Studied by 2 peopleposition of gene on a chromosome
(gene) locus
independent assortment
ability for any allele to be found in any cell
3 factors affecting genetic variation
crossing over,
independent assortment,
random fertilisation
when does independent assortment happen
metaphase 1
when does crossing over happen
prophase 1
F1 generation
offspring when 2 differently homozygous individuals are crossed, always heterozygous (e.g. AA x aa = Aa)
F2 generation
offspring when 2 of the F1 are crossed
test cross
crossing of an unknown with one showing recessive phenotype
how does proximity of gene loci affect crossing over
increasing distance increases probability of crossing over
sex linkage definition- which sexes of offspring cannot inherit from which parent?
gene found on X or Y chromosome (e.g. factor VIII, causing haemophilia, is on X chromosome)
if X linked, male offspring cannot get it (X from mother, Y from father)
if Y linked, female offspring cannot get it (XX)
typical ratio of dihybrid cross (both heterozygous)
9:3:3:1
epistasis
2 or more genes on different chromosomes affect the same feature
autosomal linkage
2 or more genes on the same non sex chromosome
how does crossing over interact with autosomal linkage
recombinants made- linkage broken by crossing over
location of crossing over
chiasmata
how could an allele cause a specific phenotype? (2)
enzyme not coded for- enzyme cascade disabled,
shift in protein structure (e.g. sickle cell anaemia) or no protein made
genetic sequence causing Huntington’s disease
repeated CAG triplets- HTT gene on chromosome 4 coding for huntingtin
genetic sequence causing haemophilia
f8 gene- codes for coagulation factor 8, abnormal allele results in abnormal/less/absence of factor 8
Le/le effects on plants- what makes abnormal and how is it treated? (3)
Le codes for enzyme for synthesis of gibberellin,
le, recessive, produces non functional,
lele is dwarf plant, treated by applying gibberellin
A and purpose
promoter region for regulatory gene/lacI- binds to RNA polymerase for transcription of lacI
B and purpose
lacI- regulatory gene coding for repressor protein to bind to operator region
C and purpose
promoter region for structural genes- binds to RNA polymerase for transcription of structural genes
D and purpose
operator region- repressor protein binds so RNA polymerase cannot bind to structural gene promoter
E and purpose
lacZ- codes for B-galactosidase to hydrolyse lactose → glucose/galactose
F and purpose
lacY- codes for lactose permease to make cell more permeable to lactose
G and purpose
lacA- codes for transacetylase
which parts of this belong to the lac operon?
C, D, E, F, G (structural gene promoter, operator, and 3 lac genes)
What happens to the lac operon when lactose is taken up by a bacterium? (3)
lactose acts as effector molecule and binds to repressor protein,
lactose distorts protein shape and preventing it from binding to the operator site,
mRNA binds to promoter region and structural genes are transcribed, allowing for breakdown of lactose
structural gene
gene coding for production of a protein used by a cell (could be actual structures or enzymes)
regulatory gene
gene expression controlled by other genes close to it (on the same DNA molecule)
inducible enzyme
enzyme synthesised only when substrate present
repressible enzyme
binding of effector to repressor helps it bind to operator, stopping transcription- enzyme synthesised when substrate is not present
in which organisms are operons found
prokaryotes
transcription factor definition- in which organisms are they found
protein binding to DNA at a promoter sequence affecting transcription (could increase or decrease rate)- only eukaryotes
how does gibberellin stimulate amylase production (5)
DELLA proteins are repressor proteins and bind to PIF (transcription factor),
PIF cannot bind to promoter of amylase gene,
gibberellin binds to receptor and enzyme, DELLA breaks down,
PIF no longer bound to DELLA and binds to promoter region,
amylase gene transcribed
Note 
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