Genetics Tutorial

1. Genetics Tutorial Introduction Punnett Square – 1 Trait Punnett Square – 2 Traits Product Rule

2. In this tutorial, you will learn: • Important terms used in genetics. • How to use a Punnett square to determine the outcome of a cross with • 1 trait or • 2 traits • How to use the product rule to determine the outcome of a cross with any number of traits. Credits: Figures and images by N. Wheat unless otherwise noted. Funded by Title V-STEM grant P031S090007.

3. Introduction • Information that will guide the development of an organism is contained in that organism’s DNA. Every species has a characteristic number of DNA molecules called chromosomes.

4. Introduction (2) • An individual receives one complete set of chromosomes from each parent, resulting in two complete sets. This is the diploidcondition (2n).

5. Chromosomes • Chromosomes occur in pairs called homologous chromosomes. • One from each parent.

6. Genes are the functional unit of heredity • Chromosomes are made up of genesthat code for traits. • A gene is found at a specific location or locuson a chromosome.

7. Genes & Alleles • Different versions of genes are called alleles. • Purple flowers vs. white in pea plants • Gene = flower color, allele = white or purple

8. Alleles • There can be any number of allelesfor a given gene, although an individual can have only two alleles(one on each homologous chromosome). • A, B, O blood type in humans

9. Polygenic Traits • Some traits are controlled by just one gene, others are influenced by many genes (polygenic). • Height in humans

10. Question 1 A, B and O are _______ of the human blood type __________. • Genes, genes • Genes, alleles • Alleles, genes • Alleles, alleles

11. Question 1 Sorry! • That is incorrect. • Try again!

12. Question 1 Congratulations! • You are correct!

13. Homozygous & Heterozygous • Since an individual has two sets of chromosomes, it will have two copies of each gene (one originally coming from each parent). These two copies may be the same allele, or they may be different. • Homozygous– both alleles are the same. • Heterozygous– two different alleles.

14. Question 2 Which of the following represents the homozygous condition? • AA • Aa • aa • Both AA and aa

15. Question 2 Sorry! • That is incorrect – be sure your answer is complete. • Try again!

16. Question 2 Congratulations! • You are correct!

17. Dominant & Recessive • A trait is dominantif it is expressed in an individual with one or two copies of the allele: • Purple flower color in peas: P= purple p= white. • The dominant allele is represented by a capitol letter, recessive by the lower case letter. • PP – homozygous dominant – two copies of the dominant (purple) allele. • Pp – heterozygous– one purple allele, one white allele (flowers appear purple).

18. Recessive • The trait is said to be recessiveif it is necessary for an individual to have two copies of the allele in order to express the trait. • pp – two white flower alleles (homozygous).

19. Question 3 Purple flower color in peas is dominant over white. Which of the following pairs of alleles would give purple flowers? • PP • Pp • pp • Both PP and Pp

20. Question 3 Sorry! • That is incorrect. • Try again!

21. Question 3 Congratulations! • You are correct!

22. Question 4 Now, which of the following pairs of alleles would give white flowers? • PP • Pp • pp • Both PP and Pp

23. Question 4 Sorry! • That is incorrect. • Try again!

24. Question 4 Congratulations! • You are correct!

25. Genotype • Genotyperefers to the alleles that are actually present. • PP, Pp, pp in our flower color example. • The purple phenotype may have PP or Pp genotype. Back to question 5

26. Phenotype • Phenotyperefers to the visible or expressed characteristics of the trait. • What does it look like? • Purple or white for our flower color example. Back to question 8

27. Heredity – Passing on Traits • An individual can pass on genetic information to its offspring. In order to avoid doubling the number of chromosomes in each generation, cells must be created that carry only one set of chromosomes (haploidor 1n). • An individual can pass along either of the two alleles it carries for a trait, but not both. • A Pp individual can pass on either P or p. • These haploid cells (eggs or sperm) are formed during meiosis.

28. Meiosis • Meiosisis a type of cell division that occurs in two parts. • Before division starts, each chromosome makes a copy of itself. These identical copies (called sister chromatids) remain connected at the centromere.

29. Meiosis (2) • In the first part of meiosis, homologous chromosomes are separated. • The cells are now haploid. • During the second part of meiosis, the sister chromatids are pulled apart. • This part is like regular cell division (mitosis). • The division of one diploid cell will result in 4 haploid cells. • Each cell is different.

31. Heredity • We can look at how traits are passed from one generation to another individually or two at a time using a Punnett square.

32. Heredity (2) • For our example, we will use the ball python. There are many mutations that breeders want to incorporate into their animals. • Albino – a simple recessive trait • Pinstripe – a dominant pattern mutation

33. Punnett Square – 1 Trait • First let’s focus on the albino trait. It is recessiveso: • AA & Aa individuals will have normal coloration. • aa individuals will be albino.

34. Monohybrid Cross • In a monohybrid cross we will cross two animals that are heterozygous for albino. • Aa x Aa • We want to know, statistically, what kind of offspring to expect. • Each parent can donate only one allele for the albino gene. • A heterozygote (Aa) can donate either an A or an a – not both. • An albino must receive an afrom both parents.

35. Punnett Square – 1 Trait Example • Place the alleles that may be donated by each parent across the top and along the sides. • Fill in the boxes: • 1AA - normal • 2Aa – normal, heterozygous for albino • 1aa - albino Back to question 8

36. Question 5 Which is the genotype? • Normal or albino • AA, Aa, or aa • Both are considered to be the genotype. • Neither of these is the genotype.

37. Question 5 Sorry! • That is incorrect. • Find information on genotype. • Try again!

38. Question 5 Congratulations! • You are correct!

39. Let’s try another example! • If we have a male that is heterozygous for albino and an albino female, what kind of offspring do we get? X

40. Question 6 What is the genotype of this pairing? • Aa x Aa • AA x aa • Aa x aa • aa x aa

41. Question 6 Sorry! • That is incorrect. • Try again!

42. Question 6 Congratulations! • You are correct!

43. Question 7 Which of these Punnett squares is correct?

44. Question 7 Sorry! • That is incorrect. • Try again!

45. Question 7 Congratulations! • You are correct!

46. Question 8 What are the phenotypes of the offspring? • All normal appearing offspring • All albino offspring • 3:1 normal to albino • 2:2 normal to albino

47. Question 8 Sorry! • That is incorrect. • Review Phenotype • Review Punnett squares • Try again!

48. Question 8 Congratulations! • You are correct!

49. Punnett Square – 2 Traits • We can also use the Punnett square to track two traits at once. • Remember each gamete (egg or sperm) will contain one allele for each trait. • So, the possible combinations of alleles that we will place on our Punnett squares will always have one letter for each trait.

50. Dihybrid Cross • In a dihybrid cross, both animals are heterozygous for two traits – here, albino (recessive) and pinstripe (dominant). • AaPp x AaPp • The parents will have normal coloration (Aa) and they will be Pinstripes (Pp).