genetics Flashcards
why are males more likely to suffer from recessive diseases?
beacuase all genes on the non-homologous section of the chromosome have no corresponding chromatid on the Y chromosome, therefore will be expressed in the phenotype
autosomes
other chromosomes in the body (not sex chromosomes) - 22 pairs we inherit
codominance
when alleles of a gene have equal dominance - meaning that individual will have a different phenotype to either of the homozygous individuals, as both alleles expressed in phenotype
gene pool
all the alleles of a gene within a population of a species
allele frequency
number of organisms in a community which carry a particular allele
hardy-weinberg equation
1 = p2 + 2pq + q2
what does hardy-weinberg equation predict
frequency of dominant and recessive alleles in a population as long as certain factors remain the same
assumptions made about hardy-weinberg equation (5)
- no mutations arise
- population is isolated - no allele flow in or out of pop.
- no selection - all alleles equally as likely to be passed on
- population is large
- mating is random
gene
a short section of DNA which determines a particular characteristic
variation
minor differences between individuals of the same species
monohybrid inheritance
inheritance of a single characteristic
locus
position of a gene on a chromosome
multiple alleles
some genes may have multiple alleles to code for 1 phenotype (eg. blood groups) but a gene will only EVER consist of 2 alleles
heterosomes
sex chromosomes
why are recessive alleles on non-homologous part of X chromosome always shown in the phenotype of a male?
- because no corresponding chromatid on Y
- means mutated recessive alleles will be seen resulting in sex-linked disease
dihybrid inheritance
inheritance of 2 pairs of charecteristics (eg. tall plants an purple flowers)
what phenotype ratios will you usually get with dihybrid inheritance (homozygous individuals - eg. TT, tt, RR, rr)
9:3:3:1
co-dominant genes
both alleles in a gene are equally expressed (eg. black + white = grey offspring) – alleles are both equally as dominant
when will you see 9:3:3:1 dihybrid inheritance
when NO crossing over in Meiosis occurs
epistasis
- occurs?
expression of one gene hides the expression of another
- metabolic proceses controlled by enzymes coded for by different genes
principle that hard Weinberg is based on
frequency of dominant and recessive alleles in a population will remain the same from generation to generation provided certain conditions remain the same
transcription factors
specific molecules which move fro, cytoplasm, into nucleus to switch on/off genes so that transcription ca occur/be prevented
how do transcription factors work?
- transcription factor has site which is complimentary to specific base sequence on DNA
- when it binds to PROMOTER REGION It causes transcription of the base to begin
- mRNA produced and information it carries is translated into a polypeptide
how does oestrogen activate transcription factor?
- lipid soluble so diffuses into cytoplasm, through phospholipid bilayer membrane
- binds to receptor site on transcription factors as it has a complimentary shape
- changing the shape of the DNA binding site on the transcription factor so it can now bind to base sequence on DNA
- transcription factor enters nucleus through nuclear pore - binds to specific PROMOTER REGION of DNA
- combination of transcription factor with DNA stimulates transcription of gene which makes up that portion of DNA - gene switched on
phenotype
physical characteristics due to genotype and environmental factors
Recessive epistasis
Recessive epistasis is where the epistatic allele (the allele that masks another gene) is recessive therefore 2 copied must be present to effect expression of another gene
phenotypic ratio
ratio of different phenotypes in offspring
linked genes
- why?
ones on same autosome - because they’ll stay together during independent segregation of chromosomes in meiosis 1
the closer 2 linked genes are…
why?
the more closely they are linked
because they are less likely to be split up by crossing over
if 2 genes are autosomally linked you won’t..
get expected phenotypic ratio you expect in offspring of a cross
what does a 12:3:4 ratio suggest?
dominant epistasis
stages of gene cloning using plasmids
- gene of intrest is isolated
-
what is p and q in HW?
allelic frequency
what is p2 and q2 in HW?
phenotypic frequency
genetic causes of variation (4)
- mutation
- crossing over of chromatids in meiosis 1 means each of 4 daughter cells formed have chromatids with different alleles
- independent segregation of chromosomes
- random fertilisation of gametes in sexual reproduction
how does independent segregation cause variation
- each homologous pair of chromosomes is made up of 1 maternal + 1 paternal - when separated in meiosis 1 its random which chromosome from which pair ends up In daughter cells as line up randomly along equator of cell ∴ different combinations of maternal and paternal chromosomes = variation in offspring
factors causing variation
genetic AND environmental
features of genetically varied group of organisms:
organisms fit into a few discrete categories with no intermediate types )eg. Blood groups) - often controlled by a single gene
types of environmental factors influencing variation (3)
- climatic conditions (temp, rainfall, sunlight)
- soil conditions (pH)
- food availability
features of an environmentally varied group of organisms:
often a continuum of characteristics - can plot a distribution curve
- variation is controlled by many genes - polygenes
law of independent assortment
each member of a pair of alleles may combine randomly with each other/another pair
autosomal linkage
2+ genes on same autosome are linked
linkage group
all genes on a chromosome
epistasis
when expression of allele of one gene masks or affects expression of another in the phenotype
problems with injecting insulin into another person
- cost
- immune response
- risk of infection
recombinant DNA
DNA from 2 different organisms combined
overall process of making recombinant DNA
- genes isolated
- genes cloned
- transferred to microorganism
- microorganism grows and acts as a factory for continual production of desired protein
transgenic
organism containing recombinant DNA
why does recombinant DNA work in producing transgenic organisms
because genetic code is universal - mechanisms of transcription and translation are the same
3 methods of producing DNA fragments
1 - conversion of RNA to cDNA by REVERSE TRANSCRIPTASE
2 - using RESTRICTION ENDONUCLEASES to cut fragments containing desired gene from DNA
3 - creating gene in GENE MACHINE
how does reverse transcriptase work in producing DNA fragments
- cell which rapidly produces protein is selected (as have a large amount of relevant DNA ∴ easily extracted
- reverse transcriptase used to make cDA from mRNA
- DNA polymerase used to join complimentary nucleotides on cDNA template to make double strand w required gene
how does restriction endonucleases work in producing DNA fragments
- cute double strand at specific base sequence (many types each cutting at different base sequences = recognition sites)
- if cut in staggered fashion they leave unpaired, exposed bases on each end of DNA strand
how does gene machine work in producing DNA fragments
- amino acid sequence used to work out DNA triplet found from desired protein
- desired nucleotide base sequence fed into computer
- sequence checked to make sure it meets safety standards
- computer designs series of overlapping nucleotides - assemble into desired gene
- gene replicated in PCR (complimentary strand assembled and multiplied to give many copied)
- inserted into vector using sticky ends
advantages of gene machine in production of DNA fragments (3)
- DNA produced is free of nucleotides
- great accuracy
- any nucleotide sequence can be produced
what does in vivo cloning produce?
bacteria with recombinant DNA which PRODUCE desired protein
what does in vitro cloning involve
PCR
PCR
polymerase chain reaction
process of in vivo cloning
- same restriction endonuclease used to cut DNA fragments (via hydrolysis reactions) and plasmid so that sticky ends are complimentary
- joined using DNA ligase
- promoter region needed for binding of transcription factors ( and terminator region )
- plasmid added to bacteria with DNA ligase, restriction endonuclease and primers - mixed in medium containing calcium ions at correct temp making membrane permeable
why may not all bacteria take up plasmid with desired gene
- only a few bacteria take up plasmid
- some plasmids close up again before gene is inserted
- some sticky ends on the gene fragments join together to make plasmids
how to identify genes which have taken up plasmid WITH gene?
replica plating
PCR process
- seperation of 2 DNA strands by breaking H bonds - 95C
- addition of primers at 55C - primers join to ends by complimentary base pairing giving starting sequence for DNA polymerase
- synthesis of DNA - temp raised to 72C - optimum temp for DNA polymerase making phosphodiester bonds via condensation reactions
number of gene fragments in PCR increases…
exponentially
cell differentiation
process by which cells develop into specialised cell suited for its role
stem cells
cells which can differentiate into other types of cell
sources of stem cells (4)
- embryonic stem cells
- umbilical cord stem cells
- placental stem cells
- adult (eg. bone marrow)
totipotent stem cells
- what?
- where?
- differentiate into ANY cell
- in zygote
pluripotent stem cells
- what?
- where?
- differentiate into ALMOST any cell type
- embroyos
multipotent stem cells
- what?
- where?
- differentiate into LIMITED NUMBER of of specialised cells
- in adults
unipotent stem cells
- what?
- where?
- differentiate into SINGLE TYPE of cell
- tissues/organs
Induced pluripotent cell (iPS)
type of pluripotent cell which is produced in lab by genetic alteration of any unipotent body cell to make it acquire characteristics of embryonic stem cells
what does iPS cell formation involve?
transcription factors and genes
uses of iPS cells (5)
- regrow damaged tissues - eg skin grafts treating: - leukaemia - parkinsons - multiple sclerosis - type 1 diabetes
main genetic sources of variation
- metaphase 1 - random assortment of HOMOLOGOUS CHROMOSOMES + crossing over of alleles
