March 06, 2012

1. March 06, 2012 • Today’s lesson will begin with a pre-assessment. Please find your seats and take out a pen or pencil. • You have approximately 15 minutes to complete the pre-assessment. • When you have finished, place it on the lab demonstration in the front of the class.

2. Bell Ringer – 03/06/2012 • List 5 characteristics that can be passed on through families. Can you explain why some characteristics are absent in one generation but may reappear in future generations (5 minutes) • Think Pair Share – Now with a neighbor share and discuss your answers (5 minutes)

7. Genetics • The study of how characteristics are transmitted from parents to offspring is called genetics. • Heredity is the passing of traits from parents to offspring, and genetics is the study of how those traits are passed.

8. Gregor Mendel • “Father of Genetics” • Studied many plants, but he is remembered most for his experiments with Pisum sativum, a species of garden peas.

9. Think Pair Share • First, think on your own reasons why Mendel choose pea plants for his experiment. • In approximately 5 minutes discuss your answers with a neighbor.

10. Why did Mendel choose pea plants for his experiment? • Distinctive measureable traits • Easy to breed • Short breeding period • Large number of offspring • Ability to self and cross pollinate

11. Mendel’s Garden Peas • Mendel observed 7 characteristics of pea plants. • Plant height (traits: long and short) • Flower position along stem (traits: axial and terminal) • Pod color (traits: green and yellow) • Pod appearance (traits: inflated and constricted • Seed texture (traits: round and wrinkled) • Seed color (traits: yellow and green • Flower color (traits: purple and white)

13. Traits • A characteristic is a heritable trait, such as flower color. • A trait is defined as a genetically determined variant of a characteristic, such as a yellow flower color.

14. Mendel’s Methods • Mendel was able to observe how traits were passed by carefully controlling how pea plants were pollinated. • Pollination – occurs when pollen grains produced in the male reproductive parts of a flower are transferred to the female reproductive part. • Self pollination –pollen is transferred from a flower to a flower on the same plant • Cross pollination – occurs between flowers of two plants

15. Mendel’s Experiments • Initially, Mendel studied each characteristic and its contrasting traits individually. • He began by growing plants that were true breeding for each trait. • Plants that are true-breeding, or pure, for a trait always produce offspring with that trait when they self pollinate. (Pea plants that are true breeding for the trait that have yellow pods offspring will have yellow pods).

16. Mendel’s Experiment Generations • Parental (P) generation – true breeding parents • F1 generation – the offspring of the Parental (P) generation • F2 generation – the offspring of the F1 generation

18. “Crash the Board” • On the board, I have the following categories: Learned, Want to Learn, and Confused About • Write a comment, question, etc for each category

19. Mendelian Genetics – 03/07/2012 • Design a newspaper ad that might have attracted someone such as Mendel to purchase Pisum Sativum for genetic research. Be creative, use color, and include illustrations! • What did you include?

20. Mendel’s Results and Conclusions • 1st – Mendel crossed a plant true-bleeding for green parts with one true-breeding for yellow pods • Results – only green podded plants • What’s this generation called?

21. Mendels Results and Conclusions • 2nd – Mendel allowed the F1 generation to self pollinate and seeds. When the F2 plants grew, he observed ¾ of the F2 generation had green pods and ¼ had yellow pods • What does it mean to self-pollinate?

22. Mendel’s Results and Conclusions • Mendel concluded that inherited traits are controlled by factors, that occur in pairs. • In his experiments on pea plants, one factor in a pair masked the other. The trait that masked the other was called the dominant trait. • The trait that was masked was called the recessive trait.

23. Bell Ringer – Think Pair Share • Briefly on your own for the bell ringer define the following terms: Heredity, trait, gene, allele, dominant, recessive. • Once you have attempted to define all terms, discuss with a neighbor your definitions.

24. Mendels Results and Conclusions • The Law of Segregation “1st Law” – explains how alleles are separated during meiosis. • Mendel concluded that the paired alleles separate during formation of reproductive cells. • The law of segregation states that a pair of alleles is segregated, or separated, during the formation of gametes. • During fertilization (when sperm & egg unit), each parent organism donates one copy of each gene to the offspring.

26. Mendels Results and Conclusions • The Law of Independent Assortment “2nd Law” – states that segregation of the alleles of one trait does not affect the segregation of the alleles of another trait. • Mendel also crossed plants that differed in two characteristics, such as flower color and seed color • Mendel found that a pea plant receiving an allele dominant for one trait will not necessarily receive an allele dominant for another trait. • This law holds true for all genes unless the genes are linked. In this case, the genes that do not independently segregate during gamete formation, usually because they are in close proximity on the same chromosome.

27. Law (Principle) of Dominance • Some alleles are dominant whereas others are recessive. • Organism with a dominant allele for a particular trait will always have that trait expressed (seen) • Shown by a capital letter • Organism with a recessive allele for a particular trait will only be expressed when the dominant allele is not present • Shown by a lowercase letter

28. Mendel Graphic Organizer

29. Homozygous • Since organisms receive one gene for a chromosome pair from each parent, organisms can be heterozygous or homozygous for each trait. • Homozygous (“homo” meaning same) – two identical alleles for a trait • Alleles can either be homozygous dominant (TT) or homozygous recessive (Tt) • Ex: TT, tt, PP, pp, etc

30. Heterozygous • Heterozygous (“hetero” meaning different) – two different alleles for a trait. One is dominant, the other recessive. • Ex: Tt, Pp

31. Genotype • Genotype (Genetic Makeup) – reveals the type of alleles that an organisms has • TT represents a homozygous dominant genotype. • Therefore, what does tt and Tt represent?

32. Phenotype • Phenotype (Physical Characteristics) – is a description of the way that a trait is expressed, for example (B) is the allele for black hair and (b) is the allele for brown hair. Therefore, what would my phenotype be if my genotype was BB, Bb, or bb?

34. Review! • Carmen has brown eyes, would this be her genotype or phenotype? • Nolan has blonde hair, would this be his genotype or phenotype? • The genotype for tall flowers is TT, would the flower be homozygous dominant or homozygous recessive ? Why? • The genotype for a pea plant flower color that is homozygous recessive would be PP or pp?

35. Remember …. • Genotype = Genetic Makeup • Phenotype = Physical Appearance • Homozygous = “Homo” = the same alleles • Heterozygous = “Hetero” = different alleles • Dominant = masks or dominates other allele; Capital Letter • Recessive = the allele that is masked unless present with another recessive allele; Lowercase letter

36. Punnett Squares • A Punnett Square can be used to predict genetic combinations in offpsirng. • A monohybrid cross examines the inheritance of one trait. (Ex. Seed color, flower color, etc) • A dihybrid cross examines the inheritance of two different traits.

37. Let’s Practice Punnett Square Fun 

38. Bell Ringer – March 18, 2012 • In pea plants, purple flower color (P) is dominant over white (p). Write the specific phenotype for the following: PP, Pp, and pp. • In rabbits, the allele for black coats (B) is dominant over the allele for brown coat color (b). • What would be the genotype for a homozygous black coat? • What would be the genotype for a homozygous brown coat? • What would be the genotype for heterozygous black coat? • Figure out the F1 generation for the following parents: Bb x Bb (Monohybrid Punnett square)

39. Mendel’s Peas (again!) Mendel had observed that the seeds of his pea plants varied in several ways – among them, whether the peas were round or wrinkled and whether they were green or yellow. He did monohybrid crosses on both characteristics, but then decided to look at how they were inherited together….

40. There are four possible combinations of the two characteristics. Peas can be: • 1) round and yellow • 2) round and green • 3) wrinkled and yellow • 4) wrinkled and green

42. F2 : : : 9 3 3 1 Round Yellow Round Green Wrinkled Yellow Wrinkled Green This is the typical ratio expected in a dihybrid cross.

43. New developments since Mendel’s principles of genetics Gene linkage simply means that genes that are located on the same chromosome will be inherited together. These genes travel together during gamete formation. This is an exception to the Mendelian principle of independent assortment because linked genes do not segregate independently.

44. New developments since Mendel’s principles of genetics • Crossing-over is a process in which alleles in close proximity to each other on homologous chromosomes are exchanged. This results in new combinations of alleles. • When chromosomes pair up during Meiosis I, sometimes sections of the two chromosomes become crossed. The two crossed sections break off and usually reattach. • When the genes are rearranged, new combinations of alleles are formed (see B

45. New developments since Mendel’s principles of genetics • Incomplete dominance is a condition in which one allele is not completely dominant over another. The phenotype expressed is somewhere between the two possible parent phenotypes. • Codominance occurs when both alleles for a gene are expressed completely. The phenotype expressed shows evidence of both alleles being present. • These conditions go beyond Mendel’s principle of dominance.

46. New developments since Mendel’s principles of genetics • Multiple alleles can exist for a particular trait even though only two alleles are inherited. For example, three alleles exist for blood type (A, B, and O), which result in four different blood groups. • Polygenic traits are traits that are controlled by two or more genes. These traits often show a great variety of phenotypes, e.g. skin color. • Mendel’s principles of genetics does not explain that many traits are controlled by more than one gene.

47. New developments since Mendel’s principles of genetics • Sex-linked traits are the result of genes that are carried on either the X or the Y chromosome. • This is an exception to Mendel’s principle of independent assortment which does not explain sex-linked traits. • In most organisms that undergo sexual reproduction, one pair of chromosomes (the sex chromosomes) determines the sex of the organism. • The gender of humans is determined by X and Y chromosomes. • The pair of sex chromosomes in females consists of two X chromosomes, each carrying genes for the same traits; the pair of sex chromosomes in males consists of one X chromosome and one Y chromosome. • During Meiosis I, when chromosome pairs separate, each gamete from the female parent receives an X chromosome, but the gametes from the male parent can either receive an X chromosome or a Y chromosome.