Download Biological vocabulary glossary, part 1

Genetics and Evolution
Trait: ​any characteristic of an individual (e.g. height,
colour)
Gene:​ a region of DNA that codes for a protein (or
sometimes, some other functional region, such as an
RNA)
Genome:​ entire set of genetic information that an
organism carries.
Proteins:​ large biomolecules that perform most of the
biochemical functions in an organism (see Molecular
biology).
Allele:​ A specific variant of a gene (for example, the gene that codes for colour in peas could have two
alleles: one for red colour and one for white colour).
dominant allele: ​trait always shows up in the organism when the allele is present
recessive allele: ​hidden whenever the dominant allele is present
Incomplete dominance: o
​ ccurs when one allele is only partially dominant - both alleles
contribute.
Phenotype: ​an organism's physical appearance, set of traits
Genotype: ​a particular set of alleles. Genotype can refer to an organism's entire genetic makeup or
the alleles at a particular set of genes.
Haploid:​ organism with only one set of genes (e.g. bacteria, but also unfertilized eggs, sperm,
or male bees)
Diploid:​ organism with two sets of ​homologous chromosomes ​ (e.g. humans)
Polyploid:​ organism possessing multiple sets of genes (some plants, such as wheat)
The genotype, together with environmental influences, determines the phenotype.
Chromosome​: A compact structure containing most of the DNA.
Pleiotropy:​ when a single gene influences multiple traits.
Polygenic trait: ​ a trait that is determined by many genes.
Locus:​ a specific location on the chromosome.
Gametes: ​Two cells that fuse with each other to produce the fertilized egg in organisms that reproduce
sexually. (E.g. sperm and egg). These cells are haploid - have only one set of genes.
Germline: ​The cells which give rise to the gametes.​ Mutations​ (see below) occurring in the germline
will be passed on to the offspring. S
​ omatic mutations a
​ re mutations occurring somewhere else in the
body, not in the germline. A somatic mutation occurring during development will be passed on to all
cells which are generated by division of the cell in which it first occurred.
Development: ​The process by which a single fertilized egg cell develops into a mature multicellular
organism by many rounds of cell division and differentiation.
Meiosis:​ A specialized type of cell division important in sexual reproduction for producing the gametes.
Homologous chromosomes: ​Two chromosomes that pair up during meiosis. One set comes from the
male parent and one set comes from the female parent. Two homologous chromosomes have the
same genes at the same loci.
Homozygous: ​At a particular locus, diploid organisms (like animals) have two copies of the gene at
that locus. An organism where these two copies are identical is called homozygous.
Heterozygous: ​an organism that has different alleles for a particular gene is called heterozygous.
Genetic marker: ​alleles that produce detectable phenotypic differences useful in genetic analysis.
Allele frequency: ​The fraction of all genes in a population that carry the given allele.
Independent assortment:​ one of Mendel’s principles that states that genes for different traits can
segregate independently during the formation of gametes; applies when genes are on different
chromosomes.
Adaptation​: A heritable characteristic that increases an organism’s ability to survive and reproduce in
an environment.
Forces in evolution​: Selection, mutation, genetic drift and gene flow:
Selection:
directional selection:​ form of natural
selection in which individuals at one end of
a distribution curve have higher fitness
than individuals in the middle or at the
other end of the curve. Example: A
population in which individuals that have
longer legs always have a higher chance of
producing offspring.
stabilizing selection:​ form of natural
selection in which individuals near the
center of a distribution curve have higher fitness than individuals at either end of the curve.
Example: A population in which individuals with an intermediate body mass have a higher
chance of survival, because individuals that are too big are at higher risk of starving and
individuals that are too small are at higher risk of freezing. Thought to be the most prevalent
form of natural selection in nature.
Natural selection is the only force that can systematically lead to adaptation.
Mutation: ​Random and spontaneously occurring changes in an organism's genome. See Molecular
biology.
Genetic drift:​ random change in allele frequencies due to sampling from a finite population.
Gene flow:​ exchange of genes between different populations. Migration can be a source of gene flow.
Recombination: ​The process by which genetic material is reshuffled and joined to other genetic
material. It leads to the offspring having a different combination of traits than either parent.
The​ absolute fitness ​of a genotype or phenotype is usually defined as the average number of
offspring contributed to the next generation by individuals of this genotype/phenotype.
Relative fitness​: The absolute fitness standardized in some way. Usually the highest fitness is set to
one and the other fitnesses are scaled independently (e.g. one could write 1:1-s:1-t)
Hardy-Weinberg principle:​ allele frequencies in a population remain constant unless one or more
evolutionary forces cause those frequencies to change.
Molecular biology:
DNA:​ Carrier of the genetic information. Consists of two polymer strands​ ​(long chain-like molecules
composed of smaller subunits) which are​ coiled around each other to form a double helix. The detailed
structure is as follows:
Ribose​, or deoxyribose is a molecule of sugar from which the backbone of RNA (DNA) is created.
A ​base​ is attached to the sugar; this is the part of the DNA encoding genetic information. ​The
sequence ​(order) of bases in the DNA determines the sequence of amino acids in the protein (see
below).
The bases that occur in DNA are C​ytosine​ (C),​ guanine​ (G),​ adenine​ (A), or​ thymine​ (T). Instead of
Thymine, Uracil (U) is used in RNA; the other bases stay the same. A​ phosphate group​ links together
sugar backbone and bases.
Together, these three elements create a ​nucleotide​ - the basic unit of DNA (and RNA).
Consecutive nucleotides hold together by binding the sugar to the phosphate group of the next
nucleotide via covalent bonds. The bases on opposing strands are bound together by hydrogen bonds.
Adding nucleotides together creates a long chain - one strand of DNA. The second strand is
complementary​ - C is complementary with G, and A with T. The two strands are thus ‘negatives’ of
one another. A gene is ‘read out’ from only one of the two strands (some genes from one, others from
the other).
The term ​base pair ​refers to the combination of one base with its corresponding base in the
complementary DNA strand.
DNA is extremely stable.
Protein​: ​Proteins are large molecules that perform most functions in living organisms. Like DNA and
RNA, the most basic structure of a protein is a chain composed of smaller subunits. The subunits in the
protein are called amino acids. Different proteins consist of a different sequence of amino acids. The
sequence of amino acids determines how the chain folds in upon itself, creating the three dimensional
structure of the protein; this determines the protein’s function. Proteins that are incorrectly folded can
malfunction and have serious consequences for the organism.
Each amino acid is encoded by a combination of three bases in the DNA; a ​codon (​ see below).
A linear chain of amino acid residues is called polypeptide. A protein contains at least one polypeptide,
but can contain more. The amino acids making up a polypeptide are bound together by covalent
peptide bonds.
Protein structure:
Primary:​ The​ primary structure​ of a protein refers to the linear sequence of amino acids in the
polypeptide chain. The primary structure is held together by​ covalent bonds​ such as​ peptide bonds​,
which are made during the process of​ protein biosynthesis​.
Secondary:​ ​alpha helices​ and ​beta chains​ – highly regular structures. Defined by hydrogen bonds
between the main chain peptide groups. Alpha helices or beta chains both saturate all the hydrogen
bond donors and acceptors in the backbone (and are therefore very stable). There can also be loops or
other ordered but not so regular structures.
RNA​: Another biopolymer, similar to DNA. RNA differs from DNA only in that it uses Uracil instead of
Thymine, and has ribose as the backbone sugar. RNA is important in coding, decoding, and regulation
of genes​; for example, as an intermediary between the DNA and the protein sequence (the so-called
messenger RNA; see Gene Expression).
Gene structure:
Intron:​ part of the sequence of a gene which
is removed (​spliced out​) from the mRNA
before it is translated into a protein. The
proportion of introns varies widely between
organisms.
Exon:​ part of the sequence of a gene which
makes it into the final mRNA that will be translated into a protein. (​Exome: ​the set of all exons,
so the entire protein-coding part of an organism’s genome, without the rest.)
Promoter:​ specific region of a gene where RNA polymerase can bind and begin transcription
Edited from: http://www.protocol-online.org/biology-forums-2/posts/26935.html
From genes to traits:
Gene Expression:
Transcription:​ synthesis of an RNA molecule from a
DNA template
Translation:​ process by which the sequence of bases of
the RNA produced in the previous step is converted into
the sequence of amino acids of a protein.
Codon:​ a​ sequence of three​ nucleotide bases in
messenger RNA (The RNA produced after transcription,
abbreviation mRNA) that specify a particular amino acid
to be incorporated into a protein.
The genetic code is ​redundant​, meaning that multiple combinations of three bases can encode the
same amino acid; but each combination of three bases codes for no more than 1 amino acid. For this
reason, not all mutations in the DNA sequence change the sequence of amino acids in the protein they
code for.
Stop codon: ​Codon which does not encode any amino acid, and causes translation to stop (also called
a ​nonsense codon​).
Anticodon: ​group of three bases on a transcript RNA molecule (tRNA) that are complementary to the
three bases of a codon of mRNA.
Catalyst: ​substance that speeds up the rate of a chemical reaction.
Enzyme:​ protein catalyst that speeds up the rate of specific biological reactions, ​for instance DNA
synthesis, or metabolic processes.
For the copying of DNA (i.e., replication), the two strands are separated and each strand is again
completed with the complementary sequence.
Replication:​ DNA to DNA. replication occurs with the assistance of several proteins, that 1) open the
double strand 2) read it and add new complimentary nucleotides. This creates 2 identical double
strands of DNA.
Mutation: ​A change in the DNA sequence (e.g. during replication).
Point mutation: ​A change of a single base pair in the DNA sequence.
Insertion: ​One or more base pairs are inserted in the DNA sequence.
Deletion: ​One or more base pairs are deleted from the DNA sequence.
Frameshift mutation: ​An insertion or deletion of a size which is not a multiple of 3, leading to a shift in
the ​reading frame​: all the rest of the gene will be read in the wrong way, because the wrong sets of 3
nucleotides will be read as codons.
Nonsense mutation:​ Point mutation causing a stop codon to appear in a location in a gene other than
its end. The resulting gene would be only partially translated, leading to a truncated protein.
Missense mutation ​or ​Nonsynonymous mutation: P
​ oint mutation changing a codon into one coding
for a different amino acid.
Synonymous mutation: ​point mutation resulting in a codon still coding for the same amino acid as
before the mutation.
Gene expression​: The process by which information from a gene is used to synthesize a functional
protein. The two main steps are transcription and translation:
Transcription​: copying of DNA to messenger RNA (mRNA) which leaves the nucleus.
Translation​: of messenger RNA to the corresponding amino acid (AA) chain; mediated by a
large complex of proteins and RNA, the r​ ibosome​. Small pieces of RNA (transcript RNA,
abbreviated as tRNA) are recruited. These tRNAs include an ​anticodon​ that is attached to the
corresponding amino acid. The tRNA anticodon binds to the complementary codon on the
mRNA, and the amino-acid it carries is joined to the growing protein. The reading frame then
shifts by 3 bases, and another tRNA is recruited, attaching its AA to the previous AA. This
process of translation produces a long chain of AAs - a protein.
Eukaryote​: Organism whose cells contain a nucleus and other o
​ rganelles,​ enclosed by a membrane.
Prokaryote: ​An organism that doesn’t have a membrane-bound nucleus. Bacteria and Archaea are
prokaryotes.