Concept 2: Living things inherit TRAITS in PATTERNS… We can PREDICT Traits!

Review: Observe the Family Below and list some observable TRAITS What traits seem to have been passed down?

Traits Review Some traits are inherited Some traits are acquired Similar to the traits your parents have Eye color Hair color Height Number of arms Some traits are acquired These traits your develop over your lifetime Athletic ability Reading and writing Language

Review: Traits are coded by GENES Genes are made out of DNA Genes are located on your chromosomes You (human) contain 23 pairs of chromosomes (homologs). Individuals inherit genes from their parents Half of your genetic material is from your mom and half is from your dad. Crossing over during meiosis leads to genetic variation.

Traits are Controlled by Interactions of Genes Each homolog (pair of chromosomes) contains sites where genes are located. The gene will be present on both of the chromosome pairs, however the form of the gene may be different Different forms of the same gene are called alleles

The Father of Genetics Gregor Mendel performed the first major experiments investigating heredity (how genes are passed on) University trained in Mathematics and Science Experimented between 1856-1863 Investigated inheritance among pea plants in his monastery’s garden

Mendel’s Experiment Observed eight different traits of pea plants: •Plant height •Seed shape •Pod shape •Flower postion •Pod postion •Seed color •Flower color •Pod color Using one trait at a time, Mendel crossed two plants who were opposite forms of the same trait Example: Trait – plant height Tall plant vs. a dwarf plant

Mendel’s Conclusions Each plant must have two “factors” for each possible trait, one factor from each parent Some forms of a trait can be masked Traits able to be masked can only be seen if both the plant’s factors are for that form of the trait Mendel’s “factors” are now known as genes and alleles

Genetic Terms Phenotype describes the physical characteristic that is displayed by your genes; observable (eye color, hair color) Genotype describes the actual genes that you have on your DNA; not always obvious (increased risk of Breast Cancer)

Two Forms of Every Gene Mendel found that your have two copies of each allele (one from your dad and one from your mom). Alleles can be Dominant or Recessive Dominant Allele Always expressed as a capitol letter (T) Physically expressed, regardless of the other allele it is paired with (Tt or TT) Recessive Allele Physically expressed only when paired with another recessive allele (tt) Always expressed in a lowercase letter (t)

Take Away Messages The interactions of the alleles determines the phenotype of a certain trait. Mendel found that there are two factors that come together when determining traits (one gene from your mom and one from your dad). Alleles can either be recessive or dominant. In order for a recessive trait to be observed, there must be TWO copies of that recessive allele. In order for a dominant trait to be observed, there must be ONE dominant allele present.