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ANSWER KEY Review Questions for 8th Grade Science Midyear Exam, Part I (Due Tuesday, January 31, 2017) COMPLETION OF THIS ENTIRE PACKET IS WORTH A 20-POINT QUIZ! NO LATE OR PARTIAL CREDIT WILL BE GIVEN! Write your answers in the spaces provided. As answer keys will be provided on Tuesday, January 31, and answers will be discussed in class, NO LATE CREDIT WILL BE GIVEN. Be prepared to ask questions! Use your classwork, notes, homework, Discovery Education Techbook, the Internet, etc. to answer the questions. # Question Answer Use the Punnett square: It is controlled by a dominant allele, which means that if a seed has even one copy of the allele for yellow seed color, then its seeds will be yellow. 1 Is yellow seed color controlled by a dominant allele or a recessive allele? 2 3 4 Black fur is dominant in rabbits. What combination of alleles must a white rabbit have? The dominant allele for squash color is yellow (Y). What is the genotype of a yellow squash plant that is heterozygous? Tall stem is dominant in pea plants. What are the possible genotypes of a tall pea plant? 5 Black fur is dominant in guinea pigs. A homozygous black guinea pig and a white guinea pig have offspring; list the possible genotype(s) of their offspring. 6 For the offspring in #5, list the possible phenotype(s). 7 Grasshoppers have 24 chromosomes in each of their body cells. How many chromosomes are in each grasshopper sex cell? If black fur is dominant, then the white rabbit has to have two copies of the recessive allele for white fur. Its genotype would have to be bb. BB or Bb would be black. Yy: A heterozygous genotype means that it has two different alleles for skin color. The allele for green skin color (y) doesn’t show up in the phenotype because it is recessive. TT and Tt both result in a tall offspring. Tall is the dominant form of the height gene, so having even one copy of the allele for tall results in a tall phenotype. There is a 0% chance that the offspring will have white fur. All of the offspring are heterozygous (Bb), and black fur (B) is dominant, so only black fur shows up. All of the offspring have the black fur phenotype. (Their genotype is Bb). If grasshoppers have 24 chromosomes in each body cell, then their sex cells have 12 chromosomes. Each sex cell has half the number of chromosomes as a body cell so that when they combine to make an offspring, the offspring has the right number of chromosomes. Explain how a Punnett square models sexual reproduction. A Punnett square shows the possible combination of alleles from sperm and egg. The possible combinations for the offspring are shown inside of the Punnett square. 8 Describe the relationship between DNA, genes and chromosomes. DNA makes up genes, and genes make up chromosomes. 9 10 Use the figure in #9. Describe the functions of (1) DNA, (2) genes and (3) chromosomes? 1. DNA is a molecule that makes up the code for traits for all living things. 2. Each gene is a segment of DNA that codes for a particular trait. 3. Chromosomes are structures that hold the genes. Chromosomes stay in the nucleus of the cell of eukaryotes. 11 Where in the cell are the chromosomes located? 1. 12 What are the three possible effects of mutations? Mutations can be helpful; helpful mutations help an organism to survive and/or reproduce. 2. Mutations can be harmful; these hurt an organism’s chance of survival and/or reproduction. 3. Neutral mutations neither help nor hurt an organism’s chances. True or false? If it is false, change the underlined word to make the sentence true. 13 Heredity is the process by which traits are passed from parents to offspring. TRUE, and genetics is the scientific study of heredity. True or false? If it is false, change the underlined word to make the sentence true. 14 15 An organism’s physical appearance is its genotype. FALSE: An organism’s physical appearance is its phenotype. An organism’s pair of alleles for a particular trait is its genotype Corn has been selectively bred for many Corn has been selectively bred to create larger cobs, sweeter generations. kernels, more kernels per cob, to resist diseases and pests, and for Name two traits that humans have selectively many other traits. bred for in corn. Potatoes reproduce by budding. Is this an example of sexual or asexual reproduction? This is an example of asexual reproduction because there is only one parent. The cutting has the same DNA as the parent plant—that is why it is called a clone. 16 17 18 What is the main advantage of sexual reproduction over asexual reproduction? What is a genetically modified organism? In sexual reproduction, each offspring has a different and new combination of traits from its two parents. This new combination allows each offspring to have a different chance of survival under different conditions. When the environment changes, at least some of the offspring are likely to survive. A genetically modified organism is a living thing that has had its genes changed by human activity. This can be done through selective breeding or through genetic engineering. 19 List 2 examples of genetically modified organisms. Some GMOs that we went over in class include: Bt corn, golden rice, spider goats a. inbreeding c. DNA fingerprinting 20 Inserting a human gene into a bacterial chromosome is an example of: (circle one) b. selective breeding d. genetic engineering Genetic engineering is the process by which scientists change the genetic makeup of an organism. In this example, scientists take a gene from one species (humans) and put it into the genome of another (a bacteria). This is done to create human proteins such as insulin.