CHAPTER 9 FUNDAMENTALS OF GENETICS. Mendel, Punnett Squares, and Meiosis. GENETICS: FACT or FICTION?. 1. Genetic testing can identify all genetic disorders. 2. Obesity, heart disease, high blood pressure & intelligence are genetically predetermined.
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CHAPTER 9 FUNDAMENTALS OF GENETICS Mendel, Punnett Squares, and Meiosis
GENETICS: FACT or FICTION? • 1. Genetic testing can identify all genetic disorders. • 2. Obesity, heart disease, high blood pressure & intelligence are genetically predetermined. • 3. There are few genetically altered food products on the market. • 4. Genetically altered foods are not as healthy and do not taste as good as the real thing. • 5. Employers can screen employees’ genetics. • 6. You can choose/buy traits for your child (designer babies). • 7. A human has been cloned. • 8. Dinosaurs can be cloned. • 9. Biotechnology can help save endangered animals. • 10. Stem cells can cure several diseases/disorders. • 11. Genetically designed crops and farm animals is a new technology. • 12. Biotech animals are only found in laboratories. • 13. Biotechnology can only help cure genetic disorders, not common diseases. • 14. Organs from other animals can be used for human transplants (xenotransplantation). • 15. Cloned animals are not as healthy and live shorter lives than normal animals.
MENDEL’S LEGACY • Heredity is the key to differences between species. It is how traits get passed from one generation to the next • The branch of biology that studies heredity is called genetics Early Ideas About Heredity • Blending inheritance is what most people believed prior to Mendel’s work. According to this belief, the traits of both parents were expressed as a 50/50 mix in the offspring Gregor Mendel – an Austrian monk born in 1822, was a teacher of math and science - used garden peas to study heredity - Why were peas a good choice?
MENDEL’S LEGACY • Peas exhibited 7 visible characteristics and they only occurred in 2 contrasting forms or variations • Peas produce many offspring from a single mating & can create many generations in a short period of time – important b/c heredity is related to probability which requires large #’s to be studied • Peas normally self-pollinate b/c their petals enclose their reproductive organs (stamen & pistol) which made them ideal for Mendel to examine crosses between plants with contrasting traits
MENDEL’S LEGACY VOCABULARY • Trait – variations of a specific characteristic • Fertilization (pollination in plants) - the joining of a male and a female reproductive cell during sexual reproduction • Self-pollination – pollen of one plant fertilizes the eggs cells of the same plant • Cross-pollination – pollen of one plant fertilizes the egg cells of a different plant • It produces seeds that are the offspring of 2 different plants • Pure breed(true-breeding) – if a plant self-pollinates, it would only produce offspring identical to the parent plant • When Mendel crossed plants with 2 different variations of a trait, he produced hybrids • See Chart for List of Dominant/Recessive Traits (pg176)
PEA PLANT TRAITS Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall
Making a Cross P generation(parental) – the original pair of plants used in the cross F1 generation(first filial) – the offspring of the P generation Mendel’s Cross P gen. crossed a Tall plant with a Short plant What is the trait being tested? Resulting F1 gen. was ALL Tall plants MENDEL’S LEGACY P Generation F1 Generation Tall Short Tall Tall
MENDEL’S LEGACY • RESULTS - Hybrids showed just one of the parents traits, not a “blending” • MENDEL’S 2 CONCLUSIONS: • 2 individual factors, which do not blend with one another, control each trait of a living thing and are passed from one generation to the next • A gene is a small segment of DNA that codes for a single characteristic • Different forms of a gene are called alleles • Second conclusion is his Principle of Dominance • Some factors are dominant while others are recessive • Dominant alleles will ALWAYS exhibit that form of the trait because it will mask a recessive trait • Recessive alleles will only exhibit that form of the trait when a dominant allele is NOT present • Which alleles are dominant for each of the garden pea traits?
MENDEL’S LEGACY • Mendel’s Second Cross • F2 generation(second filial) – the offspring produced by crossing the F1 gen. • Resulting F2 gen. was mostly Tall, BUT some Short plants reappeared. P Generation F1 Generation F2 Generation Tall Short Tall Tall Tall Tall Tall Short
MENDEL’S LEGACY • Mendel’s Conclusion • Principle of Segregation – during the formation of gametes (sex cells) the two alleles for a trait are separated into different gametes • Ex. Some gametes formed by the F1 gen. contained the Tall allele, while others received the Short allele (See Figure 11-5 pg. 266)
Does the segregation of one pair of alleles for one trait affect the segregation of the pair of alleles of another trait? One – Factor Cross (monohybrid) – a cross involving only one trait (2 alleles) Two – Factor Cross (dihybrid) – a cross involving 2 traits ( 2 pairs of alleles) Ex. Cross a purebred parent with round yellow peas with a purebred parent with wrinkled green peas. R = round, r = wrinkled Y = yellow, y = green P = RRYY x rryy MENDEL’S LEGACY
Ex. Cross a purebred parent with round yellow peas with a purebred parent with wrinkled green peas. F1 Results: ALL offspring Phenotype = round yellow peas ALL offspring Genotype = RrYy F2 Results: Offspring Phenotypes Round yellow Round green Wrinkled yellow Wrinkled green (9:3:3:1) Offspring Genotypes RRYY RRYy RRyy RrYY RrYy Rryy rrYY rrYy rryy MENDEL’S LEGACY
MENDEL’S LEGACY • Principle of Independent Assortment – the alleles or genes of different traits can segregate independently from each other during the formation of gametes • Ex. – in the cross between RrYy x RrYy, the seed shape had no effect on the seed color • Accounts for the variety within a species
Probability – the likelihood that a particular event will happen #of events that will occur Probability = ---------------------------------------- # of events possible Ex. Coin Flip – there are 2 possible outcomes (heads or tails) There is an equal chance of either occurring, therefore the probability is 1 chance in 2 = ½ or 50% What is the probability of getting heads up 5x in a row? ½ x ½ x ½ x ½ x ½ = 1/32 GENETIC CROSSES • Coin Flip vs. Genetics – allele segregation is completely random like the results of a coin flip *PAST OUTCOMES do NOT effect future ones
GENETIC CROSSES • Punnett Squares are diagrams used to determine possible allele combinations and predict results of a cross • Each Dominant/Recessive trait is assigned a single letter. • The Dominant allele is represented by a capital letter. • The Recessive allele is represented by a lower case letter. • Ex. T = tall, t = short
Homozygous (true-breeding, purebred) – 2 identical alleles Ex. TT and tt Heterozygous (hybrid) – 2 different alleles Ex. Tt Phenotype – the physical appearance of an organism Ex. Tall and short Genotype – the genetic makeup of an organism Ex. TT, Tt, and tt ***NOTE – Dominant alleles are listed first in a genotype*** GENETIC CROSSES
GENETIC CROSSES • Show the genotypes of two reproductive cells called gametes (sperm & egg) on the outside of the box. These are the 2 parents being crossed or bred. • The possible gene combinations of the offspring of this cross are shown on the inside of the boxes.
GENETIC CROSSES • Key – shows the letters assigned to the genotypes and the genotypes of the parents • KEY: Tall = T Short = t P = TT x tt • ANSWERING QUESTIONS • Offspring Genotypes • TT, Tt, tt • Ratio 0:4:0, Percentage 100% Tt • Offspring Phenotypes • Tall, Short • Ratio 4:0, Percentage 100% Tall • Now do an F1 Cross
GENETIC CROSSES • Punnett squares can help predict the average outcome of a cross, BUT cannot precisely predict the exact numbers • Punnett squares can also help predict parent genotypes by running a test cross and recording the results of the offspring in a Punnett square.
GENETIC CROSSES • Testcross (backcross) – a cross performed to determine the genotype of an organism that exhibits a dominant phenotype • The unknown is best crossed with a homozygous recessive b/c the probability of revealing the unknown geno. Is better
GENETIC CROSSES • Incomplete Dominance – one allele is not dominant over the other, instead the heterozygous genotype shows an intermediate form of phenotype • Ex. Four O’clock plants • RR = red • rr = white • Rr = pink
GENETIC CROSSES • Codominance – in a heterozygous genotype, both alleles can be seen • Ex. Chicken Feather Color • BB = black feathers • WW = white feathers • BW = speckled feathers