Observing Patterns in Inherited Traits Chapter 11 Updated Reading 11.1-11.3 Not 11.5-11.7
What you absolutely need to know Punnett Square with monohybrid and dihybrid cross Heterozygous, homozygous, alleles, locus, gene Test cross, P, F1, F2 Mendel and his work
Early Ideas about Heredity People knew that sperm and eggs transmitted information about traits Blending theory Problem: Would expect variation to disappear Variation in traits persists
No Blending Involved We cannot say that a red flower crossed with a what flower produces a pink flower.
Name this man
Gregor Mendel Strong background in plant breeding and mathematics Using pea plants, found indirect but observable evidence of how parents transmit genes to offspring
Genetic Terms A pair of homologous chromosomes A gene locus A pair of alleles Three pairs of genes
The Garden Pea Plant Self-pollinating True breeding (different alleles not normally introduced) Can be experimentally crosspollinated
Impact of Mendel s Work Mendel presented his results in 1865 Paper received little notice Mendel discontinued his experiments in 1871 Paper rediscovered in 1900 and finally appreciated
Genes Units of information about specific traits Passed from parents to offspring Each has a specific location (locus) on a chromosome
Alleles Different molecular forms of a gene Arise by mutation Dominant allele masks a recessive allele that is paired with it
Allele Combinations Homozygous having two identical alleles at a locus AA or aa Heterozygous having two different alleles at a locus Aa
Genotype & Phenotype Genotype refers to particular genes an individual carries Phenotype refers to an individual s observable traits Cannot always determine genotype by observing phenotype. Ex. A blond haired person can produce a red-haired offspring
Tracking Generations Parental generation mates to produce P First-generation offspring F 1 mate to produce Second-generation offspring F 2
Monohybrid Crosses Use F 1 offspring of parents that breed true for different forms of a trait: (AA x aa = Aa) The experiment itself is a cross between two identical F 1 heterozygotes, which are the monohybrids (Aa x Aa)
F 1 Results of One Monohybrid Cross
Punnett Square of a Monohybrid Cross Female gametes A a Male gametes A a AA Aa Aa aa Dominant phenotype can arise 3 ways, recessive only 1
F 2 Results of Monohybrid Cross
Testcross Individual that shows dominant phenotype is crossed with individual with recessive phenotype (AA x aa) Examining offspring allows you to determine the genotype of the dominant individual
Dominance Relations Complete dominance Incomplete dominance Heterozygote phenotype is somewhere between that of two homozyotes Codominance Non-identical alleles specify two phenotypes that are both expressed in heterozygotes
F 1 Results of Mendel s Dihybrid Crosses All plants displayed the dominant form of both traits: AaBb We now know: All plants inherited one allele for each trait from each parent All plants were heterozygous (AaBb)
F 1 Results of Mendel s Dihybrid Crosses All plants displayed the dominant form of both traits: AaBb We now know: All plants inherited one allele for each trait from each parent All plants were heterozygous (AaBb)
Dihybrid Cross Experimental cross between individuals that are homozygous for different versions of two traits
Now we want to try two traits Purple AA Tall BB Parent with purple flowers and and long stems = AABB Purple AA Tall BB Parent with white flowers and short stems White aa and short stems bb Dihybrid cross is AABB x aabb
Phenotypic Ratios in F 2 AaBb X AaBb Four Phenotypes: Tall, purple-flowered (9/16) Tall, white-flowered (3/16) Dwarf, purple-flowered (3/16) Dwarf, white-flowered (1/16)
AaBb x AaBb produces the following gametes If the two traits are coded for by genes on separate chromosome s, sixteen gamete combinations are possible