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Transcript
HEREDITY AND GENETICS Gregor Mendel - Used pea plants for experiments - Crossbred, testing ONE trait at a time - Color, height, etc. Heredity - Passing of traits from parents to offspring Offspring - Product or child that is the result of reproduction by the parents 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 - Offspring are not identical 3. 1. 2. Characteristic - Feature we see on the outside - 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 (offspring identical to parents) 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 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 MEIOSIS Walter Sutton - Studied meiosis in grasshoppers - Determined that genes are located on chromosomes Steps in Meiosis - Two phases: Phase I and Phase II - 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 - Carry genes Sex Chromosomes - Determine sex of organism (male or female) - Females have 2 X chromosomes (XX) - Males have 1 X and 1 Y (XY) Sex-Linked Disorders - Sex chromosomes carry genes for certain disorders Ex: Color blindness is 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