Chapter 8 Gregor Mendel and Heredity

Sections 1-4 Section 1: The origins of genetics. Section 2: Mendel’s Theory Section 3: Studying Heredity Section 4: Complex Patterns of Heredity

Intro to Genetics

The Origin of Genetics Heredity is the passing of traits from parents to offspring. Over 100 years ago, An Austrian monk (Gregor Mendel) carried out experiments with pea plants (Father of Genetics) Genetics is the branch of biology that focuses on heredity

Gregor Mendel

Why did Mendel Breed Pea Plants? Several pea traits exist in two clearly different forms Plants male/female reproductive parts are enclosed in same flower (self pollination) Pea is small, grows easily, matures quickly and produces many offspring

Traits Expressed as Simple Ratios Mendel’s initial experiments were monohybrid crosses (1 pair of contrasting traits) Mendel’s Process –Step 1- Mendel allowed the plants to self pollinate to ensure that they were true breeding. Purple plants produce purple offspring. –Step 2 - Mendel then cross pollinated two P generation plants. Offspring called F1 generation –Step 3 - Mendel allowed the F1 generation to self pollinate. (F2 generation) –He found a 3:1 ratio of offspring. Purple:White

Mendel’s Hypotheses For each inherited trait, there 2 copies of gene. (one from mom/dad) There are alternative version of genes (alleles) - purple/white) When 2 different alleles are present, the dominant one is shown. (recessive is hidden) Homozygous- 2 alleles of a gene are the same (PP or pp) Heterozygous- if the 2 alleles for a gene are different (Pp) Genotype is the allele combination Phenotype is the physical appearance of the trait

The Laws of Heredity Law of Segregation states that the alleles separate during meiosis Law of Independent Assortment states that alleles of different genes separate independently of one another during meiosis.

Punnett Squares Punnett squares are diagrams used to predict the outcome of a genetic cross by considering all possible combinations Probability is the likelihood that a specific event will occur

Pedigree Pedigree is a family history that shows how a trait is inherited over several generations. Using a pedigree scientist can determine –Autosomal/ sex linked –Dominant recessive –Hetero/homozygous

Complex Patterns of Heredity Polygenic Trait-- when several genes influence a trait (height, weight, hair color) Incomplete Dominance- when one trait is not totally dominant (red/white = pink) Multiple alleles- genes with three or more alleles (ABO blood groups: A, B, AB, O) Codominance- two dominant alleles are expressed (AB- both are dominant) Traits Influenced by Environment - artic fox fur, hydrangea plant - acidic neutral, skin color in humans, height is influenced by nutrition

Genetic Disorders

Treating Genetic Disorders Genetic counseling is a form of medical guidance that informs people about genetic problems that could affect their offspring PKU - genetic disorder- person lacks an enzyme that converts one amino acid into another. Can be diagnosed soon after birth and treated w/ diet. Gene Therapy- the correction of certain recessive disorders by replacing defective genes