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Title: How to distinguish between recessive lethal alleles and dominant lethal alleles? Post by: nursenerd on Feb 23, 2013 How to distinguish between recessive lethal alleles and dominant lethal alleles?
Oh well, what exactly do you call a lethal allele in the first place? Thanks in advance :) Title: How to distinguish between recessive lethal alleles and dominant lethal alleles? Post by: asmckinley on Feb 23, 2013 Content hidden
Title: How to distinguish between recessive lethal alleles and dominant lethal alleles? Post by: Smntnl on Feb 23, 2013 Dominant Lethal Alleles are rarely considered in genetics. As they cannot be inherited. Which makes sense because how can you give a allele to your offspring if you don't survive the prenatal phase. Dominant lethal alleles can only occur due to spontaneous mutation - and will kill the offspring.
Recessive lethal alleles are more interesting, the offspring can survive with one copy of the gene (heterozygous). Therefore, the ratio would be 2:1 - as the homozygous rec. would be dead. A lethal allele is just an allele that causes the offspring to be inviable. Title: How to distinguish between recessive lethal alleles and dominant lethal alleles? Post by: RIVAS3 on Feb 23, 2013 "Alleles that cause an organism to die only if present in homozygous condition are called lethal alleles, where the gene involved is an essential gene.
Examples of diseases caused by recessive lethal alleles are cystic fibrosis, Tay-Sachs disease, sickle-cell anemia, and brachydactyly. Huntington's disease is caused by a dominant lethal allele and even though it is not described as lethal, it is invariably lethal in that the victim experiences gradual neural degeneration and mental deterioration for some years before death occurs. This gene causes a death if both recessive alleles are possessed by the same individual. Recessive lethal alleles don't cause death in the heterozygous form because a certain threshold of protein output is maintained. In the homozygous form, the protein output doesn't meet the threshold, causing death." To explain it in simple terms, for a certain gene you have recessive allele (lets call it r) and dominant allele (R). Now, if you are heterozygous - you have Rr then you don't die from a recessive lethal allele, for that you need to have rr - both alleles must be the recessive ones. If we are talking about a dominant lethal allele - the chance to get it is much higher (because its the dominant one) so if you have RR or Rr - then it will be lethal (the chance to have the other combination is only 25%). |