Introduction to Genetics and Heredity

Introduction to Genetics and HeredityHypotheses about genesIn the 1800s scientist argued between two hypothesis regarding genes and how they are passed on to offspringBlended hypothesis - states that the traits from two parents are mixed to become a third trait

Particulate hypothesis states that the traits from two parents are joined but remain discrete, and can be separated again to their original forms

Which hypothesis seems more logical to you?Remember from MeiosisAll organisms pass on inherited information using haploid gametes.

XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXHuman zygotes have 23 pairs of chromosomesHuman ZygoteWho was Gregor Mendel?

-Austrian monk -Did work with pea plants-Know as the Father of GeneticsGenetics the scientific study of heredityMendels workHe selectively bred pea plantsFertilization when male and female reproductive cells joinMale pollen or spermFemale eggsGamete the individual egg or spermSeed fertilized egg or new cell (zygote)

Selective breedingTrue-breeding if they were allowed to self-breed they would have identical offspring

Self-breeding Sperm and egg from the same flower fertilize

Selective breedingCross-pollinationMendel took pollen from one plant and fertilized eggs from other plants

Genes and DominanceTraits a specific characteristic (ex. Brown hair) Seed color Plant height Parental generation (P) Original pair of plants Filial generation (F1) offspring, progeny Hybrids offspring of crosses between parents with different traits

Remember from MeiosisGenes chemical factors that determine traits (Hair color)Alleles different forms of traits (Brown hair, blue eyes) (like T or t for tallness in pea plants).

What Mendel found..Dominant Trait the observed trait that masks another trait (written as an upper case letter). Recessive Trait trait that can be masked by a dominant trait (written as a lower case letter).Tall is dominant to short in pea plants, so the gene for tallness is represented by an upper case T and shortness is represented by a lower-case t.

Mendels Results

Mendel's observations from these experiments can be summarized in two principles:The principle of segregation A parent passes on at random only one allele for each trait to each offspringThe two alleles for each trait separate during meiosis. The principle of independent assortmentA random distribution of alleles occurs during gamete formation. Genes on separate chromosomes sort independently during meiosis.

Diploid A cell with two of each kind of chromosome (1 from each parent)

We say the cell is a diploid cell or 2n(This supports Mendels conclusion that organisms have two factors alleles for each trait)Haploid A cell with one of each kind of chromosome (gametes)

We say the cell is a haploid or n(This supports Mendels conclusion that parents give one allele for each trait to their offspring)

Phenotype & GenotypePhenotypeThe way an organism looks and behavesEx. Tall, yellow, blond, blue eyesGenotypeThe gene combination an organism containsEx. TT or Tt for tallHomozygous two alleles are the same, TTHeterozygous two alleles are different, Tt