The biological process by which new individuals are formed.

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Spermatogenesis; maternal homologs

What is the probability that, in an organism with a haploid number of 10, a sperm will be formed that contains all 10 chromosomes whose centromeres were derived from maternal homologs? I have ...
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1answer
30 views

Are there other methods besides surgery and hormonal treatments to help undescended testicles? [on hold]

I've been doing some reading on undescended testicles and common treatments. It looks like the most common treatment for a baby is to give it time to see if the testicles drop on their own. If not, ...
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34 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 ...
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67 views

is it necessary that every theca of an angiospermic anther must contain two microsporangia

i basically don't know the procedure or sequence of steps involved in the formation of anthers but i have read it somewhere it is formed from the dedifferentiation of shoot apical meristem of the ...
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86 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 ...
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38 views

Waste generation by embryo [closed]

How does an embryo produce waste products even when its organ systems are not developed fully ? How does the placenta identify or differentiate waste materials from embryo ? Which organelle or ...
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2answers
115 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 ...
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1answer
60 views

Two-fold cost of sex and r/K selection theory

This article cites a bunch of articles (I haven't been through them) that the effect of the two-fold cost of sex is "reduced" in stable environment or in K-selected environment. It says: [..] the ...
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78 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 ...
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53 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 ...
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249 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 ...
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Division of Polar Body

The first polar body formed after meiosis-I is completed in oocyte, may or may not divide. Why is the statement that "it may or may not divide"? Is it random ?
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Are chromosomes from each parent split between gametes with equal probability (esp. in humans)?

I've recently read a little on Wikipedia about genetics, but I can't find a direct answer to this question. My rough understanding is this: Both males and females have pairs of chromosomes, one ...
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1answer
29 views

What is the name of this type of inflorescence?

I was having a look at a rhizophora plant (from the mangrove family), and I got curious about its inflorescence. I can't make out what kind of inflorescence it is. Here is a photo of the ...
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1answer
95 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
44 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 ...
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1answer
46 views

Confusion regarding seedless grape and the normal process of germination

In general, does seedless grape by definition contains seed or is the seed small enough that the process of ingestion creates the illusion that there is no seed? If the latter is true, is the ...
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2answers
488 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 ...
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0answers
17 views

Is asexual and sexual reproduction a universal feature of Bryozoans?

I found some clues that most, if not all, bryozoans can reproduce and multiply by asexual and sexual means, for example: Thomsen & Hakansson 1995: "Sexual Versus Asexual Dispersal in Clonal ...
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3answers
110 views

Could a sperm be altered to contain a female's genetics?

while discussing with a friend a while back on the likelihood a Funtari (a woman with both fully developed and functioning sets of genitalia) existing in real life we got into a discussion of weather ...
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3answers
103 views

Does any animal species have two sexes and more genders?

Does it exist any animal species that have two sexes and a kind of different internal diversification in two genders or more? I mean no something like different-task-based diversity but something ...
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1answer
44 views

Advantages of bisexual reproduction over asexual one toward species promotion? [duplicate]

Are there any advantages of bisexual reproduction over asexual one towards species conservation and promotion? Do animals that have two or more sexes have more chances to reproduce? Does anybody had a ...
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18 views

Chemical events of fertilization

During the acrosome reaction, the activation enzyme present in the sperm dissolves the corona radiata and zona pellucida enabling the sperm to reach the plasma membrane of the egg. Also calcium and ...
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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 ...
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28 views

Effect of the health of the male parent at the time of conceiving

Does it matter at all in determining the traits of a baby what the current health of the father is? For example, let's say I got diabetes at the age of 40 because of the poor lifestyle choices. Will ...
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3answers
106 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 ...
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151 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 ?
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53 views

Evolution from Mating types to different sexes

Imagine a lineage of multicellular organisms that had mating types and evolved their mating types into sexes. What are the possible mechanisms that might have brought this lineage to evolve sexes from ...
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108 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 ...
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1answer
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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 ...
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1answer
55 views

Do chickens always lay eggs?

http://de.wikipedia.org/wiki/Hühnerei says it takes up to 24 h for a chicken to produce an egg. Is that dependent on the chickens nutrition, i.e., if it does not get enough food or the wrong kind, ...
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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 ...
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1answer
29 views

Fertilization of an egg by two sperm

What happens when two sperm fertilize an egg? This can be either naturally or by experiment.
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1answer
40 views

Mutated Sperm - What happens?

I saw on TV that not all sperm are the same. Some have mutations like 2 and 3 tails? There were other mutations as well. If one of these mutated sperm actually fertilized an egg, would the embryo ...
3
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1answer
96 views

Meiosis vs. Mitosis

Meiosis is a type of cell division that reduces the chromosome number from 2n to n to make gametes viable for reproduction in humans. I know that during meiosis, there is independent assortment and ...
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1answer
68 views

Bacterial Conjugation/Horizontal Gene Transfer — how does the plasmid exchange work?

So according to a PPT I'm reading, bacterial conjugation works by the two bacteria joining pili and exchanging plasmids. So how exactly do the plasmids get across the gap? If I understand this ...
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1answer
28 views

Surrogacy Post Fertilization

The wikipedia page on surrogacy highlights two main forms of surrogacy: Traditional Surrogacy and Gestational Surrogacy. Traditional surrogacy inseminates the surrogate mother with sperm, while ...
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2answers
115 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 ...
3
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0answers
110 views

Do Asian women have more difficult births than Europeans?

I recently heard a claim that Asians in general have more difficult births than Europeans. Is this true? I have found a few studies(1,2) on the effect of ethnicity on birth outcomes but they seem to ...
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1answer
32 views

Book on yeast reproduction, evolution and on the use of yeast as model organism

I am looking for a good book in: Yeast reproduction mating types Recombination mating type determination mechanism Yeast evolution Yeast as model organism and its use in experimental biology It ...
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2answers
126 views

Can diploidy evolve in absence of sexual reproduction?

Theoretical question Can diploidy (or polyploidy) evolve from a haploid lineage in the absence of sexual reproduction ? For what theoretical reason? How can such evolution take place? Empirical ...
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20 views

recombinant gametes

Suppose you are able to observe under a microscope the total number of meiotic divisions occurring in one gonad of a given individual and to outnumber exactly the crossovers between two given ...
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1answer
42 views

Reduction of size in diatoms due to asexual reproduction

From this we can see that diatoms reduce their size after asexual reproduction. This would ultimately lead to nonviable small size. Is there any mechanism to avoid this ?
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1answer
38 views

maximum # of generations possible in a population of cannibalistic rats

Assume a sufficiently large population of rats (to allow genetic variation and facilitate inbreeding) in a place with abundant water, sunlight, shelter but no food. For how many generations can this ...
6
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1answer
366 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 ...
2
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2answers
89 views

Stay young by reinserting own DNA from years ago?

As far as I know, the DNA sequence becomes shorter every time a cell divides. A shorter sequence results in information loss and aging characteristics. As a countermeasure, shouldn't one stay young ...
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4answers
1k views

Can the third sex be categorized as Male or Female?

Hijra are people who have a penis (not sure if sexually active) but look much like a female (perhaps for some feminine biological property). Wikipedia says they are "physiological males who have ...
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1answer
89 views

Why do some animals and fungi prefer asexual reproduction?

Animals like Sponges and Hydra and fungi like Yeast and Mushroom can reproduce both asexually and sexually. However, they only reproduce sexually if the 'circumstances' are 'bad'. Is there a specific ...
6
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0answers
74 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 ...
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1answer
229 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 ...