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8.1 OBJECTIVES
Discuss Mendel’s experiments and his results.
Explain the three principles of genetics Mendel obtained through his experiments.
Solve genetics problems using Punnett Squares.
8.1 PRINCIPLES OF GENETICS
Discuss Mendel’s experiments and results. Explain the three principles of genetics
Mendel obtained through his experiments. Solve genetics problems using Punnett
squares.
PRINCIPLES OF GENETICS
The passing of traits from parents to offspring is termed heredity.
Can we predict certain traits? Can we determine what types of genetic
information parents have by looking at certain traits of the offspring?
We can answer these questions through genetics – the science of heredity.
ORIGIN OF GENETICS
Father of genetics: Gregor Mendel (1882-1884)
Tended to a garden of pea plants in a monastery.
Published results from 8 years of research, only to be ignored until 1900.
MENDEL’S EXPERIMENTS
Peas are grown easily and produce large numbers of offspring in a short time.
Chose 7 traits to study:
Seed Shape
Seed Color
Flower Color
Flower Position
Pod Color
Pod Shape
Plant Height
Dominant Trait
Round Yellow
Purple Axial (side) Green Inflated Long
Recessive Trait
Wrinkled Green
White Terminal (tips)
Yellow Constricted Short
MENDEL’S PROCESS
Mendel crossed pea plants w/ different traits. Offspring of parental cross were called F1
Offspring of F1 crosses called F2. He noted for each trait, there was a dominant
and recessive form. In his crosses, recessive trait disappeared in
F1 generation and then reappeared in F2.
MENDEL’S HYPOTHESIS
He reasoned that for every trait, there must be a pair of factors.
He called them characters, but we now know them as genes.
One gene came from each parent.
THE TEST OF SEGREGATION
He predicted if the F1 purple flowered plants were crossed with white flowered plants, he would get ratios different from any of his previously obtained ratios.
TERMINOLOGY
Each alternative form of a gene for a certain trait are called alleles.
Combination of genes for a given trait referred to as genotype. Example: WW and Ww
The physical appearance of a trait is the phenotype. Example: Blue and brown eyes.
Homozygous = two of same alleles: WW or ww (homozygous dominant and homozygous recessive)
Heterozygous = two different alleles: Ww
8.2 SOLVING GENETICS PROBLEMS
Objectives: Apply the rules of probability to solve
genetics problems. Demonstrate the inheritance of traits
resulting from incomplete dominance, codominance, and multiple alleles.
PROBABILITY
What is the probability of getting heads or tails when you toss a coin?
There is a list of steps to follow on page 208 in text, but we have already been doing this.
Remember, we can find either genotypic or phenotypic ratios.
8.3 THE CHROMOSOME THEORY OF HEREDITY
Walter Sutton’s work showed good evidence that genes reside on chromosomes.
Some genes appear only on sex chromosomes.
XX = female and XY = male in humans. Different combinations for different species. Example: Grasshoppers X = male and YY =
female. Sex-linked traits are traits that result from
genes on the sex chromosomes.
SEX-LINKED TRAITS IN HUMANS
Hemophilia – gene is a recessive gene found on the X chromosome. Mostly, males get the disease.
Color-blindness is the same way.