Genetics and Probability. Mendel s Work & Probability and Genetics (Sections 1 & 2 of Chapter 3)

Transcription

1 Genetics and Probability Mendel s Work & Probability and Genetics (Sections 1 & 2 of Chapter 3)

2 *Gregor Mendel was a young priest from Central Europe who studied math and science at the University of Vienna. * *After leaving the university, he returned to his monastery and began teaching at a local high school. *As part of his duties, Gregor Mendel also cared for the monastery s garden where he grew hundreds of pea plants. He noticed that some of the pea plants had different characteristics than the others and became curious. Apparently he didn t have a lot of meetings at his high school and therefore had some free time think...about plants. : )

3 *TRAITS are physical characteristics. *He noticed that sometimes the traits of the offspring pea plants were similar to the parents and then other times they were different. The passing of traits from parents to offspring is known as HEREDITY. *Over the course of ten years, he experimented, studied, and documented thousands of pea plants, their traits and how they were passed to their offspring. The scientific study of heredity is called GENETICS. Gregor Mendel formed the basis for genetics and for that reason he is called the Father of Genetics. (yes, a PUN is intended there we believe) : )

4 *To observe how traits were passed from parents to offspring, Mendel had to know which plants were the parents and which were were the offspring. Pea plants usually self-pollinate which means the pea plants usually contain the genetic information from the mother and the father plant on ONE plant.

5 *In flowers, the PISTIL produces the female sex cell or eggs, while the STAMENS produce the male sex cells or POLLEN. In many flowers, if the pollen isn t moved by the wind or insects, a single plant will pollinate itself. Pollination is the coming together of the male and female sex cells in plants.

6 * Mendel figured out to take the male sex cells (pollen) from stamen of one pea plant flower and place it on the pistil of another plant, fertilizing the egg cells and creating offspring that were a mixture of two different parents. By doing this, he created the process of CROSS- POLLINATION. Doing this with animals has created different breeds of dogs, cats, cows, etc with the desired traits.

7 *Mendel crossed plants that had opposite forms of traits. For instance, he crossed short plants with tall plants. When he crossed these opposite plants, he made sure he used plants that were PUREBRED, which means an organism that always produces offspring with the same form of a trait for several generations.

8 *He began by crossing purebred tall plants with purebred short plants. The first generation that were produced were all TALL. The next generation after that, 75% were tall while 25% were short. Hmmm... *From this, Mendel decided that traits must be controlled by individual factors and that the factors must exist in pairs and that one of the pairs of these factors comes from the mother and the other of the pair of factors comes from the father. *He also reasoned that one of the factors in a pair can mask or hide the trait of another one. In the pea plants, Tallness covered up shortness.

9 *The factors that control traits are known as GENES. The different forms of a gene are known as ALLELES. *DOMINANT ALLELES are ones whose trait always show up in an organism. A RECESSIVE ALLELE is one whose trait is masked when a dominant allele is present. The only time a recessive allele shows up in an organism is when both of the gene pair are recessive alleles. Think of a tall person standing in front of a short person. Where d they go?

10 *If an organism has a gene pair for a trait with both a recessive and a dominant allele together, the organism is considered to be HYBRID. (A hybrid car uses both gas and electricity to move) *To make it easier to follow, dominant alleles are represented by a capital letter, while recessive alleles are represented by the same letter usually, only lower case.

11 Probability & Genetics

12 *If you tossed a coin 10 times, how many times would you expect it to land with the head side up? 5 times, right? Is that a guarantee? No. But, the probability that the coin will land heads up is, 1 in 2 or 1/2 or 50%. It doesn t matter how many times you do the coin toss, the probability remains the same because there are only 2 possible outcomes...unless the coin lands on its edge. : ) If that happens, YOU win.

13 *PROBABILITY is the likelihood that a particular event will occur. Mendel discovered that probability can be used to predict the results of genetic crosses using a tool call a Punnett Square. *A PUNNETT SQUARE is a chart that shows all the possible combinations of alleles that can result from the crossing of two parents. It works like mathematical puzzle, but it s easy. Check out the example below. Across the top of the square is the gene pair for one parent who is hybrid for the trait. Down the left hand side is the gene pair for the other parent who is also hybrid for the trait. Since both parents are hybrids and the dominant allele is present, it is the one that will show up and both parents are tall.

14 *Each letter on the top of the square must be copied into the boxes below them, within the square. *Each letter to the left of the square must be copied into the boxes to the right in order to end up with a pair of alleles in each of the four inner boxes.

15 *When looking at the offspring above (the gene pairs found inside each of the four squares) we see: -TT, which represents purebred or HOMOZYGOUS DOMINANT offspring which will be tall. (Homozygous means two identical alleles for a trait.)! - Tt, which represents hybrid or HETEROZYGOUS offspring which will also be tall. (Heterozygous means two different alleles for a trait.) -tt, which represents purebred or HOMOZYGOUS RECESSIVE offspring which will be short

16 *When considering probability, each box inside the Punnett Square represents 25%.! 25% X 4 = 100%. With the previous Punnett square, we would expect 75% of the offspring to be tall and 25% to be short.

17 An organism s PHENOTYPE is its physical appearance or its visible traits. The phenotype of 75% of the offspring from the Punnett Square is TALL. An organism s GENOTYPE (think genes) is its gene pair or allele combination. 25% of! the offspring in the above Punnett square are tt.

18 * Occasionally, for some traits, alleles are neither dominant nor recessive. Instead, both traits are expressed. This is called CODOMINANCE. In the example below, the black and white alleles are codominant so both show up and all the offspring end up having w black AND white feathers.

19 Or in the case of these carnations, since neither white nor red are dominant, instead they are codominant, crossing one red and one white carnation gives offspring that are all pink.

20 The Cell and Inheritance * American geneticist, Walter Sutton, studied the cells of grasshoppers, in particular, he studied the sex cells or GAMETES, eggs and sperm and how they formed. *GAMETES is the name given to the sex or reproductive cells. *While observing the formation of the eggs in female grasshoppers and sperm in male grasshoppers, he noticed that the number of chromosome changed between number in the egg and sperm as compared to after fertilization took place and the number found in the ZYGOTE that was formed.

21 *Sutton knew grasshoppers had 24 chromosomes in each of their body cells and those chromosomes were always in pairs, 12 pairs.(watch the math between pairs and individual chromosomes) One of the chromosomes in that pair came from the father while the other one in each of the pair come from the mother. *However, when grasshoppers produced their sex cells, each sex cell only had only 12 chromosomes, exactly half of the rest of the grasshopper s cells. These cells, with half the number of the chromosomes, were later called HAPLOID cells. *When the egg and the sperm came together during FERTILIZATION, the resulting cell, a ZYGOTE, had 24 chromosomes again, like the rest of the grasshopper s cells.

22 *All of the these clues led Walter Sutton to realize that Chromosomes must be the key to offspring having half their genetic information from their mother and half from the father = 4! *However, the question came up, how do the sex cells/ Gametes end up with only half the number of the chromosomes as the rest of the body cells? The answer is the process of MEIOSIS. *You recall, MITOSIS is the process of a cell duplicating all its genetic information and and then dividing into two new, IDENTICAL cells than have the exact same number of chromosomes as the parent cell they came from. MITOSIS, makes MY body s cells!

23 *MEIOSIS is the process by which four sex cells/gametes (sperm and egg) are produced from one single cell. MEIOSIS made ME! These sex cells have exactly half the number of chromosomes as the cells from which they came. (They are HAPLOID ((think half )) while body cells, that contain a full set of chromosomes, are called DIPLOID.) *In the process of meiosis, a single cell makes two exact copies of itself, including all chromosomes, full of all the genetic information. Then those two cells split their chromosome pairs in half, then each half set of chromosomes goes on to become a sex cell/gamete, sperm in males and egg in females. Which of that pair of split chromosome pair goes to which egg or sperm is like flipping a coin.

24 MITOSIS MEIOSIS Meiosis

25 *For this reason, when an offspring is created through fertilization, it receives half of its genetic information from its mother and half from its father. This is why you may have some traits of your mother AND some traits of your father.

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27 *Obviously, since Sutton s time, research has continued on the chromosomes of different organisms, especially humans. *Each normal, human cells contains 46 chromosomes/ 23 pairs of chromosomes. *Although humans have only 23 pairs of chromosomes, we have more than 50-60,000 individual genes and each of these control your traits.

28 Human Chromosome Pairs

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31 A GENE is like a barcode...the different combinations of thick and thin lines can be interpreted by a computer as instructions. The different combinations of A,T,C,G (A = Adenine T = Thymine C = Cytosine G=Guanine ) give instructions to cells.

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33 The DNA Connection The Basics of DNA Your body contains 50 trillion tiny cells, and almost every one of them contains the complete set of instructions for making you. These instructions are encoded in your DNA. DNA is a long, laddershaped molecule. Each rung on the ladder is made up of a pair of interlocking units, called bases, that are designated by the four letters in the DNA alphabet - A, T, G and C. 'A' always pairs with 'T', and 'G' always pairs with 'C'. (A = Adenine T = Thymine C = Cytosine G=Guanine )

34 DNA Replication - Simple

35 DNA Replication - Detailed

36 DNA is organized into Chromosomes The extremely long molecules of DNA in your cells are organized and packaged into pieces called chromosomes. Humans have the 23 pairs of chromosomes mentioned and shown previously. Other organisms have different numbers of chromosome pairs - for example, chimpanzees have 24 pairs. The number of chromosomes doesn't determine how complex an organism is - bananas have 11 pairs of chromosomes, while fruit flies have only 4.

37 Chromosome are Organized Into Genes Chromosomes are further organized into short segments of DNA called genes. If you imagine your DNA as a cookbook, then your genes are the recipes. Written in the DNA alphabet - A, T, C, and G - the recipes tell your cells how to function and what traits to express. For example, if you have curly hair, it is because the genes you inherited from your parents are instructing your hair follicle cells to make curly strands. (A = Adenine T = Thymine C = Cytosine G=Guanine )

38 Genes Make Proteins Cells use the recipes written in your genes to make proteins - just like you use recipes from a cookbook to make dinner. Proteins do much of the work in your cells and your body as a whole. Some proteins give cells their shape and structure. Others help cells carry out biological processes like digesting food or carrying oxygen in the blood. Using different combinations of the As, Cs, Ts and Gs, DNA creates the different proteins - just as you use different combinations of the same ingredients to make different meals.

39 Turn to page 101 in ithe orange textbook!

40 * Genetic Switches Control the Traits Cells Express Cells come in a dizzying array of types; there are brain cells and blood cells, skin cells and liver cells and bone cells. But every cell contains the same instructions in the form of DNA. So how do cells know whether to make an eye or a foot? The answer lies in intricate systems of genetic switches. Master genes turn other genes on and off, making sure that the right proteins are made at the right time in the right cells.

41 Sometimes the copy of this genetic information has mistakes... *A MUTATION is when there is a change that occurs in a gene or a chromosome. *The word MUTATION, comes from the Latin word meaning change.

42 Two General Types of Mutations: 1. Some are the result of small changes in an organism s hereditary material, during the DNA copying process. 2. Other mutations occur when chromosomes don t separate correctly during meiosis, resulting in too many or too few chromosomes such as the extra chromosome that causes Down s Syndrome.

43 Some mutations are harmful, some are helpful, some are neither harmful nor helpful. 1.Mutations are harmful if they reduce the organism s chance to survive and reproduce. Examples would be an organism being albino and reducing their camouflage abilities to protect them from predators or cancer where mutated cells over-run the healthy cells of the body.

44 1.Mutations are helpful if they increase the organism s chances to survive or reproduce. A gene mutation in a potato resulted in a new variety called the Katahdin, a potato that is resistant to some diseases. Tolerance of Lactose (milk sugar) is a mutation. Before, the majority of the population was Lactose Intolerant. Since it s beneficial to be able to drink vitamin-andmineral-rich cow s milk, now the majority of the population can consume lactose.

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47 Human Inheritance: Traits Controlled by Single Genes *Many traits, like those in pea plants are controlled by a single gene with two alleles, with those alleles being any combination of dominant or recessive. *Many human traits are also controlled by a single gene or pair of alleles. When this occurs, there a typically on two possible phenotypes. *A widow s peak is one of those traits. For this reason, in humans, the only two possible phenotypes are: HAVE A WIDOW S PEAK or NO WIDOW S PEAK. There is nothing in between.

48 Widow s Peak vs. None

49 Widow s Peak...gone BAD!

50 Consider: Do you think height is controlled by one pair of alleles in humans? Yes/No and explain

51 Record the height of students...here One at a time, stand with your back to the board, long enough for me to mark your height.

52 Multiple Alleles *Some human traits are controlled by a single gene, but that gene can have MORE than two alleles, not just dominant or recessive. These genes are said to have MULTIPLE ALLELES. These are like different flavors of pudding. They re all pudding, but there are more than two flavors.

53 Multiple Alleles *Although a gene may have more than two forms, a human can only carry a pair, or two alleles in each gene because a gene is made of chromosomes and chromosomes always come in pairs. *Human blood types are controlled by a gene that has THREE alleles. The different combinations of these alleles result in the different types of blood in humans.

54 Traits Controlled by Many Genes *Some traits in humans show a large number of phenotypes, not just two or four, but MANY. As an example there are at least FOUR genes that control height in humans so there are MANY combinations of genes and their alleles resulting in a great differentiation in heights in humans. *Skin color is controlled by many genes.

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56 ...and so is height.

57 ! Consider: How would the heights of humans be different if the trait of height was controlled by one gene/only one pair of alleles in that gene?

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59 Congratulations! It s a baby *Among the 23 pairs of chromosomes in each body cell of humans, there is one pair known as the SEX CHROMOSOMES. This pair determine if a person is male or female. *XX is the chromosome pair code for FEMALES and XY is for males. *If a Y is present, the offspring will be male, therefore it s considered that the sperm/male

60 Consider: Use a Punnett square to cross a male and a female. What % of the offspring would we expect to have the genotype XY?

61 Pedigrees *One important tool that geneticists use to trace the inheritance of traits in humans is a PEDIGREE. A pedigree is a chart or family tree that tracks which members of a family have a particular trait.

62 Pedigree

63 Human Genetic Disorders A GENETIC DISORDER is an abnormal condition that a person inherits through genes or chromosomes. These are caused by mutations (changes in a person s DNA).

64 Human Genetic Disorders *A familiar genetic disorder is DOWN SYNDROME. Down Syndrome results from the incomplete separation of a chromosome pair during meiosis. This gives each cell an extra chromosome at the 21st pair of chromosomes. The result in humans is a distinctive physical appearance.

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66 Down Syndrome

67 ADVANCES IN GENETICS Three methods people have used to develop organisms with desirable traits are: 1. SELECTIVE BREEDING, 2. CLONING, and 3. GENETIC ENGINEERING.

68 Selective Breeding 1. SELECTIVE BREEDING is the process of selecting a few organisms with desired traits to serve as parents of the next generation. This is used!for plants, vegetables, and even can created our many breeds of dogs.

69 Cloning 2. CLONING is creating an offspring that is genetically identical to the parent. In plants this is can be simple such as in self-pollination or in taking a cutting from a plant, putting it in water and letting it grow roots, then planting it.

70 Cloning *In animals, cloning is a much more complicated process since animals typically are a combination of the genetic information from TWO parents.

71 Cloning...Bad?

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73 Cloning *The first genetically cloned animal was DOLLY the sheep who was born in To make Dolly, a fertilized egg was removed from one sheep, its nucleus was removed and was replaced with the nucleus from a cell from a 6 year old sheep. That egg was then placed into the uterus of a third sheep where it grew. Dolly was born 5 months later. Dolly is a genetic clone of the 6 year old sheep.

74 Genetic Engineering 3.GENETIC ENGINEERING (sometimes called GENE SPLICING) is the process where genes from one organism are transferred into the DNA of another organism. Genetic engineering is used to produce medicines such as insulin for diabetics, improve food crops, and to try and cure some genetic disorders.

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78 DNA Fingerprinting *DNA is different for EVERY person except identical twins. Since EVERY cell inside human bodies contains an identical copy of DNA (besides the gametes/sex cells) AND individual cells are often left behind by criminals at crime scenes, specialist can pull the DNA from those cells and compare it to the DNA of suspects in custody or to DNA from other crime scenes. If the compared DNA is a match, this absolutely ties criminals to crime scenes and the crimes themselves.

79 DNA Fingerprinting

80 Human Genome Project *A GENOME is all the DNA in one cell of an organism. *The goal of the Human Genome Project (HGP) is to identify the DNA sequence of every gene in the human genome. *The 23 pairs of chromosomes that make up the human genome may contain 60-80,000 genes or around 3,000,000,000 DNA base pairs.

81 Human Genome Project * By identifying each of these base pairs, scientists will know the DNA sequence of every human gene, and thus the amino acid sequence used to make every protein. * This information may help us understand how we develop from a zygote to an adult and identify when things go wrong and be able to fix it.

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83 Genetics - From Pea Plants to The Human Genome Project

84 THE END