Genetics Primer to Evolution Goal: Provide you with just enough background to understand how Evolution works. We will revisit this material in much greater depth later in the year.

Objective 1: What is a gene?

Summary: What is a gene? Understand the following statements: DNA is a double chain of nucleotides, that come in four kinds (A, C, G, T). Proteins are chains of amino acids, that have specific functions in the organism. The order of the nucleotides in the DNA encodes for the order of amino acids in a protein. A gene is a region in the long DNA that encodes for one protein.

DNA is a double chain of nucleotides, that come in four kinds (A, C, G, T). Perspective: Cells, Chromosome, DNA, Nucleotides

Nucleotides are molecules that are very similar to each other, except for one part: (You do not need to memorize this now, it is just mentioned to make things concrete) A G C T

DNA is made in fact of TWO chains of nucleotides, which ALWAYS obey the pairing rules: A opposite T and C opposite G (This will explain how DNA replicates when a new cell is made, but that’s for later).

The order of nucleotides (AGGTCATCC, TGCCTAAC, or whatever it is) in the DNA provides the information of making another kind of molecule, Proteins. Proteins are also chains of small molecules, called amino acids. There are 20 kinds of amino acids, and each protein has a specific order of these amino acids in the chain. The order of amino acids will determine how the entire chain will fold into a certain shape, and therefore will determine what the protein will be able to do.

Here are example of a few different proteins (colors are only for clarity. Proteins are usually colorless)

Stated Clearly: What is DNA and how does it work? The order of nucleotides is read in the cell to give the order of amino acids in the protein. It is done through an intermediate molecule called RNA (but that’s for later).

DNA is a very long molecule made of millions of nucleotides DNA is a very long molecule made of millions of nucleotides. It has many regions that contain information for proteins, and between them there are chains of nucleotides that we don’t always know what they do. A stretch of nucleotides that encodes for a single protein is called a GENE. Every single DNA molecule contains thousands of different genes.

- ALL genes are written in the same genetic code. Stated Clearly: What exactly is a Gene? A gene is a stretch of DNA that codes for a protein. Genes can differ between organisms, but there are genes that many, or even all organisms have in common. - ALL genes are written in the same genetic code.

(What causes genetic variation?) Objective 2: How do genes change? (What causes genetic variation?)

Mutations can have a negative, positive or no effect on the organism. Stated Clearly: How does new genetic information evolve? DNA Replication is pretty accurate but it is not perfect. Sometimes mistakes occur, and sometimes they are not corrected. Even if these mistakes, called mutations, can be increased (by radiation, for example), their location along the DNA sequence is RANDOM. Mutations can have a negative, positive or no effect on the organism.

How does a gene cause a trait? Example: Sickle Cell Anemia Objective 3: How does a gene cause a trait? Example: Sickle Cell Anemia

A gene encodes for a protein, and the protein molecule does a certain function that affects the organism. For example, the gene for hemoglobin encodes for the hemoglobin protein, which carries oxygen in the blood, and the blood will deliver the oxygen to the entire body. But when there is a mutation in the hemoglobin gene, it causes an error in the amino acid order of the hemoglobin protein. This protein will now fold incorrectly and cause multiple symptoms.

http://www.pol2e.com/mc09.02.html

Example: Normal and Sickle Cell Anemia Objective 4: How are genes passed on? Example: Normal and Sickle Cell Anemia

Most organisms on Earth reproduce sexually, meaning that every organism has two parents. An offspring is formed when the sperm cell from the father fuses with an egg from the mother, and the combined cell multiplies and grows into an embryo

As a result of having two parents, every gene comes in pairs, one from each parent. But the gene that comes from the mother is not necessarily identical to the gene that comes from the father. Hb Hb: Gene for hemoglobin, Can be HbA (normal) or HbS (Sickle cell)

A – stands for the dominant allele a – stands for the recessive allele In simple cases of inheritance, there are two versions of a gene (called alleles), and if they both show up in the organism, only one of them will have an effect. It is the same as saying that one allele is dominant and other one is recessive. Standard symbols: A – stands for the dominant allele a – stands for the recessive allele AA – effect 1 aa – effect 2 Aa – effect 1

A few useful terms: Pair of alleles for a certain gene: genotype Homozygous genotype: aa, AA Heterozygous genotype: Aa The resulting effect of the genes on the organism: Phenotype Accordingly: “Homozygous dominant (AA) and heterozygous (Aa) individuals share the same phenotype”.

No Symptoms Symptoms In the case of Sickle Cell Anemia: The allele HbA for normal hemoglobin is dominant over the allele HbS for sickle cell disease, because when they are mixed, there are no symptoms.

The genetics of sickle cell anemia (Jamaica) A parent that is healthy but has a sickle cell allele, is called a carrier. If both parents are carriers, there is a 25% chance for them to have a child with sickle cell disease. Can you see why?

Case I

HbA/HbS HbS Case II

How Does Natural Selection Happen? Objective 5: How Does Natural Selection Happen? Example: Case of Sickle Cell Anemia in Africa

Natural Selection occurs at the level of the population, not the individual. A gene pool is the collection of all the genes, with all their versions (alleles) in the population. When natural selection occurs, it means that changes occurred in the abundance (or frequency) of certain alleles in the gene pool. Alleles that have a negative effect on the organism are likely to reduce, whereas alleles that have a positive effect are likely to increase in frequency.

Natural Selection: Changes in the gene pool Bozeman Science: Natural Selection Natural Selection: Changes in the gene pool Example: Peppered Moth, watch 0-5:30 min Bozeman: Examples of Natural Selection Blueberries, Seashells, Sickle Cell Anemia, Tuberculosis (TB) antibiotic resistance