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Genetics The study of heredity…whatever that means. Heredity-The passing of traits from parents to progeny (offspring…ummm…kids…do flowers have kids?). Who was Gregor Mendel? He was a dude who studied peas in the 1850’s…WOW…that sounds exciting! Actually, he experimented with pea plants to see how traits were inherited (passed from parent to offspring). What did he do…exactly? Well…he crossed purebred plants (that means the parents have similar traits so the offspring always have the same trait as the parent…blue eyed parent…blue eyed kid). Then he started crossing different types (like green with yellow instead of green with green). He figured out that individual factors were controlling what he saw in the plants. These are called…GENES! Genes Remember that a GENE is a specific sequence of nucleotides within the DNA molecule. So…a GENE contains the “code” for a particular trait (like blue hair and blonde eyes). Also remember that when cells are dividing (MITOSIS in the cell cycle), the DNA is packed together forming a structure we call a CHROMOSOME. Alleles These are the various forms of a gene (remember…genes control traits). Alleles control the inheritance of traits. There are two forms and they’re represented by letters of the alphabet. Some traits are determined by one allele and some are multi-allelic. In sexual reproduction, one allele come from the male and one comes from the female, so…there will be two (2) alleles. Let’s Start with the Simplest Type… Complete Dominance… one allele is dominant over another. DOMINANT (capital letters): If this allele is there…the trait shows up. Recessive (lower case letters): If this allele is there…the trait won’t show up if a dominant allele is also there. Huh? Ok, let’s say that B = Brown fur and b= white fur. What organism? Doesn’t matter…let’s say the Alaskan Shortnose Squeezle. If mom and dad each contribute a B gene, then the squeezle offspring has brown fur (BB) If mom gives up a B and dad a b, then the squeezle kid still has brown fur…why? As long as the is a B…there will be brown fur, because B is DOMINANT. Now…if mom gives up a b and so does dad (bb), then bingo…white furred squeezle (and we all know how good those are grilled). bb…two recessive alleles. Unfortunately…all of this junk has names that you gotta know. Fortunately…you already know a bunch of them Phenotypes & Genotypes Phenotype: the physical characteristics of offspring (blue eyes, straight hair, blood type). Genotype: the actual genetic makeup of the offspring (Bb, rr, TT). Genotypes can be as follows… Genotypes: Combinations of Alleles Homozygous: two of the same alleles…BB, RR, rr, ss…get it? Homozygous Dominant…two dominant alleles…QQ, LL, DD. Homozygous Recessive…two recessive alleles…dd, ss, ff. Heterozygous: one of each allele, one dominant and one recessive…Ff, Bb, Aa Punnett Squares Used to determine the possible outcomes based upon the GENOTYPE of the parents. You can determine the GENOTYPIC RATIO & PHENOTYPIC RATIO from this information. They look like this: Try These … 1. 2. 3. Red flowers are dominant (R) Yellow flowers are recessive (r) Homozygous Dominant x Heterozygous Homozygous Recessive x Homozygous Dominant Heterozygous x Heterozygous