CHAPTER 11 – INTRODUCTION TO GENETICS

1. CHAPTER 11 – INTRODUCTION TO GENETICS SECTION 1 – THE WORK OF GREGOR MENDEL

2. Every living thing – plant, animal, microbe, or human being – has a set of characteristics inherited from its parent or parents. • Genetics – is the scientific study of heredity.

3. Gregor Mendel’s Peas • Gregor Mendel was born in 1822 in what is now the Czech Republic. • After becoming a priest, Mendel spent several years studying science and mathematics at the University of Vienna

4. He spent the next 14 years working in the monastery and teaching at the high school. • In addition to his teaching duties, Mendel was in charge of the monastery garden. • In this garden, he was to do the work that changed biology forever. • Gregor Mendel is considered the father of genetics.

5. Mendel worked with ordinary garden peas. • Pea flowers are normally self-pollinating, which means that sperm cells in pollen fertilize the egg cells in the same flower. • The seeds that are produced by self-pollination inherit all of their characteristics from the single plant that bore them • In effect, they have a single parent.

6. These plants were true-breeding plants. Meaning, if they were allowed to pollinate, they would produce offspring identical to themselves. • Mendel had several stocks of true-breeding plants. • Some produced on tall plants, some short, some only green seeds, some yellow.

7. Mendel wanted to cross-breed plants. • To do this, he transferred pollen from one true-breeding plant to another. • This made it possible for Mendel to cross-breed plants with different characteristics and then study the results.

8. Genes and Dominance • Mendel studied seven different contrasting pea plant traits. • A trait is a specific characteristic, such as seed color or plant height. • The original pair of plants is the P (parental) generation. • The offspring are called the F1 generation, or first filial generation. • Another name for the offspring of crosses between parents with different traits is a hybrid.

9. Did the characters of the parent plants blend in the offspring? • No. • To Mendel’s surprise, all of the offspring in the F1 generation had the character of only one parent. The other parent’s trait seemed to have disappeared.

10. From this set of experiments, Mendel drew two conclusions. • 1. Biological inheritance is determined by factors called genes that are passed from one generation to the next. • 2. Genes occur in two forms. For example, in genes for height one form produces tall plants, and the other form produces tall plants. • The different forms of a gene are called alleles.

11. The principle of dominance states that some alleles are dominant and others are recessive.

12. Organisms with a dominant allele for a particular form of a trait will always exhibit that form of the trait. • Organisms with a recessive allele for a particular form of a trait will exhibit that form only when paired with another recessive allele.

13. Segregation • Mendel wanted the answer to another question: Had the recessive trait disappeared , or were they still present in the F1 plants? • To answer this question, he allowed all seven kinds of F1 hybrid plants to self-pollinate and created the F2 generation.

14. To his surprise, the recessive gene reappeared in the F2 generation.

15. So, the moral of the story……. • When each F1 plant flowers and produces gametes (sex cells), the two alleles segregate from each other so that each gamete carries only a single copy of each gene. Therefore, each F1 plant produces two types of gametes – those with the allele for a dominant trait and those with the allele for a recessive trait.

17. CHAPTER 11 SECTION 2 PROBABILITY AND PUNNETT SQUARES

18. Genetics and Probability • The likelihood that a particular event will occur is called probability. • For example, you have a 1 in 2 chance a getting heads when flipping a coin or a 50% chance. • The principles of probability can be used to predict the outcomes of genetic crosses.

19. Punnett Squares • Punnett Squares can be used to predict and compare the genetic variations that will result from a cross.

20. Organisms that have two identical alleles for a particular trait are said to homozygous. TT or tt. • Organisms that have two different alleles for the same trait are heterozygous or hybrids Tt.

21. Genotype – is your genetic makeup. • Phenotype – are your physical characteristics, or what you can see on the outside.

22. CHAPTER 11, SECTION 3 EXPLORING MENDELIAN GENETICS

23. Independent Assortment • The Principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes. Independent assortment helps account for the many genetic variations observed in plants, animals, and other organisms. • In a two trait cross between two heterozygous individuals, the ratio will always be a 9:3:3:1 ratio.

24. A summary of Mendel’s Principles • 1. The inheritance of biological characteristics is determined by individual units known as genes. Genes are passed from parents to their offspring. • 2. In cases in which two or more forms (alleles) of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. • 3. In most sexually reproducing organisms, each adult has two copies of each gene, one from each parent. These genes are segregated from each other when gametes are formed. • 4. The alleles for different genes usually segregate independently of one another.

25. Beyond Dominant and Recessive Alleles • Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.

26. Incomplete Dominance – In incomplete dominance, the heterozygous phenotype is somewhere in between the two homozygous phenotypes. • Ex. Crossing red and white flowers to get pink flowers.

27. Codominance – in codominance, both alleles contribute to the phenotype. • Ex. Crossing a black chicken with a white chicken, will give you a black and white chicken. • Human blood types are also codominant.

28. Multiple Alleles – many genes have more than two alleles. It does not mean that an individual can have more than two alleles. It only means that more than two possible alleles exist in a population. • Ex. Coat color in rabbits

29. Polygenic Traits – These are traits that are controlled by two or more genes. • Ex. Human skin color. There are four different genes that control it.