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Genetics Ms Morin May 2008 TRAITS : Physical characteristics of an organism inherited from parents and passed on from one generation to the next. HEREDITY: The passing of the traits from parents to offspring. GENETICS: Study of heredity. Common Traits Eye color Eye shape Hair color Height Coat color seed color petal color seed texture blood type Seed shape There are also MANY biochemical traits that are unseen (having certain enzymes, for example) The genetic diversity of James Bond http://www.athro.com/ evo/gen/geframe.htm Chromosomes & Genes Our body cells have 46 chromosomes found in 23 pairs Egg and sperm cells have 23 chromosomes each- no pairs. There are a total of between 20,000 and 30,000 genes on our 23 pairs of chromosomes. Traits are controlled by genes. Genes are segments of DNA on a chromosome that code for a specific trait Each gene holds the DNA “code” to make one protein. http://www.ncbi.nlm.nih.gov/bo oks/bv.fcgi?call=bv.View..Sho wTOC&rid=gnd.TOC&depth=2 Different forms of the same gene are called alleles. Simple traits are controlled by 2 alleles of the same gene: we inherit 2 alleles of each gene for every simple trait. 1 allele is inherited from female sex cell (the egg from the mom) 1 allele is inherited from male sex cells (the sperm from the dad) Different forms of a gene Different forms of genes are called alleles. Alleles can be dominant or recessive. DOMINANT= trait is always expressed no matter what the other allele is.. RECESSIVE = trait is only expressed if the other allele for that gene is also recessive. We use a capital letter to represent a dominant allele and a lower case for recessive alleles Purebred or Hybrid? PUREBRED: two identical alleles for a trait HYBRID= two different alleles for a trait ExamplePurebred Dominant BB Purebred Recessive bb Hybrid Bb PHENOTYPE- visible traits or physical appearance of an organism Examples- blue eyes, short, black fur GENOTYPE- genetic makeup of an organism- its allele combination Examples- bb, Tt, GG Punnett Squares What is it? A chart showing all the possible combinations of alleles. Geneticists use them to predict outcomes. (male) (female) 1. 2. 3. Trait- Hitchhikers Thumb Hitchhiker’s Thumb is dominant (H). No hitchhiker’s Thumb is recessive (h) Cross- purebred Hitchhiker’s thumb female X non-Hitchhiker’s thumb male 4. Offspring predictions Genotype: ______%=4/4 = Hh Phenotype: _____%= 4/4= Hitchhiker’s Thumb Gregory Mendel Father of genetics Univ. of Vienna monk 1851 Wondered why different pea plants had different characteristics He observed that many pea plants’ traits were similar to their parents Mendel’s Experiment First generation F1 Second generation F2 purebred tall X purebred short TT x tt Phenotype= Genotype= Tt X Tt Phenotype= Genotype= Mendel’s Conclusions When you cross 2 purebred plants – 1st generation only saw the dominant trait (Tall; Purple flowers- next slide) – 2nd generation showed purebred and hybrid. (Tall & short; Purple &White) 1866- he presented his work but it wasn’t looked at by the scientific world until 1900! Probability and Genetics PROBABILITY: A number that describes how likely it is that an event will occur # times event occurs # possible outcomes = probability *Results do not affect future results HOMOZYGOUS- 2 identical alleles: tt, TT same thing as purebred HETEROZYGOUS- 2 different alleles: Example: Tt same thing as hybrid Incomplete Dominance alleles are not dominant nor recessive the phenotype is a blend of the two alleles. (Notice the use of all capital letters.) Codominance* neither allele is dominant or recessive * the two different traits appear together in the organism * example: ABO blood type