The process of passing genetic material from one generation to the next depends completely on how cells grow and divide. To reproduce, a simple organism such as bacteria or yeast simply copies its DNA (through a process called replication) and splits in two. But organisms that reproduce sexually go through a complicated dance that includes mixing and matching strands of DNA (a process called recombination) and then reducing the amount of DNA in special sex cells to arrive at completely new genetic combinations for their offspring.
There are two basic kinds of organisms — ones with a nucleus and those without a nucleus (a compartment filled with DNA surrounded by a membrane called a nuclear envelope):
<span>Prokaryotes: Organisms whose cells lack a nucleus and therefore have DNA floating loosely in the liquid center of the cell. Prokaryotes divide, and thus reproduce, by simple mitosis.</span><span>Eukaryotes: Organisms that have a well-defined nucleus to house and protect the DNA. Eukaryotes divide by meiosis for sexual reproduction.</span>
Explanation:
<h2>It is interesting to note that CO2 is still believed to be the No 1 greenhouse gas instead of water vapour. Many excellent climate scientist (e.g. Richard Lindzen, Roy Spencer, John Christy, etc) have dealt with the issue and shown both in books and research articles that CO2 is a very minor player governing global climate.</h2><h2>So what drives climate?</h2><h2>The answer must obviously be found in the hydrological cycle, where the oceans play a major role together with extraterrestrial process with the Sun having the ultimate role. We know that solar energy (insolation) does not vary sufficiently to explain the climatic excursion our planet has experienced on a short and long term. It is sufficient to consider the Little Ice Age and the Medieval Warm Period, not mentioning the past ice ages, to understand that there are many complicated factors to consider before we can explain climate variability.</h2><h2>Solar activity is naturally a major player but this does not mean only total solar insolation (TSI) but also solar magnetic activity. Also the gravitational influence of the entire solar system must be taken in account, not forgetting our own natural satellite, the Moon, influencing at least ocean tides. Very interesting views on climate variability and cosmic activity have been presented by Henrik Svensmark.</h2><h2>A very simplistic example how the water cycle could adjust climate is the following mental construct: The Sun warms the ocean surface increasing evaporation. Increase in water vapour content decreases the density of the air, which thus rises to higher altitudes where eventually adiabatic cooling reaches a level where water vapour starts to condense. The availability of condensation nuclei, possibly enhanced by high energy cosmic radiation especially during low level solar magnetic activity, leads to strong cloud formation. This eventually limits solar warming of the ocean surface and decreases evaporation with less cloud formation. This entire cycle can be compared to a very effective thermostat, by some aptly termed the water thermostat responsible for keeping global temperatures at a suitable level depending on local conditions</h2>
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<em>the process by which green plants and some other organisms use sunlight to synthesize nutrients from carbon dioxide and water. Photosynthesis in plants generally involves the green pigment chlorophyll and generates oxygen as a by-product.</em>
<span>Spermatozoa are the mature male gametes in many sexually reproducing organisms. Thus, spermatogenesis is the male version of gametogenesis, of which the female equivalent is oogenesis. In mammals it occurs in the seminiferous tubules of the male testes in a stepwise fashion.</span>
Answer:
A person who receives a gene for sickle cell disease from one parent and a normal gene from the other has a condition called "sickle cell trait." Sickle cell trait produces no symptoms or problems for most people. Sickle cell disease can neither be contracted nor passed on to another person.