Fundamentals of Genetics

1. Fundamentals of Genetics Chapter 9 (pgs 164-178) Mrs. McNamara - Biology

2. Heredity and Genetics Parents pass certain traits to their offspring.

4. Landon (left) at 6 months and Gavin (right) at 3.5 months. On the left, cousins; on the right, brothers! Notice the similarities and differences!

5. Part 1

6. Key Concepts • Genes are particulate and are inherited according to Mendel’s laws. • Mendel learned about heredity by conducting experiments. • Genes are carried on chromosomes. • Alleles and genes interact to produce phenotypes.

7. Heredity • Your combination of traits received for each characteristic are unique to you. • Your mother and father each contribute to your genetic makeup. • For example: the color of your hair, the size of your feet and the shape of your nose are some of your traits.

8. Heredity • Heredity- The passing of traits from parents to offspring. • Genetics-The branch of biology that studies heredity. • Geneticists-Biologists who study heredity.

9. Look at the photographs to the right. • What traits have these babies inherited from their parent?

10. DNA & HEREDITY • Remember that traits are passed from parents to offspring (inherited) by the passing of DNA from parents to their offspring.

11. Gregor Mendel • Called the “Father of Genetics” • In the late 1800’s Mendel began studying the passing of traits from parents to offspring. • He, too wanted to know why certain patterns of traits showed up in living things. • Analyzed pea plants to look for patterns in how traits were passed from parents to offspring.

12. Gregor Mendel While trying to develop new color variations of flowers Mendel began experimenting…..

13. Gregor Mendel’s Experiment • He studied 7 characteristics (genes), each with 2 contrasting traits (alleles) available. • CHARACTERISTIC-a distinguishing quality that an organism exhibits. • Ex: height, hair color, eye color, skin color. • TRAIT- specific hereditary options available to be inherited for each characteristic. • Ex: tall height/short height, brown hair/blonde hair, brown eyes/blue eyes, Dark skin/ light skin.

15. Gregor Mendel’s Experiment • He started by growing plants that were PURE-having a trait and always passing that trait to their offspring.

16. Gregor Mendel’s Experiment • Then, Mendel bredplants that had different traits to see what the offspring would look like. • The first plants he crossed he called the “Parental Generation” (P)

17. Gregor Mendel’s Experiment • In his first crosses, Mendel found that only one of the two traits appeared in the offspring plants (F1 generation – children of P generation). • For example, when he crossbred tall pea plants with short pea plants, the offspring (F1) were always tall.

18. Gregor Mendel’s Experiment • After his first crosses, Mendel took those offspring plants (F1) and crossed them. • In these second crosses, both traits showed up again in the F2 generation. (F2 GENERATION-offspring of the F1 generation).

19. Gregor Mendel’s Experiment • The same results happened in every experiment. One trait, like being tall, was always present in the first generation (F1). • The other trait, like being short, seemed to go away; only to reappear again in the second generation. • This happened with every set of traits that Mendel studied in the same proportions..

21. MENDEL’S 3 CONCLUSIONS: • 1. Law (Principle) of Dominance and Recessiveness • 2. Law (Principle) of Segregation • 3. Law (Principle) ofIndependent Assortment

22. 1. Law of Dominance and Recessiveness From these experiments, Mendel discovered that traits from one parent may hide traits from the other parent. He also found that certain traits would always show themselves over other traits. • These traits he called DOMINANT-can mask or dominate the other trait and is displayed most often.

23. The hidden or masked traits he called RECESSIVE-the trait that can be covered up; is displayed less often. • Ex: the trait (allele) for tall is dominant over the trait (allele) for short, so the short allele would be the recessive allele.

25. Genes • Mendel hypothesized that something in the pea plants was controlling the characteristics that came through • He called these controls “factors” (We now know that these characteristicsare controlled by Genes-pieces of DNA that code for a characteristic (protein that is made).)

26. Genes • Mendel also figured out that for each trait, the plant had two factors, or a pair of factors, controlling the expression of each trait. • Each pair consists of alternate forms (alleles) of the same gene; one from mother and one from father.

27. Genes • Dominant traits were controlled by dominant alleles and recessive traits were controlled by recessive alleles.

28. Genes • Letters are used to represent the alleles that carry the trait found on genes. A letter represents a trait. • CAPITAL if the gene that controls the trait is dominant. • Lowercase if the gene is recessive. • T- represents a dominant allele for tallness • t – represents a recessive allele for lack of tallness, or shortness

29. Genotype and Phenotype • Genotype- The genetic combination, or pair of alleles an organism inherits for a certain trait. • Phenotype- The appearance of a trait in an organism. • Ex: A plant's genotype is TT. Its phenotype is tall.

31. Blue alleles b b Phenotype (blue eyes) Genotype (bb)

32. Like and Unlike Alleles • HOMOZYGOUS- organism has 2 of the same alleles for a trait. • Homozygous Dominant-has 2 dominant alleles; dominant trait is displayed • Ex: TT = tall pea plant • Homozygous Recessive-has 2 recessive alleles; recessive trait is displayed • Ex: tt = short pea plant • HETEROZYGOUS-organism has 1 dominant and 1 recessive allele; the dominant trait is displayed. • Ex: Tt = tall pea plant

33. Blue alleles Brown Allele Blue Allele b b b B Homozygous – alleles are the same Heterozygous – alleles are different

34. Two Like Alleles X = X =

35. Two Unlike Alleles • If youcrossbred homozygous tall plants (TT) (purebred) with homozygous short plants (tt) (purebred)… All of the offspring are tall! WHY? X = All of the offspring had received a tall gene (T) from one parent and a short gene (t) from the other parent.

36. Organisms with different genotypes may have the same phenotype. • For example, a homozygous tall plant (TT) and a heterozygous tall plant (Tt) have different genotypes. • However, they have the same phenotype, which is tall. tt TT Tt Tall Tt Tall Tall Tall TT Tt Tt Tall Short tt

37. Traits of Humans Remember, the combination of alleles makes you look the way you do. You get traits from your parents, just like pea plants do. For example, the trait of earlobe shape in humans is inherited. There is an allele for free earlobes and an allele for attached earlobes. The allele for free earlobes is dominant, and the allele for attached earlobes is recessive. This is one of 9000 traits in humans controlled by a single gene.

38. MENDEL’S LAWS OF INHERITANCE Mendel developed the following three laws to describe how an organism's various traits are inherited and expressed. • The Law of Dominance and Recessiveness. • The Law of Segregation. • The Law of Independent Assortment.

39. 2. The Law (Principle) of Segregation: • Organisms have 2 copies of each gene (one from mom and one from dad), but put only 1 copy in each sperm or egg. • During fertilization, the alleles come together and new combinations of alleles are randomly formed. • The trait observed in an individual depends on the two copies of the gene it inherits from its parents.

41. 3. The Law (Principle) of Independent Assortment: • The alleles for different genes, on different chromosomes, are not connected. • The chromosomes are distributed into gametes independently (randomly) during meiosis, not based on the distribution of any other chromosome. • EX: in pea plants, a gamete that receives a dominant (yellow) allele for pea color can receive either a dominant (round) or recessive (wrinkled) allele for pea shape • However, if two genes are located on the same chromosome, they are inherited together .

42. Principle of Independent Assortment

43. 3. The Law (Principle) of Independent Assortment: http://www.sumanasinc.com/webcontent/animations/content/independentassortment.html

44. PART 2

45. Key Concepts • Alleles and genes interact to produce phenotypes. • Observing and individual’s phenotype is not sufficient for determining its genotype. • The outcome of a genetic cross can be predicted.

46. AFTER MENDEL • Today, Geneticists rely on Mendel’s work to predict the likely outcome of genetic crosses.

47. Punnett Squares • Probability is the likelihood that a chance event will occur. • The value of studying genetics is in understanding how we can predict how likely it is to inherit a particular trait. • One of the easiest ways to calculate the mathematical probability of inheriting a specific trait was invented by an early 20th century English geneticist named Reginald Punnett .

48. Punnett Squares • MONOHYBRID CROSS-cross between 2 individuals involving 1 pair of contrasting traits (2 alleles).

49. Punnett Squares • His technique employs what we now call a Punnett square. • Punnett square-chart that shows the possible allele combinations for potential offspring of two parents whose genotypes are known.

50. How to Use a Punnett Square • The results of Mendel’s experiments with two homozygous plants can be shown using a Punnett Square…Let’s try it! STEP 1 - Draw a chart with four boxes. STEP 2 - Above the two boxes going across, write the symbol for a the first parent’s alleles (in this case…homozygous tall plant (TT)) with one letter over each box. T T