Study sets, textbooks, questions
Upgrade to remove ads
Genetics Exam 2 Chapter 5: Linkage, Recombination, Mapping
Terms in this set (38)
Genes located on the same chromosome; gives fewer classes of gametes than for genes on separate chromosomes in the absence of crossing over
Four possible gametes in a 1:1:1:1 ratio, leading to four possible F2 phenotypes in a 9:3:3:1 ratio
Genes linked together on the same chromosome usually
Linked genes may become separated by
Outcome of testcross on genes on same chromosome completely linked
Only two possible gentoypes in progeny, which are parental
Outcome of testcross on independently assorting genes
1 parental:1 recombinant:1 recombinant: 1 parental
The further apart two genes are...
the greater the probability of recombination
Recombination data can be used to...
generate maps of relative locations of genes on chromosomes
Leads to separation of linked genes; random event
Offspring that are different from the parents; different allele combinations
Why do we look at males for F2 progeny in X-linked recombination?
Because females could have many different combinations from crossover events
Deviation from 1:1:1:1 segregation in F2 indicates
genes are linked
Why are only F2 male progeny counted in a cross involving X-linked genes and recombination?
The X chromosome in an F2 male is a reflection of previous meiotic recombination events between two X chromosomes in F1 female (the male only gets his X chromosome from his mother, so if there was recombination, there was definitely crossing over between his mother's two Xs)
Parental gamete classes are always __________________ recombinant gamete classes.
more numerous or equal to
Recombinant classes are never _______% of total F2 progeny.
If the recombinant frequency is equal to 50%, that means...
that the genes are very far away on the same chromosome
What is the RF of unlinked genes?
50% due to independent assortment
Recombination for a specific meiosis event
Meiosis without crossovers produces only parental gametes, and crossovers produce a 1:1 ratio of parental to recombinant gametes
2 homologs have duplicated, so now there are 2 pairs of sister chromatids=4 chromatids per tetrad; synaptonemal complex forms and homologs align along their length, facilitating crossing over; synaptonemal complex disassembles and recombination event visibly apparent and indicates points where chromosome segments have been reciprocally swapped
Chismata structure gradually dissolves
Homologous chromosome separation
What is produced by each round of meiosis in the event of crossing over?
Two recombinant and two parental gametes
Two way exchange; leads to two types of parental gametes (1:1) and two types of recombinant gametes (1:1)
Does the arrangement of parental alleles affect RF?
No, only how far apart the alleles are
How to detect autosomal linkage
Generate a dihybrid and cross to a double recessive homozygote; if you see two recombinant classes, that means there was a crossing over event that occurred
Dihybrid cross F2 ratios and information about linkage
Independently assorting genes: produces half parental and half recombinant progeny (1:1:1:1 ratio)
Completely linked genes: 1:1 progeny ratio, all parental
Crossing over (sometimes but not always: intermediate progeny ratios, parental progeny outnumbers recombinant
What would happen if recombination did not occur?
Nondisjunction would happen often during meiosis I, because the synaptonemal complexes help homologs to pair and disappear during prophase I (chromosomes still attached by chiasmata and cohesin)
1 percent recombination=
1 RF=1 map unit (mu)=1 centiMorgan (cM)
Recombination frequencies can be used as a measure of
physical distance between two linked genes
Crossing individuals and tracing two 2 traits at a time for many different genes, which helps us to map the genes based off of RF
Two-point crosses are used to establish
relative gene position (left to right orientation is arbitrary, but the order of genes is not)
Genes chained together by linkage relationships; synonymous with a chromosome (also equals one DNA molecule)
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; time and labor consuming; order of genes corresponds to the actual order of genes, but actual physical distance doesn't always show direct correspondence to genetic distance; recombination hotspots
If the recombination frequency is greater than 50%...
we have to think about recombination nodules rather than just pure distance (RF becomes less precise estimator of genetic distance at large physical distances)
Small regions of DNA where the frequency of recombination is much higher than average
Limits to correspondence between map and physical distance
Double, triple, and more crossovers; 50% limit on observable recombination frequency; non-uniform recombination frequency across chromosomes; recombination rates differ between species and across the genome (recombination hotspots)
Recombination frequency between two genes vary from
0% (complete linkage) to 50% (independent assortment)
Why do genes that are farther apart have higher RF?
There is a greater opportunity for chiasmata to form between them
Other sets by this creator
BSC 450 Chapter 14: Glycolysis
BSC 450 Exam 4 Structures
BSC 450 Exam 4 Chapter 13: Bioenergetics
BSC Exam 3 Chapter 11: Membranes
Other Quizlet sets
SS7G11: Southern & Eastern Asia Geographical Devel…
2do depa anato
LC Programme for Graduates Interview
Thinking in Pictures Chapter 9 Vocabulary