Genetics Exam test questions and
answers graded A+
All the genes on a single chromosome are *physically linked*.
Two genes are *genetically linked* if they segregate together in meiosis more frequently than they
segregate separately. Two physically linked genes that always segregate together show *complete
genetic linkage* (usually if they are extremely close together, almost never cross over).
Two genes on the same chromosome that usually but not always segregate together are
*incompletely or partially linked*. How can two genes be physically linked but not genetically
linked? Explain *incomplete linkage.* - ANS✅✅*Incomplete linkage:* two genes are close but not
extremely close together. -There will frequently but not always be a crossover between them.
-They will segregate together more frequently than separately in meiosis.
-There will be four kinds of gamete genotypes in unequal numbers. More *parental type gametes*
than recombinant type gametes.
Is it possible for two genes to be physically linked (be on the same chromosome) but not show
genetic linkage? - ANS✅✅Two genes can be so far apart on the same chromosome that there is
always at least one crossover between them and thus they do not appear to be "genetically linked"
although they are physically linked.
No two genes are ever permanently linked because *?* - ANS✅✅genes on the chromosome will
eventually be *separated by crossing over in meiosis*
Advantages of having many genes located on the same chromosome - ANS✅✅Genes are linked
and will be inherited together more frequently than not
Disadvantages of having many genes located on the same chromosome - ANS✅✅-genes will be
inherited together more frequently than not
Recombination compensates for these disadvantages.
1:1:1:1 - ANS✅✅2 genes are on separate chromosomes OR 2 genes are on same chromosome and
very far apart
,1:1 - ANS✅✅2 genes are on same chromosome and very close together
More parental type and fewer recombinant type progeny - ANS✅✅2 genes are on the same
chromosome and relatively close together
What is the relationship between the number of genetic linkage groups and the number of pairs of
homologous chromosomes in an organism? - ANS✅✅-the number of linkage groups is *equal* to
the number of homologous chromosomes in an organism
-Genes that are on the same chromosome are said to be in the same linkage group. Thus the number
of genes in the chromosome forms that many linkage groups and the pair to that chromosome has
the same number of linkage groups.
-However, no two genes are every permanently linked because genes on the same chromosome will
eventually be separated by crossing over in meiosis.
-Linked genes are closer together on a chromosome and will have less likely chance of
recombination whereas genes farther on the same chromosome have higher changes of
recombination and are not always linked due to that larger distance. Genes on different
chromosomes are not linked.
Thomas Hunt Morgan postulated a direct relationship between the cytological observation of
crossing over in
meiosis (with an apparent physical exchange of segments of homologous chromosomes) and the
genetic
evidence for an exchange of alleles between two homologous chromosomes. Barbara McClintock
provided the
definitive proof of Morgan's hypothesis. What was the crucial experiment? - ANS✅✅-Morgan
proposed that the *frequency of recombination* events between two genes on a chromosome is
*proportional* to the *physical distance* between those two genes.
-Multiple crossovers will sometimes cancel each other out (further apart=more likely for double
crossover)
-McClintock proved that genetic recombination is the result of a physical exchange of chromosome
segments
, -The experiment with corn examined colorless and starchy phenotype and then examined the
structure of the two chromosome 9 homologs in the colorless, starchy kernels.
If we find 50% recombinant progeny what can we conclude? - ANS✅✅Either 2 genes on separate
chromosomes or they are on the same chromosome but so far apart that they are behaving as if
they were on separate chromosomes
The frequency with which random events occur between two points is a function of the distance
between those
two points. How do we use this principle to map genes in eukaryotes? - ANS✅✅-one percent
recombination is one map unit
-distance between genes = frequency of single recombination x 100
-That distance relative to the total size lets us know how linked certain genes are and how likely they
are to segregate together or apart.
-if on the same gene, recombinant progeny frequency cannot be more than 50% so if it is, we know
those genes are not on the same chromosome
If the frequency of recombinant progeny (the recombination frequency) from a cross between one
individual
heterozygous at two loci and a second individual homozygous recessive at both of those loci is less
than 50%, the two genes in question are genetically linked. What can we conclude about the genetic
and physical linkage of
two genes when the recombination frequency between those two genes is equal to 50%? -
ANS✅✅When it is equal to 50%, that means that only a single crossover occurred and 50% were
recombinant progeny. Double crossovers are 0% and cancel each other out. A perfect 50% over
many trials and progeny means that the two genes are as far as they can be on the same
chromosome or at the very least very far because they almost always recombine without being on
different chromosomes.
Why is crossing over, or recombination, in meiosis a genetic advantage for an organism? Why is
crossing over an advantage for a geneticist? - ANS✅✅-increases genetic diversity within a
population since progeny will be recombinants of their parents genome so not exactly like either
-advantageous for a geneticist because crossing over and recombination information is helpful in
mapping genes and tracking certain traits or the influence of other factors on traits within a
population
answers graded A+
All the genes on a single chromosome are *physically linked*.
Two genes are *genetically linked* if they segregate together in meiosis more frequently than they
segregate separately. Two physically linked genes that always segregate together show *complete
genetic linkage* (usually if they are extremely close together, almost never cross over).
Two genes on the same chromosome that usually but not always segregate together are
*incompletely or partially linked*. How can two genes be physically linked but not genetically
linked? Explain *incomplete linkage.* - ANS✅✅*Incomplete linkage:* two genes are close but not
extremely close together. -There will frequently but not always be a crossover between them.
-They will segregate together more frequently than separately in meiosis.
-There will be four kinds of gamete genotypes in unequal numbers. More *parental type gametes*
than recombinant type gametes.
Is it possible for two genes to be physically linked (be on the same chromosome) but not show
genetic linkage? - ANS✅✅Two genes can be so far apart on the same chromosome that there is
always at least one crossover between them and thus they do not appear to be "genetically linked"
although they are physically linked.
No two genes are ever permanently linked because *?* - ANS✅✅genes on the chromosome will
eventually be *separated by crossing over in meiosis*
Advantages of having many genes located on the same chromosome - ANS✅✅Genes are linked
and will be inherited together more frequently than not
Disadvantages of having many genes located on the same chromosome - ANS✅✅-genes will be
inherited together more frequently than not
Recombination compensates for these disadvantages.
1:1:1:1 - ANS✅✅2 genes are on separate chromosomes OR 2 genes are on same chromosome and
very far apart
,1:1 - ANS✅✅2 genes are on same chromosome and very close together
More parental type and fewer recombinant type progeny - ANS✅✅2 genes are on the same
chromosome and relatively close together
What is the relationship between the number of genetic linkage groups and the number of pairs of
homologous chromosomes in an organism? - ANS✅✅-the number of linkage groups is *equal* to
the number of homologous chromosomes in an organism
-Genes that are on the same chromosome are said to be in the same linkage group. Thus the number
of genes in the chromosome forms that many linkage groups and the pair to that chromosome has
the same number of linkage groups.
-However, no two genes are every permanently linked because genes on the same chromosome will
eventually be separated by crossing over in meiosis.
-Linked genes are closer together on a chromosome and will have less likely chance of
recombination whereas genes farther on the same chromosome have higher changes of
recombination and are not always linked due to that larger distance. Genes on different
chromosomes are not linked.
Thomas Hunt Morgan postulated a direct relationship between the cytological observation of
crossing over in
meiosis (with an apparent physical exchange of segments of homologous chromosomes) and the
genetic
evidence for an exchange of alleles between two homologous chromosomes. Barbara McClintock
provided the
definitive proof of Morgan's hypothesis. What was the crucial experiment? - ANS✅✅-Morgan
proposed that the *frequency of recombination* events between two genes on a chromosome is
*proportional* to the *physical distance* between those two genes.
-Multiple crossovers will sometimes cancel each other out (further apart=more likely for double
crossover)
-McClintock proved that genetic recombination is the result of a physical exchange of chromosome
segments
, -The experiment with corn examined colorless and starchy phenotype and then examined the
structure of the two chromosome 9 homologs in the colorless, starchy kernels.
If we find 50% recombinant progeny what can we conclude? - ANS✅✅Either 2 genes on separate
chromosomes or they are on the same chromosome but so far apart that they are behaving as if
they were on separate chromosomes
The frequency with which random events occur between two points is a function of the distance
between those
two points. How do we use this principle to map genes in eukaryotes? - ANS✅✅-one percent
recombination is one map unit
-distance between genes = frequency of single recombination x 100
-That distance relative to the total size lets us know how linked certain genes are and how likely they
are to segregate together or apart.
-if on the same gene, recombinant progeny frequency cannot be more than 50% so if it is, we know
those genes are not on the same chromosome
If the frequency of recombinant progeny (the recombination frequency) from a cross between one
individual
heterozygous at two loci and a second individual homozygous recessive at both of those loci is less
than 50%, the two genes in question are genetically linked. What can we conclude about the genetic
and physical linkage of
two genes when the recombination frequency between those two genes is equal to 50%? -
ANS✅✅When it is equal to 50%, that means that only a single crossover occurred and 50% were
recombinant progeny. Double crossovers are 0% and cancel each other out. A perfect 50% over
many trials and progeny means that the two genes are as far as they can be on the same
chromosome or at the very least very far because they almost always recombine without being on
different chromosomes.
Why is crossing over, or recombination, in meiosis a genetic advantage for an organism? Why is
crossing over an advantage for a geneticist? - ANS✅✅-increases genetic diversity within a
population since progeny will be recombinants of their parents genome so not exactly like either
-advantageous for a geneticist because crossing over and recombination information is helpful in
mapping genes and tracking certain traits or the influence of other factors on traits within a
population
