Download Genetic Terminology

HEREDITY
 Heredity - Continuity of biological traits from
one generation to the next.
 Genetics: is the branch of science that deals with
the inheritance of biological characteristics. The
study of gene structure and action and the patterns
of inheritance of traits from parent to offspring.
 Genes: Units of inheritance usually occurring at
specific locations, or loci, on a chromosome. A gene
may be made up of hundreds of thousands of DNA
bases. Genes are responsible for the hereditary
traits in plants and animals.
CHROMOSOMES
 Thread-like, gene-carrying bodies in the
nucleus of a cell.
Chromosomes are
composed primarily of DNA and
protein.
They are visible only under
magnification during certain stages of cell
division. Humans have 46 chromosomes in
each somatic cell and 23 in each sex cell.
DNA
(deoxyribonucleic acid)
 A large organic molecule that stores the
genetic code for the synthesis of
proteins. DNA is composed of sugars,
phosphates and bases arranged in a double
helix
shaped
molecular
structure.
Segments of DNA in
chromosomes correspond to specific
genes.
Genetic Terminology
 Allele: An alternative form of a gene that
occurs at the same locus on homologous
chromosomes, e.g., A, B, and O genes are
alleles.
 Anticodon: A sequence of three bases in tRNA
that is complementary to a codon in mRNA.
Enables tRNA to sequence amino acids in the
order specified by mRNA.
 Autosome:
A
non-sex
chromosome.
Synonymous with somatic chromosomes
(chromosome pairs 1-22).
 Chromosome: Rod-shaped structures within the
cell nucleus that carry genes encoded by DNA.
 Co-dominant: Genes are co-dominant if both
alleles are expressed in the heterozygous state.
 Codon: A sequence of three bases in DNA or
RNA that codes for a single amino acid. Enables
specific proteins to be made by specific genes.
 Crossing over: The exchange of genetic material
between members of a pair of homologous
chromosomes.
 Diploid number of chromosomes: The number of
chromosomes found in somatic cells, which in
humans is 46.
 DNA: Deoxyribonucleic acid. Composed of nucleic
acids, these molecules encode the genes that allow
genetic information to be passed to offspring.
 DNA polymerases: Enzymes that can synthesize
new DNA strands using previously synthesized
DNA (or RNA) as a template.
 Dominant gene: A gene is dominant if it is
expressed when heterozygous but its allele is not,
e.g. in the tall pea plants the T gene is dominant
(expressed in both TT and Tt genotypes) and the t
gene is recessive.
 Gamete: A reproductive sex cell (ovum or
sperm) with the haploid number (23) of
chromosomes that results from meiosis.
 Gene: A segment of a DNA molecule that codes
for the synthesis of a single polypeptide.
 Genome: Term used to denote the entire DNA
sequence (gene content) of a gamete, person,
population, or species.
 Genotype: All of the alleles present at the locus
(or closely linked loci) of a blood group system,
indicating
chromosomal
alignment
if
appropriate. Genotypes are indicated by
superscripts, underlining, or italics.
 Haploid number of chromosomes: The number of
chromosomes found in sex cells, which in humans is
23.
 Heterozygous: The situation in which allelic genes
are different, e.g. the Kk genotype in the Kell BGS
or the Fya Fyb genotype in the Duffy BGS.
 Homozygous: The situation in which allelic genes
are identical, e.g., the KK genotype or the Fya Fya
genotype.
 Human Genome Project: A worldwide project to
map and sequence the human genome. The
ultimate goal is to produce the complete nucleotide
sequence of every human chromosome.
 Karyotype: A photomicrograph (photograph
taken through a microscope) of all the
chromosomes in a person, arranged in standard
classification (from #1 chromosomes through to
the sex chromosomes).
 Linkage: Genes are linked if they are on the
same chromosome within a measurable
distance of each other and are normally
inherited together, e.g., Lutheran and Secretor
genes are linked as are the Dd, Cc, Ee sub loci in
the Rh BGS.
 Locus: The location of allelic genes on the
chromosome, e.g., A, B, and O genes occur at
the ABO locus. (Plural = loci)
 Mapping of genes: A variety of processes that include
discovering that a gene is linked to another gene (which can
serve as a marker for it), assigning genes to particular
chromosomes, assigning genes to specific regions on
chromosomes, and determining nucleotide sequences on
chromosomes.
 Meiosis: The type of cell division that occurs in sex cells by
which gametes having the haploid number of chromosomes
are produced from diploid cells.
 Messenger RNA (mRNA): Type of RNA polymerase using
DNA as a template. Contains the codons that encompass
the genetic codes to be translated into protein.
 Mitosis: Cell division that results in the formation of two
cells, each with the same number of chromosomes as the
parent cells.
 Mutation: A permanent inheritable change in a
single gene (point mutation) that results in the
existence of two or more alleles occurring at the
same locus.
 Nucleic acids: Polymers of phosphorylated
nucleosides, the building blocks of DNA and
RNA.
 Nucleoside: The building blocks of RNA and
DNA. Compounds consisting of a purine
(adenine or guanine) or pyrimidine (thymine or
cytosine) attached to ribose (in RNA) or
deoxyribose (in DNA) at the 11 carbon.
 Pedigree: A diagram representing a family tree.
 Phenotype: The antigens (traits) that result from
those genes that are directly expressed (can be
directly antigen typed), e.g., group A in the ABO.
 Plasmid: Extrachromosomal circular DNA in
bacteria. Plasmids can independently replicate
and encode a product for drug resistance or some
other advantage. Used in molecular genetics as
vectors for cloned segments of DNA.
 Polymerase chain reaction: An in vitro method of
amplifying DNA sequences hundreds of millions
to billions of times in a few hours.
 Polymorphism: The existence of two or more
different phenotypes resulting from two or
more alleles, each with an appreciable
frequency. Most blood group systems are
polymorphic.
 Polypeptides: Polymers of amino acids that
form the building blocks of proteins.
 Population genetics: The branch of genetics that
deals with how genes are distributed in
populations and how gene and genotype
frequencies stay constant or change.
Calculations are based on the Hardy-Weinberg
law.
 Recessive: Genes are recessive if the phenotype that
they code for is only expressed when the genes are
homozygous, e.g., le le genes, in the Lewis system
or h h genes in the ABO BGS.
 Recombinant: A person who has a new combination
of genes not found together on the chromosome in
either parent, e.g., an MS/Ns offspring whose
parents are Ms/NS and MS/MS. A recombinant
results from crossing over in one parent.
 Recombinant DNA: In molecular genetics, artificially
made DNA composed of fragments of DNA from
different chromosomes (often from different
species) that have been joined together (spliced) by
genetic engineering.
 Restriction endonucleases: DNA enzymes of
bacterial origin that can cleave DNA at internal
positions on a strand because they recognize
specific sequences (usually 4-6 base pairs).
 Restriction fragment length polymorphisms
(RFLP): Regions of DNA of varying lengths that
can be cut out of DNA by restriction
endonucleases. Because the fragment lengths
vary among individuals, they are polymorphic
and can be used as genetic markers.
 Ribosomal RNA (rRNA): Type of RNA found in
ribosomes, the site of protein synthesis in the
cytoplasm.
 RNA Ribonucleic acid: Nucleic acids that are
formed using DNA as a template. Similar to
DNA except has ribose in place of deoxyribose
and uracil in place of thymine.
 Sex chromosomes: The chromosomes that
determine sex. XX in females and XY in males.
 Sex-linked: An outdated term for genes on the
X chromosome. Historically synonymous for Xlinked since, apart from genes essential for
male sex determination, the Y chromosome
appears to have few recognized gene loci.
 Somatic chromosome: A non-sex chromosome
(soma=body). Synonym is autosome.
 Syntenic: Genes are on the same chromosome
but are not close enough for linkage to be
demonstrated.
 Transcription: Synthesis of single-stranded RNA
by RNA polymerase using DNA as a template.
The process in the nucleus whereby DNA is
transcribed into mRNA.
 Transfer RNA (t RNA):Type of RNA that
facilitates translation of mRNA into protein.
Contains anti codons that provide the molecular
link between the codons of mRNA and the
amino acid sequences of proteins.
 Translation: The process of
translating the codon sequence in
mRNA into polypeptides with the
help of tRNA and ribosomes.
 Trans position: Genes in the trans
position are on opposite
chromosomes of a pair of
homologous chromosomes. In the
genotype CDe/cde, for example, D
and c genes are in the trans position.
 X-chromosome: The sex
chromosome present in double dose
in females (XX) and in single dose in
males (XY).
 X-linked: Genes on the X
chromosome, e.g., genes for
hemophilia A, hemophilia B, and Xga
blood group genes.
 Y-chromosome: The sex
chromosome present only in males
(XY).