heredity

Introduction
Basic features of heredity
- Prescientific conceptions of heredity
- Mendelian genetics
  - Discovery and rediscovery of Mendel’s laws
  - Universality of Mendel’s laws
  - Allelic interactions
    - Dominance relationships
    - Multiple alleles
  - Gene interactions
    - Epistatic genes
    - Complementation
    - Polygenic inheritance
- Heredity and environment
  - Preformism and epigenesis
  - Heritability
The physical basis of heredity
- Chromosomes and genes
  - The behaviour of chromosomes during cell division
    - During mitosis
    - During meiosis
  - Linkage of traits
    - Simple linkage
    - Sex linkage
  - Chromosomal aberrations
    - Changes in chromosome structure
      Deletions
      Duplications
      Inversions
      Translocations
    - Changes in chromosome number
      Polyploids
      Aneuploids
- Molecular genetics
  - DNA as the agent of heredity
  - Structure and composition of DNA
  - DNA replication
  - Expression of the genetic code: transcription and translation
    - Transcription
    - The genetic code
    - Translation
  - Gene mutation
    - Mechanisms of mutation
    - Repair of mutation
  - Regulation of gene expression
  - Repetitive DNA
  - Extranuclear DNA
Heredity and evolution
- Population genetics
  - Hardy-Weinberg equilibrium
  - Changes in gene frequencies
    - Selection
    - Mutation
    - Nonrandom mating
    - Random genetic drift
- Microevolution
  - DNA phylogeny
  - Synteny
  - Polyploidy
- Human evolution

References & Edit History Related Topics

Images & Videos

Four kittens with different fur patterns-three tabby and one black-and-white-lying together in a box, illustrating genetic variation among offspring.

Carolus Linnaeus.

Black and white portrait of Jean-Baptiste Lamarck, French naturalist, shown from the chest up wearing a high-collared shirt, cravat, and jacket.

Mendel's law of segregationCross of a purple-flowered and a white-flowered strain of peas; R stands for the gene for purple flowers and r for the gene for white flowers.

Mendel's law of independent assortmentCross of peas having yellow round seeds with peas having green wrinkled seeds. A stands for the gene for yellow and a for the gene for green; B stands for the gene for a round surface and b for the gene for a wrinkled surface.

Diagram illustrating sex-linked inheritance of white and red eye color in Drosophila fruit flies, showing genetic crosses between white-eyed and red-eyed males and females, with chromosomes and resulting eye color traits mapped through two generations.

What are chromosomes?

A step-by-step diagram shows the stages of mitosis in a somatic cell, illustrating chromosome duplication, alignment, separation, and the formation of two identical daughter cells, with labeled cell structures and brief descriptions of each phase.

A step-by-step diagram of meiosis, showing the stages of sex cell division. Illustrated cells depict chromosome behavior, cell membrane changes, and the formation of four daughter cells, each with half the chromosome number of the original cell. Labels and brief descriptions explain key processes such as homologous chromosome pairing, crossing over, and separation of chromatids.

At a Glance

Chromosomes are inside the cells of every living thing. They are so small that they can only be seen through a powerful microscope.

heredity summary

heredity: Media

genetics

Videos

Four kittens with different fur patterns-three tabby and one black-and-white-lying together in a box, illustrating genetic variation among offspring.

Why Are Children Slightly Different From Their Parents?

Each offspring is a combination of its two parents, receiving some dominant traits...

Video: Encyclopædia Britannica, Inc.

What are chromosomes?

What are chromosomes?

Each species has a unique set of chromosomes which are the carriers of genetic information.

Video: Encyclopædia Britannica, Inc.

Witness a living plant cell's chromosomes carrying genetic material duplicate during the process of mitosis

Witness a living plant cell's chromosomes carrying genetic material duplicate during the process of mitosis

Time-lapse photography of a live plant cell nucleus undergoing mitosis.

Video: Encyclopædia Britannica, Inc.

Gregor Mendel's discovery of heredity laws

Gregor Mendel's discovery of heredity laws

An introduction to Austrian botanist, teacher, and Augustinian prelate Gregor Mendel's...

Video: Encyclopædia Britannica, Inc.

Images

Carolus Linnaeus.

Carolus Linnaeus.

Courtesy of the National Museum, Stockholm

Charles Darwin

Charles Darwin

Charles Darwin, carbon-print photograph by Julia Margaret Cameron, 1868.

Julia Margaret Cameron/Library of Congress, Washington, D.C. (LC-DIG-ds-16381)

Black and white portrait of Jean-Baptiste Lamarck, French naturalist, shown from the chest up wearing a high-collared shirt, cravat, and jacket.

Jean-Baptiste Lamarck

Jean-Baptiste Lamarck.

© Morphart Creation/Shutterstock.com

Mendel's law of segregationCross of a purple-flowered and a white-flowered strain of peas; R stands for the gene for purple flowers and r for the gene for white flowers.

Mendel's law of segregationCross...

Encyclopædia Britannica, Inc.

Mendel's law of independent assortmentCross of peas having yellow round seeds with peas having green wrinkled seeds. A stands for the gene for yellow and a for the gene for green; B stands for the gene for a round surface and b for the gene for a wrinkled surface.

Mendel's law of independent assortmentCross...

Encyclopædia Britannica, Inc.

Diagram illustrating sex-linked inheritance of white and red eye color in Drosophila fruit flies, showing genetic crosses between white-eyed and red-eyed males and females, with chromosomes and resulting eye color traits mapped through two generations.

sex-linked inheritance

Sex-linked inheritance of white eyes in Drosophila flies.

Encyclopædia Britannica, Inc.

A step-by-step diagram shows the stages of mitosis in a somatic cell, illustrating chromosome duplication, alignment, separation, and the formation of two identical daughter cells, with labeled cell structures and brief descriptions of each phase.

mitosis

Mitosis, the process in which a cell gives rise to two genetically identical daughter...

Encyclopædia Britannica, Inc.

A step-by-step diagram of meiosis, showing the stages of sex cell division. Illustrated cells depict chromosome behavior, cell membrane changes, and the formation of four daughter cells, each with half the chromosome number of the original cell. Labels and brief descriptions explain key processes such as homologous chromosome pairing, crossing over, and separation of chromatids.

Gamete formation in meiosis

Meiosis, the process in which gametes (sex cells) form.

Encyclopædia Britannica, Inc.

Behaviour of chromosomes at meiosis.

Behaviour of chromosomes at meiosis.

Encyclopædia Britannica, Inc.

The initial proposal of DNA structure

The initial proposal of DNA structure

The structure of DNA proposed by James Watson and Francis Crick, which was accompanied...

Encyclopædia Britannica, Inc.

Diagram illustrating semiconservative DNA replication, showing a double helix unwinding into two template strands. New nucleotides are added by DNA polymerase to form leading and lagging strands, with Okazaki fragments joined by DNA ligase. Helicase, single-strand binding proteins, and the replication fork are labeled.

semiconservative DNA replication

In semiconservative DNA replication an existing DNA molecule is separated into two...

Encyclopædia Britannica, Inc.

Diagram of DNA replication in higher organisms showing a double helix unwinding at multiple origins, with enzymes such as helicase, polymerase, ligase, and topoisomerase labeled, along with replication forks, Okazaki fragments, and direction of strand synthesis.

DNA replication in higher organisms begins at multiple origins of replication and...

Encyclopædia Britannica, Inc.

Diagram illustrating the process of protein synthesis: DNA unzips in the nucleus, messenger RNA (mRNA) forms on the DNA strands, and then mRNA moves to a ribosome where transfer RNA (tRNA) helps assemble amino acids into a protein chain.

DNA and protein synthesis

DNA in the cell nucleus carries a genetic code, which consists of sequences of adenine...

Encyclopædia Britannica, Inc.

Diagram showing protein synthesis: The top section illustrates ribosomes moving along messenger RNA to build a protein chain. The bottom section details transfer RNA molecules matching codons on the mRNA within a ribosome, adding amino acids to a growing polypeptide chain.

Protein synthesis

Ribosomes are key components of protein synthesis in cells.

Encyclopædia Britannica, Inc.

Model of the operon and its relation to the regulator gene.

Model of the operon and its relation to the regulator gene.

Encyclopædia Britannica, Inc.

Punnett square diagrams are used to predict all the possible gene combinations that could result from the mating of parents with known genotypes for a particular trait. A monohybrid cross represents the inheritance pattern of a single trait, whereas a dihybrid cross represents the inheritance patterns of two traits that are linked.

Punnett square diagrams are used to predict all the possible gene combinations that...

Encyclopædia Britannica, Inc.

Diagram showing how point mutations, or single nucleotide changes in a codon, result in different amino acids in a protein. The central isoleucine codon (AUA) is surrounded by other codons, each differing by one nucleotide, with corresponding amino acid molecular structures and color-coded atoms.

point mutation

The effect of base substitutions, or point mutations, on the messenger-RNA codon...

Encyclopædia Britannica, Inc.

industrial melanism in the peppered moth

industrial melanism in the peppered moth

The light gray form of the peppered moth (Biston betularia) is inconspicuous...

From the experiments of Dr. H.B.D. Kettlewell, University of Oxford; photographs by John S. Haywood

Adaptive radiation in Galapagos finches

Adaptive radiation in Galapagos finches

Fourteen species of Galapagos finches that evolved from a common ancestor. The different...

Encyclopædia Britannica, Inc.

A branching phylogenetic tree diagram shows evolutionary relationships among various organisms, from Neurospora mold to humans, based on differences in cytochrome c gene sequences. Each branch is labeled with nucleotide substitution values and illustrated with animal or organism icons along the tree.

phylogeny

Phylogeny based on differences in the protein sequence of cytochrome c.

Encyclopædia Britannica, Inc.

Diagram showing front and side views of the pelvis in a chimpanzee, Australopithecus, and modern human, highlighting differences in iliac blade shape, hip joint orientation, and leg stance.

The pelvis and leg bones of three great apes

Comparison of the pelvis and lower limbs of a chimpanzee, an australopith, and a...

Encyclopædia Britannica, Inc.

Chromosomes are inside the cells of every living thing. They are so small that they can only be seen through a powerful microscope.

Chromosomes are inside the cells of every living thing. They are so small that they...

© James Cavallini—BSIP/age fotostock

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