Amnion
The thin membrane that lines the fluid-filled sac in which the embryo develops in higher vertebrates, reptiles and birds.

Amniotic fluid
Liquid contents of the amniotic sac of higher vertebrates, containing cells of the embryo (not of the mother).Both fluid and cells are used for diagnosis of genetic abnormalities in the embryo or foetus

Amorph null mutation
A mutation that obliterates gene function.

Amorphous
having no long-range order.

AMP (adenosine monophosphate)
See ATP.

Amphidiploid
A species or type of plant derived from doubling the chromosomes in the F1 hybrid of two species; an allopolyploid. In an amphidiploid the two species are known, whereas in other allopolyploids they may not be known.

Amphimixis
True sexual reproduction involving the fusion of male and female gametes and the formation of a zygote.

Amplification
1. Treatment (e.g., use of chloramphenicol) designed to increase the proportion of plasmid DNA relative to that of bacterial (host) DNA.
2. Replication of a gene library in bulk.
3. Duplication of gene(s) within a chromosomal segment.
4. Creation of many copies of a segment of DNA by the polymerase chain reaction (PCR)