Mendelian Genetics


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  • There are roughly 20,000 genes in the human genome, which accounts for only about 1% of all the DNA found in a cell.
  • "introns" turned on, "exons" are segments that are turned off (not used to code for proteins).
  • P = parental, F1 = first filial, F2 = second filial generation
  • Mendelian Genetics

    1. 1. Mendels Laws of Genetics How traits are passed from parents to offspring.
    2. 2. Genetics A gene is a segment of DNA that codes for a protein which determines one particular trait Genetics is the study of how genes are passed on from parents to offspring
    3. 3. Differentiation Genes signal different cells to create proteins that give them unique shapes & functions These cells grow & divide to make tissues that form the organs of the developing baby
    4. 4. Fertilization: new life is formed Life begins when two gametes (sperm + egg) join A complete set of chromosomes results (23 + 23) The zygote starts as a single cell, but soon begins to divide (via mitosis = identical cells) Genes are "turned" on and off, causing cells to differentiate (change to have different forms/jobs)
    5. 5. Heredity & Inherited Traits The chromosomes from your mom and dad have given your cells instructions to make YOU! Each characteristic you inherited from your parents is called a trait (eye color, earlobe shape, height, personality traits, etc.) For each trait, you have a pair of alleles (onefrom your mother andone from your father)
    6. 6. Alleles: variations of a gene Gene AllelesEye Color Blue, brown, green, hazelPea height Tall, shortPea color Yellow, greenFlower position Axial, terminal
    7. 7. Gregor Mendel  An Austrian scientist-turned-monk noticed patterns in the monasterys garden  Studied the inherited traits of pea plants and found predictable, numerical ratios in the offspring  Observed some traits were dominant over others (i.e. yellow peas overpowered or occurred1822-1884 more often than green pea seeds)
    8. 8. Mendels Experiments He wondered if traits seen in different generations of pea plants were • determined by environmental factors (soil composition, temperature, sunlight) OR • "handed down" by parents (chromosomes werent even discovered yet, so he had no idea how) In his highly controlled experiments, he tested the hypothesis that each trait was determined by a set (not one, but TWO) inherited factors from each parent Do you see the Scientific Method at work here?
    9. 9. Dominant and Recessive Traits
    10. 10. Mendel’s Crosses Observed phenotype, the outward expression of the genes the F1 generation are tall, showing that trait is dominant The dwarf plant has the recessive trait (it is overpowered by the tall allele)
    11. 11. Genotypes: Genes and Alleles  The genetic make-up of an organism is its genotype  Every organism is diploid (has 2 copies of each chromosome)  Each trait is designated by a different letter  DOMINANT ALLELES ARE CAPITAL LETTERS  recessive alleles are lowercase letters
    12. 12. Genotype determines Phenotype Homozygous means the two alleles are the same Heterozygous means the two alleles are different Genotype Genotype Phenotype Homozygous TT Dominant dominant Homozygous tt Recessive recessive Heterozygous Tt Dominant
    13. 13. Punnet Square: Monohybrid Cross Used to predict the outcome of a genetic cross
    14. 14. Dihybrid Cross What happens to two genes on different chromosomes? Homologous pairs of meiotic chromosomes line up randomly at the equatorial plane in Metaphase I The two traits separate during meiosis, resulting in offspring with different combinations of traits This results in four different possible combinations of chromosomes and genes in the gametes
    15. 15. The Law of Segregation Diploid chromosomes of parents undergo meiosis Alleles separate as they become haploid egg or sperm They are combined again during fertilization to produce a diploid offspring
    16. 16. Which traits are dominant?
    17. 17. Independent Assortment & Segregation