GENETICS. What is genetics?

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1 GENETICS What is genetics? Genetics is the study of heredity. Genes, made of DNA, are the instruction manuals for making proteins, which combine in many ways to create all the parts of our bodies. Genes are arranged in a defined order in packaging units called chromosomes. Proteins also help to create unique body features called traits. Some traits are visible, like eye color. Others are not, like the ability to fight certain diseases. Scientists who study genetics are called geneticists. What is a genome? A genome is all of the genetic information or hereditary material in an organism. The genomes of individuals within a species are more similar to each other than they are to the genomes of individuals of other species. Does everybody have the same genes? Yes and no. While the human genome is mostly the same in all people, slight differences exist. This genetic variation, spread across many genes, makes up about one-tenth of a percent of each person's DNA. Yet these small differences are enough to create people with different appearances and different health. These differences are often inherited, so the more closely related two people are, the more similar their DNA is likely to be.

2 GENETIC VARIATION What is genetic variation? Simply speaking, variation is difference. Genetic variation is a difference in DNA. The letters of DNA are molecules called nucleotides: adenine, cytosine, guanine and thymine (A,C,G,T) strung together in long chains called sequences. The occasional single-letter differences that distinguish DNA among people are called single-nucleotide polymorphisms (SNPs, pronounced "snips"). Does everybody have the same number of genes? Usually, but not always. A key type of genetic variation is copy number variation, which has been observed in identical twins that otherwise have identical DNA. Typically, everyone has two copies of each gene, one inherited from each parent. But scientists are learning that these DNA regions can carry anywhere from zero to more than a dozen copies of a gene. In some cases, researchers have found, one twin's DNA differs from the other's by having different numbers of copies of the same gene. This can affect the gene s activity level, which can affect traits. Are there other types of genetic variation? Yes. Another type of genetic variation that goes beyond differences in DNA sequence is epigenetics. This type of variation arises from chemical tags that attach to DNA and affect how it gets read. The chemical tags, called epigenetic markings, act as switches that control how genes can be read. Is genetic variation related to health and disease? Yes. Minor differences in DNA sequence have an effect on health and disease risk. Because parents pass on their genes to offspring, some diseases tend to cluster in families, similar to other inherited traits such as some aspects of physical appearance. In addition, epigenetic markings have been associated with some types of disease, such as cancer. However, it is important to recognize that many factors other than genes, including diet, exercise and environmental exposures, also contribute to health and disease.

3 Genetic variation Without genetic variation, some of the basic mechanisms of evolutionary change cannot operate. There are three primary sources of genetic variation, which we will learn more about: 1. Mutations are changes in the DNA. A single mutation can have a large effect, but in many cases, evolutionary change is based on the accumulation of many mutations. 2. Gene flow is any movement of genes from one population to another and is an important source of genetic variation. 3. Sex can introduce new gene combinations into a population. This genetic shuffling is another important source of genetic variation.

4 Mutations Mutation is a change in DNA, the hereditary material of life. An organism's DNA affects how it looks, how it behaves, and its physiology all aspects of its life. So a change in an organism's DNA can cause changes in all aspects of its life. Mutations are random Mutations can be beneficial, neutral, or harmful for the organism, but mutations do not "try" to supply what the organism "needs." In this respect, mutations are random whether a particular mutation happens or not is unrelated to how useful that mutation would be. Not all mutations matter to evolution Since all cells in our body contain DNA, there are lots of places for mutations to occur; however, not all mutations matter for evolution. Somatic mutations occur in non-reproductive cells and won't be passed onto offspring. For example, the golden color on half of this Red Delicious apple was caused by a somatic mutation. The seeds of this apple do not carry the mutation. Gene flow Gene flow also called migration is any movement of genes from one population to another. Gene flow includes lots of different kinds of events, such as pollen being blown to a new destination or people moving to new cities or countries. If genes are carried to a population where those genes previously did not exist, gene flow can be a very important source of genetic variation. In the graphic below, the gene for brown coloration moves from one population to another.

5 Sex and genetic shuffling Sex can introduce new gene combinations into a population and is an important source of genetic variation. You probably know from experience that siblings are not genetically identical to their parents or to each other (except, of course, for identical twins). That's because when organisms reproduce sexually, some genetic "shuffling" occurs, bringing together new combinations of genes. For example, you might have bushy eyebrows and a big nose since your mom had genes associated with bushy eyebrows and your dad had genes associated with a big nose. These combinations can be good, bad, or neutral. If your spouse is wild about the bushy eyebrows/big nose combination, you were lucky and hit on a winning combination! This shuffling is important for evolution because it can introduce new combinations of genes every generation. However, it can also break up "good" combinations of genes.

6 Name: Section: Date: Genetic Variation and its Relationship to Meiosis and Sexual Reproduction - Genetics is: - Genes are: - Genes are arranged: - What is a genome? - What is genetic variation?

7 - Three things that cause genetic variation: o o o - Why genetic variation is important: o - The role mitosis and meiosis play in genetic variation: o

8 Genetic Variation and its Relationship to Meiosis and Sexual Reproduction THESE NOTES COME STRAIGHT FROM THE READING: - Genetics is: the study of heredity - Genes are made of DNA and are the instruction manual for making proteins, which combine I many ways to create all the parts of our bodies. - Genes are arranged: in a defined order in packaging unit called chromosomes. - What is a genome? All the genetic information or hereditary material in an organism. - What is genetic variation? Variation = difference. Genetic variation is a different in DNA. THESE NOTES REFERENCE THE READING BUT DO NOT COME STRAIGHT FROM IT: - Three things that cause genetic variation: o Mutations: random changes in DNA can lead to new combinations and more differences. o Gene flow: the movement of genes into and out of a population can create new combination and more differences. o Sex: combining genes from different lineages creates new genetic combinations and more differences. - Why genetic variation is important: o Differences are good. When a population has genetic variation, it I less likely that a single event or disease can take out of the entire population. It is more likely that at least a part of the population would be able to survive and reproduce. - The role mitosis and meiosis play in genetic variation: o Mitosis does not affect genetic variation, because it creates cells that are identical to the parent cell, they don t increase the amount of difference. o Meiosis increases genetic variation, because of cross over and then fertilization.