The phenotype of organism is the result of the interaction between genotype and environment.[2-3]Therefore, not all phenotypes of organisms can be inherited.
For example, human suntanned skin comes from the interaction between phenotype and sunlight, so suntanned skin will not be passed on to future generations.However, due to genotype differences, some people tan more easily than others.[4]
Molecular mechanism of heredity
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Parents' traits are determined byDNA(a molecule encoding genetic information) from one generationGenetic transmissionTo the next generation.[2]DNA contains four interchangeableBase, specificDNA moleculeThe sequence of the upper base determinesgenetic information。[5]In cells passing throughmitosisBefore division, DNA is copied, so every daughter cell contains its parentDNA sequence。
DNA moleculeA part of the sequence with functional units in is called gene, and different genes have different base sequences.In cells,Long chainDNA forms condensed structures called chromosomes.BiologyHomologous chromosomeThe form of inheriting from parentsgenetic materialThese homologous chromosomes contain unique combinations of DNA sequences encoding genes.
The specific position of DNA sequence in chromosome is calledGene locus/Locus。If the DNA sequence of a specific locus is different between individuals, the different forms of this sequence are calledAllele。Mutations can change the DNA sequence and produce new alleles.If mutations occur within the gene, the new allele may affect the characteristics controlled by the gene, thus changing the phenotype of the organism.[6]
Although this simple correspondence between alleles and traits works in some cases, most traits of organisms are more complex, and they are controlled by multiple interacting genes within and between organisms.[7]
Developmental biologists believe that complex interactions in genetic networks and intercellular communication may lead togenetic variation, may be biologicaldevelopmental plasticityAnd directionality.[8]
Theoretical history
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Traditional Genetics
The ancient understanding of heredity changed into two controversial theories in the 18th century:GradualismDoctrine andApriorismThey represent two different views on genetic understanding.
fromAristotleCreatedGradualismAccording to the theory, the embryo develops continuously, and the modification of parents' characteristics can be transferred to the embryo in its life cycle.This theory is based onAcquired traitsThe genetic theory.
ApriorismDirectly opposed to the theory of gradualism, believing thatSpermatocyteIt will evolve and produce offspring similar to its parents, but this theory was interrupted by the cell theory in the 19th century, that is, lifeBasic unitIt is a cell, not some pre formed part of an organism.However, through artificial selection, people can domesticate animals and plants.Inheritance of acquired traits is alsoLamarckPart of early evolutionary thinking.
Until Mendel proposed that the traits were heritable through his pea plant demonstration,[9]Traditional genetics becomesMendelian inheritance。
Modern Genetics
In the 1930s, the work of Fisher and others led to Mendelian inheritance andBiometric technologyAnd formed the modern evolutionary synthesis theory.This theory makes up for the fact that experimental geneticists andnaturalistThe gap between the two also makes up for the gap between the twopaleontologistThe gap between.[10]
Modern evolutionary synthesis theory believes that:
(1) All evolutionary phenomena can be applied to the known genetic mechanism and naturalist'sObservational evidenceIn a consistent way.
(2) Evolution is gradual: small genetic changes are rearranged through natural selection.Interspecies (or other groups)DiscontinuityIt is interpreted as the gradual occurrence of geographical separation and extinction.
If at least one copy existsAlleleIf the controlled phenotype can be expressed (with phenotype), the allele isDominant alleleThe heredity controlled by this gene isDominant inheritance。For example, in peas, controlPodsThe green allele G is sexual to the allele g that controls the yellow of the pod, so it has GG（Homozygote）Or Gg（Heterozygote）Pea plants with allele pairs will have green pods.Because the allele controlling the yellow pod isRecessive inheritanceTherefore, the role of this allele can only be seen when gg exists (homozygote).
Mendelian inheritance
Mendelian inheritance means that any trait is strictlyMendel's lawSegregated inheritance.For example, "B" represents the dominant allele of purple flowers, and "b" represents the recessive allele of white flowers.One parent variety has two alleles for purple flowers (BB), while the other has two alleles for white flowers (bb).After fertilization, F1 hybrids inherited one allele for purple flowers and one allele for white flowers respectively.All F1 hybrids (Bb) have purple flowers, because the dominant B allele has complete effect in the heterozygote, while the recessive b allele has no effect on flower color.For F2 plants, the ratio of plants with purple flowers to plants with white flowers (3:1) is called phenotypic ratio.The genotype ratio was 1 BB: 2 Bb: 1 bb.
Non Mendelian inheritance
Non Mendelian inheritance refers to the inheritance of any offspring character that is not separated according to Mendelian law.If the genotype of the parents in the genetic hybridization is known, Mendel's law can be used to determine the expected phenotype distribution of the offspring population.The proportion of phenotypes observed in offspringpredicted valueMismatched inheritance is non Mendelian inheritance.
