42
votes
Accepted
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 ...
- 51k
42
votes
Accepted
What's the difference between male and female?
Sexes (male and female) are generally defined in terms of Anisogamy, which means that there are size differences between the gametes (i.e. the reproductive cells that fuse at fertilization). The sex ...
- 16.6k
23
votes
How does DNA still work after recombination?
One must always be careful not to stretch an analogy further than it can withstand, but since you started these analogies, I will follow up on them and explain the small mistake you've done in their ...
- 67.5k
18
votes
Is Mutation Theory still "valid" for complex organisms?
Change in genetic variance
From what I have been taught, Natural Selection (or even Artificial Selection) is great for panning favorable genes from a species and bringing them to the fore, however, ...
- 67.5k
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 ...
- 8,754
16
votes
Accepted
How does DNA still work after recombination?
Homologous DNA recombination does not swap parts randomly in the sense that any two bits of DNA can swap places. DNA recombination is random in the sense that it may or may not occur. In fact DNA ...
- 176
13
votes
Accepted
Do wolves mate with siblings?
Mating with siblings or incestuous relationships (breeding within blood relatives) enhances the chance of expression of disadvantageous characteristics (mostly recessive alleles). Therefore, natural ...
12
votes
Is Mutation Theory still "valid" for complex organisms?
You're right that the mutation must be in a germ cell in order to be passed on. Most errors are introduced during DNA replication (at a rate of around 10-10), which occurs a number of times between ...
- 17.5k
10
votes
Among primates, is it true that homosexual behavior is extremely unnatural and uncommon?
First Antonio Pardo is not a biologist, he is a professor of bioethics and his degrees are in medicine and philosophy.
Second, Clearly he does not know anything about primates, since there is one ...
- 13.1k
8
votes
Accepted
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 ...
- 8,718
8
votes
Accepted
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 ...
- 16.6k
7
votes
Accepted
No. of meiotic divisions to produce specific no. of seeds
Assuming that you have studied megasporogenesis and microsporogenesis. To produce a seed, you require the production of pollen(n) and egg(n) and their fusion.
Let's start with pollen grain(n):
4 ...
- 3,239
7
votes
Accepted
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 ...
- 1,227
7
votes
Do wolves mate with siblings?
I am not a wolf expert, unfortunately, but was able to find an article focused on just this question with grey wolf packs (1). The article studies relatedness via microsatellite locations in the DNA ...
- 577
6
votes
Accepted
Is Parthenogenesis known as Sexual reproduction or Asexual reproduction?
Only a matter of definition
It is only a matter of definition. When it comes to sex, there is such a diversity of mating system that it is very hard to make a good definition that won't be challenged ...
- 67.5k
6
votes
Accepted
Why can't two different genetically species reproduce to give a viable offspring?
The short answer is that "different species" are defined as "not being able to produce viable offspring". So the answer to your question is that it's a tautology; it's that way because that's how it'...
- 14.1k
6
votes
Accepted
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, ...
- 2,876
6
votes
In men, why do over 80% of sperm have abnormal form?
So I've dug a bit into how a 'normal morphological' form is defined and characterised, since assessing morphology into 'normal' and 'not normal' is always a very tricky thing.
Looking into the ...
- 4,296
6
votes
Accepted
What are these structures inside a cut open Allamanda blanchetti?
The third photo gets to the heart of the matter. Here's an enlargement:
The gold-colored areas are the anthers of some of the stamens, the filaments of which are fused with the tissue of the petal. (...
- 8,718
5
votes
How does sexual reproduction generate more genetic variation?
Short answer it doesn't. Sexual reproduction generates new combinations of traits and increases the difference between individuals in the same populations.
New combinations means beneficial traits ...
- 13.1k
5
votes
Accepted
Why are male gametes and female gametes not equally sized
Gerardo is correct that female designates the bigger gamete, so there's nothing important about the terms "male" and "female" here. But I'd like to also respond to your initial question of how the ...
- 76
5
votes
Why does inbreed produce a higher percentage of abnormal babies?
Many disease/abnormality causing alleles of a genes are maintained in populations through their recessive nature. That is to say, in order for the disease to manifest itself in offspring they must in ...
- 116
5
votes
Accepted
Why isn't the ovum reabsorbed into the body (like sperms) if it is not fertilised?
Apparently they are
Technically speaking, the ovum is not shed because it does not exist unless and until fertilization occurs. Development leading up to the ovum otherwise stops before the final ...
- 2,343
4
votes
Accepted
How can a haploid plant be bisexual?
Meiosis does not determine sexual form. Eukaryotes use meiosis and fertilization to recombine genes to form new combinations. Meiosis does produce haploid cells from diploid cells, but that has ...
- 8,718
4
votes
why has evolution favored sexual reproduction using two mates over sexual reproduction using three mates?
Let's break it down: The chance that two individuals of distinct gender meet at one location in space time is tremendously higher than for three. We could do some math here (assuming biased random ...
- 176
4
votes
No. of meiotic divisions to produce specific no. of seeds
For producing $x$ number of seeds (or say zygote) $x$ number of egg cells must fuse with $x$ number of male gametes.
In angiosperms, 1 meiotic division of Megaspore mother cell leads to formation of ...
- 8,754
4
votes
Does sperm weight causes sex ratio?
Probably not! There are certainly some physical reasons to doubt it. Looks like the mass difference between X and Y sperm is on the order of 0.1 picograms: X chromosome "weight"?
First, ...
- 279
4
votes
How does sexual reproduction generate more genetic variation?
There are two questions here. 1) What is genetic variance? It is actually clearly defined. 2) How does sexual reproduction generate more genetic variation?
What is genetic variance?
Assuming bi-...
- 67.5k
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