A report on Heredity

Heredity of phenotypic traits: a father and son with prominent ears and crowns
DNA structure. Bases are in the centre, surrounded by phosphate–sugar chains in a double helix.
Aristotle's model of inheritance. The heat/cold part is largely symmetrical, though influenced on the father's side by other factors; but the form part is not.
Table showing how the genes exchange according to segregation or independent assortment during meiosis and how this translates into Mendel's laws
An example pedigree chart of an autosomal dominant disorder.
An example pedigree chart of an autosomal recessive disorder.
An example pedigree chart of a sex-linked disorder (the gene is on the X chromosome)
Hereditary defects in enzymes are generally inherited in an autosomal fashion because there are more non-X chromosomes than X-chromosomes, and a recessive fashion because the enzymes from the unaffected genes are generally sufficient to prevent symptoms in carriers.
On the other hand, hereditary defects in structural proteins (such as osteogenesis imperfecta, Marfan's syndrome and many Ehlers–Danlos syndromes) are generally autosomal dominant, because it is enough that some components are defective to make the whole structure dysfunctional. This is a dominant-negative process, wherein a mutated gene product adversely affects the non-mutated gene product within the same cell.

Passing on of traits from parents to their offspring; either through asexual reproduction or sexual reproduction, the offspring cells or organisms acquire the genetic information of their parents.

- Heredity
Heredity of phenotypic traits: a father and son with prominent ears and crowns

24 related topics with Alpha

Overall

Blending inheritance leads to the averaging out of every characteristic, which as the engineer Fleeming Jenkin pointed out, makes evolution by natural selection impossible.

Genetics

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Blending inheritance leads to the averaging out of every characteristic, which as the engineer Fleeming Jenkin pointed out, makes evolution by natural selection impossible.
Morgan's observation of sex-linked inheritance of a mutation causing white eyes in Drosophila led him to the hypothesis that genes are located upon chromosomes.
DNA, the molecular basis for biological inheritance. Each strand of DNA is a chain of nucleotides, matching each other in the center to form what look like rungs on a twisted ladder.
A Punnett square depicting a cross between two pea plants heterozygous for purple (B) and white (b) blossoms.
Genetic pedigree charts help track the inheritance patterns of traits.
Human height is a trait with complex genetic causes. Francis Galton's data from 1889 shows the relationship between offspring height as a function of mean parent height.
The molecular structure of DNA. Bases pair through the arrangement of hydrogen bonding between the strands.
DNA sequence
Walther Flemming's 1882 diagram of eukaryotic cell division. Chromosomes are copied, condensed, and organized. Then, as the cell divides, chromosome copies separate into the daughter cells.
Thomas Hunt Morgan's 1916 illustration of a double crossover between chromosomes.
The genetic code: Using a triplet code, DNA, through a messenger RNA intermediary, specifies a protein.
Siamese cats have a temperature-sensitive pigment-production mutation.
Transcription factors bind to DNA, influencing the transcription of associated genes.
Gene duplication allows diversification by providing redundancy: one gene can mutate and lose its original function without harming the organism.
This is a diagram showing mutations in an RNA sequence. Figure (1) is a normal RNA sequence, consisting of 4 codons. Figure (2) shows a missense, single point, non silent mutation. Figures (3 and 4) both show frameshift mutations, which is why they are grouped together. Figure 3 shows a deletion of the second base pair in the second codon. Figure 4 shows an insertion in the third base pair of the second codon. Figure (5) shows a repeat expansion, where an entire codon is duplicated.
An evolutionary tree of eukaryotic organisms, constructed by the comparison of several orthologous gene sequences.
The common fruit fly (Drosophila melanogaster) is a popular model organism in genetics research.
Schematic relationship between biochemistry, genetics and molecular biology.
Colonies of E. coli produced by cellular cloning. A similar methodology is often used in molecular cloning.

Genetics is a branch of biology concerned with the study of genes, genetic variation, and heredity in organisms.

Gregor Mendel

Gene

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Gregor Mendel
Fluorescent microscopy image of a human female karyotype, showing 23 pairs of chromosomes. The DNA is stained red, with regions rich in housekeeping genes further stained in green. The largest chromosomes are around 10 times the size of the smallest.
Schematic of a single-stranded RNA molecule illustrating a series of three-base codons. Each three-nucleotide codon corresponds to an amino acid when translated to protein
Protein coding genes are transcribed to an mRNA intermediate, then translated to a functional protein. RNA-coding genes are transcribed to a functional non-coding RNA.
Inheritance of a gene that has two different alleles (blue and white). The gene is located on an autosomal chromosome. The white allele is recessive to the blue allele. The probability of each outcome in the children's generation is one quarter, or 25 percent.
A sequence alignment, produced by ClustalO, of mammalian histone proteins
Evolutionary fate of duplicate genes.
Depiction of numbers of genes for representative plants (green), vertebrates (blue), invertebrates (orange), fungi (yellow), bacteria (purple), and viruses (grey). An inset on the right shows the smaller genomes expanded 100-fold area-wise.
Gene functions in the minimal genome of the synthetic organism, Syn 3.
Comparison of conventional plant breeding with transgenic and cisgenic genetic modification.

In biology, a gene (from γένος, ; meaning generation or birth or gender) is a basic unit of heredity and a sequence of nucleotides in DNA that encodes the synthesis of a gene product, either RNA or protein.

Lucretius

Evolution

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Lucretius
Alfred Russel Wallace
Thomas Robert Malthus
In 1842, Charles Darwin penned his first sketch of On the Origin of Species.
DNA structure. Bases are in the centre, surrounded by phosphate–sugar chains in a double helix.
Duplication of part of a chromosome
This diagram illustrates the twofold cost of sex. If each individual were to contribute to the same number of offspring (two), (a) the sexual population remains the same size each generation, where the (b) Asexual reproduction population doubles in size each generation.
Mutation followed by natural selection results in a population with darker colouration.
Simulation of genetic drift of 20 unlinked alleles in populations of 10 (top) and 100 (bottom). Drift to fixation is more rapid in the smaller population.
Homologous bones in the limbs of tetrapods. The bones of these animals have the same basic structure, but have been adapted for specific uses.
A baleen whale skeleton. Letters a and b label flipper bones, which were adapted from front leg bones, while c indicates vestigial leg bones, both suggesting an adaptation from land to sea.
Common garter snake (Thamnophis sirtalis sirtalis) has evolved resistance to the defensive substance tetrodotoxin in its amphibian prey.
The four geographic modes of speciation
Geographical isolation of finches on the Galápagos Islands produced over a dozen new species.
Tyrannosaurus rex. Non-avian dinosaurs died out in the Cretaceous–Paleogene extinction event at the end of the Cretaceous period.
The hominoids are descendants of a common ancestor.
As evolution became widely accepted in the 1870s, caricatures of Charles Darwin with an ape or monkey body symbolised evolution.

Evolution is change in the heritable characteristics of biological populations over successive generations.

Modern biology began in the nineteenth century with Charles Darwin's work on evolution by natural selection.

Natural selection

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Differential survival and reproduction of individuals due to differences in phenotype.

Differential survival and reproduction of individuals due to differences in phenotype.

Modern biology began in the nineteenth century with Charles Darwin's work on evolution by natural selection.
Aristotle considered whether different forms could have appeared, only the useful ones surviving.
Part of Thomas Malthus's table of population growth in England 1780–1810, from his Essay on the Principle of Population, 6th edition, 1826
Charles Darwin noted that pigeon fanciers had created many kinds of pigeon, such as Tumblers (1, 12), Fantails (13), and Pouters (14) by selective breeding.
Evolutionary developmental biology relates the evolution of form to the precise pattern of gene activity, here gap genes in the fruit fly, during embryonic development.
During the industrial revolution, pollution killed many lichens, leaving tree trunks dark. A dark (melanic) morph of the peppered moth largely replaced the formerly usual light morph (both shown here). Since the moths are subject to predation by birds hunting by sight, the colour change offers better camouflage against the changed background, suggesting natural selection at work.
1: directional selection: a single extreme phenotype favoured. 2, stabilizing selection: intermediate favoured over extremes. 3: disruptive selection: extremes favoured over intermediate. X-axis: phenotypic trait Y-axis: number of organisms Group A: original population Group B: after selection
Different types of selection act at each life cycle stage of a sexually reproducing organism.
The peacock's elaborate plumage is mentioned by Darwin as an example of sexual selection, and is a classic example of Fisherian runaway, driven to its conspicuous size and coloration through mate choice by females over many generations.
Selection in action: resistance to antibiotics grows though the survival of individuals less affected by the antibiotic. Their offspring inherit the resistance.

It is a key mechanism of evolution, the change in the heritable traits characteristic of a population over generations.

Gregor Mendel, the Moravian Augustinian monk who founded the modern science of genetics

Mendelian inheritance

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Gregor Mendel, the Moravian Augustinian monk who founded the modern science of genetics
Characteristics Mendel used in his experiments
P-Generation and F1-Generation: The dominant allele for purple-red flower hides the phenotypic effect of the recessive allele for white flowers. F2-Generation: The recessive trait from the P-Generation phenotypically reappears in the individuals that are homozygous with the recessive genetic trait.
Myosotis: Colour and distribution of colours are inherited independently.
F1 generation: All individuals have the same genotype and same phenotype expressing the dominant trait ( red ).
F2 generation: The phenotypes in the second generation show a 3 : 1 ratio.
In the genotype 25 % are homozygous with the dominant trait, 50 % are heterozygous genetic carriers of the recessive trait, 25 % are homozygous with the recessive genetic trait and expressing the recessive character.
In Mirabilis jalapa and Antirrhinum majus are examples for intermediate inheritance. As seen in the F1-generation, heterozygous plants have " light pink " flowers—a mix of " red " and "white". The F2-generation shows a 1:2:1 ratio of red : light pink : white
A Punnett square for one of Mendel's pea plant experiments – self-fertilization of the F1 generation
Segregation and independent assortment are consistent with the chromosome theory of inheritance.
When the parents are homozygous for two different genetic traits (llSS and LL sP sP), their children in the F1 generation are heterozygous at both loci and only show the dominant phenotypes (Ll S sP). P-Generation: Each parent possesses one dominant and one recessive trait purebred (homozygous). In this example, solid coat color is indicated by S (dominant), Piebald spotting by sP (recessive), while fur length is indicated by L (short, dominant) or l (long, recessive). All individuals are equal in genotype and phenotype. In the F2 generation all combinations of coat color and fur length occur: 9 are short haired with solid colour, 3 are short haired with spotting, 3 are long haired with solid colour and 1 is long haired with spotting. The traits are inherited independently, so that new combinations can occur. Average number ratio of phenotypes 9:3:3:1
For example 3 pairs of homologous chromosomes allow 8 possible combinations, all equally likely to move into the gamete during meiosis. This is the main reason for independent assortment. The equation to determine the number of possible combinations given the number of homologous pairs = 2x (x = number of homologous pairs)

Mendelian inheritance is a type of biological inheritance that follows the principles originally proposed by Gregor Mendel in 1865 and 1866, re-discovered in 1900 by Hugo de Vries and Carl Correns, and popularized by William Bateson.

True gray eyes

Phenotypic trait

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True gray eyes

A phenotypic trait, simply trait, or character state is a distinct variant of a phenotypic characteristic of an organism; it may be either inherited or determined environmentally, but typically occurs as a combination of the two.

The shells of individuals within the bivalve mollusk species Donax variabilis show diverse coloration and  patterning in their phenotypes.

Phenotype

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Set of observable characteristics or traits of an organism.

Set of observable characteristics or traits of an organism.

The shells of individuals within the bivalve mollusk species Donax variabilis show diverse coloration and  patterning in their phenotypes.
Here the relation between genotype and phenotype is illustrated, using a Punnett square, for the character of petal color in pea plants. The letters B and b represent genes for color, and the pictures show the resultant phenotypes. This shows how multiple genotypes (BB and Bb) may yield the same phenotype (purple petals).
ABO blood groups determined through a Punnett square and displaying phenotypes and genotypes
Biston betularia morpha typica, the standard light-colored peppered moth
B.betularia morpha carbonaria, the melanic form, illustrating discontinuous variation

Wilhelm Johannsen proposed the genotype–phenotype distinction in 1911 to make clear the difference between an organism's hereditary material and what that hereditary material produces.

Diagram of a fly from Robert Hooke's innovative Micrographia, 1665

Biology

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Scientific study of life.

Scientific study of life.

Diagram of a fly from Robert Hooke's innovative Micrographia, 1665
In 1842, Charles Darwin penned his first sketch of On the Origin of Species.
In the Bohr model of an atom, electrons (blue dot) orbit around an atomic nucleus (red-filled circle) in specific atomic orbitals (grey empty circles).
Model of hydrogen bonds (1) between molecules of water
Organic compounds such as glucose are vital to organisms.
A phospholipid bilayer consists of two adjacent sheets of phospholipids, with the hydrophilic tails facing inwards and the hydrophobic heads facing outwards.
The (a) primary, (b) secondary, (c) tertiary, and (d) quaternary structures of a hemoglobin protein
Structure of an animal cell depicting various organelles
Structure of a plant cell
Example of an enzyme-catalysed exothermic reaction
Respiration in a eukaryotic cell
Photosynthesis changes sunlight into chemical energy, splits water to liberate O2, and fixes CO2 into sugar.
In meiosis, the chromosomes duplicate and the homologous chromosomes exchange genetic information during meiosis I. The daughter cells divide again in meiosis II to form haploid gametes.
Punnett square depicting a cross between two pea plants heterozygous for purple (B) and white (b) blossoms
Bases lie between two spiraling DNA strands.
The extended central dogma of molecular biology includes all the processes involved in the flow of genetic information.
Regulation of various stages of gene expression
Composition of the human genome
Construction of recombinant DNA, in which a foreign DNA fragment is inserted into a plasmid vector
Model of concentration gradient building up; fine yellow-orange outlines are cell boundaries.
Natural selection for darker traits
Comparison of allopatric, peripatric, parapatric and sympatric speciation
Bacteria – Gemmatimonas aurantiaca (-=1 Micrometer)
Archaea – Halobacteria
Diversity of protists
Diversity of plants
Diversity of fungi. Clockwise from top left: Amanita muscaria, a basidiomycete; Sarcoscypha coccinea, an ascomycete; bread covered in mold; chytrid; Aspergillus conidiophore.
Bacteriophages attached to a bacterial cell wall
Root and shoot systems in a eudicot
The xylem (blue) transports water and minerals from the roots upwards whereas the phloem (orange) transports carbohydrates between organs.
Reproduction and development in sporophytes
Negative feedback is necessary for maintaining homeostasis such as keeping body temperature constant.
Diffusion of water and ions in and out of a freshwater fish
Different digestive systems in marine fishes
Respiratory system in a bird
Circulatory systems in arthropods, fish, reptiles, and birds/mammals
Asynchronous muscles power flight in most insects. a: Wings b: Wing joint c: Dorsoventral muscles power upstrokes d: Dorsolongitudinal muscles power downstrokes.
Mouse pyramidal neurons (green) and GABAergic neurons (red)
Sexual reproduction in dragonflies
Cleavage in zebrafish embryo
Processes in the primary immune response
Brood parasites, such as the cuckoo, provide a supernormal stimulus to the parenting species.
Terrestrial biomes are shaped by temperature and precipitation.
Reaching carrying capacity through a logistic growth curve
A (a) trophic pyramid and a (b) simplified food web. The trophic pyramid represents the biomass at each level.
Fast carbon cycle showing the movement of carbon between land, atmosphere, and oceans in billions of tons per year. Yellow numbers are natural fluxes, red are human contributions, white are stored carbon. Effects of the slow carbon cycle, such as volcanic and tectonic activity, are not included.
Efforts are made to preserve the natural characteristics of Hopetoun Falls, Australia, without affecting visitors' access.

A gene is a unit of heredity that corresponds to a region of deoxyribonucleic acid (DNA) that carries genetic information that influences the form or function of an organism in specific ways.

Gregor Mendel

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Biologist, meteorologist, mathematician, Augustinian friar and abbot of St. Thomas' Abbey in Brünn (Brno), Margraviate of Moravia.

Biologist, meteorologist, mathematician, Augustinian friar and abbot of St. Thomas' Abbey in Brünn (Brno), Margraviate of Moravia.

Dominant and recessive phenotypes. (1) Parental generation. (2) F1 generation. (3) F2 generation.

Though farmers had known for millennia that crossbreeding of animals and plants could favor certain desirable traits, Mendel's pea plant experiments conducted between 1856 and 1863 established many of the rules of heredity, now referred to as the laws of Mendelian inheritance.

Charles Darwin's pangenesis theory postulated that every part of the body emits tiny particles called gemmules which migrate to the gonads and are transferred to offspring. Gemmules were thought to develop into their associated body parts as offspring matures. The theory implied that changes to the body during an organism's life would be inherited, as proposed in Lamarckism.

Pangenesis

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Charles Darwin's pangenesis theory postulated that every part of the body emits tiny particles called gemmules which migrate to the gonads and are transferred to offspring. Gemmules were thought to develop into their associated body parts as offspring matures. The theory implied that changes to the body during an organism's life would be inherited, as proposed in Lamarckism.
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Pangenesis was Charles Darwin's hypothetical mechanism for heredity, in which he proposed that each part of the body continually emitted its own type of small organic particles called gemmules that aggregated in the gonads, contributing heritable information to the gametes.