Bio 235 Exam 2 ACTUAL Exam Questions
and CORRECT Answers
Independent assortment - CORRECT ANSWER - Genes assort independently of each
other when they are on opposite chromosomes
Linkage - CORRECT ANSWER - Two genes on a single pair of homologs; exchange
occurs between two non-sister chromatids
Chiasmata - CORRECT ANSWER - Location of exchange of information between
chromatids
when does crossing over occur? - CORRECT ANSWER - prophase I of meiosis
How often does recombination occur? - CORRECT ANSWER - Very frequently
What determines how often genes will cross over? - CORRECT ANSWER - Their
distance from one another. The closer they are, the less likely they are to cross over.
What does it mean when genes are linked? - CORRECT ANSWER - they are on the same
chromosome; assort independently
Describe how geneticists detect linkage of a gene - CORRECT ANSWER - 1. Select true-
breeding lines that are homozygous dominant for one trait & homozygous recessive for the other
trait (ygr ANL / ygr ANL & YGR anl / YGR anl). Parents produce dihybrid F1 population (ygr
ANL / YGR anl)
2. Cross the F1 dihybrid with a homozygous recessive (ygr anl / ygr anl). This will result in an
F2 pop. where the dihybrid traits segregate.
3. Cross each F2 individual with a homozygous recessive
, How do you determine if the genes are linked or not after performing a test cross? - CORRECT
ANSWER - If the ratio is 1:1:1:1, they assort independently and are unlinked
If the ratio for the recombinant class is less than the parental class, you know they do not assort
independently and are linked
Parental class - CORRECT ANSWER - original arrangement of alleles on the two
chromosomes (no recombination); came from meiosis unchanged
Recombinant class - CORRECT ANSWER - does not have chromosomes passed from
parents
How is distance between genes found? - CORRECT ANSWER - The farther apart two
genes are located on a chromosome, the higher the probability that a recombinant event takes
place between them
Recombinant frequency (RF) - CORRECT ANSWER - percentage of the total progeny
that are recombinant type
6% RF = ___________ - CORRECT ANSWER - 6 map units OR 6 centimorgans
From a test cross, you observe that there are 350 offspring for each parental genotype and 150
for each recombinant genotype. What is the distance of the recombinant genes? - CORRECT
ANSWER - 30 map units
What is one problem with relying on RF in linkage mapping? - CORRECT ANSWER -
Genetic distance is massively underestimated when genes are father apart
Genetic distances are not additive - RF will never be >50%
The farther apart they are, the less reliable the numbers are
Double-crossover is more likely the further they are from each other
and CORRECT Answers
Independent assortment - CORRECT ANSWER - Genes assort independently of each
other when they are on opposite chromosomes
Linkage - CORRECT ANSWER - Two genes on a single pair of homologs; exchange
occurs between two non-sister chromatids
Chiasmata - CORRECT ANSWER - Location of exchange of information between
chromatids
when does crossing over occur? - CORRECT ANSWER - prophase I of meiosis
How often does recombination occur? - CORRECT ANSWER - Very frequently
What determines how often genes will cross over? - CORRECT ANSWER - Their
distance from one another. The closer they are, the less likely they are to cross over.
What does it mean when genes are linked? - CORRECT ANSWER - they are on the same
chromosome; assort independently
Describe how geneticists detect linkage of a gene - CORRECT ANSWER - 1. Select true-
breeding lines that are homozygous dominant for one trait & homozygous recessive for the other
trait (ygr ANL / ygr ANL & YGR anl / YGR anl). Parents produce dihybrid F1 population (ygr
ANL / YGR anl)
2. Cross the F1 dihybrid with a homozygous recessive (ygr anl / ygr anl). This will result in an
F2 pop. where the dihybrid traits segregate.
3. Cross each F2 individual with a homozygous recessive
, How do you determine if the genes are linked or not after performing a test cross? - CORRECT
ANSWER - If the ratio is 1:1:1:1, they assort independently and are unlinked
If the ratio for the recombinant class is less than the parental class, you know they do not assort
independently and are linked
Parental class - CORRECT ANSWER - original arrangement of alleles on the two
chromosomes (no recombination); came from meiosis unchanged
Recombinant class - CORRECT ANSWER - does not have chromosomes passed from
parents
How is distance between genes found? - CORRECT ANSWER - The farther apart two
genes are located on a chromosome, the higher the probability that a recombinant event takes
place between them
Recombinant frequency (RF) - CORRECT ANSWER - percentage of the total progeny
that are recombinant type
6% RF = ___________ - CORRECT ANSWER - 6 map units OR 6 centimorgans
From a test cross, you observe that there are 350 offspring for each parental genotype and 150
for each recombinant genotype. What is the distance of the recombinant genes? - CORRECT
ANSWER - 30 map units
What is one problem with relying on RF in linkage mapping? - CORRECT ANSWER -
Genetic distance is massively underestimated when genes are father apart
Genetic distances are not additive - RF will never be >50%
The farther apart they are, the less reliable the numbers are
Double-crossover is more likely the further they are from each other
