More by JV Chamary<\/h4>\n- Photosynthesis: what it is, how it works and why it fuels life on earth<\/a><\/strong><\/li>\n
- Endosymbiosis guide: what it is and why complex life needs endosymbiosis<\/a><\/strong><\/li>\n
- Torpor: what it is, why it\u2019s important and how torpor differs to hibernation and sleep<\/a><\/strong><\/li>\n
- Speciation: what a species is, and how new species form<\/a><\/strong><\/li>\n<\/ul>
<\/p><\/div> <\/section>
What is a genotype?<\/h2>\n
The genotype is the combination of genes that produces a particular phenotype. When an individual inherits one copy of a gene from its mother and one from its father, those two copies are either distinct genetic variants (alleles) or the same.<\/p>\n
Two variants will differ in their DNA sequence, but the distinction between them is traditionally represented by capital and lowercase versions of a letter.<\/p>\n
![\"""\"]( "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div> Gregor Johann Mendel, 1822 -1884. Illustration by Gordon Ross, American artist and illustrator 1873-1946, from Living Biographies of Great Scientists. \u00a9 Universal History Archive\/Universal Images Group\/Getty<\/em><\/span><\/figcaption><\/div>\nA classic example comes from Gregor Mendel \u2013 a 19th-century monk and father of genetics \u2013 who studied flower colour as part of his breeding experiments in pea plants. From a single gene with two variants, \u2018A\u2019 and \u2018a\u2019, a copy from each parent gives four possible genotypes: AA, Aa, aA, aa.<\/p>\n
By crossing two pure-bred parents \u2013 one with white flowers, the other purple \u2013 Mendel showed that offspring had purple flowers if they carried the dominant \u2018A\u2019 variant of a gene, but had to inherit both copies as the \u2018a\u2019 (recessive) variant to end-up with the white phenotype. That study inspired the concept of \u2018dominance\u2019, one of Mendel\u2019s laws of inheritance.<\/p>\n
A Punnett square (see below<\/em>) is a good way to illustrate this interaction between the variants (alleles).\u00a0 This diagram was devised by Reginald C. Punnett in 1905, and named after him. In the pea example below, two variants are used and create a two-by-two square with the results, however it is possible to add more in variants which increases the size of the square and adds in more possible results.<\/p>\n ![\"""\"]( "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div> A Punnett square showing the dominance effect in peas. \u00a9 Madeleine Price Ball via Wikimedia<\/a>, under CC0<\/em><\/span><\/figcaption><\/div>\nDoes the genotype determine the phenotype?<\/h2>\n
Sometimes, but be wary of \u2018genetic determinism\u2019! That\u2019s the belief that traits are caused by genetics alone. It\u2019s important to note that many phenotypes aren\u2019t simply \u2018monogenic\u2019 traits dictated by a single gene, as phenotypes can also be \u2018polygenic\u2019 traits that depend on multiple genes.<\/p>\n
Saying that genes determine traits is a convenient shorthand, and one genotype can actually produce a variety of different phenotypes.<\/p>\n Learn more about genetics and evolution:<\/h4>\n- What are chromosomes and why are chromosomes important?<\/a><\/li>\n
- Parthenogenesis: a guide to how virgin births occur and which species reproduce this way<\/a><\/li>\n
- Speciation: what a species is, and how new species form<\/a><\/li>\n
- News (2022): New study reveals how cancer-busting gene in elephants works<\/a><\/li>\n<\/ul>
<\/p><\/div> <\/section>
Why might a phenotype not reflect its genotype?<\/h2>\n
Because the link between them can be influenced by environmental factors, such as a habitat\u2019s resources or how an individual is raised. If you\u2019re not careful, that idea can lead you to believe that traits are determined by either genes or the environment \u2013 nature or nurture, which is another common misconception.<\/p>\n
Variation in phenotypes exist because genes aren\u2019t isolated from other factors that cause \u2018gene-by-environment\u2019 interactions. Think of twins with identical genotypes for the potential to grow muscle: only the one who lifts weights ends up with a muscular body. So a phenotype is the result of nature via nurture.<\/p>\n
How do phenotypes affect evolution?<\/h2>\n
A genotype is often invisible to natural selection because variants are hidden behind environmental factors or a genetic phenomenon like dominance.<\/p>\n
That means \u2018survival of the fittest\u2019 actually occurs between individuals according to their visible phenotype. Because only survivors pass genes to the next generation, an organism\u2019s genotype survives by being dragged along with its phenotype.<\/p>\n
That effect explains why harmful genetic variants (\u2018bad mutations\u2019) can persist in a population\u2019s gene pool over time. For example, with sickle-cell anaemia, people who inherit two copies of a defective gene have abnormal haemoglobin and short-lived, crescent-shaped red blood cells.<\/p>\n
![\"""\"]( "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div> Conceptual image of sickle cell anemia with red blood cells and white blood cells. \u00a9 Stocktrek Images\/Getty<\/em><\/span><\/figcaption><\/div>\nCarrying just one copy causes \u2018sickle-cell trait\u2019, where a person will carry the abnormal variant (and may pass it on to their children), yet won\u2019t suffer from disease.<\/p>\n
Although affected individuals are less likely to survive and reproduce, the variant survives in places where malaria is endemic because the parasite is less able to infect people with sickle-cell phenotypes.<\/p>\n
\u00a0<\/p>
What is the \u2018extended phenotype\u2019?<\/h2>\n
It\u2019s a concept proposed by the evolutionary biologist and author Richard Dawkins, who argued that a gene\u2019s effect can extend beyond the body to produce phenotypes in an organism\u2019s surroundings.<\/p>\n
<\/p><\/div> <\/section>
What is a genotype?<\/h2>\n
The genotype is the combination of genes that produces a particular phenotype. When an individual inherits one copy of a gene from its mother and one from its father, those two copies are either distinct genetic variants (alleles) or the same.<\/p>\n
Two variants will differ in their DNA sequence, but the distinction between them is traditionally represented by capital and lowercase versions of a letter.<\/p>\n
![\"""\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/23\/2022\/11\/Gregor-Mendel.-GettyImages-1062152946-8e4f06c.jpg?quality=90&resize=296%2C413"\" "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>A classic example comes from Gregor Mendel \u2013 a 19th-century monk and father of genetics \u2013 who studied flower colour as part of his breeding experiments in pea plants. From a single gene with two variants, \u2018A\u2019 and \u2018a\u2019, a copy from each parent gives four possible genotypes: AA, Aa, aA, aa.<\/p>\n
By crossing two pure-bred parents \u2013 one with white flowers, the other purple \u2013 Mendel showed that offspring had purple flowers if they carried the dominant \u2018A\u2019 variant of a gene, but had to inherit both copies as the \u2018a\u2019 (recessive) variant to end-up with the white phenotype. That study inspired the concept of \u2018dominance\u2019, one of Mendel\u2019s laws of inheritance.<\/p>\n
A Punnett square (see below<\/em>) is a good way to illustrate this interaction between the variants (alleles).\u00a0 This diagram was devised by Reginald C. Punnett in 1905, and named after him. In the pea example below, two variants are used and create a two-by-two square with the results, however it is possible to add more in variants which increases the size of the square and adds in more possible results.<\/p>\n Sometimes, but be wary of \u2018genetic determinism\u2019! That\u2019s the belief that traits are caused by genetics alone. It\u2019s important to note that many phenotypes aren\u2019t simply \u2018monogenic\u2019 traits dictated by a single gene, as phenotypes can also be \u2018polygenic\u2019 traits that depend on multiple genes.<\/p>\n Saying that genes determine traits is a convenient shorthand, and one genotype can actually produce a variety of different phenotypes.<\/p>\n <\/p><\/div> <\/section> Because the link between them can be influenced by environmental factors, such as a habitat\u2019s resources or how an individual is raised. If you\u2019re not careful, that idea can lead you to believe that traits are determined by either genes or the environment \u2013 nature or nurture, which is another common misconception.<\/p>\n Variation in phenotypes exist because genes aren\u2019t isolated from other factors that cause \u2018gene-by-environment\u2019 interactions. Think of twins with identical genotypes for the potential to grow muscle: only the one who lifts weights ends up with a muscular body. So a phenotype is the result of nature via nurture.<\/p>\n A genotype is often invisible to natural selection because variants are hidden behind environmental factors or a genetic phenomenon like dominance.<\/p>\n That means \u2018survival of the fittest\u2019 actually occurs between individuals according to their visible phenotype. Because only survivors pass genes to the next generation, an organism\u2019s genotype survives by being dragged along with its phenotype.<\/p>\n That effect explains why harmful genetic variants (\u2018bad mutations\u2019) can persist in a population\u2019s gene pool over time. For example, with sickle-cell anaemia, people who inherit two copies of a defective gene have abnormal haemoglobin and short-lived, crescent-shaped red blood cells.<\/p>\n Carrying just one copy causes \u2018sickle-cell trait\u2019, where a person will carry the abnormal variant (and may pass it on to their children), yet won\u2019t suffer from disease.<\/p>\n Although affected individuals are less likely to survive and reproduce, the variant survives in places where malaria is endemic because the parasite is less able to infect people with sickle-cell phenotypes.<\/p>\n \u00a0<\/p> It\u2019s a concept proposed by the evolutionary biologist and author Richard Dawkins, who argued that a gene\u2019s effect can extend beyond the body to produce phenotypes in an organism\u2019s surroundings.<\/p>\n![\"""\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/23\/2022\/11\/Mendel-flowers-punnet-square.-Madeleine-Price-Ball-3dceb67.jpg?quality=90&resize=413%2C413"\" "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>Does the genotype determine the phenotype?<\/h2>\n
Learn more about genetics and evolution:<\/h4>\n
Why might a phenotype not reflect its genotype?<\/h2>\n
How do phenotypes affect evolution?<\/h2>\n
![\"""\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/23\/2022\/11\/Sickle-cell-anaemia.-GettyImages-188058278-5076fa4.jpg?quality=90&crop=14px%2C0px%2C1972px%2C1314px&resize=620%2C413"\" "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>What is the \u2018extended phenotype\u2019?<\/h2>\n
![\"""\"](\""https:\/\/images.immediate.co.uk\/production\/volatile\/sites\/23\/2021\/11\/GettyImages-1313270276-65bf514.jpg?quality=90&resize=620%2C413"\" "\\"\"\"\\"\/")
<\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/source><\/picture><\/div>