Fundamentals of Genetics Chapter 6 Fundamentals of Genetics

What will we study? 6.1 Patterns of Inheritance 6.2 Principles of Inheritance 6.3 Genetics and Predictions 6.4 Difficult Predictions

6.1 Patterns of Inheritance You should be able to: Distinguish between dominant and recessive traits Analyze the results Mendel’s experiments with three generations of garden peas

History of Genetics 1st experimentation with genetics was with dogs Dogs were dangerous wild animals Now, they are domesticated

Because dogs are descended from wolves, many of the behaviors and abilities of the wolf are present in the genetic make-up of the domesticated dog (Weston-Ross,1992). What humans have done through selective breeding, particularly in the last 100 years, is to modify the wolf into a variety of breeds shapes and sizes.

Genetics The study of heredity Chromosomes, genes, DNA The transmission of traits

Trait A structure, function, or attribute that makes an individual unique Determined by a genes

Mitosis/Meiosis Interphase Chromosomes replicate

Gregor Mendel Born: 22 July 1822 Birthplace: Hyncice, Moravia (now Czech Republic) Died: 6 January 1884 Best Known As: The founding father of modern genetics

Mendel’s Experiments Studied the traits of ~20,000 pea plants for 8 years Collect data about each plant’s specific traits Applied mathematics (Punnett squares and probability) Result: explained Inheritance

Pea Plant

Pea Plant Fertilization One plant is both male and female Male: pollen (sperm) produced by anther Female: egg produced in pistil

Self-fertilization The pollen from the anther falls into the pistil of the same flower The plant gets the same genetic traits from both of parents Forms purebred offspring

Cross-pollination The pollen from one anther falls into the pistil of a different flower 2 different parents Form hybrid offspring

Offspring Purebred Called pedigreed breeding individuals of unmixed lineage over many generations Parents have same traits Hybrid Genetically dissimilar parents offspring produced by breeding plants or animals of different varieties, species, or races.

Garden Pea Plants Traits exist in 2 forms, easy to observe Reproduce in 90 days (fast) Get results quickly and easily repeatable

Mendel’s Generations P = parents F1 = first filial, first generation of pea plant offspring F2 = second filial, second generation of pea plant offspring

Blending Hypothesis Mendel expected two different traits would blend Ex. Green + yellow = chartreuse offspring NOT VALID!!!

Results of Experiments When he crossed Green + Yellow All offspring were yellow What happened to the green????

Trial 1 In cross-pollinating plants that either produce yellow or green peas exclusively Mendel found that the first offspring generation (f1) always has yellow peas.   However, the following generation (f2) consistently has a 3:1 ratio of yellow to green.

Trial 2

Mendel’s Conclusions The inheritance of each trait is determined by Genes ("units" or "factors“) that are passed on to descendents unchanged      An individual inherits a gene from each parent for each trait A trait may not show up in an individual but can still be passed on to the next generation.

Terms you must know Gene Allele Dominant allele Recessive allele

Genes Made up of DNA Found in the cell nucleus Carries instructions for the development of an organism and all its traits

Allele Any of a number of alternative forms of a gene. A dominant allele will override the traits of a recessive allele in a heterozygous pairing Example In the case of the gene for eye color One allele codes for blue eyes, one for brown eyes, one for green eyes

Traits Many traits are determined by pairs of complementary genes ( 2 genes) Each inherited from a single parent. Often these 2 genes are paired and compared

Dominant allele This allele will turn off the instructions from the recessive gene.

Recessive allele A gene only expressed in the homozygous state When paired with a dominant allele its expression is masked