The biological process by which new individuals are formed.

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1answer
5k views

Do bacteria die of old age?

I know that the cells of mammals at least stop dividing when they are old, and then die a programmed cell death. Then other cells have to replace them. But in a bacterial colony, each cell ...
15
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3answers
396 views

Are human fetuses more likely to be male?

Question: From a physiological point of view, when sex is determined in a human fetus, is it equally likely to be male or female? Studies in this area typically measure age at birth, where the data ...
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5answers
3k views

Why are not all species hermaphrodites?

If a hermaphrodite animal (like slug, snail, etc) finds a partner they can mate immediately. If another animal with "normal" reproduction (lets say a mouse) finds a partner they can only mate if they ...
14
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1k views

Why do some mammals not have testes in a scrotum?

Coming from an evolutionary approach, Is the only purpose of a scrotum to regulate the temperature of the testes? Knowing all mammals are warm blooded, shouldn't all mammals have testes in a ...
11
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98 views

Beginning of the urogenital system

Are any invertebrate nephridia (proto/meta) homologous with vertebrate kidneys in the sense that embryologically they also begin together with the genital system? When did the embryologic association ...
10
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2answers
273 views

Have we ever observed two drosophila lineages that evolved reproductive isolation in labs?

Background The standard definition of species refers to the concept of reproductive isolation. If two lineages are found to be reproductively isolated, then we consider these two lineages to belong ...
9
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584 views

Which sex has higher variance of reproductive rate in modern societies - male or females?

Who has a more varied reproduction rate in modern western societies - men or women? The average rate is the same of course, but I wonder which sex have higher variance - higher variance means that ...
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Species with reproduction barriers that can both reproduce with a third species

To start with, I do not have a sound knowledge in biology or any formal education in the area. I was told that one of the definition of a species is a reproductive barrier, which means that if two ...
9
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318 views

Do twins “run in the family”?

My wife and I recently found out that we are going to have twins and so nearly everyone asks if we have a family history of twins. Now I know that the answer for me is that it doesn't matter—as ...
8
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173 views

Why does the gender of the parent species determines the species of a hybrid offspring

I've read a little about hybrid animals, and have been amazed by the fact that the gender of the parent species determine the species of the offspring, in some hybrids. A male horse and a female ...
8
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1answer
347 views

Is sexual reproduction outside the same biological family possible? Has it ever occured successfully?

Are there any examples of two species taxonomically classified in different biological families that have successfully hybridized and produced viable offspring? If not, is there an example of where ...
8
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2answers
175 views

Why does the chance of having a baby with Down's syndrome increase with the age of the mother?

Down's syndrome occurs when either the egg or the sperm cell contain on extra chromosome 21. To my understanding, women are born with all the egg cells in place already, so there's no further cell ...
8
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1answer
457 views

Could humans and chimpanzees hybridize?

In some cases two species can hybridize. For example, Tigers and lions can hybridize to produce "Ligers". Would it also be possible for humans and chimpanzees (or any other species) to hybridize ? ...
8
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2answers
619 views

Do hormone drugs affect whether a person feels sexual attraction to males or females?

I know that ingesting testosterone and other hormonal drugs may stimulate libido and increase sexual desire. But I wonder, if a man ingests female hormones such as estrogen, will he experience sexual ...
8
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1answer
515 views

A timeline of the odds for survival for fertilized eggs and fetuses

I'm looking for data to build a timeline of the odds for survival of a fertilized egg, i.e., What are the odds it'll last a week? What are the odds it'll last a month? 2 months? (and so on ...
7
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1answer
448 views

When do most mammals mate?

Is one part of the day more prevalent then other when it comes to mammal animals mating? Is there an aggregating study that has been done to see if these living beings in nature mate mostly during day ...
7
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1answer
412 views

Do egg laying animals experience a pregnancy?

Does a female animal that lays eggs experience a pregnancy-like period of time, where she will feel and behave differently as if she were fertilized and her body is prepared to lay a fertile egg, not ...
6
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2answers
168 views

Why, specifically, does each generation, on average, improve upon the design of the species rather than degrade it?

In every non-life example I can envision, a copy of a copy is always a degraded or less pure version of the original unless some outside influence acts to correct the copy back toward the ideal ...
6
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2answers
9k views

Can positive and negative blood type of a couple lead to miscarriage?

I want to know can $+ve$ and $-ve$ blood group of a couple could be a cause of miscarriage in pregnancy?
6
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1answer
379 views

Is it purely the nervous system causing vaginal lubrication (arousal)?

My girlfriend was watching some documentary on TLC about a paralyzed woman getting pregnant. I believe that woman still has some feeling, as she spoke about feeling the effects of a bladder ...
6
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1answer
195 views

Effect of spaying on the female cat organism and health

Veterinarians often recommend spaying a female cat if the owner does not want her to have kittens. What does biology know about the effect of spaying on female cats' organism and health (apart from ...
6
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2answers
502 views

How are the gene sequences of individual sperm and egg cells “randomized”?

What I mean by "randomized" is, in the place where an egg cell or sperm cell is made, what is the mechanism by which each one is not made identically? Though I am a layman, I'm pretty sure that if the ...
6
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2answers
137 views

Why did women historically have such a high mortality rate during birth?

Historically women had a relatively high chance of dying while giving birth. At first thought it seems to me that this would be a disadvantage for the species for the obvious reason that a dead ...
6
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1answer
2k views

Why is fructose not glucose the main energy source of sperm?

The seminal fluid contains fructose as the main energy source for the sperm and not glucose. Why is fructose and not glucose the primary energy source for these sperm, since glucose is the ...
6
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1answer
141 views

Alfred Jost's rabbit experiment: how did he actually do it?

I was watching a Crash Course on Biology YouTube video by Hank Green: Great Glands - Your Endocrine System. Hank humorously describes a sex determination experiment by Alfred Jost as follows ...
6
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1answer
241 views

How selfish is Dictyostelium slug formation?

Dictyostelium is a slime mold which is well known for having a single cell free living phase and other some conditions (e.g. when food is scarce) for forming communal piles of cells called 'slugs' ...
6
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1answer
115 views

Macromolecule levels in daughter cells after fission

When a prokaryote undergoes binary fission, how are the non-DNA macromolecules distributed between the two daughter cells? This is motivated by comments on a previous question and a G+ discussion. I ...
6
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1answer
494 views

Regulation in plants bearing cleistogamous and chasmogamous flowers

In most plants bearing cleistogamous flowers, chasmogamous flowers are also borne by the plants. For example, Viola, Oxalis and Commelina contain both these kinds of flowers.( I am unaware of a ...
6
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0answers
89 views

Neuroendocrinal mechanism of parturition

My book reads, "The fetus signals that it is mature by secreting certain hormones that diffuse across the placenta into mother's blood and cause the secretion of oxytocin from her posterior ...
5
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2answers
585 views

The probability of indirect human fertilization?

What is the probability of conception in situations when sperm isn't directly ejaculated into the woman's vagina, like: The man's or the woman's hands come into contact with sperm, for example when ...
5
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3answers
216 views

Does our eyeball increase in size as we grow?

Does the size of the eye increase as we develop from the stage the complete eye first forms to infancy and then to adulthood ?
5
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1answer
198 views

What evolutionary pressures pushed Galápagos tortoises to mature so slowly and live so long?

I read that they take up to 40 years (in the wild) to reach the age of reproduction and are thought to live over 100 years, with one in captivity reaching over 170 years. Can someone explain in ...
5
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1answer
99 views

Reproduction and defecation

In mammals and birds the external reproductive organs and waste removal organs see to be the same. Is this always the case with other animals such as insects etc...? Are there any good reasons for it? ...
5
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1answer
72 views

Gender and age-specific mutation rate in plants

Background General concept According to Cochran and Harpending (2013), mothers transmits on average a number $x$ of new mutations to their offspring. This number $x$ is independent of the age of the ...
5
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0answers
168 views

Cytoplasmic determinants - protostomes and deuterostomes

Cytoplasmic determinants are spread unevenly in the egg, and so when embryo starts forming (cells start dividing), the determinants are also unequally divided between cell. This unequal distribution ...
4
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1answer
166 views

How can the child and the mother have different blood types?

As far as I know the fetus is fed by the umbilical cord which basically connects his/her circulatory system with the mother's in order to supply oxygen and nutrients. But how is this possible if they ...
4
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1answer
83 views

Why is there sperm mitochondrial suicide?

The mitochondria in the sperm are digested upon entry into the egg, making mDNA inheritance exclusively female. What is the advantage of this? Wouldn't some male mDNA be beneficial because of the ...
4
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1answer
79 views

What are possible health risks to women having large numbers of children?

What is the possible health issue the women would face in this record? The record for most children born to a single couple belongs to the first wife of Feodor Vassilyev of Russia. In 27 ...
4
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1answer
80 views

How can Taenia solium (tapeworm) lay 35,000 eggs per proglottid?

As far as I know TAENIA SOLIUM is an acoelomate which basically means that the space between the alimentary canal and the gut is completely filled [or] occupied by the mesoderm and they do not have ...
4
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3answers
162 views

Does the genetic material the sperm carries affect it's physical properties

Basically, what I'm asking is, is the actual sperm cell built from the blueprint in the DNA of the man or is it itself also a consequence of the DNA it carries? I'd like to know a few more things ...
4
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2answers
138 views

How do taenia form a species?

I know that there are many hermaphrodite animals and plants. But many of them seem to still exchange genes by mating with another member of their species. I now happened to read the Wikipedia ...
4
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2answers
124 views

Asexual reproduction and Telomeres

Many eukaryotic organisms like yeasts, hydras , planarias, plants etc reproduce asexually. Replication of End of linear DNA pose a limit to the number of cell divisions. My question : Do asexually ...
4
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1answer
375 views

Causes of monozygotic twins

Twins could be monzygotic i.e. identical twins and dizygotic i.e. non-identical twins.Well, monozygotic twins occur when a single egg is fertilized to form a zygote which later divide into separate ...
4
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1answer
364 views

Why did mammals evolve to have two testes?

What makes mammals tend to evolve to have two testes?
4
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1answer
880 views

Is ovum + ovum fertilization possible for human?

In humans is it possible to fertilize a ovum with another ovum from the same female subject? I already found some works in which the ovum is fertilized by a somatic cell (see e.g. this ), but I am ...
4
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1answer
32 views

Which C. elegans would be appropriate for general study?

Would wild type N2 be best or Dyp-11? I know they're different, but I just want to observe the worms to see life stages, movement, etc. Dyp-11 seems like it would be easy to see but N2 is the wild ...
4
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2answers
163 views

Is every part of a virus important for replication?

Is every component of a virus absolutely essential for its infection and replication in a host cell? Or can you just have parts of it to cause infection?
4
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1answer
125 views

Why isn't RH disease present in other mammals?

Basically, I have read about RH disease, Its rare but it can happen when an RH + baby is conceived by an RH - mother. This raises many questions. I have heard this problem only happens with humans, ...
4
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1answer
86 views

Why do some women have menstruation-like spotting throughout their pregnancy?

An interesting question that was asked during a lecture about human reproduction: what is the biological mechanism behind some pregnant women getting monthly spotting that they mistake for a regular ...
4
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1answer
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Are there any studies on the fertility levels of humans/mammals as a function of their stay at Antarctica?

Wikipedia, and Space.SE seem to indicate humans become infertile in space due to the increased exposure to cosmic rays. Knowing as we do that Antarctica is holey, and subject to increased radiation ...