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Genetics

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Genetics is the scientific study of genes, genetic variation, and heredity.

DNA Overview2
DNA Overview2

This branch of biology is essential because heredity drives the evolution of all living organisms. Scientists study how genes function and behave within a single cell, an entire organism, or a whole population. The field is broad enough to cover all domains of life, including bacteria, archaea, and eukarya. Modern genetics has expanded from simply tracking traits to exploring complex molecular mechanisms. It includes many specialized subfields, such as molecular genetics, epigenetics, population genetics, and paleogenetics.

At its core, inheritance occurs through discrete units called genes.

Punnett square mendel flowers
Punnett square mendel flowers

In the 19th century, many scientists believed in blending inheritance. This was the idea that offspring were a smooth, continuous blend of their parents' traits. However, Gregor Mendel proved that inheritance is actually particulate. He showed that organisms inherit distinct units that do not blend away. These units combine in specific ways to produce offspring. Today, we understand that when traits seem to blend, it is actually the result of multiple genes working together with quantitative effects.

Genes are located on structures called chromosomes within the cell.

Human karyotype with bands and sub-bands
Human karyotype with bands and sub-bands

In 1900, Nettie Stevens discovered that sex is determined by chromosomal factors. She found that females in mealworms had only X chromosomes, while males had both X and Y chromosomes. Later, in 1911, Thomas Hunt Morgan used fruit flies to show that genes are physically located on chromosomes.

Drosophila melanogaster - side (aka)
Drosophila melanogaster - side (aka)

His student, Alfred Sturtevant, further showed that genes are arranged in a linear order along these chromosomes. This discovery provided a physical map for where genetic information resides.

DNA, or deoxyribonucleic acid, is the molecule that carries this genetic information.

DNA chemical structure
DNA chemical structure

In 1953, James Watson and Francis Crick determined that DNA has a double-helix structure. This means it is shaped like a twisted ladder or a corkscrew. They reached this conclusion using X-ray crystallography work from Rosalind Franklin and Maurice Wilkins. The structure consists of two strands with nucleotides pointing inward. These nucleotides match in pairs to form the rungs of the ladder. This specific sequence of nucleotides acts as a code for the organism.

This molecular structure explains how life replicates itself.

DNA Overview2
DNA Overview2

Because the strands are complementary, they can be separated to act as templates. When the strands separate, new partner strands can be built based on the original sequence. This is known as the semi-conservative nature of DNA replication. To control cell behavior, the cell uses DNA as a template to create messenger RNA. This messenger RNA is then used to create a sequence of amino acids. This process of translating nucleotide sequences into proteins is known as the genetic code.

Genetic code
Genetic code

The history of genetics is filled with many key discoveries and figures. Before Mendel, the Hungarian noble Imre Festetics used the word "genetic" in a hereditarian context. In 1819, he published "The genetic laws of nature," where he described rules of biological inheritance. He argued that organisms inherit characteristics rather than acquiring them through experience. In the mid-19th century, Gregor Mendel performed experiments with pea plants in Brno. He used mathematics to describe how traits are handed down. While his work was not widely understood immediately, it was rediscovered in 1900 by scientists like Hugo de Vries. William Bateson later coined the term "genetics" in 1905.

Genetics also explores the relationship between nature and nurture. This concept examines how genetic processes work with an organism's environment to influence development. For example, two genetically identical corn seeds may grow very differently. One seed might be placed in a temperate climate with plenty of water. The other might be placed in an arid climate lacking rain. While their genes determine their potential height, the corn in the arid climate may only grow to half the height of the other. This shows that the intracellular or extracellular environment can change how genes are expressed.

Galton-height-regress
Galton-height-regress
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🖼️ Images & Media (20)
File:Festetics Imre-Oelenhainz.jpg
Festetics Imre-Oelenhainz.jpg
File:Blending Inheritance.svg
Blending Inheritance.svg
File:Sexlinked inheritance white.jpg
Sexlinked inheritance white.jpg
File:DNA Overview2.png
DNA Overview2.png
File:Punnett square mendel flowers.svg
Punnett square mendel flowers.svg
File:Pedigree-chart-example.svg
Pedigree-chart-example.svg
File:Galton-height-regress.png
Galton-height-regress.png
File:DNA chemical structure.svg
DNA chemical structure.svg
File:Human karyotype with bands and sub-bands.png
Human karyotype with bands and sub-bands.png
File:Zellsubstanz-Kern-Kerntheilung.jpg
Zellsubstanz-Kern-Kerntheilung.jpg
File:Morgan crossover 2 cropped.png
Morgan crossover 2 cropped.png
File:Genetic code.svg
Genetic code.svg

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