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GENETICS

GENETICS. Mendel and the Gene Idea. Genetics. The study of heredity . Gregor Mendel (1860’s) discovered the fundamental principles of genetics by breeding garden peas. He Used Plants that looked like this:. True Breeding Plants: consistently have offspring with same

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GENETICS

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  1. GENETICS

  2. Mendel and the Gene Idea

  3. Genetics • The study of heredity. • Gregor Mendel (1860’s) discovered the fundamental principles of genetics by breedinggarden peas.

  4. He Used Plants that looked like this: True Breeding Plants: consistently have offspring with same trait as parent.

  5. Genetics • Alleles 1. Alternative forms ofgenes. 2. Units that determine heritable traits.

  6. Dominant Alleles Dominant alleles (TT - tall pea plants) a. homozygous dominant Homozygous = two alleles that are the same.

  7. Recessive Alleles Recessive alleles (tt - dwarf pea plants) a. homozygous recessive Homozygous = two of the same alleles Recessive = Hidden allele when dominant is present.

  8. Mixed Alleles Heterozygous (Tt - tall pea plants) Mixed set of alleles. Dominant takes over for physical trait (phenotype).

  9. Phenotype • Outward appearance • Physical characteristics • Examples: 1. tall pea plant 2. dwarf pea plant

  10. Genotype • Arrangement of genes that produces the phenotype • Example: 1. tall pea plant TT = tall (homozygous dominant) 2. dwarf pea plant tt = dwarf (homozygous recessive) 3. tall pea plant Tt = tall (heterozygous)

  11. Punnett square • A Punnett square is used to show the possible combinations of gametes.

  12. T T t t Showing a cross with Pea Plants • tall (TT) vs. dwarf (tt) pea plants

  13. T T produces the 1st generation Tt Tt t Tt Tt t All Tt = tall (heterozygous tall) tall (TT) vs. dwarf (tt) pea plants

  14. T t T t Cross the 1st generation • tall (Tt) vs. tall (Tt) pea plants

  15. T t produces the 2nd generation Tt TT T 1/4 (25%) = TT 1/2 (50%) = Tt 1/4 (25%) = tt Tt tt t 1:2:1 genotype 3:1 phenotype tall (Tt) vs. tall (Tt) pea plants

  16. Monohybrid Cross • Mendel did A breeding experiment that tracks the inheritance of a single trait.

  17. Segregation Principle of Segregation The principle of segregation is explained by the behavior of homologous chromosomes at meiosis.

  18. Law of Independent Assortment • Genes for different traits are separated and distributed to gametes (sex cells) independently of one another

  19. Incomplete Dominance • This is when both alleles contribute to the phenotype of a heterozygous individual to produce a trait that is not exactly like either parents. • Ex: A flower has genes for white petals (W) and red petals (R). When you mix white flowers with red flowers you get pink flowers.

  20. Codominance • Two dominant alleles are expressed at the same time. • The human ABO blood group illustrates another genetic phenomenon – codominance. • The AB phenotype (genotype IA and IB is an example.

  21. Height is a polygenic trait Polygenic Inheritance – When a Single Trait is Influenced by Many Genes

  22. Multiple Alleles • Many genes are present in 3 or more versions (alleles) – this is known as multiple alleles. • The human ABO blood group is determined by three alleles (IA, IB, and i) of a single gene.

  23. Pleiotropy – When One Allele Influences Many Traits

  24. Sex-Linked Traits • Traits carried on sex chromosomes X or Y • Ex: Red green color blindness, Hemophilia

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