Genetics Flashcards
What does an autosomal recessive pedigree look like?
2 unaffected lead to 2 affected
What does an autosomal dominant pedigree look like?
2 affected lead to 2 unaffected
What does a sex-linked pedigree look like?
affect males only
genetic material on a chromosome for encoding a trait
gene
location on chromosome where a gene is located
locus
alternative forms of a gene that allow for differences such as different hair or fur colours
allele
a pair of chromosomes that contain the same genetic material
homologus chromosomes
Law of segregation
Mendel’s law that states that the pairs of homologous chromosomes separate in meiosis so that only one chromosome from each pair is present in each gamete
law of independent assortment
Each member of a pair of homologous chromosomes separates independently of the members of other pairs so the results are random
A cross between individuals that involves one pair of contrasting traits
Monohybrid cross
Cross or mating between organisms involving two pairs of contrasting traits
Dihybrid cross
the crossing of an individual of unknown genotype with a homozygous recessive individual to determine the unknown genotype
Test cross
How can you determine probabilities of dihybrid crosses without doing the table?
Do each gene separately and then multiply the probabilities
incomplete dominance
blending of expressions of alelles
Ex. red and white flower make a pink one
Codominance
both inherited alleles are completely expressed
Ex. blood type AB has dominant A and dominant B
Multiple alleles
three or more forms of a gene that code for a single trait
Ex. blood types
A type of gene interaction in which one gene alters the phenotypic effects of another gene that is independently inherited.
Ex. mice
Epistasis
pleiotropy
A single gene having multiple effects on an individuals phenotype
Ex. Sickle cell anemia leads to different health conditions, pain, stroke, high BP
What is the difference between polygenic and pleiotropic?
the probability an organism with a specific genotype will express a particular phenotype
complete: genes for a trait are expressed in all of the population who have the gene
incomplete: genes for a trait are only expressed in a percentage of the population
Penetrance
Variable expressivity
individuals with the same genotype have related phenotypes that vary in intensity
Ex. red hair gene could be light red, dark red, or any red in between
What is x-inactivation?
during embryonic development one of the two inherited X chromosomes does not uncoil into chromatin and remains as a barr body. barr bodies are not expresed
Ex. calico cats - characteristic of black and orange fur depend on which copy of the x chromosome the cell chooses to leave active
What is an example of a genetic disease that results from X-inactivation?
one or more chromosome pairs or chromatids fail to separate during mitosis
Nondisjunction
cells undergo nondisjunction have extra or missing chromosomes
Mosaicism
Single nucleotide change causing either substitution, insertion, or deletion
point mutation
frameshift mutation
insertion or deletion because they shift the reading frame
transition mutation
purine to purine or pyrimidine to pyrimidine
transversion mutation
purine to pyrimidine or vice versa
trisomy 21
down syndrome, extra copy of chromosome 21
turner syndrome
XO
female is either completely missing or partly missing an X chromosome
klinefelter’s syndrome
XXY
male born with extra X chromosome
chromosome segments are rearranged in reverse orientation
inversion
one segment of a chromosome is moved to another chromosome
translocation
What are three autosomal recessive conditions?
Phenylketonuria (PKU) - can’t produce enzyme for phenylalanine breakdown, causing phenylpyruvic acid to accumulate
Cystic fibrosis - fluid build up in respiratory tracts
Tay-sachs - lysosome defect in which cells can’t breakdown lipids for normal brain function
What are three autosomal dominant conditions?
Huntington’s - nervous system degeneration
Achondroplasia - drawfism
Hypercholesterolemia - excess blood cholesterol leading to heart disease
What are three sex-linked recessive conditions?
Hemophilia - abnormal blood clotting
Colour blindness - primarily observed in males
Muscular Dystrophy - muscle loss
what are chromosome disorders?
down syndrome - trisomy 21
turner’s syndrome - XO
klinefelter’s syndrome - XXY
cri du chat - deletion on chromosome 5
Cri du chat
deletion on chromosome 5
What is extranuclear inheritance?
the inheritance of genetic material that is not found within the nucleus (mitochondria and chloroplasts)
An organism that has two identical alleles for a trait
Homozygous
An organism that has two different alleles for a trait
Heterozygous
single copy of a gene is inherited instead of two
Ex. males inherit one X
hemizygous
Describe RNA
A, U, C, G
- single stranded
- ribose
DNA replication is (conservative/semiconservative)
semiconservative
Describe DNA replication
- DNA copies itself
- Helicase unwinds DNA and forms a replication fork
- SSBPS (single stranded binding proteins) keep DNA strands separate
- Topoisomerase (DNA Gyrase) break and rejoin the DNA double helix, preventing kinks
- DNA polymerase moves in 5’ to 3’ direction
- leading strand: works continuously
- lagging strand: has to keep going back to replication fork and work away from it which produces Okazaki fragments
- RNA primase creates small strip of RNA which DNA can work off of - DNA ligase joins okazaki fragments
catalyzes the lengthening of telomeres in germ cells
Telomerase
What are the three stop codons?
U Are Annoying (UAA)
U Go Away (UGA)
U Are Gone (UAG)
Least abundant RNA and contains codons
mRNA
the exact base pair of the third nucleotide in the codon is often not required, allowing 45 different tRNA’s to base pair with 61 codons that code for amino acids
Wobbles
What is directional selection?
the favouring of traits at one extreme of the range
superior quality of offspring resulting from crosses between two different inbred strains, species, or varities of organisms
hybrid vigor (heterosis)
when a small group of individuals migrate to a new location, the gene pool of the small group will be less than the original population; after successive generations, the genetic makeup will be unique from the original population
founder effect
Transporter of anticodons
tRNA
type of RNA that combines with proteins to form ribosomes
rRNA
What are the five requirements for hardy weignberg?
- no mutations
- no natural selection
- no gene flow
- large population
- random mating
What is the most abundant RNA?
rRNA
What are the three steps of transcription?
INITIATION
- RNA polymerase attaches to promoter (TATA BOX) and unzips DNA
ELONGATION
- assembly of RNA nucleotides using one strand of template DNA
TERMINATION
- RNA reaches AAAAAA sequence
What is the “TATA box” of prokaryotes?
Pribnow Box
What are the modifications mRNA goes through before leaving the nucleus?
- 5’ cap added for stability and attachment to ribosomes
- poly A tail added to 3’ end for stability and movmement
- RNA splicing
- introns removed
- exons join together
What occurs during translation?
INITIATION
- small ribosome subunit attaches to 5’ end of mRNA
-tRNA methionine attaches to AUG
- large ribosomal unit attaches to form complex
ELONGATION
- A site: tRNA binds and peptide bond forms
- P site: tRNA moves from A site to P site and the next tRNA joins the A site
TERMINATION
- ribosome encounters a stop codon
POST-TRANSLATION
- free-floating ribosome attaches to endoplasmic reticulum and then will go to the Golgi
What is the start codon for prokaryotes??
n-formylmethionine
When a mutation occurs, but the new codon still codes for the same amino acid, therefore there is no effect
silent mutation
the new codon codes for a stop codon
nonsense mutation
mutation where there is no change in protein function
neutral mutation
a new codon codes for a new amino acid, can be minor or fatal
missense mutation
What are the repair mechanisms in genomes?
- Proofreading: DNA polymerase
- Mismatch repair: enzymes repair what was missed by DNA polymerase
- Excision repair: enzymes remove nucleotides damaged by mutagens
- Nucleotide excision repair: can be used to repair issues like thymine dimers (does it in chunks)
- Base excision repair: same as nucleotide but only repairs the base itself
structure formed when DNA is coiled around bundles of 8-9 histone proteins, kind of like beads on a string
nucleosome
Compare and contrast euchromatin and heterochromatin
Euchromatin - chromatin is loosely bound to nucleosomes; present when DNA is actively being transcribed
Heterochromatin - areas of tightly packed nucleosomes where DNA is inactive and appears darker
DNA segments that can move to a new location on either the same or different chromosome
transposon
DNA that does not code for proteins or RNA
psuedogene
Not viruses or cells, but are infectious, mis-folded versions of proteins in the brain that cause normal versions of proteins to also become mis-folded. These are fatal and are implicated in diseases such as Mad Cow, kuru, scrapie, and Creutzfeldt-Jakob.
prions
very small circula RNA molecules that infect plants
viroids
region of DNA that controls gene transcription
operon
sequence of DNA where RNA polymerase attaches to begin transcription
promoter
region that can block action of RNA polymerase if occupied by repressor proteins
operator
DNA sequences that code for related enzymes
structural genes
located outside of the operon region and produce repressor proteins
regulatory genes
What does the Lac operon (e.coli) do?
controls the breakdown of lactose
OPTION 1
- lactose available –> binds to repressor –> inactivates it –> RNA polymerase transcribes genes
OPTION 2
- glucose is low, cAMP is high –> binds to a CAP binding site of promoter –> allows RNA polymerase to breakdown lactose
OPTION 3
- lactose and glucose high, operon shuts off because cAMP is low and can’t bind to CAP
What does the Trp operon (e.coli) do?
produces enzymes for tryptophan synthesis
tryptophan binds inactive repressor –> activates the repressor –> binds to operator –> blocks RNA polymerase
How are eukaryotic genes regulated?
- Regulatory proteins: enhancers/repressors influence RNA attachment to promoter region
- Nucleosome packing
- methylation of histones: tighter packing that prevents transcription
- acetylation of histones: uncoils chromatin, encourages transcription
- direct DNA methylation: leads to lower expression - RNA Interference
- Micro RNA (miRNA): degrades target or blocks translation
- Short interfering RNA (siRNA): similar to miRNA
How much of the human genome is non-coding DNA?
97%
