Final Exam Review
PWS 275
Genetics and Reproduction
1. What is chromosome linkage? What does crossing over with linked genes look like?
What is incomplete linkage? Complete linkage?
a. Linkage- some genes segregate as part of the same chromosome and are
moved as a single unit
i. No independent assortment
Crossing Over- during prophase I of meiosis I, homologs are paired
- recombination of alleles
-The frequency of crossing over is proportional to the distance between the loci
- Complete Linkage:
- If no crossing over occurs between 2 genes on same chromo, only two genetically
different gametes are forms
- Allelles are segregated with gametes
- Incomplete Linkage:
When there is some crossing over between linked genes (producing new combinations of
traits)
2. How does complete linkage alter the phenotypic and genotypic ratios?
- If complete linkage exists between two genes because of close proximity
OR
Organisms that are heterozygous at both loci are mated
THEN
- a unique F2 ratio is created
~The F1 forms only parental gametes because of complete linkage
, After fertilization, the F2 is produced in a 1:2:1 pheno and geno ratio
3.[2.] What are linkage groups? In theory, what are the number of linkage groups to be
expected?
- Linkage Groups: Can be established (Usually one for each chromosome)
- THEORY: Number of linkage groups should equal the haploid number of chromos
4.[3.] How can crossing over and linkage groups be used to map genes on chromosomes?
What is chromosome mapping? Who was Thomas Morgan? What did Morgan’s
crosses in fruit flies tell us? Who was FA Janssens? How did his cytological work
confirm and enlighten Morgan’s conclusions? Who was Alfred Sturtevant? What did
he suggest to Morgan? How did he use Morgan’s work to create a chromosomal map
of a linkage group?
Mapping: Crossing over serves as the basis for setermining the distance between
genes during mapping
- Thomas Morgan(1910)
Investigated numerous drosophila mutations located on the X chromosome
Crosses between 2 X linked traits (mutant white eye and miniature wing), the majority
of the F2 showed parental phenotypes
HOWEVER
A high proportion of the offspring showed the mutant genes had separated
- Morgans Questions: -What was the source of the gene separation? And why did it
vary depending on the different X linked genes?
* Linked genes exist in a linear order along the chromosome and a variab;e amount
of change occurs between any two genes (TWO GENES THAT ARE CLOSER TO EACHER
ARE LESS LIKELY TO HAVE A CHIASMA/ THE CLOSER THEY ARE, MORE LIKELY NO
GENTEIC EXCHANGE)
-F.A. Janssens observered that the synapsed homo chromos in meiosis wrapped
around each other and created a chiasma
Thus, this chiasma could represent points of genetic change
-Alfred H. Sturtevant
, Morgan’s undergraduate student was the first to realize that the crossing over
theory could be used to map the sequence of linked genes (1913)
*perhaps the freq. of recombination between linked genes are additive and the
order of the X gene chromos are: YELLOW-WHITE-MINIATURE
5.[4.] What are the two methods for early mapping of human chromosomes? What is
the LOD score method? What is Synteny testing with somatic cell hybridization?
- LOD Score Method
o Statistical method used to determine whether two loci are linked or unlinked
from pedigree analysis
1) probability is calculated that family pedigrees with 2+ traits means
nonlinkage
2)probability is calculatedthat the identical family data results from
linkage with a specified recombination freq.
Ratio of these prob. Values is then computed and converted to a
logarithm of these values (reflects the for or against odds of
linkage)
3) A lod (log of the odds) score of 4= a linkage is 10,000 times more
likely than nonlinkage
Lods of 3-4 mean linkage
- Synteny testing with somatic cell hybridization
o Two cells in a culture can be induced to fuse into a hybrid cell
When fused, a “HETEROKARYON” is produced containing two nuclei in
a common cytoplasm
the nuclei fuse to create a synkaron
o After a few generations, chromos from one parent are lost
Responsible gene resides on one of the human chromo remaining in a
hybrid cell
o USED FOR SYNTENY TESTING
, 6.[5.] What is the sub-discipline of developmental genetics? Genetic analysis and
molecular biology have shown all multicellular organisms share many genes, genetic
pathways, and molecular signaling mechanisms in the processes leading from zygote
to the adult. Why do you think this is so? What is meant by evolutionary conservation
of developmental mechanisms?
-Genetic analysis and molecular biology conclude:
– All multicellular organisms share many genes, genetic pathways, and molecular
signaling mechanisms (zygote to adulte)
*GENERAL PROCESSES IN DEVELOPMENT:
- 1) How the adult body plan of animals is laid down in the embryo
- @) The Prgram of gene expression that turns undifferentiated cells into
differentiated cells
PWS 275
Genetics and Reproduction
1. What is chromosome linkage? What does crossing over with linked genes look like?
What is incomplete linkage? Complete linkage?
a. Linkage- some genes segregate as part of the same chromosome and are
moved as a single unit
i. No independent assortment
Crossing Over- during prophase I of meiosis I, homologs are paired
- recombination of alleles
-The frequency of crossing over is proportional to the distance between the loci
- Complete Linkage:
- If no crossing over occurs between 2 genes on same chromo, only two genetically
different gametes are forms
- Allelles are segregated with gametes
- Incomplete Linkage:
When there is some crossing over between linked genes (producing new combinations of
traits)
2. How does complete linkage alter the phenotypic and genotypic ratios?
- If complete linkage exists between two genes because of close proximity
OR
Organisms that are heterozygous at both loci are mated
THEN
- a unique F2 ratio is created
~The F1 forms only parental gametes because of complete linkage
, After fertilization, the F2 is produced in a 1:2:1 pheno and geno ratio
3.[2.] What are linkage groups? In theory, what are the number of linkage groups to be
expected?
- Linkage Groups: Can be established (Usually one for each chromosome)
- THEORY: Number of linkage groups should equal the haploid number of chromos
4.[3.] How can crossing over and linkage groups be used to map genes on chromosomes?
What is chromosome mapping? Who was Thomas Morgan? What did Morgan’s
crosses in fruit flies tell us? Who was FA Janssens? How did his cytological work
confirm and enlighten Morgan’s conclusions? Who was Alfred Sturtevant? What did
he suggest to Morgan? How did he use Morgan’s work to create a chromosomal map
of a linkage group?
Mapping: Crossing over serves as the basis for setermining the distance between
genes during mapping
- Thomas Morgan(1910)
Investigated numerous drosophila mutations located on the X chromosome
Crosses between 2 X linked traits (mutant white eye and miniature wing), the majority
of the F2 showed parental phenotypes
HOWEVER
A high proportion of the offspring showed the mutant genes had separated
- Morgans Questions: -What was the source of the gene separation? And why did it
vary depending on the different X linked genes?
* Linked genes exist in a linear order along the chromosome and a variab;e amount
of change occurs between any two genes (TWO GENES THAT ARE CLOSER TO EACHER
ARE LESS LIKELY TO HAVE A CHIASMA/ THE CLOSER THEY ARE, MORE LIKELY NO
GENTEIC EXCHANGE)
-F.A. Janssens observered that the synapsed homo chromos in meiosis wrapped
around each other and created a chiasma
Thus, this chiasma could represent points of genetic change
-Alfred H. Sturtevant
, Morgan’s undergraduate student was the first to realize that the crossing over
theory could be used to map the sequence of linked genes (1913)
*perhaps the freq. of recombination between linked genes are additive and the
order of the X gene chromos are: YELLOW-WHITE-MINIATURE
5.[4.] What are the two methods for early mapping of human chromosomes? What is
the LOD score method? What is Synteny testing with somatic cell hybridization?
- LOD Score Method
o Statistical method used to determine whether two loci are linked or unlinked
from pedigree analysis
1) probability is calculated that family pedigrees with 2+ traits means
nonlinkage
2)probability is calculatedthat the identical family data results from
linkage with a specified recombination freq.
Ratio of these prob. Values is then computed and converted to a
logarithm of these values (reflects the for or against odds of
linkage)
3) A lod (log of the odds) score of 4= a linkage is 10,000 times more
likely than nonlinkage
Lods of 3-4 mean linkage
- Synteny testing with somatic cell hybridization
o Two cells in a culture can be induced to fuse into a hybrid cell
When fused, a “HETEROKARYON” is produced containing two nuclei in
a common cytoplasm
the nuclei fuse to create a synkaron
o After a few generations, chromos from one parent are lost
Responsible gene resides on one of the human chromo remaining in a
hybrid cell
o USED FOR SYNTENY TESTING
, 6.[5.] What is the sub-discipline of developmental genetics? Genetic analysis and
molecular biology have shown all multicellular organisms share many genes, genetic
pathways, and molecular signaling mechanisms in the processes leading from zygote
to the adult. Why do you think this is so? What is meant by evolutionary conservation
of developmental mechanisms?
-Genetic analysis and molecular biology conclude:
– All multicellular organisms share many genes, genetic pathways, and molecular
signaling mechanisms (zygote to adulte)
*GENERAL PROCESSES IN DEVELOPMENT:
- 1) How the adult body plan of animals is laid down in the embryo
- @) The Prgram of gene expression that turns undifferentiated cells into
differentiated cells
