Chapter 11: Introduction to Genetics Biology- Kirby

11-1: The Work of Gregor Mendel Genetics- the scientific study of heredity. Gregor Mendel- monk who used peas to understand principles of genetics. Fertilization- process in sexual reproduction in which male and female cells join to form a new cell.

11-1: The Work of Gregor Mendel True-breeding- describes self-pollinating organisms identical to themselves. Mendel’s pea plants were true-breeding (example-tall plants produced tall plants). Mendel wanted to establish cross-pollination in his plants instead. Cross-pollination- 2 different plants as parents.

11-1: The Work of Gregor Mendel Trait- a specific characteristic that varies from one individual to another. Mendel studied 7 traits in peas: seed shape, seed color, seed coat color, pod shape, pod color, flower position, and plant height. Mendel crossed plants to study these traits in offspring.

11-1: The Work of Gregor Mendel The original plants were called the Parental (P) generation. The offspring were called first filial (F1) generation. Hybrid- the offspring of crosses between parents with different traits. All the offspring had traits of one parent:

11-1: The Work of Gregor Mendel Mendel’s conclusions: 1. biological inheritance is determined by factors that are passed from one generation to the next. Genes- chemical factors that determine traits. Allele- different forms of a gene.

11-1: The Work of Gregor Mendel 2. Principle of Dominance- states that some alleles are dominant and others are recessive. Dominant-trait will be expressed. Recessive- trait will not be expressed.

11-1: The Work of Gregor Mendel Mendel crossed all the F1 generation to make a F2 generation. Some of the recessive traits appeared in the F2 generation. Segregation- separation of alleles during gamete formation. Gametes- sex cells. Each F1 plant has 2 gametes; one allele for dominant trait and one for recessive trait.

11-2: Probability & Punnett Squares Probability- the likelihood that a particular event will occur. The principles of probability can be used to predict the outcomes of genetic crosses.

11-2: Probability & Punnett Squares Punnett Square- diagram that shows the gene combinations that might result from a genetic cross. The letters of a punnett square represent alleles; uppercase=dominant, lowercase=recessive. Used to predict and compare genetic variations resulting from a cross.

11-2: Probability & Punnett Squares Homozygous- the alleles are the same; true-breeding organism-example: TT or tt. Heterozygous- the alleles are different; hybrid organism- example: Tt.

11-2: Probability & Punnett Squares Phenotype- physical characteristic- example: tall. Genotype- genetic makeup- example: TT. Organisms can have the same phenotype, but different genotypes; example: TT and Tt.

11-2: Probability & Punnett Squares Punnett Square Examples:

11-3: Exploring Mendelian Genetics Mendel wanted to know if segregation of one allele affected another pair of alleles. Example: Seed shape affect seed color? Independent Assortment- independent segregation of genes during gamete formation.

11-3: Exploring Mendelian Genetics To test independent assortment, Mendel crossed true-breeding round yellow peas (RRYY) with wrinkled green peas (rryy). F1 Cross:

11-3: Exploring Mendelian Genetics F1 genotype: RrYy Mendel crossed F1 plants to get F2 plants: The results had a 9:3:3:1 ratio.

11-3: Exploring Mendelian Genetics The principle of independent assortment states that genes for different traits can segregate independently during gamete formation. Independent assortment also helps give genetic variations in organisms.

11-3: Exploring Mendelian Genetics Some alleles are neither dominant or recessive, and many traits are controlled by multiple alleles and genes. Incomplete dominance- the heterozygous phenotype is in between the 2 homozygous phenotypes. Example- Flowers- Red (RR) & White (WW)=Pink (RW)

11-3: Exploring Mendelian Genetics Codominance- both alleles contribute to the phenotype. Example: Chicken feathers- Black (BB) & White (WW)=Speckled (BW) Multiple Alleles- 3 or more alleles of the same gene. Example: Rabbits fur- Page 273- full color, chinchilla, himalayan, and albino coat colors.

11-4: Meiosis Homologous- the chromosomes that have a corresponding chromosome from the opposite sex parent. Diploid- a cell that has both sets of homologous chromosomes (2N). Haploid- a cell that has one set of chromosomes (N).

11-4: Meiosis Meiosis- process in which the number of chromosomes per cell is cut in half through the separation of homologous chromosomes in a diploid cell. Involves 2 divisions: Meiosis I and Meiosis II

11-4: Meiosis Interphase I- Chromosomes replicate before meiosis I. Prophase I- each chromosome pairs with its corresponding homologous chromosome to from a tetrad. 4 chromatids=tetrad Metaphase I- spindle fibers attach to chromosomes.

11-4: Meiosis Anaphase I- the fibers pull the homologous chromosomes toward opposite ends of the cell. Telophase I & Cytokinesis- nuclear envelopes form and the cell separates. Crossing over- the homologous chromosomes exchange alleles from their chromatids during meiosis. This produces new combinations of alleles.

11-4: Meiosis Meiosis II: Prophase II- meiosis I results in 2 haploid (N) daughter cells, each with half the number of chromosomes as the original. Metaphase II- chromosomes line up in the middle. Anaphase II- The sister chromatids separate and move toward opposite ends of the cell.

11-4: Meiosis Telophase II & Cytokinesis- meiosis II results in 4 haploid (4N) daughter cells. Gamete Formation- In males, sperm are the haploid gametes produced in meiosis. (4) In females, an egg is the haploid gamete produced in meiosis. (1)

11-4: Meiosis Mitosis vs. Meiosis Mitosis results in the production of 2 genetically identical diploid cells. Meiosis produces 4 genetically different haploid cells.

11-5: Linkage & Gene Maps Although alleles segregate by independent assortment, some genes are linked together. Gene Map- diagram showing the locations of genes on a chromosome.