How does DNA determine what an organisms looks like? Why is genetic diversity important? Students will review how DNA codes for proteins, which determines what an organism looks like and how it contributes to genetic diversity and why this is important for evolution. This teacher sheet will provide background information and answers for the Introduction to Generics student sheet.
1. Draw the central dogma for how DNA makes protein below.
DNA to (transcription) RNA to (translation) protein
Students should have a basic understanding of this concept. DNA serves as the genetic code or blueprint for all life. Based on one’s interaction with the environment and what is needed, specific genes on the DNA will be transcribed into RNA. Think of transcription as taking one form of language, as in speech or text, and having to transcribe or make a copy of it in a different form. One of the review videos mentions transcription as going to the library and not being able to check out a book and having to take notes on a separate sheet of paper to take with you. Then translation is where the RNA serves as the code to determine how the protein will be made. Specifically, RNA codes for amino acids, which serve as the building blocks for protein. A string of amino acids will then fold into a functional form, which is the protein. Have the students think of translation as taking the notes from the library and translating it into a different language. This process is very important and a mutation or change in the DNA will impact the protein.
2. Define genotype and phenotype. Which part of the central dogma above represents the genotype and which represents the phenotype?
Genotype is the genetic code such as a gene (DNA). Phenotype is the physical appearance due to the activity of proteins which are coded by a gene. The genotype translates into the phenotype.
3. Define gene and allele. Where are genes found? Where are alleles found?
Genes are specific sequences on the DNA that code for protein. Alleles are different versions of genes. Remind students that they have 46 total chromosomes but they come in 23 pairs. We receive one set from our mother and one set from our father. These chromosomes are homologous, meaning they contain the same genes but can vary with different alleles or versions of those genes. For example, a child may receive a blue allele for the eye color gene from one parent and a brown allele for the eye color gene from the other. Different alleles and different combinations of these alleles allow for genetic diversity. This is why you don't have a sibling that looks identical to you (unless you have an identical twin). Genes and alleles are found on DNA which is folded around proteins and further compacted into chromosomes.
4. What is heredity? How many chromosomes do you get from each parent?
Heredity is the passing of genetic traits to offspring. Offspring receive 23 chromosomes from each parent. There are 22 autosomes (all other chromosomes) and one sex chromosome (X or Y) from each parent.
5. What does genetic diversity mean? Why is this important for natural selection and evolution?
Genetic diversity is the diversity at the level of our genes. It is the variation in the alleles present in a population that makes up genetic diversity. Natural selection acts on this variation in a population and the ones that are best adapted to the environment due to these traits will be more successful at surviving and reproducing. This will ensure that these traits will pass on to future generations and then over time the population can evolve to have these traits. There are many sources of genetic diversity. Random mutations can occur in the DNA to bring about new proteins and traits that can be beneficial. During sexual reproduction, there is random shuffling of alleles that allows for variation in offspring. In the book, it mentions cases of how inbreeding and low genetic fitness are harmful to the survival of populations. However, with the case of the right whales in chapter 4, the whales have low genetic diversity yet have survived for a very long time.
6. In your own words briefly describe CRISPR-Cas9 and one genetics application it can be used for.
Answers may vary and students really don't need to go into great detail. Here is a more detailed response: CRISPR-Cas9 is a system used by bacteria to make an inventory of viral DNA from bacteriophages (viruses that specifically infect bacteria) that have infected them. It is their version of acquired immunity. The components are the Cas9 protein, which recognizes this viral DNA and chews it up, and the guide RNA, which is a complementary sequence that guides Cas9 to the viral DNA. This system has been further developed for use in genome editing in other cells in which guide RNA can be designed to target specifc genes by the Cas9 protein. These genes can either be removed or removed and replaced with another gene.
Applications: repair mutated genes in patients and treat disease; edit human embryos; de-extinction projectsThis teacher sheet is a part of the Resurrection Science lesson.