Georgia Standards SB 2 c Using Mendels laws

Georgia Standards: SB 2 c: Using Mendel’s laws, explain the role of meiosis in reproductive variability. SB 2 e: Compare the advantages of sexual reproduction and asexual reproduction in different situations. Essential Questions: • How do you predict the probability of various genotypes inherited and the expressed phenotypes? • How does meiosis generate variation in offspring?

Gregor Mendel: Father of Genetics • Genetics is the scientific study of heredity. • Gregor Mendel (1860’s) an Austrian Monk, was interested in figuring out how heredity was determined in plants and animals. – used pea plants – quantitative approach to collect data. • Mendel studied seven different pea plant traits. – Seed shape & color, pod shape & color, flower height & position and seed coat color • A trait is a specific characteristic, such as seed color or plant height, that varies from one individual to another.

Gregor Mendel’s Experiment: • Mendel crossed plants with each of the seven contrasting traits and studied their offspring. • Mendel called each original pair of plants the P (parental) generation. – These peas were true-breeding (self-pollination), meaning that if they were allowed to self-pollinate, they would produce offspring identical to themselves.

Gregor Mendel’s Experiment: • He called the offspring of the P -generation, the F 1, or “first filial, ” generation. Filius is the Latin word for “son. ” • The offspring of crosses between parents with different traits are called hybrids. – These pea plants were cross pollinated. • The F 1 generation was allowed to self-pollinate to produce the F 2 Generation – In cross-pollination, male sex cells in pollen from the flower on one plant fertilize the egg cells of a flower on another plant. • Out of 929 F 2 Generation plants, 705 were purple and 224 were white. – Ration of 3 purple to 1 white

How do we find the results of a genetic cross? • The principles of probability can be used to predict the outcomes of genetic crosses. • The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square. (See note sheet)

Gregor Mendel’s Conclusions: • Genes and Dominance – Mendel’s first conclusion was that biological inheritance is determined by factors (genes) that are passed from one generation to the next. • Each of the traits Mendel studied was controlled by one gene that occurred in two contrasting forms. • The different forms of a gene are called alleles

Punnett Squares • Organisms that have two identical alleles for a particular trait—TT or tt in this example—are said to be homozygous • Organisms that have two different alleles for the same trait are heterozygous (Ex: Tt) • Homozygous organisms are true-breeding for a particular trait. Heterozygous organisms are hybrid for a particular trait.

Punnett Squares • They do not, however, have the same genotype, or genetic makeup. • All of the tall plants have the same phenotype, or physical characteristics.

Gregor Mendel’s Conclusions: • Mendel’s second conclusion is called the principle of dominance, which states that some alleles are dominant and others are recessive. – Alleles that are expressed are considered DOMINANT. • An organism with a dominant allele for a particular form of a trait will always have that form. – Alleles that are present in the genotype, but not expressed in the phenotype are considered RECESSIVE. • An organism with a recessive allele for a particular form of a trait will have that form only when the dominant allele for the trait is not present.

Gregor Mendel’s Conclusions: • Segregation of Alleles: – When each F 1 plant flowers, the two alleles are segregated from each other so that each gamete carries only a single copy of each gene. – Therefore, each F 1 plant produces two types of gametes—those with the allele for tallness and those with the allele for shortness.

Law of Segregation: • During gamete formation, alleles are segregated from each other so that each gamete carries only a single copy of each allele. – Each F 1 plant produces two types of gametes— those with the allele for tallness and those with the allele for shortness. – The alleles are paired up again when gametes fuse during fertilization.

Did this mean that the two dominant alleles would always stay together? • (Law of Independent Assortment) – Genes for different traits can segregate independently during the formation of gametes.

Principle of dominance • Some alleles are dominant and others are recessive. • The importance of Mendel’s work on heredity was not discovered until 30 years later. • Scientist soon realized that CHROMOSOMES are the carriers of heredity.

A Summary of Mendel’s Principles • Genes determine inheritance of biological characteristics. • Genes are passed from parents to offspring • In most sexually reproducing organisms, each adult has two copies of each gene— one from each parent. These genes are segregated from each during gamete formation. • Some forms of the gene may be dominant and • The alleles for different others may be genes are assorted recessive. independently of one another.

Probability and Punnett Squares • The principles of probability can be used to predict the outcomes of genetic crosses. • The gene combinations that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square. (See note sheet)

Monohybrid Cross (One Trait) Punnett square • This Punnett square shows the probability of each possible outcome of a cross between hybrid tall (Tt) pea plants. • Genotype: 25% TT, 50% Tt, 25%tt (1: 2: 1) • Phenotype: 75% Tall, 25% short (3: 1)

A Dihybrid Cross: F 1 • Dihybrid Cross: – Shows inheritences of two traits at once • F 1 Mendel crossed plants that were homozygous dominant for round yellow peas with plants that were homozygous recessive for wrinkled green peas. All of the F 1 offspring were heterozygous dominant for round yellow peas.

Did this mean that the two dominant alleles would always stay together? Or would they “segregate independently. ” • Dihybrid Cross: – Shows inheritences of two traits at once – Two plants, both heterozygous for seed shape and color were crossed.

Dihybrid Cross Problem • Determine the genotype and phenotype ratios and percents for a dihybrid cross of two plants; one that is homozygous recessive for short, purple leaves and the other that is homozygous dominant for tall, orange leaves. • Height (H-tall, h-short) • Color (C-orange, c-purple)

HC hc hc HC HC HC

• What ratio of offspring will have tall, purple flowers? • What ratio of offspring will be homozygous dominant for plant height, and homozygous recessive for plant color? • What ratio of offspring will be homozygous recessive for plant height and homozygous dominant for plant color?

Pop Quiz: Use Book- Chp. 10. 2 1. What are dominant and recessive alleles? 2. What happens to alleles during segregation? 3. What did Mendel conclude determines biological inheritance? 4. Describe how Mendel cross-pollinated pea plants. 5. Describe how Mendel self-pollinated pea plants. 6. Give an example of the law of independent assortment.

Concept Map Gregor Mendel experimented with concluded that Pea plants genes for different traits can segregate independently during the formation of gametes which is called the Go to Section: “Factors” determine traits Law of Independent Assortment Some alleles are dominant, and some alleles are recessive which is called the Law of Dominance Alleles are separated during gamete formation which is called the Law of Segregation

Meiosis Lab

Meiosis “Reebop” Lab: Georgia Performance Standards: SB 2 c: Using Mendel’s laws, explain the role of meiosis in reproductive variability. SB 2 e: Compare the advantages of sexual reproduction and asexual reproduction in different situations. Essential Questions: • How do you predict the probability of various genotypes inherited and the expressed phenotypes? • How does meiosis generate variation in offspring?

Warm-up: • In groups complete the meiosis and mitosis handout (front and back). • Individually compare and contrast mitosis and meiosis using your choice of presentation: – Venn Diagram, T-chart, drawing, essay

Meiosis “Reebop” Lab: • Objective: – Students will understand how meiosis produces genetic variation in offspring. – Students will understand how haploid cells are produced from diploid cells.

Procedure: • Choose which partner will be mom and which will be dad. • Take a set of colored slips of construction paper and give one set to mom and the other to dad.

Procedure: • Flip a coin to determine which alleles (dominant or recessive) each parent will have. • Heads = Dominant allele (capital letter) • Tails = Recessive allele (lowercase letter) • Build your correct “Reebop Baby”

1 antenna = AA 2 antenna= Aa No antennae = aa 1 yellow hump = MM 2 yellow humps = Mm No humps = mm ink nose = QQ Orange nose = Qq Yellow nose = qq 2 eyes = EE or Ee 3 eyes = ee 2 body segments = dd 3 body segments= DD or Dd Curly tail = TT or Tt Straight tail = tt Colored legs = LL or Ll Clear legs = ll This is an example of how your Reebop baby could look. AA, Qq, EE, Dd, Mm, Tt, Ll

Spermatogenesis – formation of sperm cells Oogenesis – formation of egg cells Meiosis produces four genetically different haploid cells.

Classwork: • Finish your Meiosis Lab questions on a separate piece of paper. • You do not need to write the questions.

Ticket Out the Door: • Use the punnet square to solve a monohybrid cross of a Reebop mom who is heterozygous for antennae crossed with a Reebop dad who is homozygous recessive for antennae. • Possible Phenotypes: – AA = 1 antenna – Aa = 2 antennae – aa = no antennae