Chapter 4 Flashcards
when does crossing over occur?
between nonsister chromatids in prophase 1 of meiosis
What occurs in independent assortment(no linkage)?
-gamete genotype/phenotype frequency 1:1:1:1
-predicts 25% of each gamete type, with parental and nonparental gametes each totaling 50%
*50% are recombinants
what are genes located on the same chromosome called?
syntenic genes
what is a characteristic of syntenic genes?
they are so close together that their alleles cannot assort independently, and so are called linked genes
when can syntenic genes assort independently?
they are far apart on a chromosome and crossing over occurs frequently between the genes
do linked genes assort independently?
no
What occurs in linked genes?
-recombination is less likely to occur, but there will be more gametes with the parental genotypes than recombinant genotypes
-both the parentals are equally frequent and sum is»_space;50% and recombinants are equally frequent and their sum is «50%
What is the value of the frequency of recombinant genes?
has a value
in between complete linkage (0%) and independent assortment (50%)
0% < FR < 50%
When 2 genes are linked, how many gamete types are possible?
4
In a recombination map for 3 genes, how many different genotypes would we expect?
8
In a recombination map using a 3-point test-cross, how do we know which genotype will be the double crossover?
the least frequent genotype because two recombination events occur less frequently than one recombination event?
What are the steps to creating a recombination map using trihybrid crosses?
- Determine if the data are consistent with linkage in the first place
- Determine the parental genotypes
- What is the gene order on the chromosome.
- Determine the recombination frequencies and map distance between gene pairs.
- Is the frequency of double crossovers consistent with the independence of single crossovers?
what is interference?
The differences between the expected and observed number of double crossovers
what is the coefficient of coincidence?
c is defined as the ratio of observed over
expected double crossovers, or in this case 0.61. (0.61=11/18.1)
I is 1 - c = 0.39, which can be interpreted as the proportion of additional double recombinants that are expected but not produced
*I can also be negative when there are more double recombinants than expected.
What is a holliday junction?
strand invasion where 1 DNA strand invades the other and is formed during the process of crossing over
