Chapter 11: Introduction to Genetics Section 1: The Work of Gregor Mendel

Are Traits Inherited? Look at your classmates. Notice differences in their characteristics. What different forms of these traits do you see? Could these traits be inherited? From whom could they be inherited? How is it possible that these traits could be found in a person and his or her biological grandparents but not in the biological parents? *

Gregor Mendel ’ s Peas What is inheritance? Attributes acquired via biological heredity from the parents. What is genetics? The scientific study of heredity. *

Gregor Mendel Who was Gregor Mendel? Austrian Monk whose study of pea plants gave us the basis of genetics. *

Peas can either self-pollenate asexually or reproduce sexually. Self pollinated plants inherit all of the traits from the plant that bore them. What are true-breeding plants? If allowed to self-pollinate, these plants would produce offspring with the same traits as themselves. What are some of the traits Mendel was looking at? Seed shape, seed coat color, pod shape, pod color, plant height, flower position. *

What are traits? A specific characteristic that varies from one individual to another and can be passed on to an offspring. Mendel crossed true- breeding plants with the 7 characteristics he was studying. P generation: parental generation. F1: First filial generation.*

What are hybrids? The offspring of crosses between parents with different traits. What happened when Mendel crossed plants with different forms of the same trait? All the offspring had one characteristic and the other characteristic disappeared. What two things did Mendel conclude? 1.) That biological inheritance is determined by factors that are found in two different forms and are passed on to offspring. We now call the factors genes. What are alleles? The different forms of a factor or gene. *

2.) The principle of dominance which states that some alleles are dominant and others are recessive. Dominant traits will be expressed in organisms that have them. Recessive traits will be expressed only if a dominant trait is not present. Tall peas are dominant over small, yellow seeds are dominant over green, etc. What is segregation? Alleles are separated during the formation of sex cells called gametes. *

Segregation Mendel now wanted to know if the missing trait was truly gone or still present in the F1 plants. What did Mendel do to answer his question? Allowed the F1 generations to cross pollinate and form a F2 generation of plants. *

Section Review What are dominant and recessive? What is segregation? What happens to alleles during segregation? What did Mendel conclude determines biological inheritance? Describe how Mendel cross-pollinated pea plants.

Chapter 11: Introduction to Genetics Section 2: Probability and Punnett Squares

Genetics and Probability What did Mendel do with his results that hadn ’ t been done before? He decided to count the results of his crosses. What did he find from his crosses of hybrid plants? About ¾ of the offspring were dominant and ¼ were recessive. He decided to use probability to explain the results.*

What is probability? The likelihood that a particular event will occur. What is the probability of my flipped coin being heads? It can be head or tails, ½ or 50% chance of heads. How about the chance of flipping a coin heads twice? ½ * ½ or ¼ or 25%. The principles of probability can be used to predict the outcomes of genetic crosses. This is possible because allele segregation is completely random. *

Punnett Squares What type of device can we use to help us determine what gene combinations are available from a genetic cross? Punnett Square What do the letters in the Punnett square represent? Alleles. What is meant by the capitals and lower case letters? Dominant and recessive alleles. Define heterozygous. The alleles are different. Tt Define homozygous. The alleles are the same. TT or tt Define phenotype. The physical characteristics. Define genotype. The genetic makeup or what the genes look like.

Quick lab on page 268

Punnett Squares T = tall plant and t = short plant T T t t TT Tt tt What are the phenotypes? ¾ or 75% tall, ¼ or 25% short. What are the genotypes? 25% homozygous dominant, 25% homozygous short, and 50% heterozygous dominant. *

Probability and Segregation Parental Cross F1 Phenotype F2 Phenotype Ratio F2 Ratio Round x Wrinkled Round 5474 Round: 1850 Wrinkled 2.96:1 Yellow x Green Seed Yellow 6022 Yellow: 2001 Green 3.01:1 Purple x White Flowers Purple 705 Purple: 224 White 3.15:1 Tall x Short Plants Tall l787 Tall: 227 Short 2.84:1

Section 11-2 Review How are the principles of probability used to predict the outcomes of genetic crosses? What is probability? What is a Punnett square? Define the terms genotype and phenotype. Cross a homozygous short plant with a heterozygous tall plant. Using a Punnett square determine the probability that you will get a tall plant?

Chapter 11: Introduction to Genetics Section 11-3: Exploring Mendelian Genetics

Independent Assortment Mendels next idea was to find out if segregation of one set of alleles affect the segregation of another pair of alleles. What is a two-factor cross? Following two different genes as they passed from one generation to the next. What were the results of the F1 generation? All plant showed dominant for both factors and must be all RrYy. Mendel then crossed the F1 generation plants and got the expected 9:3:3:1 result the Punnett square predicted. *

Copyright Pearson Prentice Hall The Punnett square predicts a 9 : 3 : 3 :1 ratio in the F 2 generation.

The results showed that the dominant alleles were independently sorted. What is independent assortment? Genes for different traits can segregate independently during the formation of gametes. *

A Summary of Mendel ’ s Principles The inheritance of biological characteristics is determined by individual units known as genes. In cases in which two or more forms of the gene for a single trait exist, some forms of the gene may be dominant and others may be recessive. In most sexually reproducing organisms, each adult has two copies of each gene – one from eath parent. These genes are segregated from each other when gametes are formed. The alleles for different genes usually segregate independently of one another. *

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

What is incomplete dominance? A case in which one allele is not completely dominant over another allele.

What is codominance? Both factors contribute to the phenotype of the organism.

What are genes that have more than two alleles called? Multiple alleles.

What is a polygenic trait? Traits that are controlled by two or more genes.

Applying Mendel ’ s Principles Scientists applied Mendel ’ s idea to other organisms such as the Drosophila melanogaster and found they follow the pattern. Drosophila are perfect because they ’ re small, easy to keep, and able to produce many offspring. Certain human traits also follow Mendel ’ s “ laws ”. *

Section 11-3 Assessment Explain what independent assortment means. Describe two inheritance patterns besides simple dominance. What is the difference between incomplete dominance and codominance? Why are fruit flies an ideal organism for genetic research? Cross true breeding round green (RRyy) seed plants with true-breeding wrinkled yellow seeds (rrYY)

Chapter 11: Introduction to Genetics Section 4: Meiosis

Chromosome Number Mendel didn ’ t know where the factors he discovered were located in the cell. He discovered segregation of alleles in his work but didn ’ t know the exact process in the cell. We know the process as meiosis. *

What is a Drosophila again? Fruit Fly. How many chromosomes does it have? 8 What do you call each pair of chromosomes? Homologous. What do you call a cell that has both sets of homologous chromosomes? Diploid: or 2N For Drosophila 2N = 8 What do you call the chromosomal make-up of a Drosophila ’ s gametes? Haploid: or N = 4

Phases of Meiosis What is meiosis? Meiosis is a process of reduction division in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell.*

What is a tetrad? Each chromosome paired with it ’ s corresponding homologous chromosome. What is crossing-over? Homologous chromosomes exchange portions of their chromatids during prophase 1. *

By cytokinesis, the cells look like cells after mitosis but they are different. Each diploid daughter cell has different chromosomes from each other and from the original mother cell. *

Unlike the first round of division, the chromosomes are not replicated before prophase II. Telophase II ends with 4 haploid daughter cells. *

In many male organisms the haploid cells lose most of their cytoplasm and form sperm. In many female organisms 3 haploid cell form polar bodies and don ’ t participate in reproduction. The 4 th keeps the cytoplasm and forms the female eggs. *

Overview Mitosis results in the production of two genetically identical diploid cells, whereas meiosis produces four genetically different haploid cells. *

Review 11-4 Describe the main results of meiosis. What are the principal differences between mitosis and meiosis? What do the terms diploid and haploid mean? What is crossing-over? Human cells have a 2N = 46. How many chromosomes in an egg cell, sperm cell, or white blood cell?

Chapter 11: Introduction to Genetics Section 5: Linkage and Gene Maps

Gene Linkage Do you think that genes on the same chromosomes assort independently just like genes on different chromosomes? No genes on the same chromosome are generally inherited together. Thomas Morgan identified more than 50 Drosophila genes and found many of them linked. Found that Drosophila had 4 linkage groups of genes and four chromosomes. What were Morgan ’ s conclusions? Each chromosome is actually a group of linked genes. Mendel ’ s principle of independent assortment holds true. It is the chromosomes, however, that assort independently, not individual genes. *

Gene Maps Are two genes on the same gene linked forever? No, crossing over can change the links. Why is this important to organisms? It helps to generate genetic diversity. How was Alfred Sturtevant able to map the Drosophila ’ s chromosome? He determined that the frequency in which linked genes were separated and recombined could give us a relative distance between genes. The relative distance between genes is given in map units. *

Drosophila ’ s Chromosome 2 Map Numbers are Map Units

Review 11-5 How does the principle of independent assortment apply to chromosomes? What are gene maps, and how are they produced? How does crossing-over make gene mapping possible? If two genes are on the same chromosome but usually assort independently, what does that tell you about how close together they are?