16-genetics

position 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