BIO 340 Genetics Exam 2 With Complete
Solutions Latest Update
What would be the appropriate null hypothesis if you want to see if two genes are
linked?
? If two genes are unlinked, the two-point test cross will give you a 1:1:1:1 phenotypic
ratio. ??
How do we test if two genes are linked?
1) Do reverse question, asking if genes assort independently.
2) If two genes are tightly linked, they do not assort independently.
3) If they are unlinked, they will assort independently.
4) Do a two-point testcross: Cross a double heterozygote with a tester, an individual
homozygous recessive for both genes
5) See results and do chi-square test. Accept or reject null hypothesis.
Differences among individuals can be due to what two things?
1) Environmental differences affecting development
2) Individual genes that differ between and/or within species
These genes that are variable are called polymorphic
Due to the peculiar set of polymorphic genes, each organism is genetically unique
All species are related in that the great majority of their genes do not vary, but are
identical from individual to individual
,What is the principle of independent assortment? Design an experiment that shows this
principle in action.
the law, discovered by Gregor Mendel, that when two or several characteristics are
inherited, the genes for those characteristics assort independently of each other in the
production of gametes, enabling the different characteristics an equal chance of
appearing together.
Di-hybrid Cross
a cross between two dissimilar lines/genes that differ in two usually investigated
characteristics. In Mendelian terminology, between alleles of both such loci, there is a
relation of complete dominance-recessive.
What phenotypic ratios are expected from a dihybrid cross for two independently
assorting genes?
9:3:3:1
Two-point Testcross
A test used to whether or not two genes assort independently.
Cross a double heterozygote with a tester, an individual homozygous recessive for both
genes:
What phenotypic ratios are expected from a two-point testcross for two independently
assorting genes?
1:1:1:1 phenotypic ratio because you are crossing a dihybrid with a homorecessive
"tester".
What are the phenotypic ratios you would predict from a two-point testcross for two
genes that are very tightly linked?
,Independence Assortment. Explain how meiosis ultimately sorts the alleles for different
genes independently of each other.
meiosis: metaphase I homologous chromosome pairs can align on metaphase plate with
mom's chromosome on left and dad's right or vice versa. when cells divide.
In addition during prophase one crossing over occurs and creates another form of
recombination.
Explain why the complementation test can tell whether two recessive mutations are
located in the same or different genes.
When you cross 2 mutants, aaBB x AAbb, and a mutation happened on different genes,
then the offspring shows wild phenotype. This is because offspring will be
heterozygotes, AaBb.
If cross result in mutant offspring then mutant on same gene. Parents: aaBB x aaB_
Progeny: aaB_
Mutual Theory of Evolution
there is little variation in mutation rate within a population
If a dihybrid cross is done for two independently assorting genes which interact by
affecting the same pathway, how will this differ from a similar cross done for two
non-interacting genes?
In case genes do not interact- phenotype will be 9:3:3:1.
If genes interact we would expect different phenotypic ratios for example 9:7 or 9:3:4
(below) etc. because both gene must be in a functional state to make product. Any
progeny with inactivated gene (aa or bb) in the pathway will express mutant colour.
What is meiotic recombination and how is it produced by:
, a) independent assortment of different chromosomes and
b) by crossing over?
Any meiotic process that generates haploid gametes with allele combinations unlike
those in parental gametes.
a) One source of meiotic recombination is independent assortment. This occurs during
metaphase I when the tetrads line up randomly at the metaphase plate with moms sister
chromatids on left and dad's on right, over vise versa. When the cells divide, it is
completely random which cell gets which.
b) Non-sister chromatids of maternal and paternal homologs cross-over in prophase I at
an X-shaped region called chaisma, segments exchange; this will lead to genetic
variation.
The closer the genes on the same chromosome, the less opportunity for recombination.
The farther away, the more chances of recombination.
How do you work out genetic distance (crossover frequency)?
Genetic distance can be estimated by measuring the recombination frequency.
What do you do to measure recombination distance between 2 genes?
1) You cross an individual heterozygous for both genes to an individual homozygous
recessive for the genes involved and this is called a two-point testcross.
2) phenotype offspring
3) find out which offsprings are recombinants and which aren't.
4) You take the recombination frequency to get a genetic distance estimate between
genes.
Solutions Latest Update
What would be the appropriate null hypothesis if you want to see if two genes are
linked?
? If two genes are unlinked, the two-point test cross will give you a 1:1:1:1 phenotypic
ratio. ??
How do we test if two genes are linked?
1) Do reverse question, asking if genes assort independently.
2) If two genes are tightly linked, they do not assort independently.
3) If they are unlinked, they will assort independently.
4) Do a two-point testcross: Cross a double heterozygote with a tester, an individual
homozygous recessive for both genes
5) See results and do chi-square test. Accept or reject null hypothesis.
Differences among individuals can be due to what two things?
1) Environmental differences affecting development
2) Individual genes that differ between and/or within species
These genes that are variable are called polymorphic
Due to the peculiar set of polymorphic genes, each organism is genetically unique
All species are related in that the great majority of their genes do not vary, but are
identical from individual to individual
,What is the principle of independent assortment? Design an experiment that shows this
principle in action.
the law, discovered by Gregor Mendel, that when two or several characteristics are
inherited, the genes for those characteristics assort independently of each other in the
production of gametes, enabling the different characteristics an equal chance of
appearing together.
Di-hybrid Cross
a cross between two dissimilar lines/genes that differ in two usually investigated
characteristics. In Mendelian terminology, between alleles of both such loci, there is a
relation of complete dominance-recessive.
What phenotypic ratios are expected from a dihybrid cross for two independently
assorting genes?
9:3:3:1
Two-point Testcross
A test used to whether or not two genes assort independently.
Cross a double heterozygote with a tester, an individual homozygous recessive for both
genes:
What phenotypic ratios are expected from a two-point testcross for two independently
assorting genes?
1:1:1:1 phenotypic ratio because you are crossing a dihybrid with a homorecessive
"tester".
What are the phenotypic ratios you would predict from a two-point testcross for two
genes that are very tightly linked?
,Independence Assortment. Explain how meiosis ultimately sorts the alleles for different
genes independently of each other.
meiosis: metaphase I homologous chromosome pairs can align on metaphase plate with
mom's chromosome on left and dad's right or vice versa. when cells divide.
In addition during prophase one crossing over occurs and creates another form of
recombination.
Explain why the complementation test can tell whether two recessive mutations are
located in the same or different genes.
When you cross 2 mutants, aaBB x AAbb, and a mutation happened on different genes,
then the offspring shows wild phenotype. This is because offspring will be
heterozygotes, AaBb.
If cross result in mutant offspring then mutant on same gene. Parents: aaBB x aaB_
Progeny: aaB_
Mutual Theory of Evolution
there is little variation in mutation rate within a population
If a dihybrid cross is done for two independently assorting genes which interact by
affecting the same pathway, how will this differ from a similar cross done for two
non-interacting genes?
In case genes do not interact- phenotype will be 9:3:3:1.
If genes interact we would expect different phenotypic ratios for example 9:7 or 9:3:4
(below) etc. because both gene must be in a functional state to make product. Any
progeny with inactivated gene (aa or bb) in the pathway will express mutant colour.
What is meiotic recombination and how is it produced by:
, a) independent assortment of different chromosomes and
b) by crossing over?
Any meiotic process that generates haploid gametes with allele combinations unlike
those in parental gametes.
a) One source of meiotic recombination is independent assortment. This occurs during
metaphase I when the tetrads line up randomly at the metaphase plate with moms sister
chromatids on left and dad's on right, over vise versa. When the cells divide, it is
completely random which cell gets which.
b) Non-sister chromatids of maternal and paternal homologs cross-over in prophase I at
an X-shaped region called chaisma, segments exchange; this will lead to genetic
variation.
The closer the genes on the same chromosome, the less opportunity for recombination.
The farther away, the more chances of recombination.
How do you work out genetic distance (crossover frequency)?
Genetic distance can be estimated by measuring the recombination frequency.
What do you do to measure recombination distance between 2 genes?
1) You cross an individual heterozygous for both genes to an individual homozygous
recessive for the genes involved and this is called a two-point testcross.
2) phenotype offspring
3) find out which offsprings are recombinants and which aren't.
4) You take the recombination frequency to get a genetic distance estimate between
genes.
