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43 votes
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Why do human females have periods?

Short answer Shedding or reabsorbing the endometrial lining is energetically advantageous to the female.The advantage of shedding over re-absorption may be that sperm-born pathogens are removed from ...
AliceD's user avatar
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27 votes
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Cells of umbilical cord - mom's or son's?

Cells of umbilical cord - mom's or son's? Answer: Son's. The interface you are looking for is in the placenta. https://en.wikipedia.org/wiki/Placenta Formally the fetal side of the placenta is ...
JayCkat's user avatar
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26 votes
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Crossbreeding mouse and chinchilla

"Chinchilla" is both a separate rodent, and also a name for a Mus musculus mouse coat color/pattern. Here it's used in the latter context. You may be more familiar with the word "agouti&...
Bryan Krause's user avatar
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21 votes
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Can a human be made with ovum but without sperm?

Nice question! It is actually very difficult to do so because humans, obviously, are far more complex than some animal species which naturally show parthenogenesis. Just to mention, there are female-...
another 'Homo sapien''s user avatar
17 votes

Do males ever produce the offspring?

Yes the males of a group of bony fish Syngnathidae can bear offsprings or as you say produce offsprings. This group includes Seahorses and Pipefishes. In some species the male have either a brood ...
Tyto alba's user avatar
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9 votes
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How do traits with no negative effects get "weeded out" via evolution?

Oops I wrote a lot! This is almost a very brief introduction to some concepts of population genetics. A little bit of terminology first Locus A locus (plur. loci) is a position on a chromosome. ...
Remi.b's user avatar
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9 votes
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If a mother had a child with her own son, could a paternity test yield positive result for the son's father?

Let's approach some different methods of distinguishing parents: 1: The Y chromosome. These are passed down from father to son. Therefore, if the baby is male, its Y chromosome will be the same as ...
Armatus's user avatar
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9 votes
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How did the orchids evolve to support pseudocopulation when they do not have any organ for vision to see how insects look like?

Evolution does not work based on an organism (or designer) "seeing" a problem and seeking a solution. Evolution via natural selection works when members of a population that have a certain heritable ...
Bryan Krause's user avatar
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9 votes
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A study has found that cell phones cause infertility, is this something to worry about or is the study flawed?

The study is basically worthless. First, the study was not constructed to test this hypothesis, so it's just something interesting that may point to future studies. It does not provide sufficient ...
John's user avatar
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9 votes

Why do OX5034 GM mosquitos require the presence of tetracycline to survive? What does the drug do in this case?

They don't go into any detail on the sites you link to and I don't have time to look into patents, but from the context it sounds like they may be using a tetracycline repressible promoter. This is ...
tyersome's user avatar
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8 votes
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Why are mice with a single X chromosome and no Y chromosome males?

Almost all mammals (including mice and humans) have two sexes where the males have a Y chromosome and an X chromosome (whereas females have two X and no Y chromosomes). This is not the only way ...
mgkrebbs's user avatar
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8 votes
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What wasp like insect breeds in clay pots with dead spiders?

It's some sort of potter wasp/mason wasp (Eumeninae). The spiders are paralyzed and brought there as food for its larvae. Here is an example of an opened nest I found on Bugguide.net that looks ...
picapica's user avatar
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8 votes
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What animal has the longest juvenile period?

As you indicate in your question, the average age of sexual maturity is probably the best way to approach this, since immaturity is usually how juveniles are defined. Age of puberty is also different ...
fileunderwater's user avatar
7 votes

Pregnancy from two parents with incompatible blood types, can it lead to complications?

The rhesus factor (the + / - part of the blood group) can cause complications with pregnancy under certain conditions and lead to the so called Rh disease: If the mother is rhesus negative and the ...
Nicolai's user avatar
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7 votes
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How many primary oocytes in human female body at birth?

Short answer: The developmental process starts from oogonia as follows: Oogonia(7million) in the foetus develops into primary oocyte(2million) in the foetus prior to gestation which again develops ...
user 33690's user avatar
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7 votes
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Do hermaphrodites have more nerve fibers in their puendal nerve?

Short answer The genitals of true intersex individuals are not duplicated. Instead, their external genital features are hybrid structures. In turn, it's not a matter of duplicated neural innervations. ...
AliceD's user avatar
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7 votes

Minimum age to reproduce

The youngest fathers recorded were 11 years old (see wikipedia > List of youngest birth fathers). The youngest mother recorded is L. Medina was 5 years, 7 months and 21 days old when giving birth, ...
Remi.b's user avatar
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7 votes
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Very frequent multiple births in humans

Risk factors for dizygotic twinning are related to multiple follicular development, and include maternal family history, ethnicity, geography, maternal parity, maternal age, and, of course, use of ...
De Novo's user avatar
  • 8,791
7 votes
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Sperm formation - Frequent Ejaculations

The arithmetic of human sperm A young, healthy man produces about 1000 sperms every second, which comes to about 90 million per day [1]. These sperms are stored in the epididymis and ductus deferens ...
Adhish's user avatar
  • 1,307
7 votes
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Is being able to interbreed and produce fertile offspring a transitive relation in biology?

The ring species conundrum As commented above, in essence this is the classic case study of ring species, and reading up on it will completely answer your question. A case of ring species is ...
S Pr's user avatar
  • 6,222
6 votes

Do only one or both pairs of homologous chromatids exchange genetic material during the process of crossing over?

Yes, it is perfectly possible for both pairs of non-sister chromatids to cross over in a single tetrad. The "standard textbook" depiction is a simplification, true tetrads can sometimes be very ...
March Ho's user avatar
  • 9,452
6 votes

Why do chickens continuously lay unfertilized eggs?

Chickens are domesticated Red Jungle Fowl. In the wild, Red Jungle Fowl live in flocks with one rooster for every few hens (where "few" is probably less than five in the wild, though in zoos flocks ...
iayork's user avatar
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6 votes
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When was it discovered XY chromosomes decide the sex of a child in humans?

The discovery of genetic sex determination, and determination of sex via male gametes (in XY species, female in ZW), occurred over some time in the late 1800's and early 1900's. Advances were made ...
rg255's user avatar
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6 votes
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How is trangender female different from normal female biologically?

Remi gives a good introduction to the various terms and definitions you should know when learning about gender identity. However, he didn't really address your basic question: What is biological ...
MattDMo's user avatar
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6 votes
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Is the sex of siblings mutually independent?

There is at least one paper that claims this: A test for heritability of the sex ratio in human genealogical data is reported here, with the finding that there is significant heritability of the ...
iayork's user avatar
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6 votes
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Which requirements are needed for 2 different species to be able to have offsprings?

Lets break this down like a logical problem. In reality, it involves the correct gene expressions at the correct time, place, etc. But that would be a book. Prezygotic reproductive isolating ...
anongoodnurse's user avatar
6 votes
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Is it Theoretically Possible to Create a Male clone from the donor Cell of a Female?

So, i want to know if the sex of the resulting clone is determined by the sex of the donor animal. Generally yes for mammals and birds. In animals where the sex is determined by sex chromosomes, ...
JayCkat's user avatar
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