Genetics

What is Genetics?  Genetics is a branch of biology that studies how characteristics are passed from one generation to the next

Important Terminology  Trait – characteristic that can vary from one organism to another and in passed from parent to offspring  Genes – biological inheritance is determined by factors passed from one generation to the next  Alleles – a gene that occurrs in two contrasting forms that produced different characteristics ( different versions of a gene )  Dominant – trait that will always be expressed if the offspring inherits it  Recessive – trait that is “ hidden ” if the dominant trait is present

Gregor Mendel  Mendel was an Austrian monk who studied math and science and taught science in a monastery  Performed experiments as he maintained the monastery garden  Performed the first scientific study of inheritance on pea plants

Mendel’s Experiments  Mendel used pea plants for many of his experiments  Parts of the flowers for reproduction  Pollen = male sex cells  Eggs in flower = female sex cells  Pea plants normally reproduce by self - pollination  Pollen fertilizes flower of the same plant  True - breeding pea plants (“ pure bred ”)  Would the new plants be identical or different than the parent? Why?

Mendel’s Experiments  Pea plants can cross - pollinate  Pollen fertilizes flower of a different plant  New plants have two parent plants  Infer if the new plants would be identical or different from the parents. Why? Mendel cross - pollinated pea plants !

Mendel’s Experiments  The first generation was called the P ( Parental ) Generation  These were the original pairs of plants  The second generation was called the F 1 ( Filial 1) Generation  These plants were the first offspring  The third generation was called the F 2 ( Filial 2) Generation  These plants were the offspring of the first offspring

Mendel’s Observations  Some traits were observed in the F 1 generation  Some traits seemed to “ skip ” a generation and show up 2 generations later in the F 2 generation

Mendelian Genetics  Traits that seem to “ skip ” a generation are recessive traits  These traits are “ masked ” by the dominant traits  The plants that had the trait but it could not be seen are called carriers

Mendel’s Laws of Inheritance  Law of Dominance  If the dominant trait is present, it will always be expressed  The recessive trait will be masked by the dominant trait

Mendel’s Laws of Inheritance  Law of Segregation  Alleles ( different forms of a gene ) will separate during meiosis

Mendel’s Laws of Inheritance  Law of Independent Assortment  Traits are not dependent on other traits to be inherited  Ex : having a baby with brown eyes does not mean he / she will have brown hair

Homosygous or Heterozygous?  Homozygous – the organism will have two dominant alleles for a certain trait or two recessive alleles  Ex : TT or tt  Heterozygous – the organism will have one dominant and one recessive allele for a trait  Ex : Tt