Introduction To Genetics- Chapter 11

I. The work of Gregor Mendel A. Gregor Mendel was born in 1822 and after becoming a priest; Mendel was a math teacher for 14 years and a monastery. Mendel was also in charge of the monastery garden.

I. The work of Gregor Mendel 1. Mendel carried out his work with garden peas

I. The work of Gregor Mendel 2. Fertilization is the fusion of an egg and a sperm.   3. True breeding plants are plants that were allowed to self-pollinate and the offspring would be exactly like the parent.

I. The work of Gregor Mendel

11-1 The Work of Gregor Mendel Mendel’s experiments The first thing Mendel did was create a “pure” generation or true-breeding generation. He made sure that certain pea plants were only able to self pollinate, eliminating unwanted traits. He did this by cutting away the stamen, or male part of each flower

11-1 The Work of Gregor Mendel Figure 11-3 Mendel’s Seven F1 Crosses on Pea Plants Section 11-1 Mendel’s experiments Seed Shape Seed Color Seed Coat Color Pod Shape Pod Color Flower Position Plant Height Round Yellow Gray Smooth Green Axial Tall Wrinkled Green White Constricted Yellow Terminal Short Round Yellow Gray Smooth Green Axial Tall *Flower color – purple (P) vs. white (p) Seed coat color and flower color are often put in for one another – thus, the EIGHT traits!!! Go to Section:

Genes and dominance Trait : a characteristic 11-1 The Work of Gregor Mendel Genes and dominance Trait : a characteristic Mendel studied seven of these traits After Mendel ensured that his true-breeding generation was pure, he then crossed plants showing contrasting traits. He called the offspring the F1 generation or first filial.

11-1 The Work of Gregor Mendel What will happen when pure yellow peas are crossed with pure green peas? All of the offspring were yellow. Hybrids = the offspring of crosses between parents with contrasting traits

What did Mendel conclude? 11-1 The Work of Gregor Mendel What did Mendel conclude? Inheritance is determined by factors passed on from one generation to another. Mendel knew nothing about chromosomes, genes, or DNA. Why? These terms hadn’t yet been defined.

What were Mendel’s “factors” 11-1 The Work of Gregor Mendel What were Mendel’s “factors” The ‘factors” that Mendel mentioned were the genes. Each gene has different forms called alleles Mendel’s second principle stated that some alleles are dominant and some are recessive.

11-1 The Work of Gregor Mendel Mendel’s second cross He allowed the F1 generation to self-pollinate thus producing the F2 generation. Did the recessive allele completely disappear? What happened when he crossed two yellow pea hybrid (F1) plants?

Results: ¾ of the peas were yellow, ¼ of the peas were green. 11-1 The Work of Gregor Mendel Results: ¾ of the peas were yellow, ¼ of the peas were green. During the formation of the sex cells or gametes, the alleles separated or segregated to different gametes. (pollen and egg)

Punnett square example 11-2 Probability and Punnett Squares Punnett square example

Reading Punnett squares 11-2 Probability and Punnett Squares Reading Punnett squares Gametes are placed above and to the left of the square Offspring are placed in the square. Capital letters (Y) represent dominant alleles. Lower case letters (y) represent recessive alleles.

Phenotype vs genotype Genotype The genetic makeup 11-2 Probability and Punnett Squares Phenotype vs genotype Genotype The genetic makeup Symbolized with letters Tt or TT Phenotype Physical appearance of the organism Expression of the trait Short, tall, yellow, smooth, etc.

11-2 Probability and Punnett Squares Genes and Dominance 1. The different forms of a gene is called and an alleles.   2. The principal of dominance states that some alleles are dominant and others are recessive.

Genes and Dominance Pinky Finger Traits 11-2 Probability and Punnett Squares Genes and Dominance Pinky Finger Traits At Paris Gibson Ed Center we tested dominant and recessive traits in our school population. We tested pinky finger traits, whereby, the bent finger is dominant and the straight finger is recessive.

11-2 Probability and Punnett Squares C. Segregation 1. Each trait has two genes, one from the mother and one from the father.   2. Traits can be either dominant or recessive. 3. A dominant trait only needs one gene in order to be expressed.

11-2 Probability and Punnett Squares C. Segregation 4. A recessive trait needs two genes in order to be expressed.  

11-2 Probability and Punnett Squares

C. Segregation 5. Egg and sperm are sex cells called gametes. 11-2 Probability and Punnett Squares C. Segregation 5. Egg and sperm are sex cells called gametes.   6. Segregation is the separation of alleles during gamete formation.

11-2 Probability and Punnett Squares

II. Probability and Punnett Squares A. Genetics and Probability  1. The likelihood that a particular event will occur is called probability.   2. The principals of probability can be used to predict the outcome of genetic crosses.

II. Probability and Punnett Squares

11-2 Probability and Punnett Squares B. Punnett Squares 1. The gene combination that might result from a genetic cross can be determined by drawing a diagram known as a Punnett square.   2. Punnett squares can be used to predict and compare the genetic variations that will result from a cross.

11-2 Probability and Punnett Squares

11-2 Probability and Punnett Squares B. Punnett Squares 3. Each trait has two genes- one from the mother and one from the father.   4. Alleles can be homozygous – having the same traits. 5. Alleles can be heterozygous- having different traits.

11-2 Probability and Punnett Squares B. Punnett Squares

11-2 Probability and Punnett Squares B. Punnett Squares 6. Physical characteristics are called the phenotype.   7. Genetic make up is the genotype.

11-2 Probability and Punnett Squares

III. Exploring Mendalian Genetics 11-3 Exploring Mendelian Genetics III. Exploring Mendalian Genetics A. Independent assortment 1. Genes segregate independently.

III. Exploring Mendalian Genetics 11-3 Exploring Mendelian Genetics III. Exploring Mendalian Genetics 2. The principle of independent assortment states that genes for different traits can segregate independently during the formation of gametes.   3. Independent assortment helps account for the many genetic variations observed in plants, animals and other organisms.

11-3 Exploring Mendelian Genetics

The dihybrid cross Punnett square on board: 11-3 Exploring Mendelian Genetics The dihybrid cross Punnett square on board:

B. A summary of Mendel’s Principals 11-3 Exploring Mendelian Genetics B. A summary of Mendel’s Principals 1. Genes are passed from parent to offspring.   2. Some forms of a gene may be dominant and others recessive.

B. A summary of Mendel’s Principals 11-3 Exploring Mendelian Genetics B. A summary of Mendel’s Principals 3. In most sexually producing 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.

C. Beyond Dominance and Recessive alleles 11-3 Exploring Mendelian Genetics C. Beyond Dominance and Recessive alleles 1. Some alleles are neither dominant nor recessive, and many traits are controlled by multiple alleles or multiple genes.   2. Cases in which one allele is not completely dominant over another are called incomplete dominance.

Incomplete dominance A situation in which neither allele is dominant. 11-3 Exploring Mendelian Genetics Incomplete dominance A situation in which neither allele is dominant. When both alleles are present a “new” phenotype appears that is a blend of each allele. Alleles will be represented by capital letters only.

11-3 Exploring Mendelian Genetics Incomplete dominance Example: White (W) and Red (R) is both dominate. If WW X RR the F1 generation would be WR= pink.

What happens when a red flower is crossed with a white flower? 11-3 Exploring Mendelian Genetics What happens when a red flower is crossed with a white flower? According to Mendel either some white and some red or all offspring either red or white. All are pink

11-3 Exploring Mendelian Genetics

C. Beyond Dominance and Recessive alleles 11-3 Exploring Mendelian Genetics C. Beyond Dominance and Recessive alleles 3. Codominance is when both alleles contribute to the phenotype.   Example: Feather colors

C. Beyond Dominance and Recessive alleles 11-3 Exploring Mendelian Genetics C. Beyond Dominance and Recessive alleles 4. Many genes have more than two alleles and are referred to have multiple alleles.   a. This means that more than two possible alleles exist in a population. Example: colors of rabbits see page 273.

C. Beyond Dominance and Recessive alleles 11-3 Exploring Mendelian Genetics C. Beyond Dominance and Recessive alleles

C. Beyond Dominance and Recessive alleles 11-3 Exploring Mendelian Genetics C. Beyond Dominance and Recessive alleles   5. Traits that are controlled by two or more genes are said to be polygenic traits, which means, “having many genes.” a. Example: eye color has many different genes.

Meiosis Division of Sex Cells

11-4 Meiosis The Point of 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.  

2 types: Spermatogeneis & Oogenesis 11-4 Meiosis 2 types: Spermatogeneis & Oogenesis

Meiosis Diploid – 2 sets of chromosomes Haploid – 1 set of chromosomes Homologous – chromosomes that each have a corresponding chromosome from the opposite sex parent

11-4 Meiosis Meiosis

Meiosis A. Chromosome number   1. Every individual has two sets of chromosomes. One from the mother one from the father. When the chromosomes pair up for the same trait they are called homologous chromosomes.

11-4 Meiosis Meiosis 2. A cell that contains homologous chromosomes (2 genes) is said to be diploid/ 2n.   3. Gametes (egg /sperm) have only one chromosome and are said to be haploid/ n.

11-4 Meiosis Meiosis Meiosis I- The homologous chromosomes line up BUT then they CROSS OVER, exchanging genetic information. Meiosis II- The two cells produced by meiosis I now enter a second meiotic division. The final product = start with 1 cell with 46 chromosomes and get 4 DIFFERENT cells each with 23 chromosomes.  

11-4 Meiosis

Meiosis Stages Meiosis usually involves 2 distinct stages Meiosis I (animation) Meiosis II (animation)

11-4 Meiosis 57

11-4 Meiosis 58

11-4 Meiosis Prophase I Each chromosome pairs with its corresponding homologous chromosome to form a tetrad. There are 4 chromosomes in a tetrad. The pairing of homologous chromosomes is the key to understanding meiosis. Crossing-over may occur here Crossing-over is when chromosomes overlap and exchange portions of their chromatids.

11-4 Meiosis

11-4 Meiosis Prophase I

11-4 Meiosis Metaphase I Spindle fibers attach to the chromosomes

11-4 Meiosis Metaphase I

11-4 Meiosis Anaphase I The fibers pull the homologous chromosomes toward opposite ends of the cell.

11-4 Meiosis Anaphase I

Telophase I & Cytokinesis 11-4 Meiosis Telophase I & Cytokinesis Nuclear membranes form. The cell separates into 2 cells.

11-4 Meiosis Telophase I

Prophase II Meiosis I results in two haploid (N) cells. Each cell has half the number of chromosomes as the original cell.

11-4 Meiosis Prophase II

Metaphase II The chromosomes line up similar to metaphase in mitosis. 11-4 Meiosis Metaphase II The chromosomes line up similar to metaphase in mitosis.

11-4 Meiosis Metaphase II

11-4 Meiosis Anaphase II Sister chromatids separate and move to opposite ends of the cell.

11-4 Meiosis Anaphase II

11-4 Meiosis Telophase II Meiosis II results in 4 haploid cells.

11-4 Meiosis Telophase II

Gamete Formation In males, meiosis results in 4 sperm cells In females, meiosis results in 1 egg cell and three polar bodies, which are not used in reproduction.

Net result: Spermatogensis 4 mature sperm 11-4 Meiosis Net result: Spermatogensis 4 mature sperm Each sperm has exactly half the number of chromosomes as the father. Oogensis 1 mature ova or egg. Each egg has exactly half the number of chromosomes as the mother.

2 types: Spermatogeneis & Oogenesis 11-4 Meiosis 2 types: Spermatogeneis & Oogenesis

Mitosis vs Meiosis Mitosis Meiosis Results in 2 Diploid Cells (2N) 4 Haploid Cells (N) Cells are Genetically Identical Genetically Different Occurs in Somatic (Body) Cells Sex Cells

V. Linkage and gene maps A. Gene linkage   1. Thomas Hunt Morgan research on fruit flies led him to the principal of linkage. 2. Morgan discovered that many genes appeared “linked” together.

11-5 Linkage and Gene Maps V. Linkage and gene maps

11-5 Linkage and Gene Maps V. Linkage and gene maps 3. It is the chromosomes, however, that assort independently not individual genes.   4. Mendel DID miss gene linkage.

11-5 Linkage and Gene Maps V. Linkage and gene maps 5. Even though if two genes are found on the same chromosome this does not mean they are linked forever. Crossing over can occur.   6. Crossing over creates genetic diversity.

11-5 Linkage and Gene Maps V. Linkage and gene maps 7. A gene map shows the relative location of each gene. See page 280 figure 11.9

11-5 Linkage and Gene Maps

Alleles, alternative versions of a gene

Pedigree analysis

Testing a fetus for genetic disorders