CHAPTER 10: MENDEL AND MEIOSIS Mrs. Geist, Swansboro HS, Biology, Spring

Standard  SCOS 3.03: Interpret and predict patterns of inheritance.  Dominant, recessive and intermediate traits.  Multiple alleles.  Polygenic traits.  Sex-linked traits.  Independent assortment.  Test cross.  Pedigrees.  Punnett squares.

Objectives  Introduce basic principles of probability.  Summarize the three major steps of Gregor Mendel’s garden pea experiments.  Describe the principle of dominance.

Warm-up 02/21/2010  Genetics Facts and Fallacies Quiz  Answer the questions to the best of your ability.  This is not a true quiz. Your answers will not be graded.

Think-Pair-Share  If I flip a coin, what is the chance that it will land on heads? (Include fractions and percentages).  What is the chance that it will land on tails? (Include fractions and percentages).  Distinguish between recessive and dominant alleles. Provide an example of each.

Introduction to Genetics  Genetics- the scientific study of heredity.  Fertilization- process in sexual reproduction in which male and female reproductive cells join to form a new cell.  Pollen- contains the male reproductive cells, or sperm.  Carpel- the female part that produces eggs. Cross-pollination produces seeds that had two different plants as parents.

Blending Hypothesis  1800’s- Red-flowered plants and yellow-flowered plants blend to produce orange-flowered plants  Similar to blending red and yellow paint to make orange paint  Based on this hypothesis, all offspring of orange- flowered plants would also have orange-flowered plants.  Eventually rejected because it could not explain how traits that disappear in one generation could reappear in later generations

10-1 Gregor Mendel  “Father of genetics”  Austrian monk.  His work was important to the understanding of heredity.  Mendel carried out his studies on ordinary garden peas.

Garden Peas  Pea flowers are self-pollinating.  Sperm cells in pollen fertilize the egg cells in the same flower.  True-breeding  if allowed to self-pollinate, would produce offspring identical to themselves.

Genes and Dominance  Trait- a specific characteristic that varies from 1 individual to another  Mendel studied 7 pea plant traits, each with two contrasting characters.  Cross Pollination- joining male and female reproductive cells from two different plants

Genes and Dominance  Each original pair of plants is the P 1 (parental) generation.  The offspring are called the F 1, or “first filial,” generation.  Hybrids- The offspring of crosses between parents with different traits.  The F 1 hybrid plants all had the character of only one of the parents

When Mendel crossed plants with contrasting characters for the same trait, the resulting offspring only had one of the characters. Mendel concluded that some alleles are dominant and others are recessive.

Copyright Pearson Prentice Hall Mendel’s Seven F 1 Crosses on Pea Plants

Genes  Mendel's first conclusion was that biological inheritance is determined by factors that are passed from one generation to the next.  Genes- factors that determine traits  Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms that produced different characters for each trait.  Alleles- the different forms of a gene

Principle of Dominance  Mendel’s second conclusion is called the principle of dominance.  The principle of dominance states that some alleles are dominant and others are recessive.  An organism with a dominant allele for a trait will always exhibit that form of the trait.  An organism with the recessive allele for a trait will exhibit that form only when the dominant allele for that trait is not present.

Copyright Pearson Prentice Hall  Gametes are also known as genes. sex cells. alleles. hybrids.

Copyright Pearson Prentice Hall  The offspring of crosses between parents with different traits are called alleles. hybrids. gametes. dominant.

Copyright Pearson Prentice Hall  In Mendel’s pea experiments, the male gametes are the eggs. seeds. pollen. sperm.

Copyright Pearson Prentice Hall  In a cross of a true-breeding tall pea plant with a true- breeding short pea plant, the F 1 generation consists of all short plants. all tall plants. half tall plants and half short plants. all plants of intermediate height.

Copyright Pearson Prentice Hall  If a particular form of a trait is always present when the allele controlling it is present, then the allele must be mixed. recessive. hybrid. dominant.

Segregation  When Mendel crossed pea plants differing in one trait, one form of the trait disappeared until the second generation of offspring.  Law of segregation- every individual has 2 alleles of each gene and when gametes are produced, each gamete receives 1 of these alleles

Alleles separate during gamete formation.

Basic Probability  Probability- the likelihood that a particular event will occur.  Coin flip: The probability that a single coin flip will come up heads is 1 chance in 2. This is ½, or 50%.  If you flip a coin 3 times in a row, what is the probability that it will land heads up every time? ½ x ½ x ½ = 1/8  The principles of probability can be used to predict the outcomes of genetic crosses.

Punnett Squares  Punnett Squares can be used to determine the gene combinations that might result from a genetic cross.  A capital letter, T, represents the dominant allele for tall.  A lowercase letter, t, represents the recessive allele for short.  Gametes produced by each F 1 parent are shown along the top and left side.  Possible gene combinations for the F 2 offspring appear in the four boxes.

Homozygous vs. Heterozygous  Organisms that have two identical alleles for a particular trait are said to be homozygous.  A.k.a. “true-breeding”  Organisms that have two different alleles for the same trait are heterozygous.  A.k.a. “hybrid”

Phenotype & Genotype  All of the tall plants have the same phenotype, or physical characteristics.  The tall plants do not have the same genotype, or genetic makeup.  One third of the tall plants are TT, while two thirds of the tall plants are Tt.

Probability  One fourth (1/4) of the F 2 plants have two alleles for tallness (TT).  2/4 or 1/2 have one allele for tall (T), and one for short (t).  One fourth (1/4) of the F 2 have two alleles for short (tt).

Probabilities Predict Averages  Because the allele for tallness (T) is dominant over the allele for shortness (t), 3/4 of the F 2 plants should be tall.  The ratio of tall plants (TT or Tt) to short (tt) plants is 3:1.

Copyright Pearson Prentice Hall  Probability can be used to predict average outcome of many events. precise outcome of any event. how many offspring a cross will produce. which organisms will mate with each other.

Copyright Pearson Prentice Hall  Compared to 4 flips of a coin, 400 flips of the coin is more likely to produce about 50% heads and 50% tails. less likely to produce about 50% heads and 50% tails. guaranteed to produce exactly 50% heads and 50% tails. equally likely to produce about 50% heads and 50% tails.

Copyright Pearson Prentice Hall  Organisms that have two different alleles for a particular trait are said to be hybrid. heterozygous. homozygous. recessive.

Copyright Pearson Prentice Hall  Two F 1 plants that are homozygous for shortness are crossed. What percentage of the offspring will be tall? 100% 50% 0% 25%

Copyright Pearson Prentice Hall  The Punnett square allows you to predict only the phenotypes of the offspring from a cross. only the genotypes of the offspring from a cross. both the genotypes and the phenotypes from a cross. neither the genotypes nor the phenotypes from a cross.