32

Proteins and peptides vary across species, even if we give them the same name. Some are very homologous among even distantly related organisms, others differ even within a genus. Of course there are also variations across individuals of the same species. Insulin from pigs and horses is pig or horse insulin. It differs slightly from human insulin because the ...


12

This is a venerable fact. Exceptions in D. melanogaster strain Y-007 have been observed and D. ananassae has consistent male cross-overs, but this work dates back to the 1970s. This Current Biology 2002 paper is not exactly new, but sheds some light on the issue in question. In male Drosophila melanogaster, meiosis occurs in the absence of ...


11

When you say, why don't we see more sexually reproducing species than asexual, I presume you are referring to bacteria, protists, archaea, some fungi, etc. Most multicellular organisims do reproduce sexually, which makes sense since an organism would need to be multicellular to have cells specialized for gametes. As you stated, the advantage is that sexual ...


11

Understanding the statistics we use when talking about recombination rate is an important question that is unfortunately too often dismissed in an intro course to evolutionary biology or population genetics and that is misunderstood by many. Short answer A recombination rate and a genetic distance (in centiMorgan) are two different things. While the ...


7

I got $26$% as the answer. To get a recombination between C and E, there are two possible mechanisms:- C and D produce a recombinant, but D and E remain linked, therefore the final genotype will be a recombinant considering C and E(Chiasmata between C and D). Here $P_1=P_{CD}\times P'_{DE}$ where $P$ is the probability of recombination and $P'=1-P$ is ...


7

Just to be clear, markers on different linkage groups (chromosomes) do not recombine 50% of the time. It is just that unlinked mutations co-segregate 50% of the time. This is a direct quote from Strickberger's textbook "Genetics" 3rd ed. 1985 p 397: > After many tests involving numerous sex-linked genes, the entire X chromosome of D. melanogaster was ...


6

This just in addition to @anongoodnurse's excellent answer. It was mentioned in the OP that asexual organisms do not undergo recombination; this is not true. Recombination is used for integration of foreign DNA into prokaryotic chromosomes and for repair. Also, don't underestimate the power of mutational change in rapidly reproducing organisms. While ...


6

Ns are not non-recombinant at the genomic level. What you know is that they do not show recombination events at the risk allele locus as subjects carrying the marker A1 show signs of the disease and similarly healthy subject do not carry the marker A1. Hence they are called non-recombinant. On top of that 3rd generation subjects (excepted III6) show ...


4

Hopefully this syllogism will answer your question. Given the following premises: In the absence of selection, fitness of individuals are at a theoretical maximum. If a theoretical maximum fitness is achieved then effective population size is maximum. If there is an allele that confers both increased and decreased fitness you have a genetic conflict (e.g. ...


4

This is a little tricky. First of all lets be clear about 'bringing together favorable alleles' (or any alleles) represented by site mutations on 2 chromosomes: --------A------------------ X ------------------B-------- If the two dashed lines are two copies of the same chromosome, then a recombination event at X may produce: --------A-...


4

It is my understanding that a non-allelic gene is one that affects another's traits, but is not as a typical dominant / recessive manner. If I am correct, this is the same thing as epistasis - meaning that one gene modifies how another is expressed. There exists epistatic genes for horse coat color. One gene is the coat color itself (horses may have either ...


4

To the best of my knowledge there is no strong evidence as to the reason why. The most reasonable explanation seems to be that it evolved as a crude mechanism for preventing recombination of the male sex-chromosome. You might then ask why a mechanism targeted to the sex-chromosome specifically (as in humans) did not evolve to which I'd suggest that ...


4

Mitochondrial DNA is circular, like bacterial DNA, and around 16.6 Kb long. It codes for 37 genes in total but the majority of these are simply the machinery for gene expression (curiously, mitochondria have a slightly different codon->amino acid translation 'table' to nuclear DNA) and so just 13 code for proteins. Single mitochondria usually have multiple ...


4

Back-of-the-envelope calculation The definition of the centimorgan is that it is the length of DNA in a chromosome corresponding to a 1% chance of crossover occurring. In human chromosomes 1 cM = approx. 1Mbp. Your value for the length of DNA in the genome = 3.3 Gbp = 3300 MBp Ignoring complications like the Poisson distribution: 1 cM corresponds to ...


4

No, similarity is not measured in base pairs. They are talking of regions of cross-over being marked by at least 200bp of highly similar sequence between the two strands involved in exchange.


3

This phenomena is known as achiasmy, where recombination is absent in one sex in a species. The Haldane Huxley rule states that in achiasmic species, the sex without recombination will always be the heterogametic sex (XY or ZW). This is basically the only consistent rule relating to recombination. There seem to be exceptions to every other theory and pattern ...


3

If rates of meiotic recombination DIDN'T vary across species - THIS would require an explanation! After all, evolution creates diversity, not homogeneity. I can only wonder that more recombination would allow for a faster diversification. The more DNA you shuffle, the more distinct each individual offspring may be (though I'm not 100% sure). The ...


3

"On average, between two and three crossover events occur on each pair of human chromosomes during meiotic division I" according to Molecular Biology of the Cell. 4th edition by Alberts B, Johnson A, Lewis J, et al. For simplicity we will call that 2.5 events per pair. Each of those pairs ultimately forms 4 gametes. Each event connects one chromosome to ...


3

First off this is called genetic mosaicism and indeed mitotic recombination is a contribution factor. Mitotic crossover events involve the exchange, by homologous recombination, of regions of chromosomes. 60% of homologous recombination events might occur during G1 and 40% of those event occurs after chromosomes are replicated (see this paper). For twin ...


3

Yes, you could imagine a situation where two functional alleles could produce a recombinant which was non-functional. chromosome 1 has A and B at positions x and y - functional chromosome 2 has C and D at positions x and y - functional Recombination between positions x and y produces A/D and C/B versions of the gene. Either or both of these ...


3

A good baseline for this type of research in human genetics is Standards and guidelines for the interpretation of sequence variants from ACMG. It is a guideline for clinicians, and it gives a good sense of good variants data, bad variants data and setting up confidence level. Try to consolidate data from: Population databases GWAS databases Exome ...


2

Electroporation is a fairly common way to introduce exogenous nucleic acids into cells. Its name essentially describes the process - an electric voltage potential is applied across a biological membrane, eventually leading to the production of conducting hydrophilic pores. The image below is from the Wikipedia page linked above, showing non-conducting (upper)...


2

This is a question which is not easy to answer, especially the 50.000bp number (which I haven't found anywhere in there literature). However, I found some evidence, partly derived from plant and mammal artificial chromosomes (references 1 and 2), partly from the original publication from Murray and colleagues (reference 3). The problems with small ...


2

For lambda: If the distance between the two cos sites is less than ~37 kb, the resulting phage particle will be unstable. When the DNA is inside the capsid, it exerts pressure on the capsid. Likewise the capsid exerts an inward force on the DNA. If there is not enough DNA inside the capsid, it will implode from the inward force of the capsid. If the ...


2

One of the alleles for each gene must come from the parent on the right hand side. That parent only has a and b alleles (is homozygous) - meiotic crossing over will not change this. So the offspring must inherit at least one a and one b. That should point you to the answer.


2

I found a key paper for myself from an issue of Nature Reviews Genetics last year. It discusses and reviews how recombination affects the rate of genetic variation at the sequence level. A key concept is that of selective interference, which is what I had stumbled across in the question, this is when the efficacy of selection is reduced because "...


2

This is not easy to answer, since it depends on a number of factors. For example it is dependent on the region of the genome (there are hotspots). I found a PhD thesis, which goes into the details here and which also has a ton of interesting references: The Estimation of Recombination Rates from Population Genetic Data


2

I think you must have misremembered what you heard. The cut-off distance for genetic linkage is 50 centimorgans which corresponds to 50% recombination. In the human genome 1 centimorgan is approximately 106 base pairs, so the 'unlinked distance' is 5 * 107 base pairs.


2

As little as 14bp of homology can work. See this reference. I would recommend at least a length of 90bp but 1kb is probably overkilled. Yes both arms can have different length (staying in the same order of magnitude).


2

In my opinion the terms inducible and conditional are synonyms. Together with the term constitutive they refer to how transcription takes place, that is, the second phase in the central dogma that states that genetic information is propagated from replication to transcription to translation. The proteins that are produced during translation by ribosomes can ...


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