Chapter 6 "Survival of the Sickest"

Chapter 6 of "Survival of the Sickest", Jump into the Gene Pool, is all about genes and DNA. It starts with an introduction of the word vaccine which came form the Latin word for cow, vacca, and the Latin word for cowpox, vaccinia. The story continues to say that every person has 46 chromosomes. Each person is given 23 chromosomes from each parent, and scientist have discovered that only about 3% of the DNA is active in building cells while the other 97% "junk DNA" more commonly known now as noncoding DNA which only means it isn't responsible for making proteins. The story continues on to talk about mutations and that genetic changes can occur from errors or sometimes chemical disruptions. It explains that virus outbreaks are caused by antigenic drift, when mutation occurs in the DNA of a virus, or antigenic shift, when a virus get new genes from a related strain. The author also speaks on "jumping genes" which was discovered by Barbara McClintock. "Jumping genes" are mutations in which a DNA sequence duplicates itself in another location changing the gene sequence. There are two types of "jumping genes", DNA transposons, which work through a cut and paste process, or DNA retrotransposons, which work through a copy and paste process. This is a large part of what differentiates our noncoding DNA.

From Atoms to Traits

1. George Mendel led a series of of breeding experiments during the 1850's-60's with different pea plants that showed morphological differences. It showed how some differences in pea plants stem lengths, seed smoothness, and many other differences. Mendel's experiment showed that heritable traits were passed from parents to offspring even though they weren't always visible. This led to the discovery that this pattern is mirrored within the chromosomes in a cell nucleus.

2. James D. Watson and Francis Crick discovered that DNA is made of two stranded helix held together with pairing of the four chemical bases: adenine, cytosine, guanine, and thymine which are passed form parent to offspring. It looks like 

3.

1. Point Mutation- A single base pair is changed changing the traits of a species. An example are whippet dogs. The simple change in one base pair changes the muscle growth of the dog which changes its main skills and abilities.
2. Insertion- Additional base pairs to genes changes the traits of a species. An additional 800 base pair is added to the genes of peas to make them wrinkled rather than smooth.
3. Gene Copy Number- Duplicating by copying errors in genes can cause differences as well as variations between the same species. Chimpanzees carry one gene for the starch digesting enzyme whereas humans can carry up to 10.
4. Duplication- Strands repeating the same base pair eight or more times are called homopolymers which are prone to copying errors. In pigs two additional C-G pairs cause light colored coats, but by duplicating mistakes the pig can get dark patches.
5. Regulatory Changes- Mutations that control the genes location can transform the formation of an organism. Changes in the region of a single gene cause the difference between the bushy teosinte plant and the tall modern cornstalk.

4. Evo-devo studies the evolutionary development of organisms or the study of influential developmental genes and their role in evolution.

5. As we already know, life started in Africa. Since life started in Africa and it is shown that the gene that allows people to produce lactase is common in Saudi Arabia we can deduce that humans were originally made with the ability to produce lactase throughout their life. As modern day comes to be we see that more and more people have lost this gene. From this information we can only conclude that somewhere after the human migration from Africa people began developing a different gene that doesn't allow them to produce lactase as an adult. This gene has been passed on for centuries through travel as has now made the common person unable to produce lactase as an adult.

Founder Mutation

Founder Mutation

            Medical researchers, geneticist, and scientist have recently been able to come to the conclusion that it is possible to trace a person’s ancestry through their DNA. In genetic mutations that are hereditary these genes will be passed on to all of their future generations. This person with the initial mutation is called the founder and their genetic legacy is called the founder mutation. Many founders are identified for carrying hereditary disease like sickle-cell anemia, cystic fibrosis, and other deficiencies. This disease is created in the founder’s genes and can be shown in their DNA as well as all of their descendants. Most changes in people’s DNA are eliminated at birth, but these natural diseases are created by germ-line mutation, which survive after birth and are able to be passed on.

            There are also hot-spot mutations, which cause things like dwarfism. Hot-spot mutations occur in DNA base pairs that are prone to mutations.  People with hot-spot mutations usually have no relation to one another besides the mutation in the base pair. This is unlike founder mutations which are passed on through generations, and with founder mutations the length of the damaged DNA is shortened every generation. The stretch of damaged DNA is called the haplotype, and people with the same haplotype share a common ancestor. Tracing haplotypes is how geneticists have been able to trace the founder of the mutation and track certain populations. Disease mutations exist at a very small rate while founder mutations can be found by percent in a population.

            The article along with many people often question, “Why does evolution preserve rather than weed out such seemingly detrimental mutations”? The reason is that in order to receive the disease from the founder mutation, the offspring must receive the mutation from both parents. A person that receives it from only one parent is called a carrier. Carriers will never receive the disease, and they also receive certain advantages for carrying the mutations. A great example is sickle-cell anemia. Carriers will survive malaria infections, but a person with two copies of the mutation is prone to pain and a short life. Sickle-cell anemia has five different haplotypes meaning it was born naturally five different times showing the profitability of the mutation.

            With this information geneticist have been able to piece together the human past. They have been able to determine that humans started in Africa and that about 75,000 years ago a subgroup left Africa. This is shown in the PTC gene which the humans that left developed a mutation from a founder that allowed them not to taste certain bitterness in certain chemicals and plants. Geneticist were able to conclude that the subgroup left Africa around 75,000 years ago by studying the length of the haplotype. This is just one example for the many benefits geneticist have learned to study in our DNA to develop human evolution.