Glossary Plant Breeding

Sibs. Progeny of the same parents derived from different gametes. Also called full sibs.
Half-sibs are progeny with one parent in common. Also called siblings.
Sib Mating. The intercrossing of the progeny of the same parents, that is, brother-sister
mating. It is the closest form of inbreeding possible in self-incompatible species such
as alfalfa.
Sickle-cell Anaemia. A potentially lethal human disease caused by a mutation in a gene
that codes for the oxygen-transporting molecule, haemoglobin. Haemoglobin, which
is a conjugated protein and an integral part of red blood cells, is made up of four
polypeptide chains (2α and 2β chains). A single gene mutation causes alteration at 6 th
amino acid position in β-globin chain wherein amino acid valine is substituted for
glutamic acid [codon change: GAG (glutamic acid)→ GTG (valine)]. The altered
molecule causes red blood cells to be sickle-shaped. This trait is inherited as an
autosomal recessive.
Silencer. A cis-regulatory sequence that can reduce levels of transcription from an
adjacent promoter.
Silent mutation. Mutation in which the amino acid sequence and function of the protein
is unaltered. For example, a single gene mutation can alter the nucleotide sequence of
DNA in such a way that the altered codon encodes the same amino acid in a
polypeptide chain (CGU ↔ CGA; both coding for the same amino acid, arginine). As
amino acid sequence does not change, the mutation goes on unnoticed, that is,
silently.
Simple Recurrent Selection. A system of breeding in which the population for next
cycle of selection is synthesized from intercrosses made in all possible combinations
from a number of desirable genotypes (or their selfed progeny) of the original
population. Since testcrosses are not made, the effective use of simple recurrent
selection is restricted to characters with high heritability that can be judged visually or
by simple breeding tests (e.g. resistance to leaf blight in corn).
SINE. Short Interspersed Element; a type of small repetitive DNA sequence found
throughout the eukaryotic genome.
218