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

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Presentation on theme: "Heredity Overview How are genetic characteristics passed on from one generation to the next?"— Presentation transcript:

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

2 Cell Division Chromosomes Mitosis Meiosis
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 # of students Widow’s peak No widow’s peak Dimples No dimples Freckles No freckles Extra digits Normal digits Attached earlobes Unattached earlobes


7 Punnett Squares


9 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

10 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

11 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

12 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)

13 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

14 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

15 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

16 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

17 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

18 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

19 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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