2.  Chromosomal theory of inheritance States genes are located on chromosomes and that the behavior of chromosomes during meiosis accounts for inheritance patterns, which closely parallels predicted Mendelian patterns.  Principles of Mendelian genetics (segregation, independent assortment, and dominance) support chromosomal theory of inheritance 2

3.  Chromosomal theory of inheritance developed in 1902 by Walter Sutton proposed that genes are present on chromosomes based on observations that homologous chromosomes pair with each other during meiosis supporting evidence was provided by work with fruit flies 3

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5.  Gene Linkage – genes that are located on the same chromosome will be inherited together This is the exception to the Mendelian principle of independent assortment because linked genes do not separate independently  Lets look at the following example of fruit flies – Drosophila Melanogaster 5

6.  On the left is the expected phenotypic ratio of the offspring from a BbVv × bbvv cross (1:1:1:1). However, because the alleles BV and bv are linked, the observed phenotypic ratio is much different (5:1:1:5) than the expected ratio. 6

7.  What are the genotypes of BbVv parents? BBVV X bbvv – p generation  So what do the parents always donate to their offspring on each chromosome One parent donates chromosome with BV One parent donates chromosome with bv  Therefore the offspring BbVv is going to produce many more BV or bv since the genes are linked 7

8.  Crossing over – alleles in close proximity on homologous chromosomes are exchanged – new combinations of alleles In meiosis I segments of chromosomes entwine and exchange info Crossing over allows for greater genetic diversity 8

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10.  Multiple alleles can exist for a particular trait even though only 2 alleles are inherited. Ex 3 alleles exist for blood type (A,B, and O) which results in 4 different blood groups 10

11.  Polygenic traits – traits that are controlled by 2 or more genes. These traits show a great variety of phenotypes. ie skin color, hair color, eye color, height 11

12.  Sex-Linked traits are the result of genes that are carried on either the X or the Y chromosome.  It is another exception to the Law of Independent Assortment 12

13.  T.H. Morgan isolated a mutant white-eyed Drosophila  red-eyed female X white-eyed male gave a F 1 generation of all red eyes  Morgan concluded that red eyes are dominant 13

14.  Morgan crossed F 1 females X F 1 males (so all had red eyes)  F 2 generation contained red and white- eyed flies but all white-eyed flies were male  testcross of a F 1 female with a white-eyed male showed the viability of white-eyed females  Morgan concluded that the eye color gene is linked to the X chromosome 14

15.  Chromosomal basis of sex linkage White-eyed male flies X red-eyed females F1 flies all have red eyes F2 flies, all of the white-eyed flies are males because the Y chromosome lacks the white gene 15

16.  Sex determination in Drosophila is based on the number of X chromosomes 2 X chromosomes = female 1 X and 1 Y chromosome = male  Sex determination in humans is based on the presence of a Y chromosome 2 X chromosomes = female having a Y chromosome (XY) = male 16

17.  In many organisms, the Y chromosome is greatly reduced or inactive.  genes on the X chromosome are present in only 1 copy in males  sex-linked traits: controlled by genes present on the X chromosome  Human X-linked disorders Color blindness, Muscular dystrophy, Hemophilia, Fragile X syndrome  Sex-linked traits show inheritance patterns different than those of genes on autosomes. 17

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19.  Mitochondria and chloroplasts contain genes.  traits controlled by these genes do not follow the chromosomal theory of inheritance  genes from mitochondria and chloroplasts are often passed to the offspring by only one parent 19

20.  Maternal inheritance: uniparental (one- parent) inheritance from the mother  the mitochondria in a zygote are from the egg cell; no mitochondria come from the sperm during fertilization  in plants, the chloroplasts are often inherited from the mother, although this is species dependent 20

21.  Some human genetic disorders are caused by altered proteins.  the altered protein is encoded by a mutated DNA sequence  the altered protein does not function correctly, causing a change to the phenotype  the protein can be altered at only a single amino acid (e.g. sickle cell anemia) 21

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23.  Some genetic disorders are caused by a change in the number of chromosomes.  nondisjunction during meiosis can create gametes having one too many or one too few chromosomes  fertilization of these gametes creates trisomic or monosomic individuals  Down syndrome is trisomy of chromosome 21 23

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25.  Nondisjunction of sex chromosomes can result in: 25 SyndromeSexDisorderChromosom e # Spontaneous abortions Live births TurnerFXO451/181/ 2,500 KlinefelterMXXY OR XXXY47 or 481/3001/800 Poly-XFXXX OR XXXX47 or 4801/ 1,500 JacobsMXYY47?1/1,000 DownM or FTrisomy 21471/401/800

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27.  Genetic counseling can use pedigree analysis to determine the probability of genetic disorders in the offspring.  Some genetic disorders can be diagnosed during pregnancy.  amniocentesis collects fetal cells from the amniotic fluid for examination  chorionic villi sampling collects cells from the placenta for examination 27

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31.  A mutation is the alteration of an organism’s DNA.  Mutations can range from a change in one base pair to the insertion or deletion of large segments of DNA.  Mutations can result from a malfunction during the process of meiosis or from exposure to a physical or a chemical agent, a mutagen. 31 Mutation on the gene that produces myostatin, a protein that blocks skeletal muscle growth

32.  Most mutations are automatically repaired by the organism’s enzymes and therefore have no effect.  However, when the mutation is not repaired, the resulting altered chromosome or gene structure is then passed to all subsequent daughter cells of the mutant cell, which may have adverse or beneficial effects on the cell, the organism, and future generations. 32

33.  happens randomly every few thousand cell divisions  can be increased by exposure to mutagens like chemicals or radiation  can be in somatic cells or in germ cells (gametes)  can be POSITIVE, NEGATIVE, or NEUTRAL(silent)  are the "raw material" for evolution by natural selection 33 Video Clip

34.  "Point mutation" can be caused by single nucleotide substitution. Affects only one of the amino acids in the protein. Video Clip 34

35.  Insertions or deletions of nucleotide bases can cause even more serious problems: called a "Frameshift mutation" : insertion or deletion of a single base can throw off "reading frame" for amino acid coding. This most often renders the (coded) protein nonfunctional.Frameshift mutation 35

36.  Cancer is one of the most common diseases in the developed world:  1 in 4 deaths are due to cancer  1 in 17 deaths are due to lung cancer  Lung cancer is the most common cancer in men  Breast cancer is the most common cancer in women  There are over 100 different forms of cancer

37.  Cells can respond to physical signals from their environment Cells sense when they are too closely packed and cell division is turned off Cells sense when they are not in contact with a surface and cell division is turned on There are checkpoints along the cell life cycle where these decisions are made based on stimuli

38.  Cancer cells are examples of cells that don’t recognize normal “off” signals or there is no growth factor so they continue to divide  Cancerous cells divide repeatedly out of control even though they are not needed, they crowd out other normal cells and function abnormally. They can also destroy the correct functioning of major organs.

39.  Normally the body’s immune system will recognize that the cell is damaged and destroy it

40.  Cancer arises from the mutation of a normal gene.  Mutated genes that cause cancer are called oncogenes.  It is thought that several mutations need to occur to give rise to cancer  Cells that are old or not functioning properly normally self destruct and are replaced by new cells.  However, cancerous cells do not self destruct and continue to divide rapidly producing millions of new cancerous cells.

41.  A factor which brings about a mutation is called a mutagen.  A mutagen is mutagenic.  Any agent that causes cancer is called a carcinogen and is described as carcinogenic.  So some mutagens are carcinogenic.

42.  Ionising radiation – X Rays, UV light  Chemicals – tar from cigarettes  Virus infection – papilloma virus can be responsible for cervical cancer.  Hereditary predisposition – Some families are more susceptible to getting certain cancers. Remember you can’t inherit cancer its just that you maybe more susceptible to getting it.

43.  Benign tumours do not spread from their site of origin, but can crowd out (squash) surrounding cells eg brain tumour, warts.  Malignant tumours can spread from the original site and cause secondary tumours. This is called metastasis. They interfere with neighbouring cells and can block blood vessels, the gut, glands, lungs etc.  Why are secondary tumours so bad?  Both types of tumour can tire the body out as they both need a huge amount of nutrients to sustain the rapid growth and division of the cells.

44. What makes most tumours so lethal is their ability to metastasize -- that is, establish new tumour sites at other locations throughout the body.