topic 3 - genetics Flashcards
what is DNA
genetic blueprint which codes for and determines the characteristics of an organism
what is a gene
sequence of DNA that encodes for a specific trait
what is a locus
position of a gene on a particular chromosome
what is an allele
alternate form of a gene that codes for the different variations of a specific trait
what is an example of a gene and its potential allelic variations?
eye colour
brown, blue, green, grey
what is a gene mutation
change in the nucleotide sequence of a section of DNA coding for a specific trait
what is formed as a product of mutation?
new alleles
what are the three types of gene mutations
beneficial (missense mutations, new variations of a trait)
detrimental (nonsense mutations, abrogate the normal function)
neutral (silent mutations, have no effect on the functioning)
what is an example of a disorder caused by a gene mutation?
sickle cell anemia
what is sickle cell anemia caused by
base substitution (single base is changed in the gene sequence)
6th codon position for the beta chain of hemoglobin is changed
sickle cell anemia changes to DNA, mRNA, and polypeptide chain?
DNA: GAG –> GTG
mRNA: GAG –> GUG
Polypeptide: glutamic acid –> valine
what are the consequences of sickle cell anemia?
- alters hemoglobin structure (forms insoluble strands)
- cannot transport oxygen effectively (causes fatigue)
- red blood cells adopt a sickle shape (may form clots)
- sickle cells are destroyed at a higher rate (causes anemia)
what is the genome
totality of genetic information of a cell, organism or organelle (includes all genes)
what does the human genome consist of
46 chromosomes
3 billion base pairs
21,000 genes
what is the Human Genome Project (HGP)?
international cooperative venture established to sequence the human genome (showed that humans share the majority of their sequence)
where is the genetic material found in prokaryotes?
cytoplasm, in the nucleod
differences between prokaryotic and eukaryotic DNA?
prokaryotic DNA:
- single circular molecule made of naked DNA
- may have additional plasmids
eukaryotic DNA:
- multiple linear NA molecules packaged with histones
- no plasmids (unless genetically modified)
what are plasmids
circular DNA molecules
what do homologous chromosomes share
- the same structural features (ex. same size, same branding pattern)
- the same genes at the same loci positions
what are homologous chromosomes
paired chromosomes inherited from both parents (maternal + paternal) in sexually reproducing animals
diploid vs haploid?
diploid: 2 sets of chromosomes (i.e. body cells, as they receive genetic material from both parents)
haploid: 1 set of chromosomes (organisms only pass on half of their genetic material to reproduce)
what happens when haploid sex cells fuse?
diploid cell, grows into an organism
how is sex determined in humans?
sex chromosomes
what sex chromosomes do females possess? males?
females: XX
males: XY
what is the Y chromosome responsible for?
development of the male sex characteristics
what happens when there is no Y chromosome?
female sex organs develop
why is the father responsible for determining the sex of the offspring?
if the sperm contains a Y chromosome, embryo = boy
X chromosome = girl
the female egg will always have an X chromosome
what are the remaining chromosomes in the organism (not sex chromosomes)
autosomes
how many homologous autosomes do humans have
22 pairs
what are karyotypes?
number and types of chromosomes in a eukaryotic cell
what is a karyogram
shows the chromosomes of a cell in homologous pairs of decreasing length
when and why is karyotyping usually used?
occurs prenatally to…
- determine the gender of the unborn child
- test for chromosomal abnormalities
what is Down Syndrome?
condition whereby the individual has three copies of chromosome 21 (i.e. trisomy 21)
how does autoradiography work
- radioactive thymidine is incorporated into a cell’s DNA
- chromosomes were fixed to a photographic surface and treated with AgBr
- radiation converts silver ions into insoluble grains that is visible via electron microscopy when a film is developed
what is the point of autoradiography?
to measure the length of DNA molecules while uncoiled
who pioneered autoradiography?
John Cairn
can organisms with different diploid numbers interbreed?
unlikely as they cannot form homologous pairs in zygotes
when they do breed, offspring are infertile
what is chromosome number a characteristic feature of (?)
members of a particular species
ex. horses (diploid = 64)
summary of meiosis I?
- reduction division
- separates homologous chromosomes
- crossing over may occur during Prophase I
summary of meiosis II?
- akin to mitotic division
- separates sister chromatids
- occurs b/c DNA is replicated in interphase to create chromosomes with sister chromatids
what is meiosis?
reduction division of a diploid cell to produce four haploid cells (gametes) that are genetically distinct
what are the two cellular divisions of meiosis?
meiosis I - separates pairs of homologous chromosomes
meiosis II - separates sister chromatids
what are sister chromatids?
identical DNA molecules produced in the S phase of interphase held together by a centromere
what happens during prophase i?
chromosomes condense, nuclear membrane dissolves, homologous chromosomes form bivalents, crossing over occurs
what happens during metaphase i?
spindle fibres connect to bivalents + align them along the middle of the cell
what happens during anaphase i?
spindle fibres contract + split bivalent, homologous chromosomes move to opposite poles of the cell
what happens during telophase i?
chromosomes decondense, nuclear membrane may reform, cytokinesis
what happens during prophase ii?
chromosomes condense, nuclear membrane dissolves, centrosomes move to opposite poles (perpendicular to before)
what happens during metaphase ii?
spindle fibres from opposing centrosomes attach to chromosomes at centromere and align them along cell equator
what happens during anaphase ii?
spindle fibres contract + separate the sister chromatids, chromatids move to opposite poles
what happens during telophase ii?
chromosomes decondense, nuclear membrane reforms, cytokinesis
what is the final outcome of meiosis?
four haploid daughter cells
what are chiasmata
points where the homologous chromsomes are held together
what is synapsis
homologous chromosomes pairing up to form a bivalent
what is recombination
new gene combinations formed on chromatid
what are recombinants
nonsister chromatids that have exchanged DNA
number of possible gamete combinations?
2^n where n = haploid number
T/F: the orientation of pairs of homologous chromosomes is not random
F, random
what would happen if chromosome number was not halved in gametes?
polyploidy as the total chromosome numbers would double each generation
what are the three main sources of genetic variation arising from sexual reproduction?
- crossing over (prophase i)
- random assortment of chromosomes (metaphase i)
- random fusion of gametes from different parents
what is non-disjunction
chromosomes failing to separate correctly
what does nondisjunction result in
gametes w/ one extra or one missing chromosome
what is the effect of the age of parents on the chances of nondisjunction?
strong correlation between maternal age and occurence of non-disjunction events
what is DISCO PUG? (mitosis/meiosis differences)
Divisions (1 vs 2) Independent Assortment (N vs Y) Synapsis (N vs Y) Crossing over (N vs Y) Outcome (2 cells vs 4 cells) Ploidy (dip --> dip, dip --> hap) Use (body cells vs sex cells) genetics (identical vs genetic variation)
what is a genotype
allele combination for a specific trait
what is a penotype
physical expression of a specific trait
what are phenotypes determined by
genotype + environmental factor
what are the three possible types of allele combinations?
homozygous (both alleles are the same)
heterozygous (alleles are different)
hemizygous (only one allele, ex. X/Y gene in males)
what did Gregor Mendel’s pea experiment establish
principles of inheritance
what were the findings of Mendel’s pea experiment?
organisms have heritable factors
parents contribute equally to inheritance by supplying one version of the gene each
gametes contain only one allele of each gene
fusion of gametes results in zygotes with two alleles of each gene
what are gametes
haploid sex cells formed by meiosis
what are the two main modes of inheritance?
complete dominance
co-dominance
what is complete dominance? how is it expressed?
one allele is expressed over another
dominant is expressed in heterozygote (capitale)
recessive is masked in heterozygote (lower case)
can recessive phenotypes be expressed in heterozygotes?
no, only homozygotes as heterozygotes display the dominant phenotype
what is codominance
both alleles are equally expressed in the phenotype
what is an example of codominance?
ABO blood system
how is codominance expressed?
superscripts for the different co-dominant alleles (recessive still lower case)
how are human red blood cells categorized into different blood groups?
structure of a surface glycoprotein (antigen)
A,B, and O alleles are all controlled by a single gene. Which allele is recessive and which two are co-dominant?
A + B alleles = codominant
O = recessive
what does a monohybrid cross determine
allele combinations for potential offspring for one gene only
monohybrid cross steps?
designate letters to represent alleles
identify genotype / phenotype of parents
determine genotype of gametes
work out gamete combination with punnett grid
identify ratios of offspring
why were Mendel’s results questioned
too close to the exact ratios predicted to be genuine
what causes genetic diseases
mutations to a gene / genes
what type of allele (recessive, dominant, codominant) is responsible for the most common type of genetic diseases (????0
recessive
what is autosomal dominance?
both parents are affected by a trait but any offspring is not - trait is DOMINANT (parents are heterozygous)
what is autosomal recessive?
neither parents is affected by the trait but any offspring is, the trait must be RECESSIVE (parents must be heterozygous)
who is a carrier
heterozygous individuals that possess one copy of the faulty allele but do not develop disease symptoms
how many copies of a faulty allele does an autosomal recessive genetic disease require?
both alleles
how many copies of a faulty allele does an autosomal dominant genetic disease require to cause the disorder?
one copy
how many copies of a faulty allele does a genetic disease caused by co-dominant alleles require to occur
one copy
example of an autosomal recessive genetic disease?
cystic fibrosis
example of an autosomal dominant genetic disease?
huntington’s disease
example of a genetic disease caused by co-dominant alleles?
sickle cell anemia
what is cystic fibrosis + what is it caused by?
- caused by mutated CFTR gene (chromosome 7)
- produces thick mucus that clogs airways and causes respiratory issues
what is huntington’s disease + what is it caused by?
- caused by mutated HTT gene (chromosome 4)
- amplification of CAG repeats leading to neurodegeneration
what is sickle cell anemia + what is it caused by?
- mutated HBB gene (chromosome 11)
- leads to anemia + other complications
why are many genetic diseases rare?
any allele that adversely affects survival is unlikely to be passed on to offspring as the capacity to reproduce is unlikely
what is sex-linkage
gene controlling a characteristic is located on a sex chromosome
why are sex-linked conditions usually X-linked?
Y chromosome is much much shorter than the X chromosome and contains less genes
why can only females be carriers?
heterozygote for the recessive disease condition, males cannot be heterozygous carriers
recessive trait can be masked
what are two examples of X-linked recessive conditions?
red-green colour blindness
haemophilia
T/F: for recessive X linked conditions, affected mothers must have affected sons
T
T/F: for dominant X linked conditions, affected fathers MUST have affected daughters
T
what is a gene mutation
change to the base sequence of a gene that can affect the structure and function of the protein it encodes
what are spontaneous mutations
mutations caused by copying errors during DNA replication
what are induced mutations
mutations caused by exposure to external elements
what are three factors which can induce mutations?
radiation
chemical
biological agents
what are mutagens
agents which increase the rate of genetic mutations
what are carcinogens
mutagens which lead to the formation of cancer
what are two major examples of radiation exposure
nuclear bombing of hiroshima
accident/meltdown in chernobyl
what are some of the long-term consequences of radiation exposure?
- increased incidence of cancer
- reduced immunity (T cell count down)
- congential abnormalities
- organ specific health effects
what is a pedigree?
chart of the genetic history of a family over several generations
what are the symbols of a pedigree?
males = squares females = circles affected individual = shaded unaffected individual = unshaded mating = horizontal line generations = roman numerals age = left to right
can sex linkage be confirmed with a pedigree?
NO but patterns are there!
what is the polymerase chain reaction? (PCR)
artificial method of replicating DNA under laboratory conditions
what is gel electrophoresis?
laboratory technique used to separate and isolate proteins or DNA fragments based on mass/size
how does gel electrophoresis work?
samples placed in a block of gel + current is applied
smaller samples move faster through the gel (lower resistance)
samples move towards the anode
DNA is negatively charged (b/c of phosphate group)
proteins are treated with an anioinic detergent to impart a uniform negative charge on all molecules
what is DNA profiling?
technique by which individuals can be identified and compared via their respective DNA profiles
when is DNA profiling most commonly used?
forensic investigations paternity tests (offspring STRs are a combination of parents)
what are STRs? (short tandem repeats)
different lengths of particular DNA segments
how does DNA profiling work?
STR’s are amplified by PCR then separated by gel electrophoresis for comparison
unique profiles appear when multiple loci are compared
what is a transgenic?
new organism created as a result of gene modification
why an an organism potentially express a new trait if the appropriate gene is introduced into its genome?
genetic code is (almost) universal
process of gene transfer?
- DNA extraction (amplified using PCR)
- digestion + ligation (specific restriction enzyme + DNA ligase)
- transformation and expression (plasmid inserted into host cell + antibitioc to select for successful transgetic cells)
benefits of GM crops?
- can grow in a wide range of environments
- reduce farming costs + deforestation
- reduces spoilage
- improve nutritional standards
risks of GM crops
- unexpected health issues
- restrict access due to patent protections
- cross pollination with weeds
- reduce biodiversity (competes w native plants)
what is an example of GM crop + risks to wildlife?
Bt corn, incorporates insecticide producing gene which is toxic to monarch muterflies
what are clones
groups of genetically identical organisms or a group of cells derived from a single original parent cell
what does cloning multicellular organisms require
production of stem cells
how can stem cells be artificially generated
somatic cell nuclear transfer (SCNT)
how does somatic cell nuclear transfer work?
somatic cells are removed from donor + cultured
enucleated egg cell is fused with nucleus from donor to make a diploid egg
electric current stimulates egg to develop into embryo
embryo is implanted into surrogate
what are animal cloning methods?
binary fission
budding
fragmentation
parthenogenesis
what are plant cloning methods?
vegetative propogation
what are human cloning mechanisms?
natural mechanisms (identical twins)
what is binary fission
parental organism divides equally into two clones
ex. flatworms
what is budding
cells split off from parent, generating smaller clones
occurs in hydra
what is fragmentation
new organisms grow from separated fragment of parent
ex. annelid worm
what is parthenogenesis
embryos formed from an unfertilized diploid ova
ex. fish
what is vegetative propagation
small pieces of plant acn be induced to grow independently
why are plants capable of vegetative propagation?
adult plants possess totipotent meristematic tissue
what is a stem cutting
separated portion of a plant stem that is used to regrow a new clone
difference between identical and nonidentical twins?
identical twins: fertilized egg splits into 2
nonidentical: nonfertilized egg splits into 2, fertilized by diferent sperm
what are the two forms of artificial cloning
embryo cloning
adult cloning
what is embryo cloning + how does it work
cloning from an embryo by separating the embryonic cells into groups
embyronic stem cells are pluripotent so each cell can potentially form a cloned off spring
why can we not control the genetic features of potential clones in embryo cloning?
occurs after random fertilization
what is adult cloning?
process of somatic cell nuclear transfer
SCNT
