Episode #125 of the Stack Overflow podcast is here. We talk Tilde Club and mechanical keyboards. Listen now
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This is a interesting question and for a long time it was thought that they do not age. In the meantime there are some new papers which say that bacteria do indeed age. Aging can be defined as the accumulation of non-genetic damages (for example oxidative damage to proteins) over time. If too much of these damages are accumulated, the cell will eventually ...


39

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 with smaller gametes is defined as male and the sex with larger gametes is defined as female, and individuals that can produce both types of gametes are called ...


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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 the uterus. A more parsimonious explanation, however, is that the endometrium in primates has developed into too large of a structure to be completely reabsorbed ...


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You have clearly given this a lot of thought. Unfortunately, as @adam.r said, you are laboring under certain misapprehensions. The quick answer is that each generation does not "improve" on the last. That is a common misconception. In a bit more detail: First of all, your copying metaphor is a bad one. There was no "perfect original", I expand on this theme ...


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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 called the Chorion frondosum, which develops from the outer cells of blastocyst (trophoblast), and the maternal side of the placenta, Decidua basalis, which ...


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Firstly I'll clarify that you are talking about simultaneous hermaphrodites rather than sequential hermaphrodites (1st one sex, then the other e.g. the limpet Patella vulgata). It is perhaps easiest to address the question by countering it and asking why dioecy (2 sex systems/2 gonochoric types e.g. male and female) is better? As you have pointed out there ...


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Welcome to Biology StackExchange. Am I remembering this incorrectly? No, you're remembering it correctly. I think you're talking about slime molds. You'll find more information on the wiki page Is this the video you saw? These images are pretty cool. Is this even possible? Yes (given that it exists). There is no way to correctly answer this ...


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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-only animals also present in nature, such as New Mexico whiptail, which reproduce only by parthenogenesis, meaning that it is not as impractical as one might ...


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When dealing with humans, there are only two Biological genders as defined by the presence or absence of the Y-Chromosome. If the Y-Chromosome is not present, or through some process gets totally deactivated, the human will appear and function as a Female. XX = Female XY = Male XXY = Male (Klinefelter's Syndrome) XYY = Male (Aneuploidy - Normal ...


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Note: This is based on literature searches I've done a while ago out of general curiosity. I'm in no way an expert on human reproduction. First, I'm not sure if you are asking about evolutionary reasons or the developmental causes for for a difference in sex ratio. Here, I will focus on the developmental causes. There is much evidence for a male bias in ...


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Having descended testes is a derived characteristic within mammals; monotremes and the Afrotheria (including elephants) all retain the ancestral character state (Kleisner, et al., 2010)2. Among those mammals with descended testes, these can be ascrotal or scrotal. Testicular descent is hypothesized to have only occurred once within Mammalia, with the ...


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I think you might be confusing sex and gender. The terms are often used interchangeably, but strictly speaking, they have different biological meanings. Sex refers to the biological categorization based on genetics, reproductive organs, or similar things, whereas gender is based on social identity. For humans, there are only two sex chromosomes, X and Y, ...


18

Rice and Salt$^1$ bred fruit flies for 35 generations and from one line of flies created two groups that were isolated from each other reproductively. They could not interbreed because they no longer bred in the same environment. Depending on one's definition of 'species' this could be a case of artificial speciation. $^1$Rice WR, Salt GW (1988), Speciation ...


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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 pouch attached to the trunk or its tail while in others the egg is attached to the trunk or tail laid by the female.The fertilisation takes place in the pouch or in ...


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The Fisher's principle is not applicable to the fetuses because it has been formulated for parental expenditure and basically states that the ratio of male to female parents (implying that both parties have reached the age of fertility) will tend to 1:1. There are several mechanisms that we can use and that are mentioned in the canonical paper by James (...


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Interfamilial hybrids have never, to my knowledge, been recorded occurring naturally (without human intervention). In plants, somatic inter-familial hybrids have been produced for a wide variety of species pairs in the lab (e.g. between carrot and barley; Kisaka et al. 1997). In animals, there are some historical reports of hybrids between chickens (...


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So most cells require growth factors and survival factors to stay alive in an organism. Cells which stop receiving survival factors, such as sperm, undergo a process of programmed cell death (PCD) called apoptosis. Some cells will also undergo necrosis, or autophagy, among other types of PCD. Lachaud et al. performed a study in 2004 on the contribution of ...


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The need for birth control has been a concept for thousands of years and remains an important issue for men and women today, the need for contraception helped humans to achieve control over our population and healthy sexual relationships without having the fear of pregnancy. The medieval contraception methods mostly relies on plant based oral ...


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Short answer People with androgen insensitivity syndrome do not have a functional uterus and cannot bear a child. Background Androgen-insensitive genetic males may develop female genitalia and internal female reproductive organs. However, in both partial androgen insensitivity syndrome (PAIS) and complete androgen insensitivity syndrome (CAIS) the uterus is ...


11

I thought that the only difference between the male and female reproductive cell's DNA code is the X-Y chromosome that determines gender, not differences that can define the species of the offspring. Why does this happen? Well that is not the only difference, there are certain characters that are only transmitted by one of the parents. First of all you ...


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This isn't so precisely focused on tortoises, but a general theory in evolutionary biology for why some animals live longer is K vs r selection theory. The idea here is that animals will make a sort of evolutionary 'choice' and configure themselves to breed as numerously and quickly as they can. This is called 'r' selection, named after the constant that ...


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Sperm are cheaper than eggs According to Bateman's Principle the males of a species are (typically) more able to produce a greater variance in the number of offspring. This is because generally the males can produce many gametes and achieve many matings whereas females are limited by the number of eggs, resources, and time lost to pregnancy. Therefore, ...


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The concept of a human/chimp hybrid is called a humanzee. No humanzees have ever been recorded despite the fact that sexual intercourse between humans and chimps have been recorded on several occasions. This suggests that male-human/female-chimpanzee is not capable of producing viable offspring, at the very least. As to why, several reasons will contribute: ...


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When you say, why don't we see more sexually reproducing species than asexual, I presume you are referring to bacteria, protists, archaea, some fungi, etc. Most multicellular organisims do reproduce sexually, which makes sense since an organism would need to be multicellular to have cells specialized for gametes. As you stated, the advantage is that sexual ...


10

I want to know can +ve and -ve blood group of a couple could be a cause of miscarriage in pregnancy? Yes. In extreme cases, it can. You are talking about Rh Incompatibility, and can become a big issue when the mother has Rh(-) blood and the father has Rh(+) blood (such as the case with your cousin and his wife). What could have happened (but definitely won'...


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The blood of the fetus does not mix with the blood of the mother. Instead, the placenta provides a system where the two separate blood streams flow past each other with thin separation allowing nutrients to flow between the two streams but the not the blood cells and other large components.


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The frequency rises with maternal age due to a peculiarity of meoisis in female mammals. Meiosis is originated in the fetal ovary, arresting at metaphase I with the homologous chromosomes aligned for segregation. Cells remain in this state until the time of ovulation, often decades later in humans. The longer cells remain in the arrested state, ...


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First of all, I should quote the sentence from the MOST reliable ophthalmology sourcing in the world - American Academy of Ophthalmology: Section 11 - "Lens and Cataract" "The equatorial diameter of the unfixed human lens measures 2 mm at 12 weeks and 6 mm at 35 weeks. Both the growth and the maturation of lenticular fibers continue throughout life." The ...


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