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Hereditary Gregor Mendel - Austrian - Used Peas in for experiments Heredity - Passing of traits - From Parents to Offsprings Offspring - Product or child - From reproduction Self- Pollinating Plant - Have male and female reproductive structures - Can fertilize itself True-Breeding Plant - Can self-pollinate - Offspring is identical to parent CrossPollination - Involves two different plants - One plant fertilizes another 3. 1. 2. Characteristic - Feature - in different forms - Ex: Hair color, Eye color, Height Trait - Different forms of characteristics Breed - To mate or fertilize with another organism Mendel’s First Experiments - Crossed pea plants - Focused on 7 characteristics - One trait seemed to always disappear - One trait seemed to always stay Dominant Trait - The trait that stayed Recessive Trait - The trait that disappeared - Mendel studied one characteristic at a time - Mendel only used true-breeding plants - So he would know what to expect Mendel’s Second Experiments - Investigating recessive traits - First generation offspring were bred - Some recessive traits reappeared - Recessive traits didn’t show up as much as the dominant traits - 3:1 ratio - Realized two sets of instructions were needed - Opened the doors to modern genetics Traits and Inheritance Chapter 5: Section 2 Genes - Provide instructions - Control inherited traits Alleles - Different forms of genes - Can be the same or different details Phenotype - An organism’s appearance - Physical features - Determined by genes Genotype - An organism’s genes - Different combinations of alleles Punnett Squares - Used to organize different combinations - Possible genotypes of offspring - Dominant traits Capital Letters - Recessive traits lower case letters - Two alleles per trait (two sets of instructions) - Helps calculate probability Probability - Mathematical chance something will happen - Expressed in a fraction or percentage Homozygous - Both alleles are the same, dominant or recessive Heterozygous - Have one dominant and one recessive allele Punnett Squares - Used to organize different combinations - Possible genotypes of offspring Incomplete Dominance - Both traits appear - Neither trait is dominant nor recessive Ex: Red flower + White flower = Pink flower One gene – Many traits - One gene ONLY - Can influence many traits One trait – Many genes - Several genes involved - ONLY one trait influenced Ex: Skin color, Hair - Environment can influence traits too - Sometimes genes are not the only factor Meiosis Asexual Reproduction - Only one parent needed - Offspring is identical to parent Mitosis - Method used for eukaryotic cells to divide - Asexual reproduction is a type of mitosis Sexual Reproduction - Involves two parents - Needs sex cells - Offspring are different from parents Homologous - Pair of chromosomes Chromosomes - Carry the same genes - Sex cells only have one of the pair Meiosis - Making of sex cells - Sex cells have half as many chromosomes as non-sex cells Walter Sutton - Studied meiosis in grasshoppers - Determined that genes are located on chromosomes Steps in Meiosis - Two phases: Phase A and Phase B - Chromosomes are copied only once - Chromosomes divide twice - New cells have half as many chromosomes Meiosis Interphase Meiosis is preceded by interphase. The chromosomes have not yet condensed. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html Meiosis Interphase The chromosomes have replicated, and the chromatin begins to condense. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html Meiosis Prophase I The chromosomes are completely condensed. In meiosis (unlike mitosis), the homologous chromosomes pair with one another http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html Meiosis Metaphase I The nuclear membrane dissolves and the homologous chromosomes attach to the spindle fibers. They are preparing to go to opposite poles. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html Meiosis Anaphase I The chromosomes move to opposite ends of the cell. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html Meiosis Telophase I & Cytokinesis The cell begins to divide into two daughter cells. It is important to understand that each daughter cell can get any combination of maternal and paternal chromosomes. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html Meiosis Prophase II The cell has divided into two daughter cells. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html Meiosis Metaphase II As in Meiosis I, the chromosomes line up on the spindle fibers. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html Meiosis Anaphase II The two cells each begin to divide. As in Meiosis I, the chromosomes move to opposite ends of each cell. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html Telophase II & Cytokinesis With the formation of four cells, meiosis is over. Each of these prospective germ cells carries half the number of chromosomes of somatic cells. http://morgan.rutgers.edu/MorganWebFrames/Level1/Page7/meiosis1.html Sex - Carry genes that determine traits Chromosomes - Determine sex of organism (male or female) - Females have 2 X chromosomes (XX) - Males have 1 X and 1 Y (XY) - During meiosis, on of each of the chromosome pairs end up in a sex cell. Sex-Linked Disorders - Y chromosome does not carry all of the genes of the an X. Females have 2 X chromosomes, so they carry 2 copies of each gene found on the X. Back up gene available if one gets damaged. - Sex chromosomes carry genes for certain disorders Ex: Color blindness is on the X chromosome Mutation in a gene on the X chromosome. Pedigree - Diagram used to trace traits - Studies family history of traits - Used by genetic counselors Selective Breeding - Traits are selected or desired - Organisms with those traits are bred Marriage Mom On a pedigree: A circle represents a female A square represents a male A horizontal line connecting a male and female represents a marriage A vertical line and a bracket connect the parents to their children A circle/square that is shaded means the person HAS the trait. A circle/square that is not shaded means the person does not have the trait. Children are placed from oldest to youngest. Male- Son A key is given to explain what the trait is. Dad Has the trait Male-Son Female-Daughter Male – Son Oldest to Youngest Unaffected male Affected male Unaffected Female Affected Female I II III IV A pedigree chart shows an x linked disease if most of them males in the pedigree are affected. A pedigree chart shows an autosomal disease if there is a 50/50 ratio between men and women inheriting disease. An autosomal recessive disorder means two copies of an abnormal gene must be present in order for the disease or trait to develop.