- Some genes are
lethal when both alleles are present. Lethality can occur before or after
disease in humans is caused by a lethal allele, death occurs later in life
- Other examples:
Mouse coat color (yellow), Creeper legs in chickens, Manx Cats (no tails)
An example is the
"creeper" allele in chickens, which causes the legs to be short and
- Creeper is a
dominant gene, heteroyzous chickens display the creeper phenotype
- If two creeper
chickens are crossed, one would expect to have (from mendelian genetics) 3/4
of the offspring to be creeper and 1/4 to be normal
- Instead the
ratio obtained is 2/3 creeper and 1/3 normal.
- This occurs
because homozygous creeper chickens die.
possess a gene for producing a tail. The tailles Manx phenotype in cats is produced
by an allele that is lethal in its homozygous state. The allele interferes with
normal spinal development, in heterozygous cats this results in lack of a tail.
the cross between a manx cat and a normal cat.