Genetics

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We're all Homo here Evolution

Relevant Hominids

Charles Darwin Alfred Russel Wallace Gregor Mendel Richard Dawkins Jerry Coyne

A Gradual Science

How come there are still monkeys? Artificial selection Francis Collins Mitochondria

Plain Monkey Business

Young Earth Creationism Old Earth Creationism Intelligent Design Microevolution vs. Macroevolution v - t - e

Not to be confused with genetic fallacy.

Genetics refers to the study of heredity, genes and genetic material. Modern genetics examines how individual genes function and are expressed within the broader context of genomics, which focuses on analyzing the entirety of an organism's genetic material, and how these genetic elements interact with environmental factors to influence traits and disease.

Mendel and his peas

Mendel's famous experiments with peas pointed the way to the information that results in visible traits being binary in nature. It has since been established that the DNA molecules in the nucleus of cells carry this information, on pairs of chromosomes. Of these pairs of chromosomes, in each living creature, one originates from each parent (in the case of sexually reproducing species). This results in a continual mixing of traits present in a species across individuals.

Non-sexual gene transmission

Non-sexually reproducing organisms pass on genetic information to their offspring which is identical to their own, whether through division of single celled organisms like bacteria, or various forms of cloning used by many plants (budding, spreading via root systems, or layering of above-ground stalks that grow new roots and become independent). Many organisms, especially plants, are capable of sexual and asexual reproduction, with some alternating between the two from generation to generation.

Modern fields of study

Genetics has moved far beyond the simple tracking of traits from parent to child, however, from the identification of the DNA molecule by Watson, Crick, and Russell, through the modern sequencing of the human genome and the addition or subtraction of traits from existing species by genetic engineering.

Sequencing

Sequencing is the identification of the exact genetic code in the genome, in order to identify variant alleles, deletions, and insertions.

Next-Generation 'high-throughput' sequencing machines can process large amounts of material, and are used for Whole Gnome Sequencing (WGS), whole exome sequencing (looking at the subset of the entire genome that 'codes' for genes) or other subsets of the genome that the scientists can tailor the 'kit' to match. A common approach uses 'shotgun sequencing', where the strands of DNA are broken up into chunks that are read by the machine in no particular order. Substantial computational effort is then needed to work out where each chunk belongs.

Sanger Sequencing is an older method, less suited to sequencing such large regions, but is considered the 'gold standard'. It is often used where the region of interest is small, such as when validating results obtained from next-Gen sequencing.

In all traditional sequencing methods, the genetic material is a blend of that from a number of cells. Ideally, these cells will be of the same kind and thus be interchangeable. This is not always the case in practice and can play hob with the analysis. In particular, tumour cells can be very different to their neighbors, and those differences can have important consequences for treatment or diagnosis. A very recent development is that of single-cell sequencing, whereby single cells are isolated and sequenced separately. When it works, it provides higher quality analysis, better characterisation of tumours and reduces the need to 'purify' a sample down to a single cell type before sequencing, in cases where multiple cell types are of interest. When it works.

Gene expression

Expression analysis takes a different approach, measuring the number of chunks associated with each particular gene rather than any variants within them. This measures differences in gene regulation between samples. This is generally done to test the difference in regards to two or more different environmental factors. This is your brain on drugs, indeed.

Personality effects

One area of study is how genes can influence people's personality, this is often a study of things like the heritability of temperament traits. This combines psychology with molecular genetics, and neuroscience, so it is a multi-disciplinary approach to understanding how much genes contribute to personality. Nature or nurture is likely missing the point, which is that both nature and nurture play a role in shaping a person's personality. This is necessary because genes interact with the environment given context through a process best described by a complimentary field to genetics, which is epigenetics.

Polymerase chain reaction (PCR)

Brought to you by LSD. Or maybe scientists just have ways to cope with their workload.

PCR is the straightforward process of amplifying a small amount of DNA in vitro, producing many copies. It is a simple extension of the DNA replication process. It involves a pair of primers (usually 20-30 bps in length) flanking the DNA target sequence. This allows a DNA polymerase enzyme to start the process of adding nucleotides (DNA polymerase needs a free 3' end to add nucleotides). The DNA polymerase used is usually Taq polymerase (isolated from the bacterium Thermus aquaticus, found in the hot springs in Yellowstone National Park) as it is heat stable (although there are other heat stable DNA polymerase enzymes available, e.g. Pfu polymerase). The enzyme and primers are added into the reaction vessel, along with deoxynucleotide triphosphates and the template DNA (total reaction volume is usually about 50-100μL). This vessel is placed in a PCR machine, which runs for 30 cycles usually, with each cycle consisting of a denaturation at 94°C (DNA is denatured to allow primers access), annealing at 60°C (primers and free nucleotides hydrogen bond to complementary DNA) and an extension step at 72°C (DNA polymerase starts at the primer then moves along bonding free nucleotides together and forming a complimentary strand of DNA). This technique has had an immense impact on molecular biology, forensic science and the diagnosis of human genetic diseases.

Genetics before science

For thousands of years before the mechanisms were understood, man has been genetically engineering, by selective breeding, food crops and domesticated animals to improve their flavor, yield, hardiness, and behavior.

Evolution

The genes that underlie the passing on of traits are one of the fundamental building blocks of the process of evolution.

See also

• Gene
• Evolution
• Inbreeding
• CRISPR

External links

• genetics.org