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Fundamentals of Genetics

Fundamentals of Genetics

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Fundamentals of Genetics

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  1. Fundamentals of Genetics Section 6.3-6.6

  2. What are traits? • Trait- any characteristic that can be passed from parent to child Give some examples: • Define genetics: • Genetics is the field of biology that deals with heredity • Heredity is the passing on of characteristics from parents to offspring

  3. Who is “the father of genetics?”

  4. Gregor Mendel • Experimented with pea plants • Well suited to genetic study • grown easily in large numbers • their reproduction can be manipulated • They have both male and female reproductive organs –perfect flower

  5. What were the three key things that played an important role in the development of his laws of inheritance? -Control over breeding -Use of purebred plants -Observation of “either-or” traits that appeared in only two alternate forms

  6. Define purebred and cross • Purebred or True breeding- after self fertilization, offspring have the same traits as parents • genetically uniform • Cross: the mating of two organisms

  7. Mendel's work • P – parent generation • F1 – filial 1 generation – results from cross of parents • F2 Filial 2 generation – results when F1 generation cross breeds.

  8. Mendel’s Experiment

  9. His three conclusions… • Traits are inherited as discrete units • Organisms inherit two copies of each gene, one from each parent • Organisms donate only once copy of each gene in their gametes

  10. Mendel's Laws and Modern Genetics • Law of segregation- each pair of alleles segregates during meiosis. Half of an organisms gametes have one allele from each pair • Law of Dominance – when two different alleles are present one can dominate over the other. The expressed gene is the dominant allele. The gene that is not expressed is the recessive allele. • Law of independent assortment– gene (homologous) pairs segregate into gametes randomly and independently of each other

  11. Mendel’s work ….. • Hybrid – cross between two parents. Produces a hybrid with genetic information from both parents • Dominant trait – expressed trait in a hybrid • Recessive trait – unexpressed trait in a hybrid • Mendel hypothesized each trait was controlled by a “factor”. We know these factors today to be genes- A genetic factor that controls a trait. Each parent gives one of these factors to the offspring. These are alleles - a different version of a gene for each trait

  12. Use of letters to show traits • Genotype – the actual genetic make up of the organism. • B = brown hair – dominant trait is shown with upper case • b = blond hair – recessive trait is shown with lower case • Phenotype – the form of the trait that is observed. • Homozygous – an organism in which two alleles for a trait are identical • BB brown hair • bb blond hair • Heterozygous – an organism in which two alleles for a trait are different • Bb Brown hair

  13. A dominant allele does not necessarily mean the allele is better or stronger, simply that is masks another recessive trait! • Uppercase letters are used for dominant alleles and lowercase letters are used for recessive alleles.

  14. Who developed the Punnett square? • Reginald Punnett • What is a Punnett square? • a grid for organizing genetic information. Predicts expected outcome of a genetic cross • The axes represent the possible gamete genotypes of each parent • The grid boxes show all of the possible genotypes of offspring from those two parents

  15. Use of Punnett Square • need the alleles of parents • put alleles of one parent along top of grid, the other along the side • combine alleles • determine genotypes and phenotypes

  16. Construct a Punnett Square for one trait

  17. The principle of segregation

  18. Types of crosses • Monohybridcross - The study of only one trait. • Dihybridcross - the study of two traits at a time. • Test cross – used to distinguish heterozygous dominant individual from the recessive. A cross between an unknown and a homozygous recessive individual.

  19. Monohybrid cross

  20. Dihybrid Cross gametes

  21. The Dihybrid Cross • RrYy x RrYy • Foil Method • First • Outer • Inner • Last • Gametes After Foil • RY, Ry, rY, ry (parent 1) and RY, Ry, rY, ry (parent 2)

  22. What two things contribute to the great deal of genetic variation within species? -Independent assortment of chromosomes during meiosis -the random fertilization of gametes How many different combinations of chromosomes are possible for one couple? 70 Trillion!

  23. Independent assortment is the random distribution of homologous chromosomes during meiosis

  24. Crossing over also contributes to genetic diversity in species. What is crossing over? Crossing over is the exchange of chromosome segments between homologous chromosomes during prophase 1 of meiosis 1