Lecture 4/9 Flashcards
when genes are linked, are they on the same or different chromosomes?
the same
when genes are unlinked, are they on the same chromosome?
you can’t tell
if genes are linked, do they always show up together?
yes
what is a linkage group?
a set of genes located on the same chromosome that are inherited together
is there increased probability for recombination if genes are closer together or further apart on a chromosome?
further apart, which is why they can appear unlinked
how does one determine map distances for genes on a chromosome?
using number of recombinants
what is the notation for genes on a different chromosome?
separated by a semicolon
what does a slash represent for genes?
it separates alleles
are are the lines underneath an allele?
it is read vertically and separates homologous chromosomes
if genes are in the same linkage group, are they in cis or trans?
they can be either
what does cis mean?
on the same chromosome
what does trans mean?
on homologous chromosomes
if there’s an AA; BB x aa; bb cross and F1 are Aa; Bb what are the gametes of F1?
parental: AB and ab
recombinant: Ab and aB
which gametes are considered recombinant?
heterozygous
what is the phenotypic ratio for 2 genes on different chromosomes that are crossed with a testcross?
1:1:1:1
if linked genes aren’t close enough together on the chromosome, what happens?
they will recombine and appear to assort independently
what is the phenotypic ratio for Ab|aB x ab|ab if the genes are linked (on same chromosome)
1:1 (not 1:1:1:1)
what do you need in order to map genes on a chromosome?
marker chromosomes for each chromosome for test crosses
what test is done to determine which chromosome?
2-factor crosses (2 marker mutations)
what test is done to determine location on chromosome?
3-factor crosses
if genes are on the same chromosome and one allele of interest does not segregate with your other allele of interest, will you see those two alleles expressed together?
no
if genes are on different chromosomes and one allele of interest does not segregate with your other allele of interest, will you see those two alleles expressed together?
you might, there’s no such thing as segregating together because they’re on different alleles
for 2-factor mapping, which generation will be helpful for mapping a gene?
F2 progeny
Suppose that you are trying to map gene A in an organism with 5 chromosomes. You have recessive mutants for each chromosome and perform a test cross to determine chromosomal localization and then mate F1 progeny. If gene A phenotype is not observed in a marker, is that where the gene maps on to or not?
it is the chromosome where the gene maps onto
what are the two limitations of 2-point crosses?
- it’s difficult to determine gene order if 2 genes are close together
- can’t tell orientation of genes on chromosomes
what do you need to have already done in order to do a 3-factor cross?
a 2-factor cross
what do you need in order to do a 3-factor cross?
- 2 marker mutations on the same chromosome as the gene of interest
- need heterozygous animal to isolate recombinants and need strain homozygous for all three traits
is it common for a recombination event to occur?
no
what does the largest number of progeny correspond to in a 3-factor cross?
the parental gametes
for a 3-factor cross, how many possible points of recombination are there?
2
which is more common, a single or double recombination event?
single
what are you looking for in a 3-factor cross?
possible recombinants
what do the different numbers refer to in a 3-factor cross?
Largest number are always parental
Middle are single recombinants
Smallest are double recombinants
how do double recombinants help us?
they help determine the order of the gene
if the gene of interest is in trans to m1 and m2, can it be fully across from either of them? what does that tell us?
no it can’t, which helps determine what the possible recombinations are or cannot be
