homework - Does Human Female Meiosis II occur after fertilization with sperm?

Meiosis, as you know, have two stages, Meiosis I and II. The oocyte is arrested during metaphase II of MEOISIS II. This arrest is facilitated by a complex called "Cytostatic Factor" (CSF).

After fertilization, the sperm induces a rise in intracellular calcium ion which activates and enzyme, Calmodulin Kinase II. This complex, through a series of phosphorylation and ubiquitination, degrades the CSF comples and in turn, activates APC (Anaphase Promoting Complex). APC will then degrades cyclins, securins and this will promotes the completion of Meiois II.

Sperm must ignite some process in female that puts female meiosis II going on before sperm can fuse with egg.

I think the statement is a bit incorrect. The sperm will ignite (I prefer induce) the above changes and fuse at the same time. Because, what starts all the process above is part of the sperm's cytoplasm that need to be assimilated into the oocyte's cytoplasm.

I hope this clears it all up. Or if you are interested, I can provide the long list of signalling pathways that leads to zygotic development.

genomics - Which functional annotations could be useful?

Analyzing a genome, for a generic gene, which functional annotations (e.g from Gene Ontology) can help understanding its meaning/function or, at least, provide helpful informations?

• Annotations of that gene


• Annotations of orthologous genes (?)


• Annotations of paralogous genes (?)


• Co-expressed genes (given a biological condition) (?)


• What else?

Thank you.

evolution - Did animals evolve from plants?

See this paper "Divergence time estimates for the early history of animal phyla and the origin of plants, animals and fungi" for information on the divergence estimates (I'm not sure if there are more recent papers discussing this).

Plants, animals and fungi are eukaryotes, distinct from eubacteria and archaebacteria, which are prokaryotes. The difference being in the composition of the cell, particularly a nucleus contained within a membrane for eukaryotes, along with other membrane bound organelles, e.g. chloroplasts. They all share a common ancestor, according to this paper, that split 1.576 Bya (billion years ago) +/- 88 Mya (although it states the relationships are unresolved - it is often difficult to resolve relationships so deep in a tree). They form distinct groups known as Kingdoms under Linnaean based biological classification; the Fungi, Plantae and Animalia. Thus, in answer to your question, no, animals did not evolve from plants.

Plants have chloroplasts in their cells, which provide the ability to produce energy via photosynthesis. It is thought that the chloroplast resulted from a symbiotic relationship between early plants and a cyanobacteria in that they both relied on each other for survival and so coevolved. Animals don't contain chloroplasts and instead contain an organelle called the mitochondria (although most plants also have mitochondria), which is also thought to have been a bacterial endosymbiont, probably related to rikettsias.

Protists also contain chloroplasts. The protists are intermediate between all three groups and have been notoriously difficult to classify, being placed into a fourth Kingdom, the Protozoa, although this grouping has been contested. The current Cavalier-Smith system was proposed in 2004 and classifies life into 6 Kingdoms.

Chloroplasts are thought to have evolved from a single endosymbiotic event in Archaeplastida, although there are evidence to suggest some secondary endosymbiotic events. Check out this paper for more information; figure 1 shows the relationships between the different groups and the endosymbiotic events. The Opisthokonts are the origin of the Fungi and Animalia kingdoms.

human biology - Why Does Salt Water Help Sore Throats?

Salt water may have anti-septic properties due to the effect it has on water potential. Pure water has a water potential (Ψ) of zero. A concentrated salt solution has a lower (more-negative) water potential. The water potential of the salt solution is likely to be more negative than that of the pathogen's cytoplasm; the salt solution is therefore referred to as hypertonic. Therefore water osmoses out of the cell (osmosis being the net movement of water from a higher water potential to a lower water potential across a semi-permeable membrane). The loss of water from the pathogenic cells causes osmotic crenation - the cell becomes shrivelled and dies.

A hypotonic solution (for example cells placed into pure water) would cause the opposite effect - osmotic lysis. This is the bursting of the cell due to the movement of water into the cell. The bacterial cell wall would first have to be damaged (e.g. by penicillin). This would not be the process by which a salt solution has effect, however.

The fact that the salt water is warm in order to improve solubility may also have the side-effect of causing vasodilation around the infection, increasing the rate at which white blood cells can arrive at the infection site.

It has been more difficult to find a theory as to why a salt solution would have analgesic properties, see the comments below & previous versions of this answer.

genomics - Is it possible to trace of the ancestry of a person by only using his/her genetic information?

In short, yes, it is possible. There are companies that sequence part of your genome and then can trace it back to your ancestors. All human family trees can be traced back to their African origin 200 000 years ago, but the companies that sequence your genes do not do that. For example, 23andMe sequences only 1 million of your base pairs (single nucleotide polymorphisms (SNPs)). They trace your most recent heritage, which could lead to Europe, Africa, or Asia. They can basically trace which part of your chromosomes (and thus your ancestry) came from your mom or your dad:

Unlike the sex chromosomes and the mitochondrial DNA, which are inherited as blocks, the 22 biparental chromosomes, known as autosomes, are scrambled during reproduction. Through a process known as recombination, each parent pulls his or her paired set of 22 autosomes into chunks, then reassembles a new single set using half the material from each pair. The two single sets of chromomes from each parent are combined into a new paired set when a sperm fertilizes an egg.

You can read more about 23andMe here. There are other companies that are specialized in tracing your ancestry: Genetic Genealogy, DNA Tribes, and Heirlines.

genetics - Predicting progeny of recessive mutations using recombination

First, the recombination equation is:

cM = recombinants/(recombinants AND parentals) * 100

Let's assign the following genotypes for clarity's sake:

RR = black bristles
Rr = black bristles
rr = red bristles
SS = pebbly eyes
Ss = pebbly eyes
ss = shiny eyes

F1 cross: rrSS x RRss = RrSs (all progeny)
F2 cross: RrSs (F1) x rrss = ?

You would have the following gametes:

Parent 1, RrSs = RS, Rs, rS, rs
Parent 2, rrss = rs, rs, rs, rs

Draw your punnet square and you get the following genotypes of the offspring.

So your GENOTYPES of your F2 cross will be RrSs, Rrss, rrSs, rrss

Let's translate those to phenotypes.

RrSs: black pebbly (parental)
Rrss: black shiny (recombinant)
rrSs: red pebbly (recombinant)
rrss: red shiny (parental)

Now let's look at recombination frequency.

15cM = (recombinants/(recombinants+parentals)*100
recombinants/(parentals+recombinants) = 15/100

This tells you for every 15 recombinants, you have 85 parentals. If you scale this up to 1000, that's 150 recombinants for every 850 parentals.

Your 150 recombinants comes from 75 black/shiny and 75 red/pebbly.

Your 850 parentals ceoms from 425 black/pebbly and 425 red/shiny.

Anyways that was my attempt which appears to be directly opposite to what your answer key says. Did you copy it down correctly?

lab techniques - What effect does vortexing have on a fluid sample that simple mechanical shaking does not?

what specific effect the vortexing has that makes it better than manual shaking

In addition to @bobthejoe's answer about viscous fluids, (manual) mechanical shaking is also less consistent and more tiresome than vortexing.

If the vortexer is always at the same speed and each sample is vortexed for the same amount of time, then the shaking step will be less variable among samples. For example, the vigor of mixing an aqueous soil suspension could potentially affect the amount of aggregate decomposition and release of molecules into the suspension (I don't have a reference for this, but it is good practice to treat replicates the same to minimize any non-treatment effect).

Manual shaking is not only less consistent, it is also tiresome - especially with larger volumes (>=10ml) and large sample sizes.