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Heredity Overview

Heredity Overview. How are genetic characteristics passed on from one generation to the next?. Cell Division. Chromosomes Contains the genetic information that is passed on (made of DNA) Hominids = 46 chromosomes (23 pairs) Mitosis Body (“somatic”) cells  replaces damaged cells Meiosis

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Heredity Overview

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  1. Heredity Overview How are genetic characteristics passed on from one generation to the next?

  2. Cell Division • Chromosomes • Contains the genetic information that is passed on (made of DNA) • Hominids = 46 chromosomes (23 pairs) • Mitosis • Body (“somatic”) cells  replaces damaged cells • Meiosis • Sex cells (sperm and egg)  creates variation within the species because of the random assortment of chromosomes in the sex cells

  3. Genetic Vocabulary Review • Fertilization  joining of egg and sperm • True-breeding  produces offspring identical to themselves • Trait  specific characteristic inherited • Hybrid  offspring of parents with different traits • Gene  chemical factors (DNA) that determine traits • Allele  the different forms of a gene

  4. Principle of Dominance • States that some alleles are dominant and others are recessive • Dominant allele  will always exhibit that form of the trait (A) • Recessive allele  will only exhibit if no dominant allele is present; need 2 recessive alleles to show a recessive trait (a) • Homozygous  individuals 2 of the same alleles • Homozygous dominant: AA • Homozygous recessive: aa • Heterozygous  individuals with 2 different alleles (Aa)

  5. http://faculty.southwest.tn.edu/jiwilliams/Human_Traits.htm

  6. Punnett Squares

  7. Segregation of Genes • Alleles segregate during gamete production • Phenotype = physical characteristics (tall vs. short • Genotype = genetic makeup (AA, Aa, or aa) • Pure cross  2 parents: one homozygous dominant and one homozygous recessive • Results in F1 offspring • F1 cross  2 parents from the F1 offspring (both are heterozygous) • Results in a phenotypic ratio of 3 tall:1 short • Results in a genotypic ratio of 1 AA:2 Aa:1aa

  8. Genes and Probability • Probability – likelihood that a particular event will occur • Flipping a coin once: heads (50% or 1/2); tails (50% or 1/2) • If flipped 3 times in a row = ½ * ½ * ½ = 1/8 (or 0.125) • Probability predicts possible genetic outcomes based on the way alleles segregate in meiosis

  9. Mendelian Genetics • In Mendelian genetics, Genes must be able to independently assort • Genes must not influence each other’s inheritance • Independent assortment accounts for the genetic variation in living things

  10. Beyond Dominant and Recessive Alleles • Some alleles are neither dominant or recessive, and many traits are controlled by multiple alleles or genes • Incomplete dominance One allele is not completely dominant over the other • Codominance Both alleles contribute to phenotype • Multiple alleles (ex. blood type) • Polygenic traits  controlled by more than one gene (ex. Skin color, eye color, hair color)

  11. Genetics and the Environment • The characteristics of organisms  not solely determined by inherited genes • Determined by interaction between genes and the environment • Genes provide a plan for development  how the plan unfolds also depends on the environment

  12. Genes and Variation • 2 main sources of genetic variation: • Mutations • Gene shuffling during sexual reproduction • Gene pool  all genes (and alleles) that are present in a population • Relative frequency  # of times an allele occurs in a gene pool (given as a percentage) • Evolution is any change in the relative frequency of alleles in a population

  13. Evolution as Genetic Change • Evolutionary fitness  an organism’s success in passing genes to the next generation • Evolutionary adaptation  any genetically controlled physiological, anatomical, or behavioral trait that increases ability to pass on genes

  14. Natural Selection and Evolution • Natural Selection never acts directly on genes • Works on the entire organism…can only affect which individuals survive and reproduce • If an individual dies  does not pass on genes • ALSO…Individuals do not evolve…Populations evolve as the gene pool changes because of the relative frequency of the alleles changes

  15. How did Hominids Evolve? • Natural Selection in not the only source of evolutionary change • Genetic drift  • Individuals that carry a particular allele may leave more descendents BY CHANCE. • Over time, a series of chance occurrences can cause an allele to become common in a population • A new species can result if there is enough of a genetic difference between the original population and the new population

  16. The Process of Speciation • Formation of a new species (organisms that breed and produce fertile offspring) • As new species evolve, populations become isolated from one another • Reproductive isolation  members of 2 populations can no longer interbreed and produce fertile offspring

  17. Isolating Mechanisms • Behavioral Isolation  differences in courtship or other reproductive strategies that involve behavior • Geographic Isolation  2 populations are separated by geographic barriers • Temporal Isolation  2 or more populations reproduce at different times of the year

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