Detailed 41-page document summary of the module made from the OCR A biology book containing everything you need to know.
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a) types of gene mutations and their possible effects on protein
production and functions
i) The three types:
1) Substitution
2) Deletion
3) Insertion
ii) They types of effects that can occur
1) No effect - Normally functioning proteins are still synthesised
2) Damaging - Proteins are no longer synthesised or non functional
3) Beneficial - (Rare) A protein is synthesised and results in a new
and useful characteristic in the phenotype of an organism
b) The regulatory mechanisms that control gene expression at the
transcriptional level, Post-transcriptional level and
post-translational level
i) Transcriptional - Genes can be turned on and off
ii) Post-transcriptional - mRNA can be modified which regulates
translation and the types of proteins produced
iii) Translational - Translation can be modified after synthesis which
changes their functions
iv) Post-translational - Proteins can be modified after synthesis which
changes their functions
v) Transcriptional control: the lac operon
1) It's a group of three genes: LacZ, LacY and LacA that are
involved in the metabolism of lactose.
2) Structural genes that code for three enzymes:
Beta-Galactosidase, lactose permease and transacetylase
3) They are all transcribed onto a single long molecule of mRNA
4) LacI codes for a repressor protein that prevents the transcription
of structural genes.
5) The repressor protein is constantly produced and binds to an
area called the operator
vi) Post-transcriptional control: Primary mRNA and intron removal
1) The product of transcription is a precursor molecule - pre-mRNA
2) Modified to form mature mRNA
3) Primary mRNA is edited and introns are removed.
vii) Post-translational control: protein modifications
, 1) Addition of non protein groups like carbohydrate chains, lipids or
phosphates
2) Folding or shortening of proteins
3) Modifying amino acids and the formation of disulfide bridges
4) Modification by cAMP
c) The genetic control of the development of body plans in different
organisms
i) Homeobox genes
1) Homeobox genes are genes that contain a homeobox
2) They have 180 base pairs and 60 similar amino acids
3) Found in fungi, plants and animals
4) Homeobox genes are similar in all 3 types or organisms eg:
pax6 gene that when faulty can cause blindness in humans and
mice q
ii) Hox genes and body plans
1) Hox genes are a group of homeobox genes only found in
animals
2) Responsible for the correct positioning of body parts
3) Symmetry of body shape:
(a) Radial symmetry - seen in diploblastic animals like
jellyfish. They have no left or right sides, only a top and a
bottom
(b) Bilateral symmetry - Organisms will have a left and a right
side along with a head and tail
(c) Asymmetrical - seen mostly in animals like sponges (no
lines of symmetry)
4) Hox genes are segmented for example the rings of a worm or
the spine of a human
5) They perform specialised functions for example in humans the
hox genes near the head control the formation of the mouthparts
d) The importance of mitosis and apoptosis as mechanisms
controlling the development of body form
i) Mitosis and apoptosis work together to sculpt and shape. Apoptosis, is
especially important in the process of making body parts for sculpting
ii) The factors of regulatory genes:
1) They are dictated by the environment (both internally and
externally)
2) Light intensity
3) Change in temperatures
6.1.2 Patterns of inheritance
,a) Two parts
i) The contribution of both environmental and genetic factors
to phenotypic variation
1) Environmental factors to phenotypic variation
(a) Example: chlorosis - Yellowing of the leaves
(i) Occurs because cells aren’t producing enough
chlorophyll
(ii) This lack of chlorophyll results in the plant not
being able to produce enough food for
photosynthesis
(b) Key environmental factors to do with/cause chlorosis in
plants
(i) Lack of light
(ii) Mineral deficiencies
(iii) Viral infections
(c) Animal diet/body mass
(i) An organism's body mass is technically
determined by both genetic and environmental
factors
(ii) However being either extremely under or
overweight is usually from environmental factors
such as:
(1) Amount of quality foods eaten
(2) The quantity of exercise an organism gets
(3) If the organism has a crippling disease
(iii) But also a mutation in a specific gene can still
predispose an organism to having a higher body
mass
ii) How sexual reproduction can lead to genetic variation within
a species
1) Genetic variation is created by the versions of genes you inherit
from your parents
2) Meiosis and the random fusion of gametes at fertilisation results
in the vast genetic variation between individuals of the same
species
3) Genotype - The combination of alleles an organism inherits to
acquire a characteristic, it is the genetic make of an organism in
respect to its genes
4) Phenotype - The observable characteristics of an organism ,
usually influenced by the environment
5) Only mutations (changes) in the DNA of the gametes can be
inherited towards offspring
, 6) Dominant allele - The version of the gene that will always be
expressed if present in an organism
7) Recessive allele - The version of the gene that needs two copies
of an allele to be expressed in the phenotype of an organism
8) Homozygous - two Identical alleles for a characteristic
(a) An organism for example could be homozygous dominant
(contain two alleles for the dominant gene) or
homozygous recessive (contain two alleles for the
recessive gene)
9) Heterozygous - They have two different alleles for a
characteristic
(a) The alleles for the dominant type will always be
expressed as the recessive trait will need to always be a
homozygous recessive.
b) Two parts
i) Genetic diagrams to show patterns of inheritance
1) Performing a genetic cross
(a) State the phenotype of both parents
(b) State the genotype of both parents
(c) State the gametes for both parents (circle them)
(d) Use a punnett square to show the results of the random
fusion of gametes during fertilisation.
(e) State the proportion of each genotype (eg: 25% of
something is …)
(f) State the corresponding phenotype for each of the
possible genotypes
2) Codominance
(a) When two different alleles code for one gene
(b) Both equally dominant
(c) Both will always be expressed if present in the phenotype
3) Multiple alleles
(a) Genes with more than two versions (Eg: blood type)
4) Determining sex
(a) Determined by X and Y chromosomes
5) Sex linkage and haemophilia
(a) If a male inherits the recessive allele that codes HP. (on
the X chromosome) then it will present itself on the
phenotype as the Y chromosome will have nothing to
counteract it (a dominant gene)
ii) The use of phenotypic ratios to identify linkage (autosomal
and sex linkage)
1) Linkage
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