Chapter 5

1. Chapter 5 Heredity

2. Section 1: Objectives • To review Mendel’s Principles of Heredity. • To distinguish between dominant and recessive traits. • To explain the difference between homozygous and heterozygous traits.

3. Heredity • Heredity: passing of traits from parent to offspring • Gregor Mendel was one of the first scientists to study heredity. • What are traits?

4. Who Was Gregor Mendel? • Born in 1822 in Austria. • Grew up on a farm where he learned about flowers and fruit trees. • He entered a monestary when he was 21 years old.

5. Who Was Gregor Mendel? • Here, he was taught science and performed many scientific experiments. • He put most of his energy into research. • He discovered the principles of heredity.

6. Unraveling the Mystery • From working with plants, Mendel knew the patterns of inheritance weren’t always clear. • For example, sometimes a trait may be expressed in offspring that was not expressed in either parent.

7. Unraveling the Mystery • Mendel wanted to learn more about what caused these patterns. • To keep it simple, he studied 1 type of organism: pea plants.

8. Self-Pollinating Plants • Pea plants were a good choice for several reasons: • They grow quickly • There are many different kinds • They are self pollinating • A self pollinating plant has both male and female structures.

9. Self Pollinating Plants • Pollen from one plant can fertilize the ovule of the same plant. • Mendel was able to grow true-breeding plants. • In true-breeding plants, the offspring have the same traits as the parent.

10. Cross-Pollination • Pea plants can also cross-pollinate. • In cross-pollination, pollen from one plant fertilizes another plant. • Pollen can be carried by: • Insects • Wind

11. Characteristics • Mendel studied only 1 characteristic at a time. • A characteristic is a feature that has different forms in a population. • For example, hair color is a characteristic; different forms such as red hair or brown hair is a trait.

12. Mendel’s First Experiments • Crossed pea plants to study 7 different characteristics. • The trait that appeared most of the time was called the dominant trait. • The recessive trait was the trait that appeared less.

13. Mendel’s Second Experiments • Mendel allowed the first generation plants to self-pollinate. • He completed the exact same experiment for each of the 7 characteristics he was studying.

14. Seven Characteristics • Mendel studied each of the following: • Flower color • Seed color • Seed shape • Pod color • Pod shape • Flower position • Plant height

15. Ratios • A ratio is a relationship between 2 different numbers. • Mendel calculated the ratio for dominant to recessive traits.

16. Ratios • Example: Dominant = purple flowers Recessive = white flowers 705 purple: 224 white Ratio = 3.15:1

17. Calculate the Following Ratios • A) 6,002 yellow: 2,001 green • B) 5,474 pink: 1,850 red • C) 428 green: 152 yellow • D) 787 short: 277 tall • What do these ratios have in common?

18. Traits • Pairs of alleles (forms of a gene) can either be homozygous or heterozygous. • Homozygous: all the same letter (either all upper case or lower case) • Both dominant traits or both recessive traits • Heterozygous: one upper case and one lower case letter • One dominant trait and one recessive trait

19. Complete the Following Cross • In daisies, yellow flower color is dominant over white. Cross a homozygous yellow flowered plant with a homozygous white flowered plant. • 1) Offspring Genotype (include percentages): • 2) Offspring Phenotype (include percentages): • 3) Ratio of dominant to recessive traits:

20. Complete the Following Cross • Pick any 2 offspring from the last slide and complete a cross. Dominant and recessive traits remain the same. • 1) Offspring Genotype (include percentages): • 2) Offspring Phenotype (include percentages): • 3) Ratio of dominant to recessive traits:

21. Complete the Following Cross • In crimson clover, red flowers are dominant over pink. Cross a heterozygous red crimson clover plant with a homozygous pink crimson clover plant. • 1) Offspring Genotype (include percentages): • 2) Offspring Phenotype (include percentages): • 3) Ratio of dominant to recessive traits:

22. Complete the Following Cross • Pick any 2 offspring from the last slide and complete a cross. Dominant and recessive traits remain the same. • 1) Offspring Genotype (include percentages): • 2) Offspring Phenotype (include percentages): • 3) Ratio of dominant to recessive traits:

23. Complete the Following Cross • In grapes, purple color is dominant over green. Cross a heterozygous purple colored grape plant with a homozygous green colored grape plant. • 1) Offspring Genotype (include percentages) • 2) Offspring Phenotype (include percentages) • 3) Ratio of dominant to recessive traits:

24. Complete the Following Cross • Pick any 2 offspring from the last slide and complete a cross. Dominant and recessive traits remain the same. • 1) Offspring Genotype (include percentages): • 2) Offspring Phenotype (include percentages): • 3) Ratio of dominant to recessive traits:

25. Complete the Following Cross • In cats, black fur is dominant over brown fur. Cross a heterozygous cat with a homozygous recessive cat. • 1) Offspring Genotype (include percentages) • 2) Offspring Phenotype (include percentages) • 3) Ratio of dominant to recessive traits:

26. Chapter 5 Notebook Quiz • 1) __________ was one of the first scientists to study heredity. • 2) What is the difference between self-pollination and cross pollination? • 3) What type of plants did Mendel study? • 4) What is a characteristic? • 5) What is a ratio? • 6) How many characteristics did Mendel study?

27. Section 2: Objectives • Explain how genes and alleles are related to genotype and phenotype. • Use the information in a Punnett square. • Explain how the probability can be used to predict possible genotypes in offspring. • Describe 3 exceptions to Mendel’s observations.

28. A Great Idea • The first generation carries the instructions for both dominant and recessive traits. • Scientists now call these instructions genes, one set of instructions for an inherited trait. • The different forms of a gene are alleles.

29. Phenotyopes • Genes affect the traits of offspring. • An organism’s appearance is known as phenotype. • Examples: Red flower color, white flower color, yellow flower color

30. Genotype • Both inherited alleles together form an organism’s genotype. • Heterozygous: one dominant and one recessive trait • Homozygous: 2 dominant or 2 recessive traits

31. Probability • “The mathematical chance that something will happen” • In a coin toss, you have a 50% chance of getting heads or tails. • This is the case with inherited traits as well.

32. Probability • Written as a fraction or percentage. • If you toss a coin, the probability of tossing tails is 50%. (You will get tails half the time.)

33. Probability Example • If you roll a pair of dice, what is the probability you will roll 2 three separate times? • Count the number of faces on the dice. Put this number in the denominator. (6) • Count the number of ways you can roll 3 with one dice. Put this number in the numerator. (1)

34. Probability Example • To find the probability that you will throw 2 threes, multiply the probability of throwing the first 3 by the probability of throwing the second 3: 1/6 X 1/6 = 1/36.

35. Probability Example # 2 • What is the probability that you will roll an even number with one dice? • Count the number of faces on the dice (denominator) • Count the number of ways you can roll an even number. (numerator)

36. Incomplete Dominance • Sometimes, one trait is not completely dominant over another. • It is possible to have 2 dominant traits (co-dominance). • Sometimesgenes can affect more than one trait.

37. Environment • Genes aren’t the only influence on traits. • In some ways, the environment affects how you grow. • Example: Your genes make it possible for you to grow tall, but you need a healthy diet to reach your full potential.

38. Incomplete Dominance Example • In a rare breed of roses, white and red flower colors are dominant. What would happen if a red rose was crossed with a white rose? • Genotype: • Phenotype: • Ratio:

39. Chapter 5 Pop Quiz • 1) What is the probability of rolling an odd number with one dice? • 2) In a rare breed of sunflowers, yellow and orange are both dominant flower colors. What would happen if a yellow flower was crossed with an orange flower? Write all genotypes, phenotypes, and ratios.

40. Meiosis • Chromosomes that carry the same sets of genes are called homologous chromosomes. • These are like a “pair of shoes” because there are 2. • Sex cells are different because they have 1 chromosome.

41. Meiosis • Sex cells are made during meiosis. • Meiosis is a copying process that produces cells with half the usual number of chromosomes.

42. Meiosis • What does meiosis have to do with chromosomes? • Genes are located on chromosomes. • Understanding meiosis was critical to finding the location of genes.

43. Meiosis • During mitosis, chromosomes are copied once. • During meiosis, the nucleus divides twice. • The result is sex cells, with half the number of chromosomes as a normal body cell.

44. Chromosomes • Info. contained on chromosomes determine many of our traits. • Sex cells carry genes that determine sex of an individual. • Females: XX Males: XY

45. Pedigrees • A pedigree is a diagram that shows the occurrence of a genetic trait in several generations of a family • These are helpful in tracing/predicting diseases and traits from one generation to the next.

46. Pedigrees • Useful in predicting if a person is a carrier for a certain trait/disease. • Carriers do not always show signs of the trait/disease.

47. Cystic Fibrosis • Causes serious lung problems. • People with this disease have 2 inherited recessive alleles. • Both parents must be carriers of the trait for it to show up in their children.