Chapter Five: Linkage, Recombination, and Gene Mapping Flashcards
when genes are inherited together
genetic linkage
linked genes may become separated by ___ during ___
recombination
meiosis
genes located on the same chromosome
syntenic genes
deviation from a typical phenotypic ratio can indicate either ___ or ___
epistasis or linkage
when looking at gene linkage in a cross involving X-linked genes, only ___ are considered
male progeny (because they only have one X copy from their mother)
parental and recombinant configurations are ___ from each other
different
autosomal linkage can be detected by ___
a testcross
when looking at gene linkage for an autosomal gene, only ___ are considered
the heterozygote parent (the homozygous parent will give the same alleles whether crossing over occurs or not)
the 9:3:3:1 ratio expected for dihybrids is altered with ___
linkage
Frans Janssens observed ___ between chromosomes during prophase one
chiasmata
chiasmata is ___
the point of attachment between non sister chromatids of homologs
TH Morgan suggested that chiasmata were sites of ___ and ___
breakage and exchange
H. Creighton and B. McClintock and C. Stern showed direct evidence that genetic recombination depends on the ___
reciprocal exchange of chromosomes
alleles used as a point of reference for recombination
genetic markers
if recombination did not occur, ___ during meiosis one would happen frequently
nondisjunction
___ help homologs pair but disappear during prophase one
synaptonemal complexes
during prophase one, chromosomes are still attached with ___ and ___
chiasmata and cohesion
cohesion complex functions to ___
connect sister chromatids
percentage of total progeny that were recombinant types
recombination frequencies (RF)
RF can be used to measure ___
physical distance between two linked genes
1% RF = ___ = ___
1 map unit (m.u.)
1 centiMorgan (cM)
recombinant gametes are ___ frequent than parental gametes when genes are linked
less
the RF of unlinked genes is 50% due to ___
independent assortment
the RF of linked genes cannot exceed ___
50%
why can’t the RF of linked genes exceed 50%
meiosis without crossovers produce only parental chromosomes
single and double crossovers produce a 1:1 parental:recombinant chromosomes ratio on average
alleles are sufficiently close together on the same chromosome so that their alleles do not assort independently
linked genes
genes are either on two different chromosomes or are sufficiently far apart on the same chromosome that at least one crossover occurs between them in every meiosis
unlinked genes
in linked genes, parental ___ recombinant and RF ___ 50%
> (greater than)
< (less than)
in unlinked genes, parental ___ recombinant and RF ___ 50%
equals
equals
a genes specific location on a chromosome
locus (plural loci)
assign a gene to its locus
gene mapping
why is gene mapping important
knowing a gene’s locus can be used to isolate DNA and understand gene function
it is possible to map genes based on ___
recombination frequencies (distance between genes)
limitations of two point crosses
difficult to determine gene order if two genes are close together
actual distances between genes don’t always add up
pairwise crosses are time and labor consuming
___ provide faster and more accurate mapping than ___
three point crosses
two point crosses
comparing pairwise RF’s of three genes shows which are ___ and which are ___
furthest apart
in the middle
genes with a ___ RF will be further apart on the gene map
higher
RF numbers might not always add up completely accurate because of ___
interference (less double crossovers than expected)
occurrence of crossover in one portion of a chromosome interferes with crossover in an adjacent portion of the chromosome
chromosomal interference
genes connected by linkage relationships; when many genes per chromosome have been mapped
linkage groups
how to determine if a variation from the expected phenotypic ratio is from epistasis or linkage
chi squared
in linkage studies, the null hypothesis is that there are ___
no linkages
yeast and bread mold have a ___ state and a ___ state
haploid
diploid
all four haploid produce of yeast and bread mold meiosis are contained within ___
ascus (sac)
can germinate and survive as viable haploids that divide by mitosis
ascospores
four ascospores in a single ascus are referred to as
tetrad
mitotic recombination occurs because of ___ and can produce ___
mutations
genetic mosaics
patches of somatic tissue in flies with different phenotypes
twin spots
mitotic recombinations have major repercussions to ___
human health
portions of a yeast colony with different phenotype than the rest of the colony
sectors
___ of sector indicates when recombination took place
proportional size
if sector is the entire colony, the recombination took place ___. if sector is a small portion of the colony, the recombination took place ___
in or near the original cell
later on in the colony
crossing over occurs in ___ ONLY
prophase one
