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:

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.

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

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.

Trial 2

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.

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