Exam 2 Flashcards
Multifactorial traits are also called…
Multifactorial diseases are also called…
Quantitative traits; Complex diseases
Define Penetrance
Risk of being affected when you have a risk increasing gene
What is an isoform?
different versions/forms of a protein that may be produced from the same gene due to alternative splicing, alternative promotors
Phenocopies occur due to…
non genetic factors alone
Hemochromatosis risk is a…
functional polymorphism of the HFE gene
Risk for a disease can be ________ despite the disease being a _________ trait.
continuous; threshold
What is VARIANCE? How is it calculated?
S^2: how far distribution spreads from the mean
Calculated by finding the average squared distance from the mean:
1) Subtract individual scores from the mean
2) Square each of the differences
3) Sum the squared differences and divide by n-1
What is STANDARD DEVIATION? How is it calculated?
S; square root of the variance
What percentage is included in 1SDs, 2SDs, and 3SDs of the mean?
1SD=66%
2SD=95%
3SD=99%
What is the range of the correlation coefficient? What does it mean if it is zero?
-1 to +1; 0=no correlation
What does regression allow you to do?
Predict the value of one variable given the value of the other
In a line of best fit, the slope represents…
The value of the regression coefficient.
Define all of the following: Vp Vg Ve Vge Va Vd Vi
Vp = variance due to population Vg = variance due to genetic factors Ve = variance due to environmental factors Vge = variance due to interactions between genetic and environmental factors Va = additive genetic variance (how much offspring resemble parents) Vd = genetic variance due to dominant alleles Vi = variance due to interactions between gene alleles (like epistasis)
How do you calculate Vp?
Vp=Vg+Ve+Vge
How do you calculate Vg?
Vg=Va+Vd+Vi
What are all the variables that contribute to Vp?
Vp=Va+Vd+Vi+Ve+Vge
What is broad sense heritability and how is it calculated? What is its range?
H^2; Portion of population variance due to ALL genetic factors;
Calculated using Va, Vg, Vi
Formula: Vg/Vp = (Va+Vg+Vi)/Vp
Range: 0 to 1
What is narrow sense heritability? How is it measured? What is its range? What is another thing that this equals?
h^2; Proportion of variance due to ADDITIVE genetic factors (Va);
Formula: Va/Vp
Range: 0 to 1
Also equals the REGRESSION COEFFICIENT when (uparents, uoffspring)
What does it mean if Va is low?
Offspring do not resemble parents; other factors (like food) must contribute more heavily to phenotype
Va give you a…
Nice, normal distribution
You can study genetically identical twins to eliminate _______ meaning that all variability is due to _______.
genetic variance (Vg); all variability is due to nongenetic factors (Vp=Ve)
How do you calculate broad sense heritability for the F2 generation?
Vg/Vp=(VF2-VF1)/VF2
Because VF2=Vg+Ve
and VF1=Ve
Vg+Ve-Ve/)(Vg+Ve)=Vg/(Vg+Ve)=Vg/Vp
Using MZ and DZ twins, how to you calculate broad sense heritability?
H^2=2(rMZ-rDZ)
Where r represents the correlation coefficient between the twins PHENOTYPES
What is a selection differential? What symbol is used to represent it?
Difference between mean phenotype of the individuals chosen for breeding versus the total population’s mean
= Mean(parents)-Mean(population)
Symbol=S
How do you calculate response to selection? How is this used to calculate the new mean of the population?
R=h^2xS
where R=response to selection, S=selection differential
Long Form: R=(2(rMZ-rDZ))(Mean(parents)-Mean(population))
New Mean=Original Mean+Response to selection
New Mean=Original Mean+(h^2)(breeder’s means - population mean)
What limits the phenotypes produced by selective breeding?
Genes becomes fixed (exist at 100% frequency) because the environment might select against a very extreme version of the trait.
At this point, there is no more additive genetics inheritance (h^2=0)…which means R=(h^2)(S)=0
Heritability tells you…not…
Heritability tells you what FRACTION of the VARIANCE is due to genetic factors, NOT THE DEGREE to which a trait is determined by genetic factors.d
Heritability is specific to a particular ______ and ______.
Population and Environment
Heritability never applies to _____
Individuals
Define INBRED vs OUTBRED
Inbred: Genetically identical (Vg=0)
Outbred: Genetically non-identical (Vg is not 0)
What formula is used to estimate the number of genes that influence a trait?
(1/4)^n
where n is # of genes
Which of these is not like the others? (in regard to genes involved)
“more than 3” “at least 4” “3 or more”
“3 or more” because it includes 3 as a possible answer
Which is more detailed: GWAS or QTL?
QTL is a more detailed analysis that allow you to identify genes that influence a trait or disease
Two ways to identify QTLs:
Linkage Study: within family approach
Association Study: between groups approach (case vs control group)
What is a GWAS?
genome wide association study; uses markers from all over the genome
What has 100% penetrance?
single-gene disorders
Incomplete dominance= ______
Codominance= ________
Blending; spots
Explain how types of dominance can be different at different levels of analysis.
Incomplete dominance at cellular level (Aa produces lower level of a protein per cell), BUT recessive at clinical level (must have aa to express the disease, as Aa still makes enough of the protein to be functional).
What is the difference between dominant and recessive epistasis?
Dominant Epistasis: requires only one (heterozygous expression of) epistatic gene to cover expression of hypostatic gene – Example: Corn kernel color
Recessive Epistasis: requires homozygous expression of epistatic gene to cover expression of hypostatic gene – Example: Coat color in retrievers
What type of epistasis is blood type?
Recessive Epistasis
What genotype(s) yields the BOMBAY PHENOTYPE in blood?
hh with any combination of I alleles (can be IA_, IB_, or ii)…because compound H (dominant) is needed to bind to the terminal sugar that produces type A or B or O (non-bombay)…However, blood type is an example of recessive epistasis because two hh alleles is needed to cover the expression of the hypostatic gene (IA, IB, or ii)
What is duplicate recessive epistasis? What is an example of this?
Both genes capable of being epistatic gene if either one occurs in homozygous recessive form; a certain type of albinism (can be missing gene for tyrosine transporter gene or missing gene for enzyme tyrosinase, which makes melanin from tyrosine)…you need both to have pigment in your skin.
Both aaB_ and A_bb produce albinism
What is an allelic disorder?
Different mutations in the same gene produce different phenotypes.
Example: mutations in grown factor 2 receptor gene cause 3 different syndromes
What is pleiotropy? Give an example.
One gene influences multiple traits.
Example: same gene that gives siamese cats their coat color makes them have crossed eyes
Differentiate between SEX LIMITED and SEX INFLUENCED characteristics.
Sex Limited: Only appear in one sex (zero penetrance in one sex)
Sex Influenced: Appear in one sex more than the other
What is cytoplasmic inheritance?
Must come from mom, because a zygote gets all of its cytoplasm from mom…remember, dad ONLY CONTRIBUTES DNA (this is why the sperm is so tiny compared to the egg, as the sperm only has DNA and none of the organelles)
Define MATERNAL EFFECT genes.
A gene whose products are required for very early development of the embryo, such as the establishment of overall polarity of the embryo. These “maternal cells” disappear from the zygote after they assert their effects.
*Mutant genes not necessarily found in the offspring; only in the mother
Define MATERNALLY imprinted.
Maternally derived copy of gene is silenced; Paternally derived copy is active
What are the two types of UNIPARENTAL DISOMY? Define them.
Heterodisomy: a pair of NON-IDENTICAL CHROMOSOMES are inherited from one parent
- Meiosis 1 error
- If any genes on chromosome are imprinted, child will have either 0 or 2 active copies
Isodisomy: a SINGLE CHROMOSOME from one parent is duplicated and both copies are inherited
- Meiosis 2 error
- Can cause expression of recessive genes
What is GENETIC ANTICIPATION? What causes it?
each subsequent generation is affected more severely.
CAUSE: expansion of trinucleotide repeat sequences, which expand during meiosis
NOTE: as repeat expands (gets LONGER), there is LESS ACTIVITY in the gene
Define INCOMPLETE PENETRANCE.
The expected phenotype of a particular genotype is not expressed because of extra factors like environmental factors and effects of other genes
Differentiate between the EPIstatic and HYPOstaic gene.
Epistatic gene expression has the ability to cover expression of the hypostatic gene
When given a cross concerning two different characteristics (like hair color and hair texture), what is a good way to approach the problem?
Figure out the inheritance of each characteristic separately.
What ratio is usually associated with the presence of recessive lethal gene?
2:1
Example: The ratio of yellow:gray was found to be 2:1 –> We conclude that YY (yellow,yellow) is lethal
What ratio is associated for a trait that come from a cross between two heterozygous parents?
3:1
Where the trait that is more common is the dominant allele
What tests can be carried out to test if a particular trait is recessive lethal? How about to test that (y) is recessive to (Y)?
If YY (yellow) is recessive lethal and is dominant to gray (y) then…
(Yellow)x(Yellow) –always–> 2/3 yellow, 1/3 gray
(Gray)x(Gray) –always–> ONLY gray
If your phenotype ratios are given out of 16, this is a hint that…
You are dealing with two alleles (even if there is only one trait)
