Section Chapter 14. Go to Section:

Transcription

1 Section 12-3 Chapter 14 Go to Section:

2 Content Objectives Write these Down! I will be able to identify: The origin of genetic differences among organisms. The possible kinds of different mutations. The effects of mutations. How genetic change can occur on a larger scale.

3 Language Objectives Write this down! I will complete a graphic organizer of 16 Key terms associated with Mutation & Genetic Change, defining each term in my own words, using it correctly in a sentence, and creating a memonic that will help me remember each term and its meaning.

4 Section 12-3 Transcription Adenine (DNA and RNA) Cystosine (DNA and RNA) Guanine(DNA and RNA) Thymine (DNA only) Uracil (RNA only) RNA polymerase RNA DNA Go to Section:

5 Section 12-3 Translation Messenger RNA Messenger RNA is transcribed in the nucleus. Nucleus Ribosome Methionine Phenylalanine trna Lysine Transfer RNA mrna The mrna then enters the cytoplasm and attaches to a ribosome. Translation begins at AUG, the start codon. Each transfer RNA has an anticodon whose bases are complementary to a codon on the mrna strand. The ribosome positions the start codon to attract its anticodon, which is part of the trna that binds methionine. The ribosome also binds the next codon and its anticodon. mrna Start codon Go to Section:

6 Mutation - a change in the structure or amount of the genetic material of an organism

7 Nondisjunction - failure of homologous chromosomes to separate properly during meiosis. Results in extra or missing chromosomes

8 Polyploidy - an condition of having more than two sets of chromosomes plants only

9 Mutant A genetic mutant is an individual whose DNA or chromosomes differ from some previous or normal state.

10 Mutagens The rate of mutation can be increased by some environmental factors, called mutagens, which include many forms of radiation and some kinds of chemicals.

11 Radiation The energy that is transferred as electromagnetic waves, such as visible light and infrared waves. Radiation with sufficiently high energy can ionize atoms. Most often, this occurs when an electron is stripped (or 'knocked out') from an electron shell, which leaves the atom with a net positive charge. Because cells are made of atoms, this ionization can result in cancer

12 Anemia Anemia is a condition that develops when your blood lacks enough healthy red blood cells. These cells are the main transporters of oxygen to organs. There are over 400 types of anemia

13 Sickle Cell Anemia In sickle cell anemia, the red blood cells become rigid, sticky and are shaped like sickles or crescent moons.

14 Point Mutation a mutation in which only one nucleotide or nitrogenous base in a gene is changed

15 Missense Mutation A mutation in which only one nucleotide or nitrogenous base in a gene is changed. A change of a single nucleotide in a sequence from one kind of base to another. This kind of mutation is also called a replacement mutation.

16 Silent Mutation A mutation is silent when it has no effect on a gene s function 4

17 Frameshift Mutation A mutation, such as the insertion or deletion of a nucleotide in a coding sequence, that results in the misreading of the code during translation because of a change in the reading frame

18 Reading Frame Recall that the genetic code is read in words of three letters each (codons). The reading frame of a sequence depends on the starting point for reading.

19 Nonsense Mutation A nonsense mutation results when a codon is changed to a stop signal. In this case, the resulting string of amino acids may be cut short, and the protein may fail to function.

20 Chromosomal Mutation Chromosomes pair up and may undergo crossover. Errors in the exchange can cause chromosomal mutations 5 & 6

21 Deletion The loss of a part of DNA from a chromosome. At the end of meiosis, one of the cells will lack the genes from that missing piece. Such deletions are usually harmful.

22 Duplication A duplication occurs when a piece remains attached to its homologous chromosome after meiosis. One chromosome will then carry both alleles for each of the genes in that piece.

23 Inversion An inversion occurs when a piece reattaches to its original chromosome, but in a reverse direction.

24 Translocation A translocation occurs when a chromosome piece ends up in a completely different, nonhomologous chromosome.

25 Gene Rearrangement A chromosomal mutation can move an entire gene to a new location.

26 Germ Cells Germ cells make up gametes Somatic Cells Somatic cells make up the rest of the body cells that are not gametes.

27 7 Melanoma Melanoma is the most serious form of skin cancer. Melanoma originates in melanocytes, the cells which produce the pigment melanin that colors our skin, hair, and eyes.

28 Tumor A growth that arises from normal tissue but that grows abnormally in rate and structure and lacks a function

29 Cancer A tumor in which the cells begin dividing at an uncontrolled rate and invade other parts of the body.

30 New Alleles Any new allele must begin as a mutation of an existing allele.

31 Genetic Disorders Harmful effects produced by inherited mutations (defective alleles)

32 Down Syndrome Trisomy-21 a disorder caused by an extra twentyfirst chromosome and characterized by a number of physical and mental abnormalities.

33 1. What is the origin of genetic differences among organisms? For the most part, genetic differences among organisms originate as some kind of genetic mutation.

34 2. What are the causes of mutation? Mutations occur naturally as accidental changes to DNA or to chromosomes during the cell cycle. Enzymes repair most DNA that is mismatched during replication, but rarely, some DNA is not repaired. The rate of mutation can be increased by some environmental factors. Such factors, called mutagens, include many forms of radiation and some kinds of chemicals.

35 What are the effects of mutation? A small change in DNA may affect one or many amino acid(s) in the protein that results from a gene. A mutation may have no effect, or may harm or help in some way. The effect depends on where and when the mutation occurs.

36 4. What kinds of mutations are possible? Two main types: gene mutations and chromosomal mutations

37 7 What kinds of mutations are possible? 1. Gene mutations (replication errors) a change in the sequence of nucleotides in DNA A point mutation is a change of a single nucleotide in a sequence from one kind of base to another. (substitution) A mutation is silent when it has no effect on a gene s function. Point mutations are often silent because the genetic code is redundant (each amino acid has multiple codons). *A missense or replacement mutation results when a codon is changed such that the new codon codes for a different amino acid. *A nonsense mutation results when a codon is changed to a stop signal. In this case, the resulting string of amino acids may be cut short, and the protein may fail to function.

38 What kinds of mutations are possible? Rarely, errors in replication can cause the insertion or deletion of one or more nucleotides in a sequence. An insertion or deletion can shift the reading frame, or cause a frameshift mutation. In frameshift mutations, the remaining sequence is incorrect.

39 Section 12-4 Gene Mutations: Substitution Insertion Deletion Go to Section:

40 Chromosomal Mutations (meiosis errors) a change chromosome structure or number A. Errors in the exchange during crossing over in meiosis can cause chromosomal mutations. A deletion occurs when a piece of a chromosome is lost. At the end of meiosis, one of the cells will lack the genes from that missing piece. Such deletions are usually harmful. A duplication occurs when a piece remains attached to its homologous chromosome after meiosis. One chromosome will then carry both alleles for each of the genes in that piece. An inversion occurs when a piece reattaches to its original chromosome, but in a reverse direction. A translocation occurs when a chromosome piece ends up in a completely different, nonhomologous chromosome.

41 Chromosomal Mutations Section 12-4 Deletion Duplication Inversion Translocation Go to Section:

42 6 4. What kinds of mutations are possible? B. When homologous chromosomes fail to separate properly during meiosis (nondisjunction), gametes have extra or missing chromosomes. Examples: Autosomal - Down Syndrome - trisomy 21 Mild to severe mental retardation Increased frequency of birth defects Increased susceptibility to disease Sex Chromosome Disorders Turner s syndrome (XO): sterile females, sex organs fail to develop normally Klinefelter s syndrome (XXY): sterile males, tall stature The Y chromosome has genes necessary for the development of male characteristics.

43

44 Down s Syndrome

45 Turner s Syndrome

46 Kleinfelter s Syndrome

47 Child with Down s Syndrome

48 Intron - a nucleotide sequence that is transcribed from DNA into mrna but is cut out (not translated).

49 Exon - nucleotide sequences that are transcribed, joined together, and then translated

50 Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II

51 Nondisjunction Homologous chromosomes fail to separate Meiosis I: Nondisjunction Meiosis II