Download DNA Glossary - FutureLearn

DNA definitions
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Locus is the position of a gene on a chromosome
An allele is one of two or more forms of a gene found at the same
place on a chromosome
Genotype is the genetic make-up of a person
Phenotype is the set of observable characteristics resulting from a
given genotype
Expression is the appearance of a characteristic attributable to a
particular gene
A homozygote has identical alleles for a specified gene
A heterozygote has different alleles for a specified gene on each
chromosome
The human genome consists of the total DNA structure, consisting of
over 3 billion base pairs
Twenty-two of the 23 pairs of chromosomes look the same and carry
the same genes at the same loci. These are called Homologous
chromosomes. The exception is the pair of sex chromosomes where
the male gender- determining Y chromosome is a different size and
shape to the X chromosome.
The key points are:
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DNA is located in the chromosomes present in the nucleus of the cell.
The DNA of an individual is the same in every one of his or her cells (but
is not present in red blood cells because these cells have no nuclei) and
different from everyone else’s other than identical twins.
The DNA molecule resembles a twisted ladder or double helix.
The steps within the ladder are formed by bonding between pairs of 4
bases: guanine (G), adenine (A), thymine (T) and cytosine (C).
(A) always pairs with (T) and (G) always pairs with (C).