Survival of the Sickest Chapter 6 Summary

Human life starts with 46 genes, 23 of them are passed from the father and the other 23 from the mother, these genes help build proteins that build the human body.  These genes act as an active network, and each gene does multiple tasks, not just one, when some genes are removed the other genes help to compensate for these removed genes.

It was believed that evolution happens when mutation in genes occurs randomly, but this phenomenon is rare because there are cells that proofread the process of copying genes, and errors rarely happen. That means that evolution has to take a long time and is not random.

Nobel-prize winning scientist, Barbara McClintock found that corn genes mutated faster when the corn was under stress like drought or extreme heat. This process of mutation is called “jumping genes”, in this process the cell suppresses the proofreading cells so mutation will occur. These mutations were passed on. McClintock also found that mutations under stress happened so fast because the cells were fighting for survival.

 

Future study of human genes found that a huge percentage of human DNA is related to viruses, it is also believed that these viruses contribute to human evolution. Additionally, jumping genes phenomenon occurred in these viruses which is called retrotransposons, there is also another kind of jumping genes called DNA transposons. Both of these tranposons contribute to the rapid evolution of humans.   

 

 

"From Atoms to Traits"

1. The significance of Gregor Mendel is that through his experiments with peas in the 1850's and 1860's, he proved that variants in species are inheritable. Mendel also proved that genetic variants do not "blend" away in future generations, they reappear. This is evidence for Darwin's theory of evolution through natural selection.  

2.  James Watson and Francis Crick discovered the double helix structure for DNA.

 

3. Homopolymers are stretches of DNA with eight or more identical letters in a row are prone to copying errors during DNA replication. An example of homopolymers is microsatellites consists sequences of two or more nucleotides in a row.  The second variation in DNA is when the bases change from G to A. An example of this is in peas when the variation occurs it shortens growth.  The third variation is “jumping” elements which changes gene activity patterns by creating new regulatory sequences. An example is the wrinkly seeds of peas.  The fourth variation is the change in regulatory genes that regulate cell division. An example is the differences between the maize plant and the tesinte plant. The fifth variation is change in pigment cells. An example is the change in human skin color.

4. Evo-devo is studying the effect of changes in important developmental genes and the role they play in evolution.

5. Migration and human reliance on other animal’s milk as a source of food was a result of the mutant form of the lactase gene which is only active in infants in other mammals, continues to be active in human populations they depend on milk as nutrition.

Founder Mutation

            Founder Mutations are changes in the DNA which are inherited future generations. These mutations first occurred in an individual, the founder and were later passed on. These mutations occurred through the process of evolution, to protect against more dangerous and deadly diseases. For example, Sickle-cell anemia originated in Africa to protect against deadly malaria. Sickle- cell anemia makes the red blood cells less hospitable, and malaria only thrives in healthy red blood cells.

            Unlike Founder mutations, hotspot mutations are spontaneous mutations of genes in individuals, individuals who have these mutations are not related to one another and do not share the same DNA. People who have founder mutations have similar DNA because they share a common ancestor.

            When an individual has one copy of the mutant gene they have a better chance of survival than those who have no copies. Individuals with two copies of the mutant gene will probably die before they could reproduce. This is called balancing selection.

 

            The chromosome region surrounding the mutant gene, the haplotype, gets shorter over generations due to recombination of chromosomes. Geneticists can use the haplotypes to trace the origin of a certain population and its migration. By tracing back the founder mutation to a certain region and time in history, geneticists can find when the mutation began and the reason the mutation started.

            The knowledge of founder mutations is valuable to physicians in identifying the types of diseases to test for depending on the ethnicity of an individual. For example, African Americans are more susceptible to Sickle- cell anemia, since the population has become more mixed the study of genes became very important for physicians to establish proper treatment depending on every individual’s DNA. The studies of founder mutations help geneticists find the origins of humans and its migration. In addition, it helps doctors and physician diagnose and treat diseases.

Hardy-Weinberg Problems

In class, 10/11/13, we learned the Hardy- Weinberg formula, which determines the frequency of alleles(genes) in a population. Hardy and Weinberg argued that if five conditions are met, the population's allele and genotype frequencies will remain constant from generation to generation. The five conditions are:

The Hardy-Weinberg formula is:



Here is a Hardy- Weinberg Problem:

 In certain African countries 4% of the newborn babies have sickle-cell anemia, which is a recessive trait. Out of a random population 1,000 newborn babies, how many would you expect of the three possible genotypes?

The first thing you look for is a q(recessive allele frequency) or q^2 (homozygous recessive). The q^2 in this problem is 4% of newborn babies. In order to find q you mush square root the 4%. So the value of q is 0.2. To find p you can just subtract 1-0.2, since you know that p+q=1. p=0.8, and q=0.2.

The problem also asks for the three possible genotypes (q^2, p^2, and 2pq). In order to find these values, you must multiply  your values for q^2, p^2 and 2pq by the total population, 1000.

p=0.8

q=0.2

2pq=0.32

population=1000



Now we use these values to find the number of individuals in each genotype for this population

q^2*population=number of individuals with recessive trait(sickle-cell anemia)

(0.04)^2*1000=40 individuals

p^2*population=number of individuals with the dominant trait

(0.8)^2*1000=640 individuals

2pq*population= number of individuals with the heterozygous trait

(0.32)*1000=320 individuals

Brine Shrimp Lab and Recessive Genes

 

In class, 10/3/13, we collected the second set of data for the brine shrimp lab. In this lab we placed different concentrations of salt water (0.0%, 0.5%, 1.0%, 1.5%, and 2.0%) into Petri dishes. Then we put around 20 brine shrimp eggs and covered them. We collected data after 24 hours and saw that the Petri dish that contained 1.5%   NaCl concentration had the highest number of shrimp swimming( 10 shrimps) , the second highest was the dish containing 0.5% NaCl concentration ( 6 shrimps), and the third was the 1.0% with 4 shrimp swimming. The other two containers did not have any shrimp swimming. After 48 hours we collected more data and saw that there were less shrimp swimming than before, 8 shrimps in the 0.5% and 1 in the 1.5%. The other three containers did not have any shrimp swimming. This lab shows that some shrimp developed variations which made them more adapted to higher concentration salt water than others, and the others could not survive it. This proves the theory of natural selection because only the shrimp that had these variations were more adapted (fit) to the changing environment survived and were able to pass on their genes.

 

 

 

 

            Also in class we did an activity about recessive genes.  We had two types of beads, red beads and green beads. We assigned the red beads to be the dominant gene. We place the beads into a paper bag and selected two beads at a time. If there was a pair of green beads they would die off because it was not the dominant gene. We repeated this process several times and each time we excluded the pairs of not dominant beads. Eventually we found that the dominant gene, the red beads, became more prevalent. This activity represents an isolated community and how the genes over time become similar and recessive.