Introduction to Mendelian Genetics

1. Introduction to Mendelian Genetics Packet #19 Chapters 6 & 7

2. Mendelian Genetics • Who is Mr. Gregor Mendel? • What is he famous for? • Describe the experiments of Gregor Mendel

3. Introduction I • Heredity • The biological similarity of offspring and parents • Gene • Region of DNA, found on the chromosome, that controls a discrete hereditary characteristic of an organism

4. Introduction II • Allele • One of several alternateforms of a particular gene • Locus • Particular place along the length of a chromosome where a given gene is located

5. Introduction III • Genotype • The specific allele composition of a cell • The combination of alleles located onhomologous chromosomes that determines a specific characteristic or trait.

6. Introduction IV • Phenotype • The observablephysical or biochemicalcharacteristics of an organism, as determined by organism’s genetic makeup (genotype).

7. Introduction V • Dominant Allele • An allele that expresses its phenotype effect even when combined with a recessive allele. • Recessive Allele • An allele whose phenotype effect is not expressed unless it is combined with another recessive allele. • However, there are exceptions to this rule in specific genetic disorders. • More to come in future packets…Please hold those questions until then.

8. Introduction VI • A = dominant allele • A = recessive allele • AA = homozygous dominant genotype • Aa = heterozygous genotype • aa = homozygous recessive genotype • Genotype Variations • Homozygous dominant • Two dominant alleles • Heterozygous • One recessive allele • One dominant allele • Homozygous recessive • Two recessive alleles

9. Incomplete Dominance • Occurs when hybrids, with a heterozygous genotype, have an appearance between the phenotypes of the parental varieties.

10. Incomplete Dominance II

11. Codominance • Situation in which the phenotypes of both alleles are exhibited in a heterozygote

12. Epistasis • Phenomenon in which one gene alters the expression of another gene that is independently inherited.

13. Epistasis II

14. Sex-Linked Genes • Sex-linked genes • Genes that are found on the sex chromosomes.

15. Multiple Alleles • On some occasions, there is more than two alleles (forms) of a particular gene. • Example: - Alleles for blood group. • When discussing genotypes for blood groups, there are three alleles that one must consider • i • iA • iB • More to come on blood types later and how blood types are determined in a couple’s offspring and how blood groups impact the blood transfusions.

16. Punnett Squares • Punnett Square • A diagram used in the study of inheritance • Shows the result of random fertilization in genetic crosses. • Shows the probable results of crossing over. • More to come in the next packet.

17. Mendel’s Laws

18. Mendel’s Laws • When Mendel carried out his research, the processes of mitosis and meiosis had not yet been discovered. • However, Mendel knew, through his experiments, that genes (alleles) existed. • From Mendel’s research, he devised two laws. • Principle of Segregation • Principle (Law) of Independent Assortment

19. Principle of Segregation • Principle of Segregation • The principle states that in diploid organisms genes come in pairs and that when sex cells get produced each gamete gets one gene at random.

20. Principle of Segregation II • When developing this idea Gregor Mendel conducted a series on monohybrid (test) crosses using pea plants. • A monohybrid is when only one allele is investigated.

21. Principle of Independent Assortment • The Law of Independent Assortment states that the alleles (or separate members of a gene pair) separate independently to form the gamete. • To do this, one must be comparing at least TWO traits. • Dihybrid cross • By doing so, the traits are transferred independent from one another. • This allows for much more variation in the offspring since the alleles are randomly matched with the gamete from the other parent to form the zygote. • According to how many traits are in question, the number of possible variations can become quite high.

22. Dihybrid Cross • A dihybrid cross involves an investigation of two alleles at the same time.

23. Principle of Independent Assortment II • Mendel concluded that alleles (traits) are transmitted to offspring independently of one another. • If the genes are transmitted independently, then the genes are determined as being unlinked. • If the genes are transmitted together, the majority of the time, then the genes are determined as linked genes. • Hence, the principle of independent assortment does not apply.

24. Principle of Independent Assortment III • This law holds true as long as the two genes (traits) in question are: - • Located on separate chromosomes • Not linked together if they are located on the same chromosome. • Unlinked genes • More to come later in AP Biology • The principle of independent assortment allows/results in recombination • The presence of new gene combinations not present in the parental (P) generation.

25. Principle of Independent Assortment IV • The principle of independent assortment allows/results in recombination • The presence of new gene combinations not present in the parental (P) generation.

26. Genetic Crosses

27. Monohybrid (Test) Cross

28. Examples

29. Dihybrid Crosses

30. Examples • Parent #1 Genotype • FfEe • Parent #2 Genotype • FfEe

31. Review