single helix; IOOOs of mononucleotides
·
base determined by
sequence
bases in DNA in transcriptions
sequence of
template for protein synthesis & possesses codons
·

in
info .




form of


ERNA transfer RNA , many types ,
each binds to specific amino acid
8

long strand single ,
helix
folded into
alover-leagshape ; around 80 nucleotides
·

opposite end of acid binding site
amino

anticodon sequence 3
specific organic bases
=


of
complementary to codon on mRNA


rRNA ribosomal RNA


anticodon-I


Comparing DNA mRNA ERNA
, ,




II
DNA mRNA tRNA
--



-


double polynucleotide chain -




single polypeptide chain -




single polypeptide chain
largest molecule of the 3 smallest molecule of 3
- -




double-helix molecule (except o clover-shaped
singlehelix
-
-




in a virus
jew
deoxyribose pentose sugar pentose ribose pentose sugar
-
-




sugar
-




A 1 - C- 6-




,
-




A U
-




,
C G -
-




A U -



C G
-




,


mostly in nucleus throughout cell
activity Windthroughoutc/
-found
-




-quantity constant all cells in
-




quantity varies w/metabolic l metabolic activity
Lexcept gametes
-chemically very stable -



less stable than DNA & +RNA,
individual molecules usually broken
down in a
Jew days
-




hydrogen bonds

Información del documento

Nivel de Estudio
Tema
Subido en
13 de febrero de 2026
Número de páginas
16
Escrito en
2025/2026
Tipo
Resumen
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