List of some agricultural crops and animals with their diploid chromosome number

The chromosome number is among the primary foundation of hybridization in agricultural vegetation in addition to in animals. The diploid numbers of chromosomes are necessarily consistent within the same species. It is a very powerful matter of overview in fundamental plant breeding.
It is the overall rule that a hit crosses are more straightforward to achieve between particular person plants underneath the similar species slightly than between other species underneath the same genus (interspecific pass). Consequently, it is tougher to produce an intergeneric hybrid. In sum, folks which are closely similar taxonomically are much more more straightforward to pass.

However, it’s not the diploid chromosome quantity by myself that determines the ability of 2 folks to readily shape a hybrid. Main determinant is the karyotype, regarding the number, as well as the dimensions and shape of the chromosomes of an individual. Other issues are the kinds of sex chromosomes, lethal genes, and polyploidy.

Listed within the desk underneath are the diploid chromosome numbers of some agricultural crops and quite a lot of animal species. Sources of the information are provided.

Alfalfa Medicago sativa 32 2
Avocado Persea americana 24 4
Barley Hordeum vulgare 14 2,3
Bermudagrass Cynodon dactylon 36 2
Broad bean Vicia faba 12 3
Cashew Anacardium occidentale 42 4
Corn (maize) Zea mays 20 1,3
Cotton, American-Egyptian Gossypium barbadense 52 2
Cotton, upland Gossypium hirsutum 52 2,3
Durian Durio zibethinus 56 4
Flax Linum usitatissimum 30 2
Garden pea Pisum sativum 14 1,3
Grape Vitis vinifera 38 4
Guava Psidium guajava 22 4
Kidney bean Phaseolus vulgaris 22 3
Mango Mangifera indica 40 4
Oats, white Avena sativa 42 2
Oats, red Avena byzantina 42 2
Onion Allium cepa 16 3
Papaya Carica papaya 18 4
Peanut Arachis hypogaea 40 2
Pineapple Ananas comosus 50 4
Potato Solanum tuberosum 48 2,3
Rice Oryza sativa 24 2,3
Rye Secale cereale 14 2
Sorghum Sorghum vulgare 20 2
Soybean Glycine max 40 2
Squash Cucurbita pepo 40 3
Sugar beet Beta vulgaris 18 2
Sugar cane Saccharum officinarum 80 2
Tamarind Tamarindus indica 24 4
Tobacco Nicotiana tabacum 48 2,3
Tomato Lycopersicon esculentum 24 3
Wheat, durum Triticum durum 28 2
Wheat, common Triticum vulgare 42 2
Wheat, club Triticum compactum 42 2
Man Homo sapiens 46 1,3
Cat Felix domesticus 38 3
Cattle Bos taurus 60 3
Chicken Gallus domesticus 78 1
Dog Canis familiaris 78 3
Donkey Equus asinus 62 3
Frog Rana pipiens 26 3
Fruit fly Drosophila melanogaster 8 1,3
Grasshopper Melanoplus differentialis 24 3
Honeybee Apis mellifera 32 3
Horse Equus calibus 64 3
House fly Musca domestica 12 1,3
Mosquito Culex pipiens 6 3
Rabbit Oryctolagus cuniculus 44 3
Red ant Formica sanguinea 48 3
Rhesus monkey Macaca mulatta 42 3

1HARTL DL, FREIFELDER D, SNYDER LA. 1988. Basic Genetics. Boston, MA: Jones and Bartlett Publishers. 505 p.

2POEHLMAN JM. 1977. Breeding Field Crops. Connecticut: AVI Publishing Co., Inc. 427 p.

3STRICKBERGER MW. 1976. Genetics. 2nd ed. New York, NY: Macmillan Publishing Co., Inc. 914 p.

4VERHEIJ EWM, CORONEL RE (eds.). 1992. Plant Resources of South-East Asia No.2: Edible Fruits and Nuts. Bogor, Indonesia: Prosea Foundation. 447 p.

(Ben G. Bareja, Dec. 4, 2013) 

Gene Transfer Technology for Mushrooms: The Power and Potential for Significant Crop Improvement

Birth of Recombinant DNA Technology

In the early 1970’s, California scientists first succeeded at splicing viral and bacterial DNAs within the take a look at tube, heralding the beginning of the recombinant DNA (rDNA) generation, popularly known as genetic engineering, gene switch generation, gene splicing, molecular biotechnology, and transgenics. This new biotechnology discovered instant utility within the manufacturing of pharmaceuticals, where synthesis by way of rDNA microbes equipped a quantum jump in efficiency over the exhausting extraction of miniscule amounts from different assets. Early on it was stated that “the uses of biotechnology are only limited by the human imagination.” Today we are witnessing how this broad-based science is impacting just about each sector of our society.

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It was once right through the 1980’s when the facility and possible of the burgeoning discipline of genetic engineering was first brought to endure at the growth of agricultural productivity. The discovery of tactics to transfer genes to the major agronomic plants, together with corn, soybean, and wheat, from unrelated species provided breeders with new vistas for expanding the potency of food crop production. Remarkable development, a long way exceeding early predictions, has been made throughout the closing two decades in breeding crops with new traits comparable to insect, viral, and fungal resistance, herbicide, stress, and chilly tolerance, behind schedule senescence, advanced nutritional options, and others. The international call for for transgenic vegetation is projected to be a $25 billion market by the 12 months 2010. The growth of this business will be propelled, partially, by “Golden” rice, which was once engineered the usage of a daffodil gene to be wealthy in beta carotene and thereby the promising solution to the diet A deficiency drawback pervading the creating world.

Despite concern for the unforeseeable health and environmental dangers posed via genetically-modified (GM) plants, gene transfer generation has irreversibly revolutionized plant breeding. Today, more than 100 plant species had been changed by means of gene splicing for stepped forward assets of food, fiber, or ornamentation. More than 50 new crop types have cleared all federal regulatory requirements and stand authorized for commercial retail. Because field testing is an essential step within the commercialization process, the number of lets in issued by means of the U. S. Department of Agriculture, Animal and Plant Health and Inspection Service (APHIS) for GM vegetation provides a measure of the hobby in transgenic breeding. During a 16-year duration, more than eight,000 allows and notifications (fast-track allows) were issued, rising from a low of 9 in 1987 to a prime of one,120 in 2001 (Fig. 1). For the primary three months of 2002, 536 lets in/notifications were recorded through APHIS with 49% involving insect resistance, 33% herbicide tolerance, 7% every for product high quality and agronomic properties, and with the stability comprising fungal and viral resistance and different characteristics. Thus, the “genie out of the bottle” situation describes the standing of agricultural genetic engineering. Despite the anti-GM sentiment expressed through a vocal minority, the efficiency of the new biotechnology for downside solving has been realized to an extent this is a ways too compelling for it to be dismissed.

Genetically Engineering the Button Mushroom
For virtually as long as scientists were introducing genes into crop plants the use of molecular biotechnology, others have tried with limited success at creating a gene transfer means for Agaricus bisporus. a Big leap forward got here in 1995 with the sudden discovery that the bacterial workhorse, Agrobacterium tumefaciens, used to trip genes into vegetation, also operated with yeast fungi. Shortly thereafter, this system used to be prolonged to filamentous fungi, together with A. bisporus.

Agrobacterium is a not unusual soil bacterium with a world distribution. It causes a illness referred to as crown gall on hundreds of woody and herbaceous plant species, however maximum often pome and stone end result, brambles, and grapes. In its commonplace existence cycle, the bacterium transfers a tiny little bit of its DNA into the plant DNA resulting in the formation of galls. These galls serve as food factories for the mass manufacturing of the bacterium. Over the years, scientists learned increase disarmed strains of the bacterium that were incapable of inducing galls, but retained the facility to switch DNA. In essence, a natural biological process was once harnessed to create a bacterial delivery gadget for transferring genes into plants, and now fungi.

Figure 1. Total number of permits and notification

Though Agrobacterium used to be shown to be highly promiscuous in shuttling genes into a spectrum of plant and fungal species, the method was once still too inefficient to be carried out to the breeding of A. bisporus. More not too long ago, we devised a handy and efficient Agrobacterium-mediated ‘fruiting body’ gene transfer means conserving the promise of a formidable software for the genetic growth of the mushroom. In our experiments, a small ring of DNA wearing a gene for resistance to the antibiotic, hygromycin, was once transferred to a disarmed pressure of the Agrobacterium. The antibiotic resistance gene is known as a selectable marker, as a result of mushroom cells receiving this gene from the bacterium grow to be marked by the resistance trait and will also be decided on based on the facility to grow on a hygromycin-amended medium. The finish result is a mushroom pressure having the newly received function of hygromycin resistance. Such a strain has little business price, but somewhat the resistance trait was once a research tool that allowed us to easily resolve if the bacterium had transferred the gene to the mushroom, and exactly how successfully it did so beneath different experimental conditions. Today, and more so in the future, this gene is being replaced or complemented by means of genes that can confer commercially relevant characteristics.

Figure 2 Steps in the Agrobacterium

Figure 2 highlights the steps in the ‘fruiting body’ gene switch approach. In this procedure, gill tissue is taken from mushrooms approaching adulthood, however with the veil intact, with the intention to be sure that some degree of sterility. Next, the tissue is minimize into small pieces and vacuum-infiltrated with a suspension of Agrobacterium wearing the antibiotic resistance gene. In a process known as co-cultivation, the gill tissue and bacterium are grown in combination in the laboratory for several days, all over which time the bacterium transfers the resistance gene to the mushroom DNA. Because no longer all mushroom cells receive a replica of the gene, those who have can also be prominent from those who have not via the facility to grow at the antibiotic medium. After 7 days at the medium, mycelium of A. bisporus appears rising on the edges of probably the most gill tissue items. After 28 days, upwards of 95% of the tissue pieces may have regenerated into visual cultures. At this point, the GM cultures may also be transferred to a normal growth medium, and used to prepare grain spawn in the unusual method.

Agrobacterium is a not unusual soil bacterium with a global distribution. It reasons a illness referred to as crown gall on hundreds of woody and herbaceous plant species, however maximum regularly pome and stone end result, brambles, and grapes. In its standard existence cycle, the bacterium transfers a tiny little bit of its DNA into the plant DNA resulting within the formation of galls. These galls serve as food factories for the mass manufacturing of the bacterium. Over the years, scientists learned how you can increase disarmed strains of the bacterium that had been incapable of inducing galls, however retained the facility to switch DNA. In essence, a herbal organic process used to be harnessed to create a bacterial supply machine for moving genes into crops, and now fungi.

Though Agrobacterium used to be proven to be highly promiscuous in shuttling genes into a spectrum of plant and fungal species, the method was once nonetheless too inefficient to be carried out to the breeding of A. bisporus. More just lately, we devised a handy and efficient Agrobacterium-mediated ‘fruiting body’ gene switch way protecting the promise of a powerful device for the genetic development of the mushroom. In our experiments, a small ring of DNA sporting a gene for resistance to the antibiotic, hygromycin, used to be transferred to a disarmed strain of the Agrobacterium. The antibiotic resistance gene is referred to as a selectable marker, because mushroom cells receiving this gene from the bacterium become marked by the resistance trait and can also be selected in line with the facility to grow on a hygromycin-amended medium. The finish result is a mushroom pressure having the newly got function of hygromycin resistance. Such a strain has little business worth, but somewhat the resistance trait was once a research tool that allowed us to simply decide if the bacterium had transferred the gene to the mushroom, and precisely how successfully it did so below different experimental conditions. Today, and more so at some point, this gene is being changed or complemented by way of genes that may confer commercially related characteristics.

Figure 3 Production trail with Six GM Line

Figure 3 depicts the first of 2 cropping trials carried out at the Penn State Mushroom Research Center involving GM mushroom lines. In these trials, all six antibiotic-resistant GM strains reflected the parental business hybrid strain in colonizing the compost and casing layer. Further, the GM strains produced mushrooms having an ordinary appearance and, in some instances, yielded on a par with the economic strain (Table 1). Expression of the resistance trait within the mushrooms could be easily demonstrated via placing pieces of the cap or stem tissue at the antibiotic medium and staring at for enlargement (Figure four). These experiments had been an important, since the effects established for the primary time that a international gene could be offered into A. bisporus with no need a adverse effect on its vegetative and reproductive traits.

Table 1. Productivity of genetically-modified (GM) mushroom traces expressing the antibiotic resistance gene that were derived from a business off-white hybrid pressure.
Yield (lbs./sq. feet.)

Yield (lbs./sq. ft.)
LineTrial ITrial II
Commercial hybrid3.00 a3.68 a
GM-12.08 d0.86 d
GM-21.73 d1.45 d
GM-32.52 bc2.70 c
GM-42.12 cd2.99 bc
GM-52.90 a3.63 a
GM-62.86 ab3.59 a

Means within a column having the same letter are not significantly different according to the Waller-Duncan K-ratio t test at P<0.0001

Impact of Transgenic Breeding on Mushroom Cultivation
The overwhelming approval for the hybrid mushroom strains introduced within the 1980’s has created a close to global monoculture that is precarious from the viewpoint of disease and pest susceptibility, and has limited the selection of production traits and the variety of tolerance to environmental and cultural stresses. During the remaining 20 years, no notable advances have been made in breeding strains with strikingly advanced features. This is due in large part to the cumbersome genetics of A. bisporus and a shortage of commercially fascinating traits. There is movement afoot in the usage of conventional breeding to explore wild isolates of A. bisporus as a supply of new characteristics. Though this represents an important step against increasing the genetic base of cultivated A. bisporus, it isn’t but transparent which traits exist within the wild germplasm collection, and if they are able to be successfully bred into commercial lines.

The introduction of a facile gene transfer methodology for A. bisporus permits the exploration of genetic solutions to problems confronting the mushroom trade in a realm by no means sooner than imagined. The awesome energy of transgenics lies in what is known as the universality of the genetic code. The biochemical alphabet consisting of the letters G, A, T, and C that spells the DNA sequences of genes controlling characteristics is the same for all organisms. A scientist blindly handed a gene would have difficulty determining if its source was once a mushroom, mouse, or guy. It is that this unifying feature of genes from all walks of existence that makes transgenics so potentially robust, while it is the tools of molecular biology that unleashes this power so this doable will also be discovered. Simply said, the brand new biotechnology permits the trade of genetic data between organisms outdoor the confines of the herbal breeding barrier. No longer is the genetic improvement of the mushroom made up our minds by the query of sexual compatibility or characteristics found throughout the species.
At every other stage, gene transfer generation will hugely boost up our figuring out of the molecular mechanisms underlying commercially relevant characteristics. It additionally will serve to make stronger the muscle of our industry’s medical arm, rising from a handful of mushroom researchers to the global group of workers of molecular biologists. As one hypothetical representation, the search to reproduce tough resistance to dry bubble illness would now not be restricted to a couple of scientists looking inside A. bisporus, the place it is going to or now not exist. Instead, it would extend to ratings of scientists operating on unrelated organisms who have came upon resistance genes to other Verticillium species. Importing these genes to the mushroom for an analysis in opposition to dry bubble is now possible. As farfetched as this will likely appear, it is precisely this trans-species method that has met with business success. Genetic manipulations of this sort have been performed on crop crops and come with, importing cry genes from the Bacillus thuringiensis bacterium for insect resistance, a synthetase gene from Agrobacterium for glyphosate herbicide resistance, the nitrilase gene from the Klebsiella pneumoniae bacterium for bromoxymil herbicide resistance, a hydrolase gene from the Escherichia coli bacterium for changed fruit ripening, the barnase gene from Bacillus spp. for male sterility, and viral genes for virus illness resistance.

It cannot be overstated that gene switch technology is not a panacea whose arrival marks the departure of traditional breeding. Quite the contrary, this can be a new instrument at the disposal of the breeder that will supplement current techniques, while providing a far broader vary of options for effectively affecting genetic solutions to issues. Gene splicing will expedite the breeding process, transferring a lot of the time in development from the sphere to the laboratory. It will enable the introduction of genes with a surgical precision and from exotic sources, which another way would be unattainable through extra typical strategies. It is essential to recognize, alternatively, that after all, the forces of nature overcoming a trait (e.g., the breakdown of insect resistance) would act with the same depth at the controlling gene whether introduced by means of traditional or transgenic breeding.

The melding of gene transfer strategies with traditional techniques in a mushroom breeding program might take several paperwork initially, most effective to be continually subtle, streamlined, and stepped forward for higher efficiency and bigger effectiveness.

Many transgenic manipulations with A. bisporus will require the switch of the gene to both parental traces so that their offspring mimic the herbal inheritance process through carrying a duplicate replica of the gene. For different packages, introducing a single reproduction of the gene might succeed in the desired effect. In both case, the ensuing GM strains would possibly require additional variety ahead of emerging as worthy industrial traces

How to Run a Profitable Wholesale Cut Flower Farm

Edited by Krystle, BR, IngeborgK, Netstars22

You might enjoy the idea of spending your days in a greenhouse full of beautiful looking, wonderful smelling flowers, but if you want to make a living at it, you need to be a good business person, too. Here’s how to run an operation that will let you smell the roses (or zinnias…or chrysanthemums…) and make money at the same time.

StepsHow to Run a Profitable Wholesale Cut Flower Farm


Write a detailed business plan and have it reviewed by at least two other successful growers.


Be willing to grow anything that there’s a market for. In the U.S., avoid “commodity crops” like roses, carnations and chrysanthemums, which are grown outside of the country in places with labor and production costs are too low to compete with.


Find a void and fill it. The key is to find a niche market. One example is flowers that don’t ship well (e.g. zinnias, snapdragons) because then you won’t compete with wholesalers who bring in flowers from all over the world. Another example is growing dahlias in greenhouses during the winter, as you may be the only one providing it at that time. Vicki Stamback, a successful cut flower business owner in Oklahoma, recommends: “The harder a flower is to grow, the more money-making potential it has…If you really want to make a name for yourself in the market, do something no one else is doing.”


Build a customer base.

  • Look through the phone directory to see which florists have the biggest ads. Ask them what they have the hardest time getting at a good price.
  • Farmers’ markets are a possibility if the clientele are supportive of local farmers, but not if they attract bargain-basement shoppers.


Know the production cost of every flower that leaves your farm. You will need to have several heated greenhouses and in order to turn a net profit, you need to know exactly how much it’s costing you and how the flowers you sell are going to cover that and then some.


Set your prices. How much do you need per square foot to break even? You should be generating at least twice that. Don’t bother trying to undercut the wholesale prices; instead focus on providing a better product. Consult a publication like the USDA Wholesale Cut Flower Price Reports for reference.


Put a face to the business. To set yourself apart from the wholesalers, develop strong relationships with your customers. The key to that is consistency. Many florists might be skeptical because local growers tend to come and go. Make your deliveries reliably, get a good reputation, and your business will grow through word of mouth.

  • Be willing to make emergency trips on the weekends, but only if they buy enough to make it worthwhile.
  • Return phone calls right away.
  • Drop customers who don’t pay or who don’t buy enough.


Hire employees. You will need more employees during peak season than in winter. Don’t try to do it all alone; if you want the business to be profitable, you need to be reliable, and in order to be reliable, you need help.


Use crop rotation, cover crops and compost to build fertility and break the cycles of pests, diseases and weeds. Use organic methods if you can, but you may decide to use chemical treatment if an issue threatens to ruin an entire crop.


  • If you hire employees to make deliveries, be sure to rotate so that you still get to see the customers on a regular basis. It’s also a good idea to go on deliveries with the new driver for several weeks so that customers feel comfortable with him or her.
  • Expect to get paid every time you deliver. If a customer wants to pay every thirty days, do so only after they’ve paid reliably upon delivery for three months.


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Interesting facts about genetics

The Basics

  • Nucleotides are the alphabet of DNA. There are only four “letters” in DNA : adenine (A), thymine (T), guanine (G) and cytosine (C). They always go by pairs, A with T, and G with C. Such pairs are called “base pairs”.
  • Almost every cell in our body contains a complete copy of our genome. The exceptions are egg/sperm cells, which only carry half of our genome, as well as red blood cells and some white blood cells, which have no DNA at all (otherwise blood transfusions would often cause an immune reaction, like organ transplants).
  • If unfolded the DNA in each cell’s nucleus would be 2 metres long. Humans have an estimated 100 trillion cells. In other words, if the all the DNA from every cell in a person’s body were patched up together they would form a strand of 200 billion kilometres, or more than 1,000 times the distance between Earth and the Sun.
  • Mitochondrial DNA is found outside the cell’s nucleus, and therefore outside of the chromosomes. It consists of only 16,569 base pairs.
  • A SNP (single nucleotide polymorphism) is a mutation in a single base pair. Depending on what section of DNA is affected these mutations can have no effect at all (it is usually the case for SNP’s defining Y-DNA and mtDNA haplogroups), a change in physical appearance (e.g. eye colour), an improvement of health (e.g. increased immunity), a increased susceptibility to a disease (e.g. diabetes), or a genetic disease (e.g. cystic fibrosis).

    The Chromosomes

    • A human genome is made of 3,000 million base pairs, split into 46 chromosomes.
    • There are in fact 23 pairs of chromosomes, each person inheriting a maternal and paternal copy of each. Pairs of chromosomes are numbered from the largest (chromosome 1) to the smallest (chromosome 21). Chromosome 22 ought to be the smallest, but it was later discovered than chromosome 21 was smaller, and the established ordered was kept.
    • The sex-determining chromosomes (X and Y) are the only pair that is not symmetrical in size. The Y-chromosome possess 60 millions bases, against 153 millions for the X chromosome.
    • The reason why the Y chromosome is so much smaller than the X chromosome is that the latter possess genes that attack the Y chromosome. In response the Y chromosome has had to shut down a lot of its non-coding DNA so as to better protect itself.
    • In some rare cases people are born with one extra chromosome. Those born with three chromosome 21 have Down’s syndrome. Other possibilities is an extra X chromosome, leading to Klinefelter’s syndrome (XXY), XYY syndrome, Triple X syndrome, XXYY syndrome, 48, XXXX, or 49, XXXXX. An extra copy of any other chromosome normally results in miscarriages. Some very rare cases of autosomal trisomies can survive to birth, notably when it affects chromosomes 13 or 18, but result in seriously shortened life expectancy.
    • Humans, like most animals, are diploid, meaning that they have only two sets of chromosomes. However that is not the case of all life beings. Plants in particular are often polyploid. There are varieties of wheat that are tetraploid (four sets of chromosomes) and others that are hexaploid (six sets of chromosomes). Some strawberries can be decaploid (ten sets of chromosomes). Polyploid animals include the goldfish, salmons, and salamanders. Polyploidy occurs in some human tissues like muscles or the liver. When two or three spermatozoids fertilise an ovum at the same time, a human foetus will be triploid or tetraploid. However almost all such pregnancies end as miscarriage and those that do survive to term typically die shortly after birth.

    The Human Genome

    • The first complete human genome was only decoded in 2007. The two first individuals who got their full genome sequenced that year were Craig Venter and James D. Watson.
    • A human genome is identical at 98% to a chimpanzee’s genome. In comparison, two random human beings are in average 99.5% identical. Gorillas are 97% identical to either humans or chimps, meaning that humans are more chimp-like than gorillas.
    • Most of our genome is made of junk DNA. This junk is composed either of deactivated genes that were once useful for our non-human ancestors (like a tail), or parasitic DNA from virus that have entered our genome and replicated themselves hundreds or thousands of times over the generations, but serve no purpose. Genome size is therefore not related to the complexity of life. For example, the genome of the unicellular Amoeba dubia has been reported to contain more than 200 times the amount of DNA in humans.


    • Although autosomal DNA is inherited equally from each parent, a few genetic diseases seem to be worse when inherited from one’s father (e.g. Huntingdon’s disease), because mutations occur or repeat themselves at a higher rate in men, and increase with the father’s age. This is also why older fathers (over 40 years old) have higher chances of having children suffering from schizophrenia, depression or autism.
    • Some genes have different functions depending on whether they are inherited from one’s father or mother. These are called imprimted genes. For example, the maternal copy of a gene on chromosome 15 is known as UBE3A, while the paternal copy is SNRPN. Inheriting two paternal copies or missing the maternal copy causes Prader-Willi syndrome, whereas two maternal copies or a deletion of the paternal copy leads to the very different Angelman syndrome.
    • Rather than inheriting a homosexual gene, gay men tend to have several older brothers (including abortions and miscarriages). The reason is that the mother’s body accumulates antibodies against genes responsible for the masculinisation of the foetus’ brain at each pregnancy with a boy. The risk of male homosexuality therefore increases with the number of boy carried by a mother before. This does not apply to girls.


    • Neurotransmitters such as serotonin, dopamine, adrenaline and noradrenaline influence our mood and personality. Their levels is influenced by our environment, but the sensitivity of the brain to these neurotransmitters is genetically determined.
    • Low serotonin levels increase depression, anxiety, risk of suicide and violence. Carbohydrates and cholesterol both increase serotinin levels.
    • Excessive dopamine can lead to schizophrenia. Too low dopamine levels engender boredom and low activity, and in extreme cases Parkinson Disease. The long variants (7-repeat or more) of the dopamine receptor D4 (DRD4) causes dopamine to be consumed more quickly by the brain. People with this variant will usually have more novelty-seeking, thrill-seeking and adventurous personality than average to compensate for naturally lower dopamine levels.


    • Some people possess a deletion on the CCR5 gene, which makes them more resistant to smallpox, HIV, plague and other viruses (e.g. West Nile virus). This mutation is commonest in North-East Europe.
    • The ABO blood type is related to cholera resitance, with AB confering the strongest resistance, and O the weakest. On the other hand, the O blood group seems to be the most resistant against malaria and syphilis, and less susceptible to many kinds of cancers.
    • Many genetic diseases survived natural selection because they confer immunity against epidemic diseases. For instance, the CFTR mutation causing cystic fibrosis protects against the dysentry and fever of typhoid. Sickle-cell anaemia and thalassaemia are both protective against malaria. Genetic resistance to TB has for side-effect an increased susceptibility for osteoporosis. Tay-Sachs disease, mostly found among people of Ashkenazi Jewish ancestry, is also protective against TB.
    • Studies have shown that men and women are most attracted to the smell of people with the most different immune system from their own. This is also a way of Nature to prevent inbreeding. Differences in immune systems can be identified by comparing our HLA types, among other genes of the major histocompatibility complex (MHC).


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