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Spring 2011 Midterm Review Answers

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1 Spring 2011 Midterm Review Answers
CP BIOLOGY Ms. Morrison

2 Meiosis

3 1. What are gametes? How are they created?
Gametes are haploid cells used in sexual reproduction. Gametes are produced through the process of meiosis which is a form of cell division designed to reduce the number of chromosomes from diploid (2N) to haploid (N).

4 2. What types of cells does meiosis create
2. What types of cells does meiosis create? How are they different from those created by mitosis? Meiosis creates haploid cells – this means that they have only half the number of chromosomes found in regular body cells. Mitosis creates diploid cells that are identical to the original cell. So, mitosis is used only to reproduce cells asexually or to produce new cells in order for the organism to replace old cells or to grow.

5 3. Explain crossing over. When does it occur?
Crossing over is a process that occurs during prophase I of meiosis. During prophase I, the homologous chromosomes with their copies form a tetrad structure where all four chromatids are very close together. During this time, parts of the chromosomes can exchange portions of their chromatids.

6 3. Crossing over

7 4. Explain nondisjunction. When does it occur? What does it create?
Nondisjunction occurs during Anaphase I of meiosis. The homologous chromosomes separate during this stage of meiosis, but when nondisjunction occurs, they fail to separate properly. It creates gametes that have the wrong number of chromosomes – they do not have the chromosome or they have too many of the chromosome. Upon fertilization with another gamete, the embryo can have only one copy (monosomy) or may have three copies (trisomy).

8 DNA/Protein Synthesis

9 5. Who discovered the structure of DNA?
Watson and Crick are credited at having discovered the structure of DNA.

10 6 What is the structure of the DNA molecule called
6 What is the structure of the DNA molecule called? What makes up the sides and steps of it? The DNA molecule has a shape called a double helix. It looks like a twisted ladder. The sides of the ladder are made up of sugars and phosphate groups, while the steps are made up of nitrogenous bases.

11 7. What are nucleotides? What are the 3 parts?
The molecules is made up of units called nucleotides, which consist of three components: A 5 carbon sugar – deoxyribose A phosphate group A nitrogenous base (thymine, cytosine, guanine, and adenine) NOTE: A (adenine) always pairs with T (thymine), and G (guanine) always pairs with C (cytosine)

12 8. What is a codon? A codon consists of three consecutive nucleotides that code for a single amino acid in a protein. (It is the sequence of the nitrogenous bases that make up the codon.)

13 9. Describe what happens and where each happens: Transcription
process of copying part of a DNA nucleotide sequence into a complementary RNA sequence – making mRNA from DNA in the nucleus (instructions for making a protein) RNA polymerase binds at the correct sequence of DNA and separate the DNA strands One of the DNA strands is used as a template to make an mRNA strand The mRNA strand is edited before leaving the nucleus to go to a ribosome and be decoded

14 9. Describe what happens and where each happens: Translation
protein synthesis, process of decoding an mRNA message into a polypeptide chain, occurs in the cytoplasm at a ribosome mRNA attaches to a ribosome and the message starts being read (AUG codon) For each codon on the mRNA strand, the corresponding tRNA with the anticodon pairs up with the mRNA sequence The tRNA molecules carry the amino acids which are then bound together with a peptide bond to form the protein When the stop codon is reached, the protein is complete and it detaches from the ribosome

15 9. Describe what happens and where each happens: Replication
process in which a DNA molecule makes a copy of itself The DNA molecule “unzips” its two strands so that each strand becomes a template for making new DNA molecules – done through base pairing Each new DNA molecules has one old strand and one new strand DNA polymerase polymerizes the nucleotides into the new DNA molecule and proofreads the sequence to make sure that the bases are paired correctly


17 11. List 2 ways DNA and RNA are different.
Difference DNA RNA Bases thymine (T) uracil (U) Sugars Deoxyribose Ribose Appearance double strand (double helix) single strand

18 12. Define gene: A gene is a sequence of DNA that codes for a protein and thus determine a trait

19 13. What is the function of:
mRNA – contains the instructions for assembling amino acids into proteins, instructions come from the original DNA sequence (gene) tRNA – transfers amino acids to ribosomes during protein synthesis as specified by DNA (mRNA), each tRNA has an anticodon which determines which amino acid it transfers

20 14. Why are proteins important?
Proteins are important because they are used structurally and chemically. Structurally they make up the cytoskeleton and are involved with movement of materials in the cell and in and out of the cell. Chemically they are important because they are enzymes which are substances used to ensure that reactions proceed normally. They bring substrates together and lower the activation energy so that the chemical reaction can occur.

21 15. What do you call a change in the DNA code that causes a change in the protein that is produced?
Change in DNA code = mutation Mutations can be point mutations in which a base is replaced with another base in the sequence – this will cause only one amino acid to change. Mutations can be frameshift mutations in which a base is added or deleted from the sequence – this will cause all the amino acids past the change to be different.

22 16. Where is DNA located in an eukaryotic cell?
In eukaryotic cells, the DNA is located within the nucleus of the cell.

23 17. Must be able to convert DNA into mRNA and read the codon to make an amino acid:
DNA: TAC GGG CGA mRNA: AUG CCC GCU Amino Acid: Methionine – Proline - Alanine

24 Genetics

25 18. What is genetics? The scientific study of heredity

26 19. Who is the father of Genetics?
Gregor Mendel Austrian monk who in the mid 1800s taught high school and took care of the monastery garden Spent years studying the pea plants and controlling their breeding to collect data on genetics

27 20. Define: Genotype: genetic makeup of an organism – the actual alleles the organism has for a specific gene (trait) Phenotype: physical appearance of an organism – what the organisms looks like

28 21. Define and give an example:
Homozygous dominant – having both dominant alleles for a particular trait, ex. Tall pea plants – TT Homozygous recessive – having both recessive alleles for a particular trait, ex. Short pea plants – tt Heterozygous – having one dominant allele and one recessive allele for a particular trait, ex. Tall pea plants - Tt

29 22. What is an allele? An allele is a form of a gene.
Example – pea plant height Can be either T (tall) or t (short)

30 23. Why are Punnett squares useful (what do they tell us)?
Punnett square are diagrams used to show the genetic combinations that might result from a genetic offspring. It gives us the ability to determine the chances of sex, hair color, eye color, etc. for the offspring of two parents when you know their genetic makeup.

31 24. Define and give an example of a trait governed by:
Incomplete dominance: one allele is not completely dominant and the other is not completely recessive, ex. Four o’clock flowers – red and white flowers produce pink (two phenotypes blend) Codominance: both alleles contribute to the phenotype, ex. Cattle – red and white cattle produce roan cattle which have red and white hair together Multiple alleles: gene has more than two alleles, ex. Human blood types – have alleles for A, B, and O Sex-linked traits: genes are found only on X or Y chromosomes, ex. Color-blindness, hemophilia

32 25. On which chromosome are most sex-linked traits found?
Most sex-linked traits are found on the X chromosome because it is much larger than the Y chromosome.

33 26. What is a carrier? (think sex-linked traits)
A carrier is a person who has an allele for a particular trait or disorder but does not show it in their phenotype Example: color blindness (sex-linked) – a woman can have the allele for color blindness, but because her other allele is normal she does not have color blindness but may pass it on to her sons (have only one X chromosome)

34 27. What are gametes? Gametes are called sex cells. They are haploid cells used in sexual reproduction. Each parent provides one gamete with half the chromosomes needed to make and adult organism.

35 28. What is a karyotype? Why is it useful?
It is a picture of a person’s chromosomes – they are lined up by size and grouped in pairs. Must use cells that are in the process of mitosis, since that is the only time when the chromosomes are visible. Used to determine sex and the presence of abnormalities in the chromosomes – missing parts, too many copies, etc.

36 29. What is a pedigree? Why is it useful?
A chart that shows the relationships within a family Used to study how a trait is passed from one generation to the next Often used to track diseases or genetic disorders in a family

37 30. Define each of Mendel’s Laws:
Unit Factors: Inheritance of characteristics are determined by genes which are passed from parents to offspring. Dominance: When two or more forms of a gene exist, some are dominant and some are recessive. Segregation: Sexually reproducing adult organisms have two copies of each gene – one from each parent. These copies are segregated during gamete formation. Independent Assortment: Alleles for different genes usually segregate independently of one another during meiosis.

38 Evolution

39 31. Why is Darwin important?
Made a voyage around world and study the fossils, living specimens, and environments of many organisms. Used data collected to develop the theory of evolution. Published work in On the Origin of Species in 1859

40 32. Why are these biologists important to evolution:
Lamarck: suggested that acquired behaviors/traits could be passed on to offspring and a species could change over time (wrong) Hutton: geologist who suggested that layers on Earth form very slowly and proposed that Earth much older than thought Lyell: geologists must explain past events using processes currently happening Miller & Urey: were able to form the organic molecules necessary to life with the chemical compounds found in Earth’s early atmosphere

41 32. cont’d Lamarck – idea that species could change over time based on traits passed to offspring Hutton and Lyell – if Earth takes long time to change, then organisms must change over time and this is a slow process Miller & Urey – early conditions on Earth could have lead to the formation of living cells

42 33. Define: Natural Selection: process by which individuals that are better suited to their environment survive and reproduce most successfully; also called survival of the fittest Artificial selection: selection by humans for breeding of useful traits from the natural variation among different organisms

43 34. What is the theory of natural selection
34. What is the theory of natural selection? What are the parts of this theory? Theory of natural selection states that individuals that are better suited to their environment survive and reproduce most successfully – they show high fitness. Organisms have a struggle for existence – this must compete with other members of their species and with other species for food, living space, and other necessities of life. Organisms with adaptations that make them more successful have high fitness. Over time natural selection results in changes in the inherited characteristics of a species as successful adaptations are passed to more and more offspring.

44 35. How did the Galapagos Islands contribute to Darwin’s idea of natural selection?
The Galapagos Islands are a group of small islands off the west coast of South America. Even though the islands are close, they have very different climates – some more desert-like and others more tropical. He observed that the characteristics of many animals and plants varied noticeably among the different islands. His studies of his samples and observations lead him to realize that similar species had adapted to the different climate and vegetation available on the islands. Example, tortoises on different islands have different length necks and shells based on whether the vegetation is low to the ground or higher off the ground.

45 36. How did geographic distribution of species contribute to Darwin’s idea of natural selection?
Among the Galapagos Islands, Darwin had collected samples of many small brown birds. Much later he came to realize that despite all their physical differences they were finches and most have common from finches found on South America. So the birds had changed over time to adapt to the conditions found on the islands on which they lived. Darwin also noticed that different animals that lived in similar environments on different continents had similar structures and behaviors, so they must have adapted similarly to their environments through the process of natural selection.

46 37. Define and give an example:
Homologous structures: structures that have different mature forms but develop from the same embryonic tissues, example: 4 limbed animals with backbones have common ancestor Vestigial structures: structures that have become very reduced in size and not used in survival anymore, example: hip bones in a whale, appendix in humans

47 38. What are fossils? Why are they useful? Give 3 examples.
Fossils are the preserved remains or evidence of ancient organisms. They are useful because they provide evidence about the history of life on Earth and how organisms have changed over time. Fossils can include animal bones, imprints left behind from animals bodies, and insects and other organisms trapped in amber.

48 39. What is a species? A species a group of similar organisms that can breed with each other and produce fertile offspring.

49 40. List 4 evidences for evolution.
Fossil record – shows how living things have evolved over millions of years Geographic distribution of living species – similar species become different as adapt to different local environments while different species living in similar environments evolve common features Homologous body structures – different organisms with structures that have different forms in the mature individuals but developed from the same embryonic tissues

50 40. List 4 evidences for evolution. Cont’d
Similarities in embryonic development – many animals show similar development patterns in their embryos – help produce homologous structures

51 41. Define: Macroevolution: large scale evolutionary changes that take place over long periods of time Microevolution: evolution that involves small scale changes – changes within a species that occur over a short period of time and result in the formation of a new subspecies Adaptation: an inherited characteristic that increases an organism’s chance of survival Mutation: a change in a DNA sequence that affects genetic information

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