What are genetic balancers?
Genetic balancers are genetic constructs or chromosomal rearrangements that allow lethal or sterile mutations to be stably maintained in heterozygotes. In this chapter we use the term balancer primarily to refer to chromosomal duplications or rearrangements that suppress crossing over.
What are the three main properties of balancer chromosomes?
Typical balancer chromosomes are designed to (1) carry recessive lethal mutations themselves, eliminating homozygotes which do not carry the desired mutation; (2) suppress meiotic recombination with their homologs, which prevents de novo creation of wild-type chromosomes; and (3) carry dominant genetic markers, which …
How many chromosomes do drosophila have?
While drosophila only have a total of 4 chromosomes, they too display sexual dimorphism, with females carrying the double X chromosomes and males carrying XY. The two X chromosomes in female fruit flies, as in mammals, make them a homozygous sex as compared with the XY condition in males, known as heterozygous.
Why are Virgin flies used?
Virgin flies are needed to make sure that that the crosses are being appropriately made with the females using the desired sperms to fertilize their eggs. Female Drosophila are considered virgin eight to ten hours after they hatch from their pupa because during that time they are not receptive to male companionship and …
What animal has the most amount of chromosomes?
The organism with the highest chromosome number recorded in to date is estimated to be 1,440 (or 720 pairs) found in the adder’s tongue fern Ophioglossum reticulatum.
Is wild type always dominant?
Gain-of-function alleles are almost always dominant to the wild type allele. Hypermorph alleles produce more of the same, active product.
What are the characteristics of a balancer chromosome?
Second, balancers contain easily visualized dominant markers so that they can be followed in living flies from one generation to the next. For example, all flies with the second chromosome balancer, CyO, have curly wings. And last, most balancer chromosomes are homozygous-lethal.
What causes random mutations in the balancer chromosome?
In the modern usage of balancer chromosomes, random mutations are first induced by exposing living organisms with otherwise normal chromosomes to substances which cause DNA damage; in flies and nematodes, this usually occurs by feeding larvae ethyl methanesulfonate (EMS).
How is the deficiency bearing chromosome stable in a fly?
As a consequence, the deficiency-bearing chromosome remains stable through the crossing scheme. Second, balancers contain easily visualized dominant markers so that they can be followed in living flies from one generation to the next. For example, all flies with the second chromosome balancer, CyO, have curly wings.
How is the balancer chromosome used to suppress recombination?
To suppress recombination, balancers usually harbor multiple, nested chromosomal inversions so that synapsis between homologous chromosomes is disrupted. If crossing over does occur, it is often unbalanced, with each resulting chromatid lacking some genes and carrying two copies of others.