why do some regions in the chromosome stain darker than others?
820323
I think the answer to your question lies in the fact that some of the DNA is "wound" tighter than other sections along the chromosome.  \n\nThe tightly wound DNA is typically not transcribed in somatic cells (it might be a different story for germ line chromosomes, or chromosomes from embryonic tissue, and even stem cells for that matter).\n\nWhen a gene is constantly being transcribed, say for example genes for hemoglobin, the cell prefers to keep the region open for easy access.  It can do so by acetylation of histone molecules.  \n\nWhen histone is not acetylated, then the molecule keep the chromosome wrapped up tight.  \n\nWhen the dye attaches to the chromosome, tightly packaged DNA appears darker because there is a high concentration of dye in that smaller surface area.  \n\nSo staining helps identify euchromatin (actively transcribed DNA sequence, stains lighter) and heterochromatin ("inactive" DNA sequence, stains darker).\n\nThe dye has the propensity to stain both types of chromatin equally.  But it's the density of the dye which makes it appear darker or lighter.\n\nIt was fun thinking about your question.  Pass on the good karma!
885418
D is definitely the false answer because, in Meiosis I, the homologous chromosomes are seperated. The chromosomes are divided in Meiosis II. The seperating of the two homologous chromosomes into different daughter cells cause the number of chromosomes to be halved.\n\nE is definitely correct because the daughter cells are different from each other due to cross-over and also because of the seperation of homologous chromosomes.
548899
It could be any colour from ebony black to snow white.See the link below for an extreme example.\n\nSkin colour genetics is not simple recessive/dominant. It is a very complex trait based on at least 8 genes on 5 different chromosomes. As a result it is perfectly possible for children to be considerably darker or lighter than either parent. \n\n\nBeing "mixed heritage" makes no difference whatsoever. All humans are of mixed heritage and always have been. There isn't some hypothetical pure human heritage that has only one skin colour present.
686748
I'm going to have to go with \n\nc) trysomy\n\nbecause there is NO way that it can reveal phenotype (so A and D are out).  And I know for a fact it can reveal trysomy\n\n"Karyotype analysis can detect large chromosomal abnormalities such as loss or gain of an entire chromosome or portions of a chromsome and translocations (when a portion of a chromosome breaks off and rejoins with another chromosome, a common occurrence in leukemias)."
278087
The small, dark region in the cell nucleus is indeed called the nucleolus.  It is thought to be the site of ribosome synthesis.
707838
Darker color is dominant and lighter color is recessive as far as genetics are concerned.  More commonly, children turns out halfway between parents color.  In that sense, it is somewhat unusual that your children are completely white.\n\nBut...  I'm surprised that people near you are acting as this is such a surprising thing to happen.  It happens often enough....  One thing is for sure... if you are a mixed couple, the only thing you can do is get used to unusual and sometimes insulting comments from people.  Everybody has their own problems and prejudices.  If  you start getting upset over every comment, you'll be a wreck....\n\nI notice unusual facial expression (confused?) on people every now and then myself....
995002
Mutations occur frequently, not like in the cartoons, but small changes happen in chromosomes that are not inherited from the mother or the father.  Some of them cause terrible diseases, others may not cause problems at all.
997040
Eye color is a polyploid trait.  the actual genes occur on a couple of different chromosomes.  Sorry.  The human genome project has it mapped out which chromosomes they are my poster is at work.
117905
the chromosomes group together.
1177562
you're asking this question because the darker-skin pigment genes *do* tend to be dominant or co-dominant. the answer may go back to your father's parentage ... were his recent ancestors all latino? recessive genes can skip generations before showing up.
758075
Chromosomes are tightly packaged bundles of chromatin.  Both are composed of DNA and carry genetic information.  Chromatin condenses to chromosomes when the cell is about to divide.
193648
because light colored eyes are recessive to dark colored eyes. Dark colors are more dominant and stronger. As with most recessive genes, it is more prone to infirmity and weaknesses.
128118
To steal an answer recently posted by someone else, it simply comes down to the lack of need for dark pigmentation at high latitudes.\n\nAt low laititudes the risk of death or illness from skin cancer is higher than the risk of death from rickets. As a result people who lived at low latitides retained dark pigmentation since that provides portection from skin cancer. \n\nNote that it isn't only Asians that retained this trait.  Southern Europeans are no more or less prone to having dark hair than Asians.\n\nAt higher latitudes the risk from skin cancer declined and the risk of rickets increased. Having pale skin reduced the incidence of rickets, so pale pigmentation evolved through a reduction of eumelanin\n\nOne of the side effects of of low eumelanin levels is that it allows for multiple hair colours as well. With no eumelanin at all hair can be blonde, or it can be red colours that are difficult to achive in skin that  has high levels of eumelanin. With moderate levls hair can be brown, and with normal levels the hair can be black.\n\nPeople with normal eumelanin production can only really have one hair colour: black. That's because eumelanin covers over any other pigments.\n\n\nYou will note that it isn't only Asians who have almost exclusively black hair. It is equally Negroes, San, Aborigines, American Indians, Negritoes and so forth. European were freed up by their pale skin to express a range of skin colours not seen in normal humans.\n_________________\n\nMay said "the alleles are inherited and contained in the >>>>>>>same race."\n\nUtter Bollocks. If you are going to answer a question at least have some idea what you are talking about.\n\nThere is no such thing as a biological race. There are no alleles for black hair that are contained within the Asian race.
144099
The pairing behavior of the sex chromosomes in male and female individuals representing seven species of Peromyscus was analyzed by electron microscopy of silver-stained zygotene and pachytene configurations. Six species possess submetacentric or metacentric X chromosomes with heterochromatic short arms. Sex-chromosome pairing in these species is initiated during early pachynema at an interstitial position on the X and Y axes. Homologous synapsis then progresses in a unidirectional fashion towards the telomeres of the X short arm and the corresponding arm of the heterochromatic Y chromosome. The distinctive pattern of synaptic initiation allowed a late-synapsing bivalent in fetal oocytes to be tentatively identified as that of the X chromosomes. In contrast to the other species, Peromyscus megalops possesses an acrocentric X chromosome and a very small Y chromosome. Sex-chromosome pairing in this species is initiated at the proximal telomeric region during late zygonema, and then proceeds interstitially towards the distal end of the Y chromosome. These observations suggest that the presence of X short-arm heterochromatin and corresponding Y heterochromatin interferes with late-zygotene alignment of the pairing initiation sites, thereby delaying XY synaptic initiation until early pachynema. The pairing initiation sites are conserved in the vicinity of the X and Y centromeres in Peromyscus, and consequently the addition of heterochromatin during sex-chromosome evolution essentially displaces these sites to an interstitial position.
546665
The genes for eye color determine the amount of melanin, a dark brown pigment, produced in the iris of the eyes. Blue eyes are due to a lack of melanin, while brown eyes indicate melanin-rich irises. Thus, people with darker hair and skin have higher levels of melanin and tend to have brown eyes, while people with lighter hair and skin have lower levels of melanin and usually have lighter colored eyes.
128668
Karyotype\n\n(FISH (Fluorescent In Situ Hybridization) can also be used if visualization of certain regions on specific chromosomes is desired.)
696673
well certain genes on the chromosomes will be transfered to different ones which means the gamits produced in meiosis will have different genes than the parent and it will be a mixed half not a normal half