Mendel’s Legacy Section 9.1

Genetics- the field of biology devoted to understanding how characteristics are transmitted from parents to offspring Genetics was founded with the work of Gregor Johann Mendel

Gregor Johann Mendel Austrian monk who experimented with garden peas 1842- age 21; entered a monastery in Brunn 1851- entered the University of Vienna Heredity- the transmission of characteristics from parents to offspring

Mendel’s garden peas Mendel observed 7 characteristics of pea plants, each occurring in 2 contrasting traits. Traits- plant height (long or short stems), flower position along stem (axial or terminal), pod color (green or yellow) pod appearance (inflated or constricted), seed texture (smooth or wrinkled), & flower color (purple or white)

Mendel collected seeds from his pea plants He observed that both purple-flower and white-flower plants grew from the seeds of purple-flower plants

He also observed that both tall and short plants grew from seeds obtained from tall plants Mendel wanted to find an explanation for the variations

Mendel’s methods Mendel documented the traits of each generation’s parents by controlling how much the plants were pollinated Pollination- occurs when pollen grains produced in the male reproductive parts of the flower (anthers) are transferred to the female reproductive part of the flower (stigma)

Self-pollination- occurs when pollen is transferred from the anthers of a flower to either the stigma of the same flower or a flower on the same plant Cross-pollination- involves flowers of 2 separate plants

Self-pollination can be interrupted (and cross-pollination performed) by removing the anthers from a flower and manually transferring the anther to the stigma of another plant By doing this, Mendel was able to protect his flowers from receiving pollen that might be transferred by wind or insects, giving him more control over the pollination of his pea plants

Mendel’s experiments Plants that are pure for a trait always produce offspring with that trait strain- denotes plants that are pure for a trait P1 generation- each parental generation

F1 generation- the first filial generation F2 generation- the second filial generation

Mendel’s Crosses & Results P cross F1 generation F2 generation Actual ratio Probability ratio Axial X Terminal = Axial 651 axial 3.14:1 3:1 207 terminal Tall X Short = tall 787 tall 2.84:1 3:1 277 short Inflated X inflated 882 inflated 2.95:1 3:1 Constricted = 299 cons. Green X yellow = green 428 green 2.82:1 3:1 (pods) 152 yellow Smooth X smooth 5,474 sm. 2.96:1 3:1 Wrinkled = 1,850 wrink. Yellow X Green = yellow 6,022 yellow 3.01:1 3:1 (seeds) 2,001 green Purple X White = purple 705 purple 3.15:1 3:1 224 white

Recessive & Dominant traits Dominant factor- dominates the other factor of a specific characteristic Recessive factor- the trait that did not appear in the F1 generation but reappeared in the F2 generation

Law of segregation States that a pair of factors is segregated, or separated, during the formation of gametes.

Law of independent assortment States that factors for different characteristics are distributed to gametes independently.

Chromosomes & Genes Molecular genetics- the study of the structure and function of chromosomes and genes Allele- each of several alternatives of a gene (Mendel's factors are now called alleles.)