GENETICS & HEREDITY What makes us what we are?. Gregor Mendel Austrian monk in the 19 th century Gardener for the monastery Made observations about the.
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Gregor Mendel Austrian monk in the 19 th century Gardener for the monastery Made observations about the pea plants Was the 1 st to predict how different traits might be transferred
Why was Mendel successful? Chose subject carefully – pea plants reproduce sexually Controlled his experiments –T–Transferred pollen himself and covered plants to insure cross-pollination; did NOT allow self-pollination of flowers –S–Studied one trait at a time –D–Did mathematical analysis –S–Started with “pure” plants
Mendel’s Laws of Heredity Rule of unit factors –Each organism has 2 factors that control each of its trait. –We now know that these factors are genes (which are found on chromosomes). –The different forms of these factors are called alleles. –One factor is inherited from father ( ♂) and one factor is inherited from mother ( ♀).
Mendel’s Laws Rule of dominance –When plants are crossed, only 1 factor can be expressed. –Expressed trait dominant –Trait that is “covered up” is the recessive trait. –Dominant & recessive inherited dominant trait expressed –Recessive expressed only when 2 recessive traits are inherited.
More Mendel Laws Law of segregation –The two factors controlling the trait must be separated when sex cells (gametes) are formed. –Parents pass on randomly only one factor (allele) for each trait to each offspring.
The Last One Law of independent assortment –States that genes for different traits can segregate independently of each other during gamete formation (as long as they are on different chromosomes). –Accounts for genetic variation in organisms.
Terms Used Today Phenotype how organism looks Genotype gene combination Homozygous same 2 alleles (TT or tt) Heterozygous having different alleles (Tt)
Info from Punnett squares Possible gametes formed Possibility of offspring Probability of offspring Genotypic ratio (1 TT: 2 Tt: 1 tt) Phenotypic ratio (3 tall plants: 1 short plant)
Monohybrid Cross Looks at only 1 trait at a time Homozygous purple (PP) flowers crossed with heterozygous (Pp) flowers P1 (parental) genotypes PP x Pp
Dihybrid Cross Look at 2 traits at a time; traits NOT linked & assort independently Heterozygous axial (Aa) flowers, homozygous short (tt) plants crossed with heterozygous axial (Aa) flowers, tall (Tt) plants P1 genotypes –Aatt x AaTt