chapter 6 fundamentals of genetics. what will we study? 6.1 patterns of inheritance 6.2 principles...
TRANSCRIPT
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:
1. Distinguish between dominant and recessive traits
2. 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.
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 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
1. Traits exist in 2 forms, easy to observe
2. Reproduce in 90 days (fast)
3. 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.
Mendel’s Conclusions
1. The inheritance of each trait is determined by Genes ("units" or "factors“) that are passed on to descendents unchanged
2. An individual inherits a gene from each parent for each trait
3. A trait may not show up in an individual but can still be passed on to the next generation.
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