Genetic Linkage Flashcards
What is Mendel’s principle of segregation?
… states that for a diploid individual. the two alleles at a particular gene locus separate during meiosis and up in different gametes.
What is Mende’s principle of independent assortment?
… states that segregation of alleles at a particular genes locus occurs independently of the segregation of alleles at other loci.
What are the conditions for Mendel’s principle of independent assortment?
a) the genes in question are on separate chromosomes.
b) the genes are widely separated on the same chromosome.
Mendel’s second rule DOES NOT apply to many dihybrid crosses.
Where are genes located?
On chromosomes
Do homologous pairs segregate independently of other homologous pairs?
Yes!
How can Mendel’s principle of independent assortment be violated?
When genes are present on the same chromosomes ,i.e., they show a strong tendency to stay together and therefore co-inherited.
What are linked genes?
Genes locates close together on the same chromosome
What is a linkage group?
All of the genes on a single chromosome. They do not assort independently but tend to be co-inherited belong to a linkage group.
(rather than independently assorting during cell division, they move as a unit)
What are Syntenic genes?
Genes that reside on the same chromosomes
What is Linked Gene Inheritance?
Genes that DO NOT assort independently.
(Syntenic genes show linked gene inheritance)
How does Recombination occur?
(Hint: from P to F1)
P generation: AABB x aabb
(gamete formation)
Gametes AB ab
Fertilization
F1 generation AaBb
(gamete formation)
Gametes AB ab Ab aB
(parental combination (new combination
-nonrecombinant -recombinant
alleles) alleles)
What is the expected phenotypic ratio in F2 progeny after selfing the F1 generation in a dihybrid cross for a digenic trait? Is this seen in linkage?
The expected phenotypic ratio is- 9:3:3:1
This is NOT seen in linkage/ non-independent assortment of digenic traits.
Instead there is a predominance of progeny showing the parental type.
What are recombinant gametes?
New combinations of alleles that are not seen in the parental gametes.
What are non-recombinant gametes?
Original combinations of alleles that are found in the parental gametes.
What is the expected test cross ratio in a dihybrid cross for a digenic trait? Is this seen in linkage?
The expected test cross ratio is- 1:1:1:1
This is NOT seen in the linkage/ non-independent assortment of digenic traits.
Where does crossing over occur?
Prophase I of Meiosis I
Would crossing over occur in linkage/ do linked genes undergo crossing over?
NO! This is because the genes have to be close together on the SAME chromosome for them to be linked!
If the genes are on different chromosomes or far apart on the same chromosome they are NOT linked! Therefore, crossing over in homologous chromosomes does not occur in linked genes.
Where does Independent Assortment occur
Metaphase I of Meiosis I
AND
Metaphase II of Meiosis II
Would independent assortment occur in linkage/ do linked genes undergo independent assortment?
NO! This is because unlinked genes are the only kind of genes that can be independently assorted as they are either on different chromosomes or far apart on the same chromosome.
*accounts for genetic variation
How do we know if the genes were independently assorted?
Test cross= 1:1:1:1
(AaBb x aabb)
What is the chiasma?
The structure that forms between homologous chromosomes by crossover recombination and physically links the homologous chromosomes during meiosis.
What is Chiasma Frequency?
The frequency of chiasmata formation between two genes of interest during meiosis
What is Recombination Frequency?
The frequency of recombinant type gametes formed
Recombination Freq.= 1/2 (chiasma freq.)
Why is the Recombinant Frequency half the chiasma frequency?
Every time a chiasma forms only two of the four gametes will be recombinant types.
