* Your assessment is very important for improving the workof artificial intelligence, which forms the content of this project
Download Les 10 Deliterious Genes ppt
Epigenetics of diabetes Type 2 wikipedia , lookup
Fetal origins hypothesis wikipedia , lookup
Saethre–Chotzen syndrome wikipedia , lookup
Quantitative trait locus wikipedia , lookup
Ridge (biology) wikipedia , lookup
Oncogenomics wikipedia , lookup
X-inactivation wikipedia , lookup
Population genetics wikipedia , lookup
Genomic imprinting wikipedia , lookup
Biology and consumer behaviour wikipedia , lookup
Minimal genome wikipedia , lookup
Genome evolution wikipedia , lookup
Polycomb Group Proteins and Cancer wikipedia , lookup
Gene desert wikipedia , lookup
Genetic engineering wikipedia , lookup
Gene nomenclature wikipedia , lookup
Epigenetics of neurodegenerative diseases wikipedia , lookup
Nutriepigenomics wikipedia , lookup
Therapeutic gene modulation wikipedia , lookup
History of genetic engineering wikipedia , lookup
Public health genomics wikipedia , lookup
Epigenetics of human development wikipedia , lookup
Gene therapy wikipedia , lookup
The Selfish Gene wikipedia , lookup
Gene expression programming wikipedia , lookup
Neuronal ceroid lipofuscinosis wikipedia , lookup
Gene therapy of the human retina wikipedia , lookup
Site-specific recombinase technology wikipedia , lookup
Gene expression profiling wikipedia , lookup
Point mutation wikipedia , lookup
Vectors in gene therapy wikipedia , lookup
Artificial gene synthesis wikipedia , lookup
Genome (book) wikipedia , lookup
Deleterious Genes Introduction • A “perfect” population would not carry any deleterious genes—but as we’ve already seen, natural selection does not produce a perfect population. • Deleterious means damaging—deleterious genes will lead to mild to severely disabling or even fatal conditions at some point in life. Intro (cont’d) • We would expect natural selection to remove genes with negative effects from a population. • Individuals who carry those genes would not have the opportunity to reproduce as much, so the genes should not be passed on. • And yet we see cases where this expectation is not met . . . Why might deleterious genes exist in a population? 1. They may be maintained by heterozygote advantage. • • • Sometimes carrying two copies of a gene is disadvantageous and carrying only one copy is advantageous, In this case, natural selection will not remove the gene from the population i.e. the advantage conferred in its heterozygous state keeps the gene around. Sickle cell anemia • Autosomal recessive inheritance pattern. • The gene that causes this condition is deleterious if you carry two copies of it. Normal red blood cells (top) and sickle cells (bottom). Sickle cell anemia • If you carry only one copy of it, and live in a place where malaria is common, the gene is advantageous. • It confers resistance to malaria. Normal red blood cells (top) and sickle cells (bottom). • E.g. What is the probability of two parents, heterozygous for sickle cell anemia, having: – a child with the sickle cell condition? – A child who will be “immune” to malaria? 2. They may not really reduce fitness. • Some genetic disorders only exert their effects late in life, after reproduction has taken place. • For example, the gene that causes Huntington’s disease typically does not exert its devastating effects until after a person’s prime reproductive years. • Such genes will not be strongly selected against, because an organism’s fitness is determined by the genes it leaves in the next generation and not its life span. • Often, a fetus with homozygous dominant deleterious genes, such as Huntington’s, will not survive. 3. They may be maintained by mutation. • The mutation may keep arising in the population, even as selection weeds it out. • For example, neurofibromatosis is a genetic disease causing tumors of the nervous system—it is a dominant condition that is inherited from mutations in gametes. • Natural selection cannot completely eliminate the gene that causes this disease because new mutations arise relatively frequently – in perhaps 1 in 4000 gametes. • We are unsure of the cause of these spontaneous mutations. 4. They may be maintained by gene flow. • The gene may be common, and not deleterious, in a nearby habitat. • If migration from the nearby population is frequent, we may observe the deleterious gene in the population of interest. • For example, in places like the U.S., where malaria is not a problem, the gene that causes sickle cell anemia is strictly disadvantageous. • However, in many parts of the world, the gene that causes sickle cell anemia is more common because a single copy of it confers resistance to malaria. • This becomes the advantage—thus keeping the deleterious sickle cell gene at a high level in the population. Figure 2. Schematic representation of the effect of the sickle cell hemoglobin gene on survival in endemic malarial areas. • People with normal hemoglobin (left of the diagram) are susceptible to death from malaria. Figure 2. Schematic representation of the effect of the sickle cell hemoglobin gene on survival in endemic malarial areas. • People with sickle cell disease (right of the diagram) are susceptible to death from the complications of sickle cell disease. Figure 2. Schematic representation of the effect of the sickle cell hemoglobin gene on survival in endemic malarial areas. • People with sickle cell trait, who have one gene for hemoglobin A and one gene for hemoglobin S, have a greater chance of surviving malaria and do not suffer adverse consequences from the hemoglobin S gene. The sickle-cell trait has spread far and wide, outside the Americas. Regions where the trait is more commonly found (shown in orange stripes) overlap areas where malaria is prevalent (shown in green). RECESSIVE DELETERIOUS GENE CONDITIONS • MOST (not all) deleterious genes are recessive traits. Heterozygous people for the trait are carriers but are not afflicted by the condition. •Alkaptonuria •Sickle cell anemia •Cystic fibrosis •Tay Sachs •Duchenne’s muscular dystrophy •Adenoleukodystrophy (ALD) •Hemophilia •Alper’s syndrome •Lesch-Nyhan syndrome •Zellweger’s syndrome •PKU •Aarskog syndrome DOMINANT DELETERIOUS GENE CONDITIONS • Some deleterious genes are dominant. Heterozygous people for the trait exhibit the condition. •Brachydactyly •Congenital stationary night blindness •Fascio-scapulo-humeral muscular dystrophy •Huntington’s disease •Pseudo-achondrophastic dwarfism •NF-1 (Neurofibromatosis type 1) •Marfan syndrome •Machado-Joseph disease Poster Project: Precious Humans • See handout • Two classes – One computer day – One work day • HowStuffWorks Videos "Your Body Your Health: Sickle Cell Disease"