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Genetics & The Work of Mendel. Genetic Terminology Trait - any characteristic that can be passed from parent to offspring Heredity - passing of traits from parent to offspring Genetics - study of heredity. Gregor Mendel.
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Genetic Terminology Trait - any characteristic that can be passed from parent to offspring Heredity - passing of traits from parent to offspring Genetics - study of heredity
Gregor Mendel • Modern genetics began in the mid-1800s in an abbey garden, where a monk named Gregor Mendel documented inheritance in peas • used good experimental design • usedmathematicalanalysis • collected data & counted them • excellent example of scientific method
Mendel’s work • Bred pea plants • cross-pollinate true breeding parents • raised seed & then observed traits • allowed offspring to self-pollinate& observed next generation
true-breeding purple-flower peas true-breeding white-flower peas 100% purple-flower peas 1st generation (hybrids) 100% 75% purple-flower peas 25% white-flower peas 3:1 2nd generation Looking closer at Mendel’s work X Parents self-pollinate
What did Mendel’s findings mean? • Some traits mask others • purple & white flower colors are separate traits that do not blend • purple x white ≠ light purple • purplemaskedwhite • dominant allele • functional protein • affects characteristic • masks other alleles • recessive allele • no noticeable effect • allele makes a non-functioning protein I’ll speak for both of us! allele producingfunctional protein mutant allele malfunctioningprotein homologouschromosomes
X P purple white F1 all purple Genotype vs. phenotype • Difference between how an organism “looks” & its genetics • phenotype • description of an organism’s trait • genotype • description of an organism’s genetic makeup Explain Mendel’s results using …dominant&recessive …phenotype&genotype
PP pp x X P purple white F1 all purple Making crosses • Can represent alleles as letters • flower color alleles P or p • true-breeding purple-flower peas PP • true-breeding white-flower peas pp Pp
PP 25% male / sperm P p Pp 50% 75% P Pp female / eggs pp p 25% 25% Punnett squares Pp x Pp 1st generation (hybrids) % genotype % phenotype PP Pp Pp pp 1:2:1 3:1
Mendel’s Laws **Inheritable factors or genes are responsible for all heritable characteristics **Phenotype is based on Genotype **Each trait is based on two genes, one from the mother and the other from the father **True-breeding individuals are homozygous ( both alleles) are the same
Law of Dominance In a cross of parents that are pure for contrasting traits, only one form of the trait will appear in the next generation. All the offspring will be heterozygous and express only the dominant trait. RR x rr yields all Rr (round seeds)
Law of Segregation *During the formation of gametes (eggs or sperm), the two alleles responsible for a trait separate from each other. *Alleles for a trait are then "recombined" at fertilization, producing the genotype for the traits of the offspring.
Law of Independent Assortment *Alleles for different traits are distributed to sex cells (& offspring) independently of one another. *This law can be illustrated using dihybrid crosses. Dihybrid Cross A breeding experiment that tracks the inheritance of two traits. Mendel’s “Law of Independent Assortment” a. Each pair of alleles segregates independently during gamete formation b. Formula: 2n (n = # of heterozygotes)
