APBIO- Chpt 14A “Overview of Gregor Medel’s Discoveries”

1. APBIO- Chpt 14A “Overview of GregorMedel’s Discoveries” Warm-Up: Compare and contrast the blending hypothesis and particulate hypothesis for heredity.

2. SIMILARITIES: • Both hypotheses are related to the study and ideas of genetics and heredity. Both were accepted, at some point in time, as the means for understanding genes and traits. • DIFFERENCES: • “Blending” hypothesis: • This hypothesis proposes that the genetic material contributed by each parent mixes in a manner analogous to the way blue and yellow paints blend to make green. • Over many generations, a freely mating population should give rise to a uniform population of individuals. • However, the “blending” hypothesis appears incorrect as everyday observations and the results of breeding experiments contradict its predictions. • An alternative model, “particulate” inheritance: • Proposes that parents pass on discrete heritable units - genes - that retain their separate identities in offspring. • Genes can be sorted and passed on, generation after generation, in undiluted form. Answer to Warm-Up

3. (1) Students will be able to describe the patterns of inheritance that Mendel’s data revealed. • (2) Students will be able to summarize Mendel’s law of segregation. • (3) Students will be able to explain how there can be many versions of one gene. • (4) Students will be able to describe how genes influence the developments of traits. • (5) Students will be able to describe monohybrid and dihybrid crosses. • (6) Students will be able to explain how heredity can be illustrated mathematically. Objectives

4. KEY CONCEPT: Mendel’s research showed that traits are inherited as discrete units. Mendel & Heredity

5. 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. Mendel & Heredity

6. Mendel’s data revealed patterns of inheritance. • He made three key decisions in his experiments. • Use of purebred plants • Control over breeding • Observation of seven“either-or” traits Mendel & Heredity

7. 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 Mendel’s Experiment

8. 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

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

10. Mendel drew some important conclusions: • Traits are inherited as discrete units. • Organisms inherit two alleles (copies of each gene), one from each parent. • The two copies segregate during gamete formation. • The last two conclusions are called the law of segregation. Mendel & Heredity

11. http://www.youtube.com/watch?v=aDpLDBaEBjk&feature=related You Tube Video Clip- Gregor Mendel

12. (1) Describe the patterns of inheritance that Mendel’s data revealed. • (2) Summarize Mendel’s law of segregation. Reflection

13. KEY CONCEPT :Genes encode proteins that produce a diverse range of traits. Traits, Genes, & Alleles

14. The same gene can have many versions. • Gene- piece of DNA that directs a cell to make a certain protein. • Each gene has a locus, aspecific position/location. Traits, Genes, & Alleles

15. Allele- 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. Traits, Genes, & Alleles

16. Genotype- refers to the makeup of a specific set of genes. • i.e., Bb, BB, bb • Phenotype- is the physical expression of a trait. • i.e., blue eyes, blonde hair, tall • Two organisms can have the same phenotype but have different genotypes if one is homozygous dominant and the other is heterozygous. Traits, Genes, & Alleles

17. Alleles- 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. Traits, Genes, & Alleles

18. Both homozygous dominant (i.e., BB) and heterozygous (i.e., Bb) genotypes yield a dominant phenotype. • Most traits occur in a range and do not follow simple dominant-recessive patterns. Traits, Genes, & Alleles

19. (3) Explain how there can be many versions of one gene. • (4) Describe how genes influence the development of traits. Reflection

20. KEY CONCEPT:The inheritance of traits follows the rules of probability. Traits & Probability

21. Punnett squares illustrate genetic crosses. • The Punnett square is a grid system for predicting all possible genotypes resulting from a cross. • Axes- possible gametesof each parent. • Boxes- possible genotypesof the offspring. • The Punnett square yields the ratio of possible genotypes and phenotypes. Traits & Probability

22. Monohybrid crosses examine the inheritance of only one specific trait. • homozygous dominant-homozygous recessive: all heterozygous, all dominant Traits & Probability

23. heterozygous-heterozygous—1:2:1 homozygous dominant: heterozygous:homozygous recessive; 3:1 dominant:recessive Traits & Probability

24. heterozygous-homozygousrecessive—1:1 heterozygous:homozygousrecessive; 1:1 dominant:recessive • A testcross is a cross between an organism with an unknown genotype and an organism with the recessive phenotype. Traits & Probability

25. Dihybridcross 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 states that allele pairs separate independently of each other during meiosis. Traits & Probability

26. 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 = number of ways a specific event can occur number of total possible outcomes Probability applies to random events such as meiosis and fertilization. Traits & Probability

27. Mendel’s laws of segregation and independent assortment reflect the same laws of probability that apply to tossing coins or rolling dice. • The probability scale ranged from zero (an event with no chance of occurring) to one (an event that is certain to occur). • (1) We can use the rule of multiplication to determine the chance that two or more independent events will occur together in some specific combination. • (2) The rule of addition also applies to genetic problems. Under the rule of addition, the probability of an event that can occur two or more different ways is the sum of the separate probabilities of those ways. • We can combine the rules of multiplication and addition to solve complex problems in Mendelian genetics. Traits & Probability

28. Mendel’s laws of independent assortment and segregation explain heritable variation in terms of alternative forms of genes that are passed along according to simple rule of probability. • These laws apply not just to garden peas, but to all other diploid organisms that reproduce by sexual reproduction. • Mendel’s studies of pea inheritance endures not only in genetics, but as a case study of the power of scientific reasoning using the hypothetico-deductive approach. Summary of Mendel

29. (5) Describe monohybrid and dihybrid crosses. • (6) Explain how heredity can be illustrated mathematically. Reflection