M: Inheritance Flashcards
Allele
One form of a gene. E.g. the eye-colour gene has an allele for blue and another for brown (and several other variations of these!)
Artificial selection
The selection by humans of individual plants or animals for breeding in order to enhance a desired characteristic.
Base pairing
Complementary pairing of bases in DNA: Adenine always pairs with Thymine and Guanine pairs with Cytosine.
Carrier
A person who carries one recessive allele for a particular disease, but doesn’t have symptoms.
Chromatid
One of two daughter strands of a replicated chromosome.
Chromosomes
Red shaped structures found in the nucleus of cells, made of DNA, each carrying many genes.
Clone
An organism which is genetically identical to another. Clones can arise naturally (asexual reproduction or identical twins), or be produced artificially.
Codominance
Situation in which two alleles of a gene contribute to the phenotype of a heterozygote. E.g. blood group genes A & B are codominant.
Codon
Group of three bases, e.g. ‘CGA’ in DNA (or RNA) which codes for one amino-acid.
Continuous variation
Type of variation in which values are spread across a complete range, often with a bell-curve distribution. Quantitative variation.
Discontinuous variation
Type of variation in which values fall into distinct classes, with no continuous spread of data. Qualitative variation.
Diploid
Containing two sets of chromosomes (one set of 23 from each parent, so 46 in all) All human cells except gametes are diploid.
DNA
The material inside the nucleus of cells which carries genetic information. DNA stands for Deoxyribonucleic Acid.
Dominant
An allele that always expresses itself if present, whether it is partnered by a recessive allele or by another like itself.
Double helix
The shape of the DNA molecule: like a twisted rope ladder, with a sugar-phosphate ‘rope’ down each side, and base-pairs for the ‘rungs’.
Embryo transplanting
Genetic engineering technique in which an embryo is created from the egg of one animal fused with DNA from another animal, and then implanted into the womb of a surrogate mother.
Fermenter
Large temperature-controlled tank, in which huge numbers of bacteria can be grown quickly, e.g. to produce engineered insulin.
Fossil
Hardened remains or impression of an organism that existed in the geological past.
Gene
Unit of genetic material that is inherited from our parents. A gene is a section of DNA which codes for a protein.
Gene pool
The sum total of all the gene variations in a population or species.
Gene therapy
Treating or preventing disease by introducing or replacing specific genes inside human cells.
Genetic disease
Disease which children can inherit from their parent/s as a result of abnormalities in their genes. E.g. cystic fibrosis.
Genetic engineering
Manipulation of an organism’s DNA to change the proteins it produces. Involves transferring a gene using restriction enzymes and a vector.
Genotype
The genetic make-up of an individual organism
Haploid
Having one set of chromosomes (23, in humans). In humans and plants, only the gametes are haploid, other cells are diploid.
Heterozygous
Having different alleles for a particular characteristic
Homozygous
Having the same alleles for a particular characteristic
Hybrid vigour
The increased strength and size of a hybrid (an offspring produced as a result of breeding two genetically different organisms) compared to that of the parents.
Ligase
Enzyme used to re-join pieces of DNA in genetic engineering
Meiosis
Type of cell division which forms four genetically-different daughter cells (gametes), which are haploid.
Mitosis
A type of cell division which produces two daughter cells, both genetically identical to the parent.
Mutagen
A chemical (e.g. mustard gas) which increases the rate if mutation
Mutation
A rare error in DNA replication causing a change in an organism’s genetic information. Mutations are random events, but the chances can be increase by ionising radiation or chemical mutagens. Most mutations are harmful or neutral, but any beneficial mutation will tend to increase, by natural selection.
Natural selection
The natural process whereby the best-adapted individuals survive longer and have more offspring, thereby spreading their characteristics through a population. ‘Survival of the fittest.’
Nitrogenous bases
The chemical ‘letters’ that make up the language of DNA: Adenine (A), Cytosine (C), Guanine (G) and Thymine (T)
Nucleotide
Monomer (unit) of DNA; built from a nitrogenous base, a 5-carbon (pentose) sugar and phosphate group
Pentose sugar
A 5-carbon sugar; in DNA the sugar is deoxyribose, ribose in RNA
Phenotype
Observable characteristics of an organism - the visible expression of its genetic make-up
Plasmid
Small loop of DNA, found in bacteria, which can be used in genetic engineering as a vector to carry genes from one cell to another.
Protein synthesis
Manufacturing of proteins; occurs at ribosomes in the cytoplasm, using an RNA code copied from the DNA in the nucleus.
Purebread
Old word for homozygous, having the same alleles for a characteristic. Purebred organisms always breed true to type.
Recessive
Allele of a gene for a particular characteristic which is masked or suppressed in the presence of the dominant variant. A recessive allele’s character is only seen when it is paired with another recessive allele.
Recombinant
DNA which contains an artificially added gene, or has been exchanged between chromosomes during meiosis.
Replication
Production of an identical copy. DNA replication involves the two strands ‘unzipping’ and new nucleotides being added to each half by base-pairing: this ensures each copy is identical to the original.
Restriction enzyme
Enzyme which cuts DNA at a specific sequence of bases (e.g. TTCGAA), used in genetic engineering.
RNA
(RiboNucleic Acid) - used to convert the genetic information stored in DNA into proteins
Sex chromosomes
The pair of chromosomes that determine sex. Females have two X chromosomes and males have X & Y
Spindle fibres
Fibres produced during cell division. They contract to drag chromatids to the poles of the cell.
Triplet code
The genetic code made by a triplet of bases in the DNA chains: AAA; GCT;CAT etc.
Variation
Difference between individuals. Variations can be caused by genetic differences or the environment, or both.
Vector
A means of transferring genes during genetic engineering. Both viruses and plasmids can be used as vectors.
