Transcript File
Intro. To Genetics Chapter 11 You Only Write What You Feel Necessary This will be on my website tonight. Introduction to Genetics • “Genetics tell us we have an inherited biological blueprint that includes blood type, eye color, and height. Sometimes it’s easy to feel trapped or restricted by our genes. But the limits of our achievements stem less from our genes than from ourselves. When we think of successful people, is it because of great genes or great efforts? Without a doubt, it is the latter. What you inherit is the beginning of what you can be, not the end of it.” Traits • 1. 2. 3. 4. Look at yourselves and classmates to determine who has these traits: Widows Peak vs. straight hairline Attached vs. free earlobs Hitch-hiker’s thumb vs. straight Gapped vs. ungapped teeth Are these traits inherited? • Yes • From whom are they inherited? • From our parents Genetics •The scientific study of heredity Mendel • Important work of a monk named Gregor Mendel helped us to understand biological inheritance. • He experimented with garden pea plants. • Knew the flower part of the plant contains male and female parts. • Self-pollination occurs producing seeds that produce plants identical to the parent. • Cross-pollination produces plants from different parents • Pea plants had 8 different traits to study • Trait is a specific characteristic such as color, size, shape, etc… • Mendel is sometimes called the “father of genetics” Generations • Mendel called the original plants P generation, for parental - they were pure breeding • Offspring were exactly like their parents • Crossed tall pure with short pure to get F1(first filial) hybrid generation- all were tall. • Next generation called F2 (second filial) generation – produced when tall hybrids were bred together –some were tall, some were short. • Mendel concluded that inheritance is passed from generation to generation • Also concluded some genes are dominant, some are recessive. Probability • Likelihood that a particular event will occur • When you flip a coin, what is the probability of it being heads? Tails? • Probability can be used to predict outcome of genetic crosses • Genes segregate (separate) randomly, like a coin flip Punnett Squares • Diagram that is used to show gene combinations that might occur from a genetic cross • Letters used in Punnett square represent alleles • • • • Ex.-T=tall t=short TT = homozygous (dominant) Tt = heterozygous tt = homozygous (recessive) Important Terms!!! • Genotype – the actual DNA genetic makeup for a particular characteristic – it’s at the cellular level, you CAN'T see it! • We use letters to describe genotype, ex.-T,t,B,b,W,w,G,g, etc… • Phenotype – the result of the DNA makeup – the actual physical characteristic that you CAN see!!! • Ex-tall, short, black, white, green, yellow, round, wrinkled, etc… Principle of Independent Assortment • Genes for different traits can segregate independently during the formation of gametes (sex cells). • Mendel wondered if the gene for one trait, such as pea color, had anything to do with another trait such as pea shape. NON-MENDELIAN INHERITANCE PATTERNS • The simple rules of Mendel’s inheritance do not always apply. We will more closely examine some of these patterns. Incomplete Dominance • Neither allele is dominant over the other, so the heterozygous phenotype is a blend of the two. • Ex.- Red flower X white flower = pink. Codominance • Both alleles are present in the phenotype • For example – if the colors black and white in chickens are codominant, and the two are crossed, the offspring exhibits both as a speckled phenotype. Multiple Alleles • Sometimes a gene has more than two alleles, so an individual can have a combination of two from a pool of several. Polygenic Traits • Some traits are controlled by two or more genes. • For example, the wide range of skin color in humans is partly because more than 4 different genes control this trait. Two factor Punnett Square (Di-hybrid cross) Tall is dominant over short, black is dominant over white. 1. Draw a Punnett square showing a cross between a tall, black dog, and a short, white dog, using TTBB X ttbb. 2. Draw a Punnett square showing this cross: TtBb X TtBb. 3. What are the genotypic and phenotypic ratios of each cross?