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Genetics… it’s all about YOU! Have you ever heard someone say… “You have your father’s eyes.” or “You’ve got your mother’s smile.” or physical characteristics “You look just like your grandfather.” We all know that we get certain traits from our parents or grandparents. But have you ever wondered HOW it happens? How you got your dad’s eyes or your mom’s smile? The answer to “How does it happen?” is… GENETICS! Heredity is the passing of traits from parents to offspring. Genetics is the study of heredity. Traits are physical characteristics, like eye color, hair color, freckles, or blood-type. Who was the first person to study genetics? An Austrian priest and science teacher named Gregor Mendel Some Human Traits Dimples mid-digit hair cleft chin Tongue-roller Mendel was an Austrian monk and science teacher who was also responsible for the monastery’s garden. During the years 1856-1863, he conducted experiments with over 28,000 pea plants. His experiments were the first large-scale, long-term scientific study of heredity ever done. His work, published in 1865, was ignored at the time, because other scientists did not understand its importance. However, Mendel’s experiments with pea plants were rediscovered in 1900. He is now known as the “Father of Genetics” for his discoveries of inheritance patterns in pea plants. Mend el flower bed staircase & flower bed Photos of Brno monastery in Austria Photos of Brno monastery in Austria northern wall of the monastery’s garden beehives and apiary Mendel’s choice of pea plants for his experiments was a good choice, for 2 reasons: 1. They reproduce quickly & have many offspring 2. They have many simple, either-or traits Mendel tested 7 pea plant traits: seed shape pod color seed color pod shape Inflated Pinched flower color stem height Short flower position Side End Pea Plants In order to control which plants pollinated which plants, Mendel had to hand-pollinate every flower in the pea plants he was experimenting on. purebred purebred means that all the offspring have the same trait as the parents. Short X Short X Short Short Short In his first experiment, Mendel crossed (mated) a purebred tall pea plant with a purebred short pea plant. Short X What do you think happened? You would predict that half the offspring would be tall and half would be short, wouldn’t you? Or maybe you would predict that the offspring would all be medium height. Mendel’s first experiment Both predictions are WRONG!!! In every single experiment, Mendel found that ALL the offspring were… tall!!! Short P generation (parents) X purebred tall purebred short F1 generation (children) offspring are all tall So what happened to the “short” trait? Did it disappear? Here’s where Mendel showed true genius! What he did next was… he crossed (mated) the tall offspring from the first experiment with each other. X Mendel’s second experiment He was trying to find out if the “short” trait had really disappeared, or if it was still present in the tall pea plants, but was covered up somehow. The results from his second cross were truly amazing. What do you think happened? In EVERY SINGLE EXPERIMENT, the offspring in the second cross were: offspring of first cross (F1 generation) X Short offspring of second cross (F2 generation) 3/4 (75%) tall & 1/4 (25%) short P1 generation Here’s a summary of Mendel’s experiments X “Parents” Here’s a (purebred plants) summary of Mendel’s experiments X F1 generation “Children” (hybrid tall plants) F2 generation “Grandchildren” 75% tall 25% short Mendel tested his experiment again and again, and got the same results every time. Then he tested 6 other traits in the same way, and he got the exact same results with those traits. “Parents” P “Children” F1 “Grandchildren” F2 The F1 generation plants were always 100% the dominant trait. The F2 generation plants were always 75% the dominant trait, and 25% the recessive trait. Mendel’s actual experimental results So, what’s going on here? Mendel drew several conclusions: 1. The inheritance of each trait is determined by "factors" (now called genes) that are passed on from parents to offspring unchanged. 2. An organism inherits two factors, one from each parent, for each trait. 3. One factor can “mask” or cover up another factor. 4. A trait may not show up in an individual but can still be passed on to the next generation. Genes Mendel realized that one factor in a pair was masking, or hiding, the other factor. For instance, in his first experiment, when he crossed a purebred tall plant with a purebred short plant, all offspring were tall. Although the F1 offspring all had both tall and short factors, they only displayed the tall factor. He concluded that the tallness factor masked, or “covered up”, the shortness factor. Today, scientists refer to the “factors” that control traits as genes. Genes A gene is a section of a chromosome, which contains the instructions for a trait (Examples: plant height or flower color in pea plants, or hair color and blood type in humans) Genes All chromosomes come in pairs that are the same size, and have the same genes in the same locations. This is because an organism inherits 2 sets of chromosomes, one from the father and one from the mother. Since the chromosomes come in pairs, the genes come in pairs too. Every organism has 2 of every gene in their chromosomes. These genes are called gene pairs. Alleles • different forms of a gene For example: If the gene is for tail color If the gene is for flower in critters, the 2 alleles would be “blue tail” or “orange tail”. color in pea plants, the 2 alleles would be “purple” or “white”. Chr. Gene for tail color Blue allele Gene for flower color Orange allele Alleles • different forms of a particular gene What are some possible alleles for: ~ handedness? ~ hair color? ~ eye color? ~ hair texture? ~ dimples? Dominant and Recessive Dominant and Recessive Alleles Alleles Dominant: Alleles that cover up or hide recessive alleles. Recessive: alleles that are hidden or covered up by a dominant allele. Which of the 2 tail color alleles in critters was dominant? Homozygous and Heterozygous homozygous: has 2 identical alleles for a trait (purebred) heterozygous: has 2 different alleles for a trait (hybrid) Homozygous or Heterozygous? Homozygous or Heterozygous? TT bb Rr SS Gg tt YY Alleles Homozygous or Heterozygous? A b a c D e c d e F F G h I G B H I Genetic Notation Geneticists assign a letter to each allele for a trait. They use the first letter in the dominant trait. So, for the trait stem height, since tall is dominant, the letter “T” would be used. The dominant allele (tall) is abbreviated “T” and the recessive allele (short) is abbreviated “t”. A purebred tall plant would be TT, and a purebred short plant would be tt. A hybrid pea plant (like the tall plants in the F1 generation) would be Tt, because it has one dominant tall allele, and one recessive short allele. Genetic Notation Genotype and Phenotype An organism’s genotype is its genetic make-up. (Examples: TT, Tt, tt) An organism’s phenotype is its physical appearance. (Examples: tall plant, round seed, purple flower) Genotype Phenotype TT tall plant Tt tall plant tt short plant What would be the phenotype for the following genotypes? Genotype Gg gg Phenotype green pod GG yellow pod green pod pp white flower Pp purple flower PP purple flower Yy yellow seed RR round seed rr wrinkled seed SS side flower What are the possible genotypes for the following phenotypes? Phenotype end flower Possible Genotypes ss side flower SS, Ss green seed yy yellow seed YY, Yy round seed RR, Rr wrinkled seed tall plant short plant rr TT, Tt tt Probability… • is the likelihood (chance) that an event will happen. • is expressed as a percentage or fraction. Everyday examples of probability: • weather! Lots of times we hear predictions like “80% chance of rain,” or “20% chance of snow.” • the lottery “There’s a 1 in 10 million chance your ticket will be a winner.” • genetics is all about probability Calculating Probability Probability is calculated using this formula: Actual outcomes x 100 = Probability % Possible outcomes Example A: If I flip a coin, the probability that it will show heads is 1 out of 2, or 50%. Example B: If I roll a die, the probability that I will roll a 3 is 1 out of 6, or 16.7%. Example C: If I roll a die, the probability that I will roll an even number is 3 out of 6, or 50%. Multiple Probabilities In multiple probabilities (likelihood of 2 or more events happening at the same time), you multiply the probability of one event times the probability of the second event. Prob of Event 1 x Prob. of Event 2 = Multiple Probability For example: the probability of flipping two coins and getting 2 heads is: 1 x 1= 1 2 2 4 or 25% Probability Practice 1. What is the probability that, if I roll a pair of dice, I will get 2 sixes? 1 out of 36, or 2.8% 2. What is the probability that, if I flip a penny 10 times, I will get heads all 10 times? 1 ÷ 210, or 1/1024 3. If I’m a pea plant, and my father is hybrid tall, what is the probability that I got a t gene from him? 1/2 4. If I’m a pea plant, and my mother is hybrid tall, what is the probability that I got a t gene from her? 1/2 5. If I’m a pea plant, and both my parents are hybrid tall, what is the probability that I will get a t gene from both of them? 1/2 x 1/2 = 1/4, or 25% Probability When flipping 2 pennies, there are 4 possible outcomes: H-H H-T T-H T-T Same thing Probability Probability Probability Probability 1/4 or 25% 1/4 or 25% 1/4 or 25% 1/4 or 25% 25% + 25% = 50% How does this relate to genetics? In hybrid (heterozygous) crosses, the probabilities are the same as when flipping pennies! Punnett Squares Punnett squares are diagrams that show the probability that offspring will inherit a certain trait. For example: this is a Punnett square for a cross between two purebred (homozygous) tall pea plants. Genotype of offspring: T T T TT TT T TT TT 100% TT Phenotype of offspring: 100% tall Two purebred tall plants can only have purebred tall offspring. How To Make Punnett Squares How about a cross between two purebred short pea plants? Short t Short t Genotype of offspring: 100% tt t tt tt t tt tt Phenotype of offspring: 100% short Two purebred short plants can only have purebred short offspring. How about a cross between a purebred tall and a purebred short pea plant? t t T T Tt Tt Tt Tt Genotype: 100% Tt Phenotype: 100% tall This is a Punnett square of Mendel’s first experiment. The result is all hybrid tall offspring. Cross between 2 Hybrid (Heterozygous) tall plants T t T TT Tt t Tt tt Genotype: TT 25% Tt 50% tt 25 % Phenotype: Tall 75% Short 25% Look familiar? This is Mendel’s second cross… Okay…how about a cross between a purebred tall and a hybrid tall plant? T T T TT TT t Tt Tt Genotype: 50% TT, 50% Tt Phenotype: 100% tall How about a cross between a purebred short and a hybrid tall plant? Genotype: t t T Tt Tt t t t t t 50% Tt, 50% tt Phenotype: 50% tall, 50% short Punnett Square for Albinism in Humans In the cross Nn x Nn, where N is a dominant allele for Normal pigmentation and n is a recessive allele for no pigmentation (albinism), there is a¾_ probability the offspring will be normal pigmentation and ¼_ probability they will be albino. N n N NN Nn n Albino child, USA Nn nn Albino child, Tanzania Dirk brings his family tree to class Family Tree Exploring a Pedigree Pedigree: diagram that shows the presence of a trait in a family. A carrier is a person who does not have the recessive trait, but does have the recessive gene. (They’re hybrid) Pedigree of Queen Victoria of England for the trait of hemophilia How many children did Victoria and Albert have? How many were daughters, and how many were sons? How many of Victoria’s daughters were carriers of the hemophilia gene? How many of Victoria’s sons were hemophiliacs? How many of her grandsons were hemophiliacs? How many of her great-grandsons? Mermaid Tails Pedigree Analysis is a Key Tool in Human Genetics Analyzing a pedigree is like puzzle-building – you try things (assigning potential genotypes) until the pieces fit, and you’re as certain as you can be about genotypes and inheritance patterns (autosomal vs. X-linked; dominant vs. recessive; complete, incomplete or co-dominance). Pedigree Analysis Shea Family PedigreeBlue/non-blue eyes Shea Family PedigreeADD/non-ADD A Pedigree of a Dominant Human Trait A Pedigree of a Recessive Human Trait Note that the trait can appear in offspring of parents without the trait. Heterozygotes (hybrids) who do not show the trait are termed carriers. How many possible carriers are there on this pedigree? 7 Co-Dominance One exception to the dominant / recessive pattern is co-dominance. In this pattern, both alleles are dominant, and both traits are expressed. A capital letter represents one of the co-dominant alleles. A different capital letter represents the other co-dominant allele. In cattle, red and white coats are co-dominant. The hybrid offspring is called roan; it has both red and white hairs in its coat. RR red roan steer X RW roan WW white Co-Dominance In horses, gray horses (GG) are codominant to white horses (WW). The heterozygous horse (GW) is an appaloosa horse (a white horse with gray spots). Gray (GG) QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. X White (WW) Appaloosa (GW) BLOOD TYPE: an example of codominance in humans There are 4 blood types: A, B, AB, O Blood type is determined by 2 factors in the blood: factors A and B. •If factor A is present, you are Type A. •If factor B is present, you are Type B. •If A and B factors are present, you are Type AB. •If neither factor is present, you are Type O. • The A and B factors are co-dominant; when both are present, both are expressed. • Type O is recessive (needs two O genes to be present). Blood Type Genotypes & Phenotypes Phenotype Type A blood Genotype AA or AO Type B blood BB BO Type AB blood AB Type O blood OO or 1) What are the genotype and phenotype probabilities for the children of a man with Type A blood (homozygous) and a woman with type B blood (homozygous)? 2) What are the genotype and phenotype probabilities for the children of a man with Type O blood and a woman with Type AB blood? 1) What are the genotype and phenotype probabilities for the children of a man with Type A blood (homozygous) and a woman with Type B blood (homozygous)? 2) What are the genotype and phenotype probabilities for the children of a man with Type O blood and a woman with Type AB blood? Incomplete Dominance One thing Mendel didn’t realize was that there are some exceptions to the dominant / recessive pattern of inheritance that he observed in his pea plants. One exception is: incomplete dominance. In this pattern, one allele/trait does not completely dominate the other allele/trait. The result: the traits are blended. F1 generation: offspring of red and white flowers are all pink (a blend of the 2 parents’ colors). Incomplete dominance F2 generation: offspring of pink plants are 25% red, 25% white, and 50% pink Incomplete Dominance Here’s what’s happening: R R W RW RW W RW RW Red crossed with white makes pink offspring. R W RR RW W RW WW R Pink crossed with pink makes: 25% red 25% white 50% pink Incomplete Dominance A capital letter (P) represents one of the incompletely dominant alleles. The same capital letter prime (P1) represents the other incompletely dominant allele, so that the two do not get mixed up. In humans, curly hair (HH) A heterozygous human has wavy hair (HH1). QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. is incompletely dominant to straight hair (H1H1). Cross a person with curly hair with a person who has wavy hair. Polygenic Inheritance When a single trait is determined by more than one gene, we say that it is polygenic. Also: • eye color • hair color • blood type Height is a polygenic trait Multiple Alleles • Eye color is determined by more than one gene • Thus eye color appears to vary on an almost continuous scale from brown to green to gray to blue • Eye color is determined by three genes: one controls texture of the iris which refracts light to make blue, and a second which determines the amount of pigment, called melanin. When a small amount of melanin is present, blue or green eyes result, while brown & black eyes result from increasing amounts of melanin Eye Color Eye colors can range from the most common color, brown, to the least common, green. Rare genetic specialties can even lead to unusual eye colors: black, red, and violet. Eye color is an inherited trait influenced by more than one gene (polygenic). There are 3 genes that control eye color. One gene has Brown (B) and blue (b) alleles (Brown is dominant over blue). The 2nd gene also has 2 alleles: Green / hazel (G) and lighter color (g). Green is dominant over the lighter-color allele. Heterochromia (eyes that are different colors) Eye Color Calculator activity Hair color • Hair color is determined by more than one gene • Thus hair color appears to vary on an almost continuous scale from black to brown to blond to red • The brown and black pigment is melanin • The red pigment is an ironcontaining molecule Hair color It is thought that hair color is controlled by two genes. Brown hair Black hair Dark brown hair Red hair Auburn hair Grey (gray) hair Blonde hair White hair One gene has 2 alleles: Brown (B) and blonde (b). The 2nd gene has 2 alleles: Non-red (N) and red (n). The combination of these two genes, plus environmental factors (and age), contributes to the many different shades of hair color in humans. Skin Color Skin color is determined by the amount and type of melanin, the pigment in the skin. Skin color is determined by 6 different genes, which accounts for the vast range of different skin colors in human beings. link Chromosomes, Genes and DNA The structure and an actual picture of a chromosome. Human chromosome set from a skin cell. Chromosomes are long strands of DNA, wrapped around proteins. Humans have 46 chromosomes in every cell. Genes are sections of chromosomes. Humans have 20,000 - 25,000 genes in every cell. karyotype Karyotype: a picture of all 46 of a person’s chromosomes, arranged in 23 pairs. Note that 22 of the 23 pairs of chromosomes are the same size, and have the same banding patterns. However, the 23rd pair of chromosomes do not look alike at all. The 23rd pair of chromosomes are called the “sex” chromosomes, or “X and Y” chromosomes. The first 22 pairs of chromosomes are called “autosomal.” Make a karyotype How scientists read chromosomes Human Chromosome 1 False-color photograph shows human chromosomes, with the Chromosome 1 pair highlighted in blue. Chromosome 1 contains nearly twice as many genes as the average chromosome and makes up eight percent of the human genetic code. It is packed with 3,141 genes and linked to 350 illnesses including cancer, Alzheimer’s, Parkinson’s disease, and a gene for a common form of cleft lip and palate. X and Y Chromosomes The 23rd pair of chromosomes in humans determines a person’s gender. A female has two X chromosomes; a male has 1 X and 1 Y chromosome. Female: XX Male: XY X chromosome is much larger than the Y chromosome. B Which of these karyotypes shows a male, and which shows a female? A Gender Determination egg girl X X boy Y Genetic abnormalities of the XY Chromosomes Klinefelter Syndrome XYY syndrome Triple X syndrome Turner Syndrome Fragile X Syndrome Fragile X Syndrome Fragile X syndrome is caused by a mutation in the FMR1 gene, located on the X chromosome. The mutated gene cannot produce enough of a protein that is needed by the body's cells, especially brain cells, to develop and function normally. There are a variety of symptoms, including: Mental retardation, Hyperactivity, Short attention span, and Autism. Click here to learn more about FXS Down Syndrome QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. QuickTime™ and a TIFF (Uncompressed) decompressor are needed to see this picture. Down Syndrome, or Trisomy 21, occurs when a person has 3 copies of Chromosome 21, instead of the normal 2 copies. Other Genetic Abnormalities Who’s Got the Most Chromosomes? Who’s Got the Most Chromosomes? Plants Animals Apple 34 Dog 78 Peas 14 Frog 26 Onion 16 Goldfish 94 Potato 48 Horse 66 Rice 24 Housefly 12 Tomato 24 Human 46 Corn 20 Mosquito Click here to find out how many chromosomes other species have. 6 Mouse 40 Chicken 78 GENES BY THE NUMBERS Even though all the cells the body contain the exact same GENES BYinTHE NUMBERS genes, the genes that are “turned on” in each cell vary depending on the cell’s function. These are the numbers of working genes in different parts of the body. Brain 3195 White blood cell 2164 Liver 2091 Heart 1195 Pancreas 1094 Bone 904 Colon 879 Skeletal muscle 735 Kidney 712 Skin 629 Thyroid Gland 584 Eye 547 Small Intestine 297 Smooth muscle 127 Esophagus 76 Red blood cell 8 Some Genetics Numbers Some Genetics Numbers 3 billion base pairs 1 billion codons in one human cell there are… 25, 000 genes 46 chromosomes 6.5 feet of DNA Number of people on Earth: 7 billion Number of people with exactly your DNA ….1 YOU !!! Asexual Reproduction Asexual Reproduction organism divides and produces an exact replica (clone) of itself. Examples: bacteria, amoeba, yeast, algae • no genetic material (DNA) is exchanged. • no genetic diversity in the species (except for mutations) algae amoeba paramecium hydra (budding) Sexual Reproduction Sexual involves the mixingReproduction of DNA, usually from the union of an egg cell and a sperm cell. Examples: humans, flowers, fish, frogs, birds, snakes half the genetic material comes from the mother, and half from the father. offspring is unique (no other organism on Earth has exactly the same DNA it has) there is genetic diversity in the species, which helps ensure that a species will survive a widespread disease or environmental disaster. frogs sperm fertilizing egg paramecia hoverflies Twins and Multiple Births Twins and Multiple Births There are two types of twins, and they occur in two different ways… Fraternal twins • not identical • two eggs are fertilized at the same time Click here to learn more about twins Identical twins • identical • formed when one fertilized egg divides Chances of multiple births Twins: 1 in 90 Triplets: 1 in 8100 Quadruplets: 1 in 729,000 Multiple Births Multiple Births first set of octuplets born alive, in Houston TX, in 1998 triplets identical quadruplets van Tol quintuplets Gosselin twins & sextuplets McCaughey septuplets news on multiple births Homologous chromosomes • Two chromosomes which contain the same genes but may contain different alleles* *Alleles are different forms of the same gene. For example: the gene for eye color has many alleles: blue, green, brown, hazel, black, gray, etc. What’s Where? What’s Where? cell nucleus chromosome gene Chromosomes are made out of… DNA.