GENETICS 1 Flashcards
what is a phenotype
this is the outward and physical manifestation of an organism
what is a genotype
this is the full hereditary information of an organism even if not expressed .
what is the relationship between DNA structure an d function
DNA is transcribed into mRNA and then translated into proteins in the ribosome .
what is the structure of a DNA
made up of a pentose sugar , phosphate group and a nitrogenous base .
what is a nucleoside
a base and a pentose sugar
bonds involved in a DNA molecule
there is hydrogen bonds that are formed between the nitrogenous bases.
what are purines
they are adenine and guanine
what are pyrimidines
they are thymine , cytosine and uracil in the RNA .
complementary base pairing the number of bonds that are formed
3 bonds for cytosine and guanine
2 bonds for adenine and thymine
the largest organelle in animal cells
the nucleus which contains the DNA
site for DNA replication
nucleus
site for DNA transcription
nucleolus
what are chromosomes
they are wound DNA that are packed together into a thread like structure.
length of the DNA
2m
what are the parts of a chromosome
the two sister chromatids that are joined together by the centromere.
how many chromosomes are present in a human cell
humans have 23 pairs of chromosomes with 22 pairs being autosomal while 1 pair the 23rd being sex chromosome
how does the DNA achieve the structure to be able to be packaged into a chromosome.?
they are tightly wound on histone proteins to form a nucleosome
what is a nucleosome
DNA that is wound around a histone protein.
what does a nucleosome comprise of
comprises of eight histone proteins around which the DNA wraps 1.65 times
chromatin
mixture of DNA ,(histone) proteins and RNA which package within the nucleus.
heterochromatin
the condensed regions of the chromatin
euchromatin
the extended form of the chromatin that is exposed and less wound
process of DNA transcription and replication
1.both require the unzipping and closure of the DNA helix structure this is done by the enzyme ligase and the enzyme helicase.
2. the histone wrapping at the nucleosome has to be altered to expose more genes for the processes.
3. this is done by the addition of other molecules.
4.this is a reversible process .
modifications of the histone
addition of a methyl group
addition of an acetyl group on the histone
is histone modification reversible
yes
what kind of replication is the DNA replication
DNA replication is bidirectional and semiconservative
process of DNA replication
leading and lagging strand with the leading moving from the 5 end towards the 3 end , the lagging strand is synthesised as okazaki fragments , because it is from the 3 end towards the 5 end
behaviour of chromosomes during cell division
they cell chromosomes are most condensed during cell division.
during metaphase they align at the center of the cell .
what is a genome
refers to the amount of genes and proteins that are found in an organism .
what are exons and introns
exons are the coding region of the newly synthesised pre -mRNA while the introna are the non coding regions that are spliced out of the pre-mRNA during the formation.
why is there 20 amino acids yet there is 64 codons that are possibly to be formed.
with the exception of methionine and tryptophan other amino acids are all encoded in more than one codon .
degeneracy of the genetic code
with the exception of methionine and tryptophan they are all encoded by more than one codon; that is different codon can all code for the same amino acid
what is the main reason for redundancy
prevents the development of mutation.
single point mutations can also cause dysfunctional proteins .
a mutated haemoglobin gene causes sickle cell disease , the mutant haemoglobin is a hydrophilic glutamate that is substituted by the hydrophobic valine (Val),( GAA or GAG becomes GUA or GUG )
sickle cell disease manifestation
the glutamate amino acid is replaced by valine which is a hydrophobic molecule , this causes clumping up of the haemoglobin chains because they are attracted to each other forming a linear shape.
what is RNA
ribo- nucleic acid
types of RNA
messenger RNA
transfer RNA
ribosomal RNA
production of RNA
mRNA produced during replication and transcription.
Transfer RNA present in the ribosome that
is during translation addition of the amino acids together as they are formed through translation.
ribosomal RNA present in the ribosome subunits in the formation of RNA.
Function of the mRNA
Transcribed from DNA.
Carries information for protein synthesis.
start codon
Initiation codon also determines the reading frame of the RNA sequence.
process of transcription
transcription of DNA to form MRNA, the MRNA - process known as transcription and takes place in the nucleus.
splicing of the MRNA to remove introns and clump extrons together , happens in the nucleus.
with the help of transfer RNA and Ribosomal RNA proteins are formed.
there is post translational modifications of protein that is produced.
The tRNA sits in the p site and the a site is vacant ,the a site is where the next aminoacyl tRNA binds and there is translation leading to elongation
tRNA function
Major role is to translate mRNA sequence into amino acid sequence.
Acts as an adapter molecule between the coded amino acid and the mRNA.
production of rRNA
in the nucleus , then transported to the cytoplasm where they combine with proteins to form a ribosome.
what is the structure of a chromosome
2 chromatids that are joined together
they are joined at the middle by a centromere ,
the heterochromatin is the condensed regions of the chromatin that are inaccessible while the euchromatin is the region that is accessible , not very condensed.
there is a telomere that is located at the end of the end of the chromatin.
the heterochromatin is the most inward compared to the euchromatin .
what is known as telomere
telomere are at the edge of the chromosome , they have hundreds of copies , telomere shortening causes the cell to undergo stress which leads to trigerring of apoptosis
telomerase
enzyme that causes the addition of telomeres to prevent the shortening .
what are the phases of the cell cycle
the g0 phase, the g1 phase , s phase and the g2 phase and lastly the m phase
g1 phase
the longest phase of the cell cycle, is 10 to 12 hours long.
there is enlargement of the cell,
presence of a checkpoint ,
s phase
replication of the DNA lasts 6 to 8 hours
g 2 phase
the cell is preparing to divide
mitosis
there is production of 2 identical cells
phases of mitosis
IPMAT
prophase
the chromosomes have condensed and are visible , the nuclear membrane has disappeared, spindle fibres begin to form
metaphase
the chromosomes are at the middle of the cell, the spindle fibres have attached to the centriole , there is maximum condensation of the chromosome
anaphase
sister chromatids are separated at the chromosomes longitudinally , they move to the ends of the cell.
telophase
the nuclear membrane is formed, each cell will contain 46 chromosomes that is a diploid number.
centromere
site for the kinetochore microtubules of the spindle fibres ,
it is required for chromosome separation
chromatin
made up of heterochromatin and euchromatin , and proteins euchromatin is made up of active genes while heterochromatin is made up of silenced genes,
what are extragenic sequences
sequences that are outside of the coding regions of the gene.
examples of tandemly repeated sequences
Satellite DNA (14-500 bp repeats in of 20-100 kb arrays,
at centromeres and telomeres)( if you do not need it its is spliced out )
Minisatellite DNA (15-100 bp repeats in 1-5 kb arrays; used for DNA fingerprinting)
example of highly repeated interspersed DNA sequences
SINEs (short interspersed nuclear elements, 100-400 bp, most common are Alu elements)
LINEs (long interspersed nuclear elements, up to
6 kb, most common are L1 elements)
what is the structure of a chromatin
made up of histone proteins and DNA wrapped around it , histones have a positive charge and are packaged into units called nucleosomes.
manny nucleosomes are wrapped around to form a solenoid about 6 nucleosomes are wrapped together .
what is the purpose of packaging the DNA into solenoids
1.the packaging allows the neutralising of the negatively charged DNA with the positively charged histones .
2.The DNA is able to take less space.
3.Based on the environmental pressure and other reasons the inactive DNA can be folded in accessible regions until when they are required.
modification of the histone proteins
1.acetylation- that is addition of an acetyl group that will make the histone less positive and cause repulsion exposing the DNA .
2.methylation - addition of a methyl group the histone is the histone is made more positive and there is more attraction between the DNA and the histone protein.
metacentric chromosomes
Metacentric chromosomes have the centromere near the center of the chromosome
acrocentric chromosome
Acrocentric means that the centromere is distant from the center.
submetacentric
Submetacentric means that the centromere is slightly off-center
what is a karyotype
A karyotype is an individual’s complete set of chromosomes. The term also refers to a laboratory-produced image of a person’s chromosomes isolated from an individual cell and arranged in numerical order.
what are is fluorescence in situ hybridization
fluorescence in situ hybridization (abbreviated FISH) is a laboratory technique used to detect and locate a specific DNA sequence on a chromosome.
what are the types of FISH probes
1.unique sequence probes
2.centromeric probes for determining the chromosome number.
3.telomeric probes that is useful for detecting subtelomeric rearrangements and is often present in children with mental retardation.
4.whole chromosome probes which measures a cocktail of probes covering different parts of a particular chromosome .
process of meiosis
cell division in germ line cells to form haploid cells .The chromosomes are passed on as re-arranged copies which creates genetic diversity.
prophase 1
there is recombination between the non -sister chromatids ,there is crossing over where the allele bind and exchange materials.
metaphase 1
independent assortment of the chromosomes in the middle of the cell
gametogenesis
the process of formation of an egg or a sperm
oogenesis
Oogenesis = process of egg formation
spermatogenesis
process of sperm formation
difference between oogenesis and spermatogenesis
in oogenesis after meiosis 2 there is only one viable cell that proceeds into differentiation and becomes an egg the rest become polar bodies .however, in spermatogenesis, in meiosis 2 the 4 cells that are possibly released all go into differentiation to form sperms hence the maturation once in a month.
what are the differences between gametogenesis in males and women.
on a table
fertilisation
Two haploid cells (egg, sperm) form 1 diploid cell (zygote) – develops into embryo
Whether sperm contain an X or Y chromosome determines if embryo is female (XX) or male (XY)
Embryo contains an assortment of genes from each original parent – more genetic diversity
Mitochondria (and their DNA) come only from mother via the egg – maternal inheritance
what is a centromere
constricted region that joins the sister chromatids
made up of repetitive DNA sequences
site for the kinetochore attachment
extragenic sequences
1.tandemly repeated DNA sequences -Satellite DNA has repetition of 14 to 500 base pairs ( centromeres and telomeres ) while minisatellite has repetition of 15 to 100 base pairs ( fingerprint).
2.highly repeated interspersed DNA sequences.( that is long interspersed nuclear elements and short interspersed nuclear elements)
nucleosome packaging units
146 base pairs wrapped in 1.8 turns around 8 histone proteins.
levels of the condensed chromatin structure
level one - nucleosome
level 2 - chromatin fibre
level 3 - fibre scaffold complex
level 4- chromosome
condensation factor of DNA at the metaphase
factor of *10000 during metaphase for the DNA to be seen really well
what scientific steps does the FISH method involve
labelling with the fluorescence dye , denaturing of the DNA and later hybridization.
structure of a chromosome
made up of 2 chromatids.
p arm , the top arm while the q arm is the bottom arm of the chromatid.
metacentric chromosome
the arms seem almost at the same length
the centromere is located at the middle
sub metacentric chromosomes
the centromere is placed slightly away from the centre and the p arms are shorter but existing
acrocentric
the centromere is located almost at the apex very short to non existent p arm .
telocentric
the centromere is at the telomere hence the name telocentric there is no p arm.
what is the most prevalent Stage with incidence of chromosomal abnormalities
first trimester miscarriages that is 50%
children with mental retardation that is 35-40%
congenital malformations that is 5-10%
what are the types of chromosomal abnormalities
numerical
structural
mutational
what is the origin of chromosomal abnormalities
non -disjunction
syndrome caused by trisomy
patau - XX +13
down syndrome -XY+21
edwards -XX+18
describe non -disjunction
could happen at the meiosis one whereby two chromosomes are located on the same cell.
could happen in meiosis 2 whereby
there is failure of separation of the
sister chromatids such that each
cell has a sister chromatid instead
of a chromosome ; because of this one cell may end up with more chromosomes while another might end up with nothing on the cell.
origin of disomy
male partners
origin of trisomy
female partners
trisomy 21
inheritance of extra chromosome at location 21 which causes down syndrome.
trisomy 21 caused by non -disjunction , robertsonian translocation 4% and mosaicism (1%)
what are the characteristics of someone with downs syndrome
Characteristic facial dysmorphologies
IQ less than 50
Average life expectancy (50-60 years)
Alzheimer’s disease in later life
trisomy 13
causes Patau syndrome
extra chromosome at position 13
mostly caused by non -disjunction and mostly of maternal origin ,
also caused by unbalanced robertsonian translocation
trisomy 18
edwards syndrome
severe development problems and most patients will die within the first year.
examples of syndromes that are autosomal chromosomes aneuploidy
downs syndrome
edwards syndrome
patau syndrome
sex chromosomes aneuploidy syndromes
turners syndrome
klinefelters syndrome
turners syndrome
example of monosomy
only one sex chromosome that is X only happens in women ( can only be a man if there is a y chromosome, with this there is only an x)
characteristics of turner`s syndrome
emales of short stature and infertile- males cannot have this.
Neck webbing and widely spaced nipples
Intelligence and lifespan is normal
klinefelter`s syndrome
an extra sex chromosome
only in males
characteristics of klinefelter`s syndrome
tall stature in men and long limbs
sterility ( infertile )
mild learning disabilities
small testes
males with gynacomastia
structural abnormalities of chromosomes
1.Balanced or unbalanced rearrangements
2.Translocations
Reciprocal: involving breaks in two chromosomes with formation of two new derivative chromosomes
Robertsonian: fusion of two acrocentric chromosomes
3.Deletions
4.Insertions
5.Inversion
what are structural abnormalities
abnormalities that cause changes in the chromosome structure .
what is a balanced translocation
.there is no gain or loss of the genetic material , the genetic material is only rearranged with materials from both chromatids on both sides ..
outcomes for someone who is a balanced translocation carrier
there is a cell that is a fertilised carrier
unbalanced translocation
robertsonian translocation
reciprocal translocation
robertsonian translocation
fusion of acrocentric chromosomes at their centric ends and there is loss of the 2 p short arms. the q arms fuse to form a chromosome.
outcomes for robertsonian translocation
two unbalanced gametes fertilisation with a normal balanced gamete will form both trisomy , monosomy at chromosome 21 and 14.
deletion
breaks of some parts of the chromosome
inversion
also known as balanced rearrangement
there is an inversion of the genetic material which is reinstated in the piece of DNA.
what are genetic mutations
changes in the structure of the DNA could be in the germline or could be somatic
genetic mutation s
Germline or somatic
Gene disruption /disease-associated
Polymorphism
No phenotypic effect
Frequency >1%
where does genetic mutation happen in the gene
genetic mutations could be in the coding region or in the non coding region
examples of genetic mutations
silent
missense
non -sense
frame shift
silent mutation
synonymous e.g. CGA (Arg) to CGC (Arg), they both have the same outcome because they result in the same amino-acid formation
non -sense mutation
Nonsense e.g. CGA (Arg) to TGA (Stop) Intro of a stop codon earlier on
frameshift deletion and insertion
GA (Arg) to CCGA (Pro, then out-of-frame)
missense mutation
instead of formation of a specific amino acid there is formation of another ; example Missense e.g. CGA (Arg) to GGA (Gly)
methods of detecting mutations
1.polymerase chain reaction
2.gel electrophoresis
3.restriction fragment length polymorphism analysis.(RFLP)
4.amplification refractory mutations system (ARMS )
5.DNA sequencing
necessities for PCR
Sequence information
Oligonucleotide primers
DNA
Nucleotides
DNA polymerase
Making more of the dna and the separate nucleotides labelled with flouroscent.
techniques for PCR
denaturation - that is breaking of the hydrogen bonds across the 2 strands.
annealing that is cooling the reaction so that the primers can bind to their complementary sequences on the single stranded DNA template.
extending with the primer addition for formation of new base pairs.
polymerase chain reaction
amplification of the DNA molecules which will result in the formation of many DNA molecules.
uses the DNA polymerase hence the name for extension of the DNA.
gel electrophoresis in PCR
technique in which fragments of DNA are pulled through a gel matrix by an electric current , and it separates DNA fragments according to its size.
gel electrophoresis
Separate DNA fragments by size
Apply an electric field
DNA is negatively charged
Separate through agarose gel matrix
Visualise DNA fragments
interpretation of a gel electrophoresis photo
the small molecules will move towards the bottom of the paper ,
advantages of PCR gel photo
Speed
Ease of use
Sensitive
Robust
PCR applications
DNA cloning
DNA sequencing
In vitro mutagenesis
Gene identification
Gene expression studies
Forensic medicine
Typing genetic markers
Detection of mutations
what are the outcomes for translocation
normal with normal gamete
carrier with balanced chromosomes
unbalanced chromosome which might lead to partial trisomy and monosomy
mutation nomenclature
1.Cys64Arg - cysteine is replaced by arginine
2.662-42C >T- that is at position 42 of the 662 extron cytosine is replaced( substituted) with thymine.
3.
applications of PCR
DNA cloning
DNA sequencing
In vitro mutagenesis
Gene identification
Gene expression studies
Forensic medicine
Typing genetic markers
Detection of mutations
arms method disadvantages
Need sequence information
Limited amplification siz
arms method advantages
Cheap
Labelling not required
Electrophoresis required
Primer design critical
