Understanding Genetics: Simple vs. Complex Heredity in Plants and Animals

1. Simple Medelian Genetics Competency 12.00

2. Genetic Terminology

3. DNA • Deoxyribonucleic Acid • The major nucleic acid in organisms • Carries genetic information and is responsible for the transmission of traits.

4. Gene • A segment of DNA that codes for a specific trait in an organism.

5. Allele • An alternative form of a gene/trait. • Example: Eye color alleles are blue, green, hazel, brown • Can be homozygous or heterozygous

6. Homozygous Allele • Organism with identical alleles for a given trait • Can be dominant or recessive • Example: TT or tt

7. Heterozygous Allele • Organism with different alleles for a given trait • Ex: Tt

8. Phenotype • The physical appearance of a trait in an organism • Determined but not always indicative of the genetic makeup of the organism • Example: tall or short

9. Genotype • The genetic composition of an organism for a given trait • Often cannot be determined by looking at an organism • Example: Tt or TT, both are tall

10. Recessive Gene/Allele • Variation of a trait that can only be expressed in the absence of a dominant allele • Heterozygous individuals are carriers for recessive alleles.

11. Dominant Gene/Allele • Variation of a trait that is expressed over other variations of the same trait • Most common forms in natural populations • Some traits can be co-dominant or exhibit incomplete dominance

12. Chromosome • Long condensed strand of DNA forming in the nucleus of a cell prior to cell division • Form cells that when split, create an exact copy of DNA in the daughter cell

13. Chromatid Pairs • X-shaped structures that serve as the mechanism for the transmission of genetic material during cell division. • They are pulled apart in the process of mitosis and meiosis.

14. Heredity

15. Gregor Mendel • 1863 • Austrian monk who conducted the first genetics experiments using pea plants in the mid 1800s. • Often considered the founder of genetics and heredity.

16. What is Heredity? • Heredity is best described as the manner in which inheritable characteristics (traits) are passed from parents to offspring.

17. Heredity • A direct outcome of the RANDOM genetic recombination resulting during reproduction • Only functions in sexual reproduction • Ensures genetic diversity

18. Heredity • Determines the genetic potential of an animal, but . . . • Heredity and environmental influences determine the overall quality of the animal. • Nature versus Nurture

19. Types of Heredity • Simple Heredity • Complex Heredity • Polygenic Inheritance • Incomplete Dominance • Codominance

20. Simple Heredity • One gene controls one trait—alleles are either dominant or recessive. • Example: height and color in pea plants

22. Complex Heredity • Polygenic Inheritance • One trait is controlled by several genes and possibly environmental factors • Genes may even be located on different chromosomes

23. Complex Heredity • Polygenic Inheritance • This is a slow process requiring many generations to achieve desired results. • Example: Height in humans

24. Complex Heredity • Codominance • Multiple alleles for a given trait are not expressed over one another, but in combination. • Example: RR (Red Flower) x WW (White Flower) = RW (Red and White Striped Flower) X =

25. Incomplete Dominance • Similar to codominance, except characteristics of alleles blend instead of remaining distinct • Example: RR (Red Flower) x WW (White Flower) = RW (Pink Flower) X =

26. Heredity in Agriscience • Heredity is a huge factor in successful agricultural selective breeding programs. • Heredity is manipulated to create high quality HYBRID offspring.

27. Heredity in Agriscience • Plants and animals are inbred through several generations to isolate a specific trait or traits. • No more than 7 generations are inbred to prevent genetic disorders.

28. Heredity in Agriscience • The final generation of two different lines inbred for different traits are crossed producing offspring with the beneficial traits of both lines. • Resulting offspring possesses hybrid vigor

29. Hybrid Vigor

30. Heredity in Agriscience • Hybrid vigor usually lasts only one generation, as hybrid organisms rarely express traits true to type in offspring. • Alternative forms of the gene resurface in the new cross.

31. Heredity in Agriscience • Punnett Squares, Pedigree Charts, Genetic Mapping and DNA analysis can be used to predict heredity.

32. Punnett Squares

33. What is a Punnett Square? • A method utilizing the known genotypes of parent offsprings to predict the expression of a given trait or traits in offspring. • Must know the genotype of parents and the inheritance pattern of the trait.

34. Using Punnett Squares • When using Punnett Squares the Dominant Trait is always represented by an uppercase letter • Recessive is lowercase • Example: T=Tall, t=short

35. Using Punnett Squares • A box should be drawn with one space for each allele expressed by both parents. • In simple heredity boxes are 2x2.

36. Using Punnett Squares • The alleles for one parent should be placed above each column at the top, with the alleles for the other placed beside each row on one side. T T T t

37. Using Punnett Squares • The alleles of each parent should be distributed across and down the box. T T TT TT T t Tt Tt

38. Using Punnett Squares TT-Homozyous Dominant Tt-Heterozygous Genotype Ratio: 2:2:0 Phenotype Ratio: 4:0 T T TT TT T t Tt Tt

39. Using Punnett Squares • When crossing using complex heredity boxes are 4x4 and two different traits are being crossed.

40. Using Punnett Squares TG Tg tG tg Genotype Ratio-0:4:4:4:4:0 Phenotype Ratio- 0:8:8:0 Tg TTGg TTgg TtGg Ttgg TTGg TTgg TtGg Ttgg Tg Tg TTGg TTgg TtGg Ttgg Tg TTGg TTgg TtGg Ttgg

41. Assignment • 1. White hair (ww) x black hair (WW) • 2. blue eyes (bb) x brown eyes (Bb)