Chapter 5 Heredity

Section 1: Objectives Explain the relationship between traits and heredity. Describe the experiments of Mendel. Explain the difference between dominant and recessive traits.

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

Heredity Gregor Mendel was born in 1822 in Austria. He grew up on a farm where he learned about flowers and fruit trees. He entered a monestary when he was 21 years old.

Heredity Here, he was taught science and performed many scientific experiments. He put most of his energy into research. He discovered the principles of heredity.

Heredity 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.

Heredity Mendel wanted to learn more about what caused these patterns. To keep it simple, he studied 1 type of organism: pea plants. Why would studying 1 organism at a time be helpful in studying patterns of inheritence?

Heredity 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.

Heredity 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.

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

Heredity 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.

Heredity Mendel’s first experiments: Mendel 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.

Heredity 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.

Heredity Mendel studied each of the following characteristics: Flower color Seed color Seed shape Pod color Pod shape Flower position Plant height

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

Heredity Ratio Example: Dominant = purple flowers Recessive = white flowers 705 purple: 224 white Ratio = 3.15:1

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?

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:

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:

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:

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:

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:

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:

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?

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.

Phenotype vs. Genotype 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.

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

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

Phenotype vs. Genotype 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.

Phenotype vs. Genotype Probability is 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.)

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)

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.

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)

Phenotype vs. Genotype Incomplete dominance: Sometimes, one trait is not completely dominant over another. It is possible to have 2 dominant traits (co-dominance). Sometimes genes can affect more than one trait.

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

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:

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.

Section 3: Objectives Explain the difference between mitosis and meiosis. Describe how chromosomes determine sex. Explain why sex-linked disorders occur in 1 sex more often than in the other. Interpret a pedigree.

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.

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

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

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.

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

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

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

Meiosis Cystic fibrosis causes serious lung problems. People with cystic fibrosis disease have 2 inherited recessive alleles. Both parents must be carriers of the trait for it to show up in their children.