EVIDENCE FROM GENETICS Deduction If the hypothesis of

EVIDENCE FROM GENETICS • Deduction: If the hypothesis of evolution is correct, then we should see evidence of this in genetics • Background: Gregor Mendel (1822 -1884) Experiments with the garden pea. His paper in 1866 established the field of genetics.

In a Monastery Garden 2

He was dying. And it was January. As was fitting for an old man with swollen feet, a disagreeable kidney, and an untenable position on the chessboard, he closed his eyes. 3

He dosed in an old man’s way, thinking not of yesterday’s battle with the city alderman over the infernal tax problems of the Abbey, but of his childhood days on the farm, his sister who had forfeited her dowry so he could go to school, and his parents. He pulled his cleric’s robe tighter around his too ample frame. He was cold. And waited. For Leos. The choirmaster had promised he would play at his funeral. He smiled and remembered him as a boy. 4

For sixteen years he had been the Abbot of the Abbey—a great honor. But it had drained his strength; no longer could he tend his scientific studies. Still there were compensations, yet at the moment, on this cold January 6 th he had difficulty remembering what they were. 5

But mostly he remembered his beloved garden in the abbey where he worked so long ago. Eight years with 29, 000 pea plants to tend. 6

How long ago was it? Twenty? Thirty years? “Here boys, listen. ” He was once again a teacher at Znaim. “Listen, boys. It is possible to cross breed plants just like animals. One has to take the pollen from one plant with a small brush and carefully, so carefully, place it on another. 7

“Here I take the pollen from the male and place it upon the carpel of another plant. Then the plant does the rest. ” 8

“But why would you do that, Father? “Because I want to know the rules. There must be rules—laws of breeding, just as there are laws of physics. I want to find those rules. That is why, Master Pavel, I seek the answers. ” 9

“But how do you stop a bee bringing pollen from one plant to another to mix up your results, Father? ” “Try to guess. What should I do? ” “Possibly bring the plant inside, or cut the anther off before you pollinate the plant or cover the plant with a little sac? Or. . . maybe, Father, you just pray? ” 10

“Yes, I did most of those things. “Sometimes I did work in the greenhouse. When I worked in my garden, I covered the flower with a little cheesecloth bag. And I did have to remove the anther of the flower so that it would not fertilize itself. “And most assuredly I did pray. ” 11

“I was particularly interested in testing the old idea that the traits of the offspring were a simple blending of the characteristics of the two parents. You boys all know that you look like a combination of your two parents. Pavel, you have your mother’s nose and sense of humor and your father’s eyes and his musical talent. The same with all of us. But I had long wondered what would happen if I looked carefully at individual traits. What then? ” 12

“Here is what did happen. It is not at all what the plant scholars anticipated. The traits did not blend together. ” 13

“How can that be, Father? Where did the white go? Purple must be stronger than white. I say it dominates the white. ” “I think so too, Pavel. I think so too, but not in the way you imagine” “Let me show you another cross, this time between a tall plant and a short plant. Notice, I only watch one trait at a time. I could watch the flower color too, but that would be too complicated. Let’s just look at the height of the plant. ” 14

Monohybrid Crosses (=Breeding experiments involving one trait) • P Tall x Tall Short x Short • F 1 All Tall All Short “Here I breed two tall parents with each other and they breed true. They produce all tall children. And I breed two short plants and they breed true, yielding all short. ” 15

“But look what happens when I breed a tall and short together. ” • P Tall x Tall • F 1 F 2 Short x Short All Tall All Short All Tall 16

“It is the same thing, Father. The short has disappeared. Where has it gone? Tall is stronger than short. ” • P Tall x Tall • F 1 • F 2 Short x Short All Tall All Short All Tall The tall trait is dominant 17

“The same thing happened with these traits too. The ones on the left are dominant over those on the right. 18

I conclude that the traits do not blend together in the offspring of two parents. The blending hypothesis can be rejected! The reason that everyone thought blending was right was because they never looked at individual traits. 19

“Now look what happens when I breed the two F 2 generation tall plants together. ” § F 1 All Tall § F 2 Tall All Short Tall 787 Tall Short x and 297 Short 20

I concluded that the factors that control a trait maintain a discrete identity when passed from parent to offspring. This became known as my Law of Segregation 21

Back to Mendel. . . “But I noticed something strange when I looked at the dominant traits. ” 5474 vs. 1850 6022 vs. 2001 882 vs. 299 428 vs. 152 705 vs. 224 651 vs. 207 787 vs. 277 The dominant traits were always more common than the recessive traits 22

MENDEL’S TRAITS • • 5474/1850= 6022/2001= 882/299= 428/152= 2. 96 3. 01 2. 95 2. 82 • 705/224= 3. 15 • 651/207= 3. 14 • 787/277= 2. 84 75% show dominant traits 25% show recessive traits 23

“How could you explain this, Pater Gregor? ” “My mathematical training in the university came to my aid. My physics professor, Herr Doppler, always encouraged us to think mathematically. I asked myself could I explain this 3: 1 ratio simply? ” “Yes. Yes, and again, yes. ” 24

“Suppose that the traits were factors like particles. We could list them this way: the dominant factor T = tall plant the recessive factor t = short plant Imagine that a pure bred tall plant would have 2 TT & a pure bred short plant would have 2 tt” 25

“Then when I bred them TT x tt = ? “If they would only pass on one of their traits via the pollen or the egg, then what? ” “I have it, Father. I have it! The answer would be Tt” 26

Mendel analyzes the data Traits passed in the gametes Pollen (sperm) & eggs One factor (allele) comes from the pollen One factor (allele) comes from the egg. Note: ¾ Tall= TT, Tt, t. T ¼ Short= tt 3: 1 Phenotypic Ratio 27

Possible gamete combinations Tt tt x Tt = TT, Tt, t. T, Notice the 3: 1 ratio 28

Using a Punnett Square Alleles= Alternative forms of the same gene (T or t) Homozygous dominant Pollen Heterozygous T Eggs Suppose Tt X Tt t T TT Tt t t. T tt Heterozygous Homozygous recessive 29

Terms and Principles § § § § Dominant (e. g. Tall) Recessive (e. g. Short) Monohybrid crosses involve following 1 trait Dihybrid crosses involve following 2 traits Phenotype (visible characteristics) Genotype (genetic characteristics) Particulate theory of inheritance= 2 particles (factors) determine a trait 30

Terms and Principles § § § Alleles Homozygous dominant Homozygous recessive Heterozygous Punnett square 31

Gregor Mendel opened his eyes and saw Leos quietly putting coal on the fire. The monk reached over to his cold cigar and holding it to a candle, lit it, puffing deeply. He knew it was bad for his heart—his kidneys—his everything. A disgusting habit, he thought. He reached for his old notes, and paged along. 32

Gregor Mendel knew he was dying. He had a good life. He communicated with scientists and worshiped with God. Even now in his latter years when the business of the Abbey was so irritating, he still had his music and chess and his cigars. Always his twenty cigars a day. A small vice that God would forgive. 33

He no longer could breed mice, for they escaped too often and stunk too much. But he had his honey bees and his meteorological reports—his records. He always kept meticulous records. Records were essential, otherwise his pea experiments would have been impossible. How else could he have been able to keep track of two traits or more when he was breeding? 34

He found the section in his notes, called Dihybrid Crosses, where he analyzed 2 traits at the same time. Say, he wanted to breed a pure round yellow seed plant (both were dominant traits) with a pure wrinkled green seed (both were recessive traits), he decided that he would write it this way RRYY x rryy 35

Dihybrid Crosses (=Breeding experiments involving two traits) Seed shape = Round (R) or wrinkled (r) seeds Seed color = Yellow (Y) or green (y) seeds P RRYY F 1 Genotype x rryy Rr. Yy Phenotype Round Yellow 36

Record keeping was essential. Mendel thought the traits for seed shape and color were inherited completely separate from one another. Suppose he was correct. Set up a Punnet Square for Rr. Yy x Rr. Yy Fill in the heading of the squares Fill in 37

Dihybrid Cross Rr. Yy x Rr. Yy N I L L FI S E R A U Q S E H T Find the combinations where there are round yellow seeds 38

Theoretical possibilities Rr. Yy x Rr. Yy 9: Round Yellow 3: Round Green 3: Wrinkled Yellow 1 Wrinkled Green 39

Here are Mendel’s actual data Theoretical Ratio 9: Round Yellow 3: Round Green Wrinkled Yellow 1 Wrinkled Green Predicted 56 19 19 6 Actual 55 19 17 4 40

Mendel’s Data for the Dihybrid Cross • Consistent with the predicted 9: 3: 3: 1 ratio. • Mendel called this condition independent assortment; – Factors (genes) sort independently of one another when passed from parent to offspring. 41

Gregor Mendel died on January 6, 1884, of chronic nephritis. He entered the Abbey at the age of 21 and was ordained at the age of 25. He worked in his garden studying peas from 1856 to 1863 studying 29, 000 plants and published his landmark paper, but no one took serious notice. It was too mathematical and went against the prevailing view of blending characteristics. But he was always fond of saying, “My time will come. ” 42

Mendel is credited with three major ideas: 1) The Particle Theory of Inheritance— which states that hereditary traits act like particles, units, or factors as they are passed from generation to generation 2) His Law of Segregation –which states that his hereditary factors do not blend but remain distinct during breeding—thus, disproving the blending theory. 3) His Law of Independent Assortment –which states that character traits are not connected but are inherited independent of one another. (This law was to be soon to be modified) 43

When he died on that January 6, 1884 at the age of 61, the great composer, Leos Janacek played the organ at his funeral as promised. To his friends’ sorrow, Mendel’s papers were burned by the abbot who succeeded him. 44

Twenty-five years later his work was discovered by three botanists and his experiments became famous. His time had come. 45