Lecture 3/26 Flashcards
if there is a cross of red-eyed flies to white-eyed flies and F1 all have red eyes, what is the conclusion?
red eye is dominant to white eye
if there is a cross of female white-eyed to male red-eyed fly and the results are 1/2 red eyes (all female) and half white eyes (all male) what is the phenotypic ratio? what do we know about the gene inheritance?
1:1 and the gene inheritance is sex-linked
if you cross a XW XW with a Xw- Y, what color eyes are the progeny?
all red
if you cross a Xw- Xw- with a XW Y, what color eyes do the progeny have?
1/2 are males white, 1/2 are females red
how many single gene traits are known in humans?
about 4300
how can one study mendelian genetics in humans?
family pedigree
what three things can looking at a pedigree tell us?
dominance patterns, different alleles, whether a trait is sex-linked
what is allele frequency?
the percentage of the total number of gene copies for one allele in a population
how many alleles does each individual carry for a gene?
2
what kind of allele is usually the most common?
WT
what are rare alleles also referred to as? and what frequency is considered rare?
mutant allele, <1% frequency
what is a polymorophic gene?
a gene with more than one common allele, like blood type
what is another name for high-frequency alleles of polymorphic genes?
common variants
what shape is male on pedigrees?
square
what shape is female on pedigrees?
circle
what is considered to be consanguineous marriage?
2nd/3rd cousins or closer
what are questions to immediately ask when looking at a pedigree?
1) How frequently does the trait appear? In what sort of ratios is the trait in a generation?
2) Is one gender affected more than another? From which parent is the trait inherited?
can 2 parents with a dominant trait give rise to unaffected children?
yes
will a child with a dominant trait always have an affected parent?
yes
does a dominant gene show up in every generation?
yes
does a recessive gene show up in every generation?
no
for recessive traits, what is the only way for all children to be affected?
both parents must be homozygous recessive
what is our pedigree tip? what does it tell us?
always look for unaffected/unaffected pairings giving rise to an affected individual – always recessive unless it’s sex-linked (could also be both)
in humans, some of the most common single-gene traits are caused by what kind of alleles?
recessive
what happens in phenylketonuria (PKU)?
phenylalanine buildup or too little tyrosine/dopamine – can lead to intellectual disability, seizures, limb spasticity, etc.
are there any treatments for PKU? when do we test for it?
newborns are tested, and there is now a treatment of phenylalanine-free foods – used to be a lethal diagnosis
what is the minimum number of newborn tests in the US?
29, but it varies by state which has more than 29
what are some of the most common single-gene traits caused by dominant alleles in humans?
hypercholesterolemia and huntington disease
do mendelian genetics include X-linked genes?
no
what is incomplete dominance?
there’s an intermediate phenotype to dominant and recessive (pink flower from red and white)
what are phenotypic ratios for incomplete dominance of 1 trait?
1:2:1 instead of 3:1, they reflect the genotypic rates
what do the letters refer to in blood types?
A and B are sugars, O is no sugars
What is the allele for blood types?
I
what is codominance?
both alleles are expressed equally in the phenotype
what are the phenotypic ratios for a trait that has co-dominance?
1:2:1 – reflects genotypic ratio
what leads to an O blood type?
a mutation in glycosyltransferase in the red blood cell so you don’t get any sugars
can one gene have multiple alleles with different dominance patterns?
yes, like in blood type
is A blood type dominant to B?
no, they’re codominant
is A blood type dominant to O?
yes
Why is O blood type a universal donor?
there are no sugars to induce an immune response in the recipient
why is AB a universal receptor?
because it has A and B sugars so it won’t have an immune response to either, and any blood type can receive O
