Download Mendel and His Peas - Welcome to teachers.olatheschools.com!

Mendel and His Peas
Chapter 5, Section 1
Objectives:
Explain the experiments of Gregor Mendel.
2. Explain how genes and alleles are related
to genotypes and phenotypes.
3. Use the information in a Punnett square.
Reading Objective:
1. Summarization
1.
Question

Why does no one else in the world look
exactly like you?
Heredity



definition: the passing of traits from parents
to offspring
How can you have curly hair when both
parents have straight hair?
How can you have blue eyes when both
parents and sisters have brown eyes?
Gregor Mendel


born in 1822
in Heinzendorf, Austria
– knew about plants from
living on a farm
– after school he entered a
monastery as the
gardener
– used plants to study how
traits were passed from
parent to offspring
Garden Peas

Mendel chose to study
garden peas in his
experiments
–
–
grow quickly
self-pollinating

–
plant which contains
both male and female
reproductive structures,
creating the ability for
one flower or plant to
fertilize the eggs of the
same flower or plant
come in many varieties
Traits – Mendel chose to study 1 trait
• round/wrinkled seed shape
at a time
• green/yellow seed color
• purple/white flower color
• green/yellow pod color
• smooth/bumpy pod shape
• axial (along the stem)/terminal
(at the tip) flower position
• tall/short plant height
True-Breeding Plants
 Mendel
only used true-breeding
plants
–
when true-breeding plants selfpollinate, they ALWAYS produce
offspring with the same trait as the
parent
a
tall plant will always produce tall offspring
Cross pollination

method Mendel used to see what would
happen if he bred 2 true-breeding
plants that had different traits
–
–
the anthers of 1 plant are removed so the
plant cannot self-pollinate
the pollen from the other plant is used to
fertilize the plant without anthers
Mendel’s 1st Experiment



looked at seven characteristics
each cross was between 2 traits of each
characteristic
the offspring were referred to as First
Generation
–
Results of the First Generation
 one trait always appeared and the other trait
seemed to disappear
Mendel’s 1st Experiment (cont.)
Mendel called the trait that appeared
the “Dominant Trait”
– Mendel called the trait that
disappeared the “Recessive Trait”
–
Mendel’s 2nd Experiment
 he
allowed the first generation
plants to self-pollinate
–
results of the Second Generation
 the
–

recessive trait showed up again
Mendel counted the number of plants
with each trait that turned up in the
Second Generation
Animation
Characteristic
Dominant Trait
Recessive Trait
Flower Color
705 purple
224 white
Seed Color
6,002 yellow
2,001 green
Seed Shape
5,474 round
1,850 wrinkled
Pod Color
428 green
152 yellow
Pod Shape
882 smooth
299 bumpy
Flower Position
651 along stem
207 at tip
Plant Height
787 tall
277 short
Characteristic
Dominant Trait
Recessive Trait
Flower Color
Ratio 3.15:1
Seed Color
Ratio 3.00:1
Seed Shape
Ratio 2.96:1
Pod Color
Ratio 2.82:1
Pod Shape
Ratio 2.95:1
Flower Position
Ratio 3.14:1
Plant Height
Ratio 2.84:1
705 purple
224 white
6,002 yellow
2,001 green
5,474 round
1,850 wrinkled
428 green
152 yellow
882 smooth
299 bumpy
651 along stem
207 at tip
787 tall
277 short
Results of 2nd Generation
– The
recessive trait showed back
up, but not as often as the
dominant trait.
– All the ratios can be rounded off
to 3:1
three
dominant traits for every one
recessive trait
Brilliant Idea



results could only be explained if each plant
had 2 sets of instructions for each
characteristic
Genes: set of instructions from each parent
Alleles: forms of a gene
Punnett Squares

Punnet Squares: used to visualize the
possible combinations of alleles from parents
–
–

Genotype: the inherited combination of
alleles
–

Dominant alleles = capital letters
Recessive alleles = lower-case letters
the genes you carry
Phenotype: an organism’s physical
appearance
–
the genes you express (show)
How to Make a Punnett Square
1.
2.
3.
4.
Draw a square and divide it into 4 sections.
Write the letters that represent 1 parent/
male parent along the top.
Write the letters that represent the other
parent/ female parent along the side.
Fill in the boxes with 1 allele from each
parent.
Probability

The mathematical chance that an event
will occur.
–
Usually expressed as a fraction or
percentage.
 To
find the probability as a percentage, divide
the numerator by the denominator and then
multiply by 100.