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Fundamentals of Genetics

Fundamentals of Genetics. Genetics – field of biology devoted to understanding how characteristics are transmitted from parents to offspring. Father of Genetics Gregor Mendel Austrian Monk. Heredity – transmission of characteristics from parents to offspring Garden Peas.

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Fundamentals of Genetics

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  1. Fundamentals of Genetics Genetics – field of biology devoted to understanding how characteristics are transmitted from parents to offspring

  2. Father of GeneticsGregor MendelAustrian Monk • Heredity – transmission of characteristics from parents to offspring • Garden Peas

  3. Characteristic Traits • Plant Height Tall Short • Flower position Axial Terminal • Pod appearance Inflated Constricted • Seed Texture Smooth Wrinkled • Seed Color Yellow Green • Flower Color Purple White • Pod Color Green Yellow

  4. Mendel’s Methods • Pollination – pollen grains 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 the anthers of a flower to the stigma on a flower on the same plant • Cross-pollination – involves flowers of two separate plants

  5. Mendel’s Experiments • Grew plants PURE for a trait (always produce offspring with that trait) • STRAIN - plants that are pure for a specific trait • He allowed plants to self-pollinate for several generations to obtain 14 strains: Parental Generation (P1) • 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) • Then allowed F1 to self pollinate  second filial generation (F2)

  6. 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. interrupted the self-pollination process by removing male flower parts

  7. 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

  8. Mendel’s Conclusions • Factor – something controlling the traits (allele) • Pair of factors controls each trait (gene) • Recessive & Dominant Traits - Dominant factor – masked the other factor (appeared in F1) - Recessive – is masked by the presence of another (reappeared in F2)

  9. 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 - capital letters refer to dominant alleles T = tall - lowercase letters refer to recessive alleles t = short • Genome - All of an organism’s genetic material

  10. Genetic Crosses • Genotype – genetic makeup of an organism • TT Tt tt • Phenotype – appearance of an organism as a result of its genotype TT  Tall tt  short • Homozygous – both alleles of a pair are alike TT or tt • Heterozygous – two alleles in the pair are different Tt

  11. 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

  12. 6.5 Traits and Probability Punnett squares illustrate genetic crosses. • The Punnett square is a grid system for predicting all possible genotypes resulting from a cross. • The axes representthe possible gametesof each parent. • The boxes show thepossible genotypesof the offspring. • The Punnett square yields the ratio of possible genotypes and phenotypes.

  13. 6.5 Traits and Probability A monohybrid cross involves one trait. (12 points) Homozygous Dominant X Homozygous Recessive

  14. 6.5 Traits and Probability Heterozygous X Heterozygous

  15. Testcross • Individual of unknown genotype is crossed with a homozygous recessive individual • Determine the genotype of an individual whose phenotype is dominant

  16. 6.5 Traits and Probability Testcross (10 points): Offspring 100% Dom

  17. Complete Dominance – one allele completely dominant over the other • Incomplete dominance – two or more alleles influence the phenotype resulting in a phenotype intermediate between the dominant and recessive traits R=red W=white RW  pink

  18. Codominance – both alleles for a gene are expressed in a heterozygous offspring – neither is dominant or recessive RW  red & white polka dots

  19. Multiple Alleles – 3 or more alleles of the same gene • Blood Types • IA IB i • IAIA or IAi = Blood type A • IBIB or IBi = Blood type B • IAIB = Blood type AB • ii = Blood type O • The ABO blood types result from codominant multiple alleles.

  20. Sex-linked Inheritance • Traits controlled by genes located on the sex chromosomes • X-linked gene • Y-linked gene • X-linked traits more common in males Sex-Influenced Inheritance – traits affected by how much sex hormones are present

  21. 7.1 Chromosomes and Phenotype Punnett Square: Sex-Linked Traits • Determine Sex of Offspring • Difference in sex-linked traits.

  22. 7.1 Chromosomes and Phenotype • Male mammals have an XY genotype. • All of a male’s sex-linked genes are expressed. • Males have no second copies of sex-linked genes.

  23. 7.1 Chromosomes and Phenotype • Female mammals have an XX genotype. • X chromosome inactivation randomly “turns off” one X chromosome.

  24. 6.5 Traits and Probability A dihybrid cross involves two traits. (12 points) Homozygous Dominant for both X Homozygous Recessive for both

  25. 6.5 Traits and Probability • Probability = number of ways a specific event can occur number of total possible outcomes Heredity patterns can be calculated with probability. • Probability is the likelihood that something will happen. • Probability predicts an average number of occurrences, not an exact number of occurrences.

  26. Laws • Law of Segregation – a pair of factors is segregated, or 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) i.e. Tall plant from yellow peas

  27. 7.1 Chromosomes and Phenotype (dominant) • Mendel’s rules of inheritance apply to autosomal genetic disorders. • A heterozygote for a recessive disorder is a carrier. • Disorders caused by dominant alleles are uncommon.

  28. Polygenic Inheritance • Traits controlled by many genes • Multifactorial • ~180 genes have been described to control human height  up to 700 • Add the effect of all genes to get the manifestation of the trait • ABC – each having their own set of alleles • AaBbCc

  29. 7.2 Complex Patterns of Inheritance • An epistatic gene can interfere with other genes.

  30. 7.2 Complex Patterns of Inheritance The environment interacts with genotype. • Phenotype is a combination of genotype and environment. • The sex of sea turtles depends on both genes and the environment • Height is an example of a phenotype strongly affected by the environment.

  31. 7.2 Complex Patterns of Inheritance Order of dominance: brown > green > blue. Many genes may interact to produce one trait.

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