4/24 Flashcards
which gene follows an autosomal pattern of inheritance?
the Mic2 gene
is SRY a pseudoautosomal gene?
no, it is a Y-linked gene and it is necessary for male development
If a Mic2a male is crossed with a mic2a/2b female, then what are the outcomes for their offspring?
50% mic2a and 50% mic2a/2b
females are 50% mic 2a and 50% mic 2a/2b; males are 50% mic2a and 50% mic2b
50% mic2a and 50% 2a/2b, they are pseudoautosomal and the gene is on the X and Y chromosomes
why is it important that males get their X chromosome from their mother
X-linked recessive genes may be passed from a carrier mother and expressed in the male
when will daughters express a recessive trait?
when they get a copy from both parents, meaning both the mom and dad had the disease
if an x-linked recessive trait is found in males, will it be expressed
yes, they only have one x chromosome so it will be expressed
can a father give a x-linked disease to his son
no, they only give the y chromosome to their sons
how can an x-linked recessive disease be identified in a pedigree?
the trait tends to disappear and it often will be expressed in males as they only have one x chromosome
for a mother with a dominant x-linked trait, which offspring can she give the allele to?
both sons and daughters
for fathers, if they have an X-linked allele, who can they give it to?
daughters only
if a dad has an x-linked dominant allele, which offspring will be most affected
all of his daughters will recieve the x chromosome from him and will express the trait
what is a good indicator of a Y-linked allele in a pedigree?
the traits are only expressed in males, never females
the fathers traits are all passed to sons
what is mitochondrial inheritance?
the male mitochondria will not get shared with the egg so all mitochondrial alleles will have maternal linkage
if a male has a mitochondrial trait, will his offspring inherit the trait?
no, only maternal mitochondrial traits are inherited
for genes that are close to eachother on the same chromosome, will they follow the laws of independent assortment?
no, they will violate the expected ratios because they are linked and may undergo recombination
what is the scenario where linked genes follow Mendel’s law of independent assortment?
when genes are very far apart (50% recombination/map units, they will assort independently)
when linked genes are transmitted together, what type of phenotype will be in the majority?
parental types
what is genetic linkage
genes that are close together on a chromosome tend to be transmitted as a unit
what is a linkage unit?
this is another way to refer to chromosomes, they contain groups of linked genes
are the X and Y chromosome the same type of linkage unit?
no they are considered different
according to data, how do you know whether genes are assorting independently or if they are linked?
in the F1 cross with a tester, if the data shows equal ratios for all gametes then the genes are assorting independently. If the data shows unequal ratios that are skewed toward parent types, then the genes are linked
how do you identify which phenotypes are the parental type from the offspring generation?
the phenotypes that are in the majority will be the parental types
if the genes are 100% linked and show no recombination, what type of gametes will they have?
only parental types
when there is recombination between genes, what types of gametes will be produced?
recombinants and parents in unequal proportions
if the results of a self cross do not follow the 9:3:3:1 ratio, what does this tell you about the genes?
they genes must be linked
what is the appropriate test to determine if genes are linked or not?
the chi squared test, assuming the null hypothesis is that the genes are independently assorting
what do map distances allow us to identify?
how closely linked the genes are
what is the maximum amount of recombination that can be used to identify if genes are linked or not?
50% (50 m.u) otherwise, the genes will independently assort and follow mendels laws of independent assortment even if they are linked
if the genes are far apart, how many recombinants will be observed
many
if the genes are close, how many recombinants will be observed
fewer amounts
in the offspring of crosses involving linked genes, what phentypes are most common? least?
the most common phenotypes are the parentals, then single recombination phenotypes, then double crossover phenotypes are the most rare
when there are three linked genes, what does a double crossover tell us?
it tells us which gene is in the middle as the gene in the middle will be swapped and separated from it’s original linked genes
if you have an even number of crossover events, what result will occur
the phenotype will return to it’s original linkage state
if you have an uneven number of crossover events, what result will occur
the genes will be shuffled and unlinked, so recombinant phenotypes will be osberved
if three cross over events occur within a dihybrid, how many will be counted
technically one, the first two just reversed eachother back to the original linkage state
why are trihybrid crosses used in the evaluation of double crossover events?
in the event of a double cross over without the third gene, the linkage state will return back to it’s original state and will not be counted as a recombination, so the third gene acts as a marker
