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6.3 Mendel and Heredity 13.1 EcologistsofStudy Relationships Fundamentals Genetics Genetics – field of biology devoted to understanding how characteristics are transmitted from parents to offspring 6.3 Mendel and Heredity Father of Genetics Gregor Mendel Austrian Monk • Heredity – transmission of characteristics from parents to offspring • Garden Peas 6.3 Mendel and Heredity Characteristic 1. 2. 3. 4. 5. 6. 7. Plant Height Flower position Pod appearance Seed Texture Seed Color Flower Color Pod Color Traits Tall Axial Inflated Smooth Yellow Purple Green Short Terminal Constricted Wrinkled Green White Yellow 6.3 Mendel and Heredity Mendel’s Methods • Pollination – pollen produced in the male reproductive parts of the flower (anther) are transferred to the female reproductive part of a flower (stigma) • Self-pollination – pollen is transferred from an anther to a stigma on the same plant • Cross-pollination – involves flowers of two separate plants 6.3 Mendel and Heredity Mendel’s Experiments 1. He allowed plants to self-pollinate for several generations to obtain 14 pure strains: Parental Generation (P1) – Pure - always produce offspring with that trait – Strain - plants that are pure for a trait 2. Cross-pollinated these strains – one pure for one trait with another pure for the contrasting trait – P1 (tall) X P1 (short) First Filial Generation (F1) 3. Then allowed F1 to self pollinate second filial generation (F2) 6.3 Mendel and Heredity Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant. 6.3 Mendel and Heredity Mendel’s Results • Only one of the two traits in P1 appeared in the offspring F1 • The trait then reappeared in F2 in a ratio of 3:1 6.3 Mendel and Heredity Mendel’s Conclusions • Factor – something is controlling the traits – Allele • Pair of factors controls each trait – Gene • Recessive & Dominant Traits - Dominant Allele – masked the other factor (appeared in F1) - Recessive Allele – is masked by the presence of another (reappeared in F2) 6.3 Mendel and Heredity Chromosomes and Genes • Molecular genetics – study of the structure and function of chromosomes and genes • Gene – segment of DNA on a chromosome that controls a particular hereditary trait • Letters are used to represent alleles of genes - capital letters refer to dominant alleles T = tall - lowercase letters refer to recessive alleles t = short • Genome - All of an organism’s genetic material 6.4 Genes, Alleles 6.3 Traits, Mendel and and Heredity Genotype – genetic makeup of an organism • TT Tt tt Phenotype – appearance of an organism as a result of its genotype • Tall or short Homozygous – both alleles of a pair are alike • TT or tt Heterozygous – two alleles in the pair are different • Tt 6.5 Traits and 6.3 Mendel andProbability Heredity • The axes represent the gametes of each parent. – The boxes show the possible genotypes of the offspring. 6.5 Traits and 6.3 Mendel andProbability Heredity Genotypic ratio – ratio of the genotypes that appear in offspring • 1TT:2Tt:1tt Phenotypic ratio – ratio of the offspring's phenotypes • 3 Tall:1 short 6.5 Traits and 6.3 Mendel andProbability Heredity A monohybrid cross involves one trait (12 points) Homozygous Dominant X Homozygous Recessive 6.5 Traits and 6.3 Mendel andProbability Heredity Heterozygous X Heterozygous 6.5 Traits and 6.3 Mendel andProbability Heredity How Mendel's pea plants helped us understand genetics • http://ed.ted.com/lessons/how-mendel-s-pea-plantshelped-us-understand-genetics-hortensia-jimenez-diaz 6.5 Traits and 6.3 Mendel andProbability Heredity Testcross • Determine the genotype of an individual whose Phenotype is dominant – TT or Tt (?) • Individual of unknown genotype is crossed with a homozygous recessive individual • T? X tt 6.5 Traits and 6.3 Mendel andProbability Heredity Testcross (12 points): Offspring 100% Dom 7.2 Complex Patterns of Inheritance 6.3 Mendel and Heredity Complete Dominance – one allele completely dominant over the other Incomplete dominance – two or more alleles influence the phenotype • results in a phenotype in between the dominant and recessive • R = red W = white • RW pink 7.2 Complex Patterns of Inheritance 6.3 Mendel and Heredity Incomplete Dominance: Homozygous (1st trait) X Homozygous (2nd trait) 7.2 Complex Patterns of Inheritance 6.3 Mendel and Heredity Codominance – both alleles for a gene are expressed in a heterozygous offspring • neither is dominant or recessive • R = Red W = White • RW red & white polka dots 7.2 Complex Patterns of Inheritance 6.3 Mendel and Heredity Codominance: Heterozygous X Heterozygous 7.2 Complex Patterns of Inheritance 6.3 Mendel and Heredity Multiple Alleles – 3 or more alleles of the same gene • • • • • • • • IA or IB or i Blood Types IAIA or IBIB or IAIB ii IAi IBi = = = Blood type A = Blood type B Blood type AB Blood type O 7.2 Complex Patterns of Inheritance 6.3 Mendel and Heredity Blood Type AB X Blood Type O 7.1 and Phenotype 6.3 Chromosomes Mendel and Heredity Sex-linked Inheritance • Traits controlled by genes located on the sex chromosomes (X or Y) • X-linked traits – found on X chromosome • Y-linked traits – found on Y chromosome – X-linked traits more common in males – Y-linked traits only in males 7.1 and Phenotype 6.3 Chromosomes Mendel and Heredity X-Linked Heterozygous Female X Male with recessive trait 7.1 and Phenotype 6.3 Chromosomes Mendel and Heredity Y-Linked Female X Male with Dominant trait 7.1 and Phenotype 6.3 Chromosomes Mendel and Heredity • Female mammals have an XX genotype – X-inactivation – one X chromosome is randomly “turned off” in every cell – Ex: calico cats 7.1 and Phenotype 6.3 Chromosomes Mendel and Heredity Sex-Influenced – traits affected by how much sex hormones are present 6.5 Traits and 6.3 Mendel andProbability Heredity A dihybrid cross involves two traits (12 points) Homozygous Recessive/Heterozygous X Homozygous Dominant for both 6.5 Traits and 6.3 Mendel andProbability Heredity Heredity patterns can be calculated with probability. • Probability is the likelihood that something will happen • Predicts an average number of occurrences, not an exact number of occurrences. number of ways a specific event can occur • Probability = number of total possible outcomes 6.3 Mendel and Heredity Laws Law of Segregation – a pair of factors is separated during the formation of gametes • 1 trait: Tall from short Law of Independent Assortment – factors for different characteristics are distributed to gametes independently • All characteristics being separated from each other • Ex: Tall plant from yellow peas 7.1 and Phenotype 6.3 Chromosomes Mendel and Heredity • Autosomal genetic disorders – Carrier - A heterozygote for a recessive disorder – Disorders caused by dominant alleles are uncommon. (dominant) 6.3 Mendel and Heredity Epigenetics – study of changes in gene activity which are not caused by changes in the DNA • The changes in gene expression or phenotype have other causes • Ex: environment, other genes, etc 7.2 of Inheritance 6.3 Complex MendelPatterns and Heredity • Genes can interfere with other genes • Epistatic genes 7.2 of Inheritance 6.3 Complex MendelPatterns and Heredity Phenotype is a combination of genotype and environment. • EX: The sex of sea turtles depends on both genes and the environment • EX: Height is another example of a phenotype strongly affected by the environment. 6.3 Mendel and Heredity Polygenic Inheritance • Traits controlled by many genes • ~250 genes have been described to control human height up to 700 6.3 Mendel and Heredity Trihybrid Cross Hetero/Homo Rec/Homo Dom X Homo Rec/Hetero/Homo Dom