Chapter five, test two Flashcards
what does syntenic mean
occurring on same chromosome
what does / mean
separate genes found on the two chromosomes of a pair
if the gametes from F1 mother assort independently what is the ratio
1:1:1:1
if there is a gamete of 1:1:1:1 ratio from F1 female what are the two possible outcomes
parental type and recombinant type
1:1
what is an explanation that the F1 female is more likely to pass on parental combinations of alleles
female inhertied wy+ together from p generation mom
inherited w+y together from p generation dad
what shows linked genes
parental is greater than recombinant
if the recombinant and parental is 32 and 67 what is the conclusion
still linked but not as tight
parental combination alleles travel together more often than not
in mendels dihybrid, how does that work with linkage
the gamets dont happen in same ratio or fraction
no longer 9:3:3:1
what is the point of testcross in dihybrid
decide if parent is doubly heterozygous
who termed chiasmata
Frans janssens
what helped researchers believe recombination occurred
physical markers that showed visual abnormalities being transferred
what are genetic markers
alleles of genes that could serve as points of reference in determining whether particular progeny were the result of recombination
who came up with the experiment that confirmed the exchange of genetic traits in dihybrids was associated with physical exchange between sister chromatids
Curt Stern
physical exchange in allelic recombination
need two physical markers to show exchange
what are synaptonemal complexes
help homologous chromosomes pair with each other
what is needed to help keep sister chromatids together
cohesin
what keeps the homologous chromosomes together at the metaphase plate and thus ensure proper chromosome segregation
cohesin
who looked at linked genes
thomas hunt morgan
who came up with recombination frequency
alfred sturtevant
in a dihybrid with outcome of no cross over meiosis what will the gametes be
four parental gametes
what about a single cross over in dihybrid, what are the gametes
2 parental
2 recombinant
why is RF= 50% in a dihybrid for genes on nonhomologous chromosomes
nonhomologous chromosomes line up randomly to produce all parental or all recombinant in equal freq
meiosis that occur with one crossover bw one gene and centromere generate all four gamete types with equal freq
double cross over 2 strand produces what recombination
no recombinants
DCO 3 strand produces what recombination
50% recombinants
DCO 4 strand produces what recombination
100% recombinants
linked genes mean
must be syntenic and sufficiently close together on same chromosome
unlinked genes mean
two genes on different chromosome or two genes on same chromosome but really far apart
what are loci
maps that assign genes to specific locations on particular chromosomes
what are some limitations of two point crosses
difficult to determine gene order if some gene pairs lie very close together
actual distances dont always add up
what could be the reason why in a 3 pt cross the distance from a to B and B to C does not equal A to C
double crossover could occur
how to correct for double crossover in calculation total distance
count all recombinant numbers and count the dco twice
then divid by total progeny
what is chromosomal interference
crossovers not occurring independently of each other
what is the coefficient of coincidence
a ratio between the actual frequency of double crossovers observed in an experiment and number of double crossovers expected due to independent probabilities
what if interference equals one
no double crossovers occur in experimental progeny because one exchange effectively prevents another
what are recombination hotspots
small regions of DNA where the freq of recombination is much higher than average
is there recombination occurring during meiosis in male flies
no
what is a linkage group
genes chained together by linkage relationships
any gene on chromosome is linked to another gene on the same chromosome then what
the number of linkage groups equals the number of pairs of homologous chromosomes in the species
what is a chi square test
measures how well observed results conform to predicted ones
account for size of experimental population
what makes fungus a good species for gametes
they house all four haploid products of each meiosis in an ascus
what is the fungus sac calles
ascus
what are the haploid cells in ascus called
ascospores
the phenotype of haploid fungi is a direct representation of their…
genotype
no complications of dominance
meiosis in fungi produces
four haploid ascospores
four haploid ascospores generate what in mitosis
8 haploid cells or 4 pairs
what do the four pairs in the ascus represent
each pair represents the same genotype because they arose from mitosis
can neurospora mate asexually
use during mitosis
if neurospora come in opposite mating types what happens
zygote created and goes through mitotic cycles to reproduce
what fungi produces unordered tetrads
yeast
what fungi produces ordered tetrads
neurospora crassa
what does tetrad mean in fungi
4 pairs of 8 haploids in ascus
four products of single meiosis
tetrads can by characterized as
parental ditypes
nonparental ditypes
tetratypes
parental ditype is
parental configuration iof alleles
what is nonparental ditype
four recombinant spores , two of each type
what is tetratype
four different kinds of spores
2 recombinant and 2 parental
how is RF determined in spores
recombinant #/ total number of spores
second way to calculate RF
(NPD +1/2 (T))/ total tetrads
how to get T tetrad progeny
crossover occurs between only one of the genes and the centromere
no cross over produces what ditype
parental
single crossover produces what ditype
tetratype
double crossover 2 strand produces what ditype
parental
DCO 3 strand produces what ditype
tetratype
DCO 4 strand produces what ditype
nonparental
what is first division segregation pattern (M1)
segregation of two alleles of a single gene at first meiotic division
imaginary line drawn between 4th and 5th ascospores
cleanly separate haploid showing the two alleles
what is second division segregation pattern (M2)
crossover occurs in meiosis one
cells with only one kind of allele show up at the end of second meiotic division
not cleanly separated
how to find mu with ascospores in M2 divisions
(1/2)M2/total tetrads x 100
how do twin spots occur
during mitotic recombination
what are twin spots
adjacent islands of tissue that differ both from each other and from the tissue surrounding them
what is the function behind twin spots
when homozygous recessive phenotype cells are growing next to heterozygous cells showing dominant phenotype
how does mitotic recombination occur
homologous chromosomes pair up and non sister chromatids crossover
