Biology B

 People used to think combining two parents’ characteristics was like mixing paint…

 Monk and teacher.  Experimented with purebred tall and short peas.  Discovered some of the basic laws of heredity.  Studied seven purebred traits in peas.  Presentation to the Science Society in1866 went unnoticed.  He died in 1884 with his work still unnoticed.  His work rediscovered in  Known as the “Father of Genetics”.

 He developed pure strains of peas for seven different traits (i.e. tall or short, round or wrinkled, yellow or green, etc.)  He crossed these pure strains to produce hybrids.  He crossed thousands of plants and kept careful records for eight years.

 In peas many traits appear in two forms (i.e. tall or short, round or wrinkled, yellow or green.)  The flower is the reproductive organ and the male and female are both in the same flower.  He crossed pure strains by putting the pollen (male gamete) from one purebred pea plant on the pistil (female sex organ) of another purebred pea plant to form a hybrid or crossbred.

 He experimentally crosses different strains to develop hybrids.  He then crossed the hybrids and analyzed the results.

 Strong Hereditary traits cover weak traits.  Mendel called stronger traits  DOMINANT  Mendal called weaker traits  recessive  Dominant traits are represented by capital letters (T) while recessive traits are represented by lower case letters (t).

 Mendel crossed purebred tall plants with purebred short plants and the first generation plants were all tall.  When these tall offspring were crossed the result was a ratio of 3 tall to 1 short.

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Law of Inheritance: Inherited traits are determined by “factors” (genes) passed on from the parents. Law of Dominance: When 2 or more options exist for a trait, one may be dominant. Law of Segregation: Usually, each parent has 2 genes for each trait (1 from each of their parents) These are separated from each other when gametes (sex cells) are formed Law of Independent Assortment: Genes for different traits are separated independently of one another.

 The Law of Independent Assortment is WRONG!!!  It was a reasonable guess… but now we know that genes are not inherited as separate pieces… They come in sets! These sets are CHROMOSOMES – Collections of genes strung together.

How many do you have? 46 Where do they come from? 23 from Mom, 23 from Dad

Chromosome – structure made up of genes. Humans have 46, 23 from each parent Gene – a string of DNA controlling one trait Genotype – the genes one has… ie Bb for eye color Phenotype – what the genes produce. Brown eyes are part of my phenotype (Physical = Phenotype) Homozygous – Having two of the same gene for a trait… ie BB Heterozygous – Having two different genes for a trait… ie Bb Dominant – A gene that can mask another trait… Brown eyes are dominant to blue Recessive – a gene that can be masked by a dominant gene