History of Genetics and Mendel's Contributions

1. The student is expected to: 3F research and describe the history of biology and contributions of scientists and 6F predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybridcrosses and non-Mendelianinheritance

2. History of Genetics Gregor Mendel was an Austrian monk and scientist who was in charge of the monastery garden. Mendel studied garden peas.

3. KEY CONCEPT Mendel’s research showed that traits are inherited as discrete units.

4. Mendel laid the groundwork for genetics. • Traits are distinguishing characteristics that are inherited. • Genetics is the study of biological inheritance patterns and variation. • Gregor Mendel showed that traits are inherited as discrete units. • Many in Mendel’s day thought traits were blended.

5. Mendel’s data revealed patterns of inheritance. • Mendel made three key decisions in his experiments. • use of purebred plants • control over breeding • observation of seven“either-or” traits

6. Pea plants happened to be a good choice to study because: They are self-pollinating. He had different pea plants that were true-breeding. True-breeding - means that they are homozygous for that trait. EX. if the plants self-pollinate they produce offspring identical to each other and the parents.

7. When discussing generations’ traits, we label them as following: The true-breeding parental generation is called the “P generation”. The offspring of the two parental plants is called the “F1 generation”. A cross between F1 generation would be called “F2 generation.”

8. Mendel controlled the fertilization of his pea plants by removing the male parts, or stamens. He then fertilized the female part, or pistil, with pollen from a different pea plant. • Mendel used pollen to fertilize selected pea plants. • P generation crossed to produce F1 generation • interrupted the self-pollination process by removing male flower parts

9. Mendel allowed the resulting plants to self-pollinate. • Among the F1 generation, all plants had purple flowers • F1 plants are all heterozygous • Among the F2 generation, some plants had purple flowers and some had white

10. Original cross (P) Parental Generation (true breeding) F1 Generation (offspring) Cross pollination F2 Generation (Cross of F1 Generations)

11. Mendel’s Investigations Mendel saw that when he crossed plants with different versions of the same trait (P generation), the F1 offspring were NOT blended versions of the parents. The F1 plants resembled only one of the parents. Tall x short  all tall…

12. Mendel observed patterns in the first and second generations of his crosses.

13. purple white • Mendel drew three important conclusions. • Traits are inherited as discrete units. • Organisms inherit two copies of each gene, one from each parent. • The two copies segregateduring gamete formation. • The last two conclusions arecalled the law of segregation.

14. Mendel concluded: 1. Biological inheritance is determined by “factors” that are passed from one generation to the next. Factors were later defined as “genes”- Mendel discovered all of this without the knowledge of DNA!

15. Mendel concluded: In Mendel’s plants, there was one gene for each trait. For example, there was one gene for plant height. But, there were two versions of this gene: one for a tall plant and one for a short plant.

16. Mendel concluded: Alleles: Different versions of the same gene Remember, genes are used to make proteins. Each allele contains the DNA that codes for a slightly different version of the same protein This gives us the different characteristics for each trait

17. 2. Principal of dominance: Some alleles are dominant and some alleles are recessive. Recessive alleles are able to be masked Dominant alleles mask recessive alleles The trait that was represented in the F1 generation was the dominant trait.

18. 2. Principal of dominance: How many alleles do you have for each gene? Where do they come from? Two One comes from mother and one comes from father.

19. 3. Segregation: Observation: After seeing that his F1 plants looked like only one generation of the P generation plants, Mendel wanted to know what happened to the recessive alleles. Question: Did they disappear?

20. 3. Segregation: Experiment: Mendel self-pollinated the F1 plants, or crossed the F1 plants with each other, to produce the F2 generation. From his F1 crosses, Mendel observed: The versions of the traits coded for by recessive alleles reappeared in the F2 plants. The recessive trait was still there!

21. 3. Segregation: About 25% (or ¼) of the F2 plants exhibited the recessive version of the trait. In this case the recessive phenotype is short. The dominant phenotype, tall, was found in 75% (or ¾) of the F2 plants. P generationF1 generationF2 generation

22. Segregation of alleles during meiosis: When the F1 plants produce gametes (sex cells) and self-pollinate, the two alleles for the same gene separate from each other so that each gamete carries only one copy of each gene. Remember, gametes are haploid. In the example, we use “T” to represent the dominant, tall allele and “t” to represent the recessive, short allele.

23. The student is expected to: 6A identify components of DNA, and describe how information for specifying the traits of an organism is carried in the DNA and 6F predict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses and non-Mendelian inheritance

24. KEY CONCEPT Genes encode proteins that produce a diverse range of traits.

25. The same gene can have many versions. • A gene is a piece of DNA that directs a cell to make a certain protein. • Each gene has a locus, aspecific position on a pair ofhomologous chromosomes.

26. An allele is any alternative form of a gene occurring at a specific locus on a chromosome. • Each parent donates one allele for every gene. • Homozygous describes two alleles that are the same at a specific locus. • Heterozygous describes two alleles that are different at a specific locus.

27. Alleles can be represented using letters. • A dominant allele is expressed as a phenotype when at least one allele is dominant. • A recessive allele is expressed as a phenotype only when two copies are present. • Dominant alleles are represented by uppercase letters; recessive alleles by lowercase letters.

28. All of an organisms genetic material is called the Genome • A Genotype refers to the makeup of a specific set of alleles • A Phenotype is the physical expression of a trait

29. Key Terms in Mendelian Genetics: Dominant- allele that can mask; represented by capital letters (B, D, F, etc.) Recessive- alleles that can be masked; represented by lower case letters (b, d, f, etc.)

30. Key Terms in Mendelian Genetics: Phenotype- observable traits (brown eyes, yellow seed pods) Genotype- actual alleles; describes the genetic characteristics (BB, dd, Ff) Phenotype: brown eyes Genotype: could be BB, or Bb

31. Key Terms in Mendelian Genetics: Homozygous (True-Breeding)- having two identical alleles for the same trait (TT, tt); “homo” means same Heterozygous- having two different alleles from the same trait (Tt); “hetero” means different

32. Both homozygous dominant and heterozygous genotypes yield a dominant phenotype. • Most traits occur in a range and do not follow simple dominant-recessive patterns.

33. The student is expected to: 3F research and describe the history of biology and contributions of scientists; 6Fpredict possible outcomes of various genetic combinations such as monohybrid crosses, dihybrid crosses and non-Mendelianinheritance; 6G recognize the significance of meiosis to sexual reproduction

34. KEY CONCEPT The inheritance of traits follows the rules of probability.

35. Punnett squares illustrate genetic crosses. • The Punnett square is a grid system for predicting all possible genotypes resulting from a cross. • The axes representthe possible gametesof each parent. • The boxes show thepossible genotypesof the offspring. • The Punnett square yields the ratio of possible genotypes and phenotypes.

36. A monohybrid cross involves one trait. • Monohybrid crosses examine the inheritance of only one specific trait. • homozygous dominant-homozygous recessive: all heterozygous

37. heterozygous-heterozygous—1:2:1 homozygous dominant: heterozygous:homozygous recessive; 3:1 dominant:recessive

38. heterozygous-homozygous recessive—1:1 heterozygous:homozygous recessive; 1:1 dominant:recessive • A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype.

39. A dihybrid cross involves two traits. • Mendel’s dihybrid crosses with heterozygous plants yielded a 9:3:3:1 phenotypic ratio. • Mendel’s dihybrid crosses led to his second law,the law of independent assortment. • The law of independent assortment states that allele pairs separate independently of each other during meiosis.

40. Probability = number of ways a specific event can occur number of total possible outcomes Heredity patterns can be calculated with probability. • Probability is the likelihood that something will happen. • Probability predicts an average number of occurrences, not an exact number of occurrences. • Probability applies to random events such as meiosis and fertilization.

41. The student is expected to:6F predict possible outcomes of various genetic combinations such as monhybrid crosses, dihybrid crosses and non-Mendelian inheritanceand8G recognize the significance of meiosis to sexual reproduction

42. KEY CONCEPT Independent assortment and crossing over during meiosis result in genetic diversity.

43. Sexual reproduction creates unique combinations of genes. • Sexual reproduction creates unique combination of genes. • independent assortment of chromosomes in meiosis • random fertilization of gametes • Unique phenotypes may give a reproductive advantage to some organisms.

44. Crossing over during meiosis increases genetic diversity. • Crossing over is the exchange of chromosome segments between homologous chromosomes. • occurs during prophase I of meiosis I • results in new combinations of genes

45. Chromosomes contain many genes. • The farther apart two genes are located on a chromosome, the more likely they are to be separated by crossing over. • Genes located close together on a chromosome tend to be inherited together, which is called genetic linkage. • Genetic linkage allows the distance between two genes to be calculated.