LIVING THINGS INHERIT TRAITS IN PATTERNS PARENTS & OFFSPRING ARE SIMILAR GENES ARE ON CHROMOSOME PAIRS GREGOR MENDEL MADE SOME IMPORTANT DISCOVERIES ABOUT HEREDITY A monk, Gregor Mendel, who lived in Austria in mid-1800’s, did first major experiments on heredity. Began studying inheritance of traits among pea plants in monastery’s garden. Took detailed notes & worked with several traits (plant height, flower position, seed shape, seed color, flower color, etc.) ALLELES INTERACT TO PRODUCE TRAITS

PARENTS & OFFSPRING ARE SIMILAR Inherited Traits are characteristics passed on from your parents Acquired Traits are developed during your life (riding bike) During SEXUAL REPRODUCTION, a mom’s cell with genetic data combines with a dad’s cell with different genetic data, to create a new, unique cell, which becomes the offspring.

GENES ARE FOUND ON CHROMOSOME PAIRS GENE: unit of heredity found at a specific spot on a chromosome, codes for a particular product (that causes traits). HEREDITY: passing of genes from parent to offspring. Cells have PAIRS of chromosomes, (one part of pair from each of 2 parents). Chromosomes in a pair are called HOMOLOGS (same size & shape)

GENES FOUND ON CHROMOSOMES PAIRS cont. On each homolog, are sites where specific genes are located, used to determine specific traits (like height). Both homologs may have gene for height at spot “A”, but one may be for tall, the other short. The various forms of the same gene are called ALLELES. The alleles on a pair of homologs may or may not be different. Human chromosomes are numbered 1-22; the 23rd pair are the SEX CHROMOSOMES. Female has XX, and Males have XY.

GREGOR MENDEL Took TRUE BREEDING (always produces offspring with a particular trait if self-pollinated) plants for tall & true breeding plants for short & cross bred. All offspring tall, then let them self-pollinate, and the second generation were 75% tall & 25% short; the trait that seemed to disappear (short) in the first generation, reappeared in the second. Mendel realized there must be 2 “factors” for each possible trait (one from each parent) He felt some of these factors may be “masked” or overpowered by the other (short factor overpowered by tall factor). Today we call his “factors” genes & alleles.

ALLELES INTERACT TO MAKE TRAITS PHENOTYPE: observable characteristics of an organism (what they look like) GENOTYPE: actual genes an organism has for specific traits. DOMINANT ALLELE: is expressed in the phenotype even if only 1 is present in the genotype (eyefold allele) RECESSIVE ALLELE: is expressed in phenotype only when 2 copies are present on the homologs/chromosomes (no eyefold) Hair & skin color as well as other traits, are determined by multiple genes, not just 1 pair.