7th Grade Life Science
Mr. Fisk
Chapter 4 - Genetics: The Science of Heredity
Engage – 1. Who has different colored eyes than
their parents?
Objectives:
1. Describe the results of Mendel’s experiment.
2. Identify what controls the inheritance of traits
in organisms.
4-1 – Mendel’s Work
A. Introduction
1. Heredity – passing of physical
characteristics from parents to offspring.
2. Trait – different characteristics.
Ex. Height, color, etc.
3. Genetics - scientific study of heredity.
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7th Grade Life Science
Mr. Fisk
B. Mendel’s Experiment
1. Crossing Pea Plants
 Purebred – offspring of many
generations that have the same traits.
 F1 Offspring –
Tall Plants crossed with Short Plants
Parental generation or P Generation.
Offspring – first filial generation or
F1 Generation
Filial – filia or filius latin for “daughter”
and “son”.
 F2 Offspring – offspring of F1
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7th Grade Life Science
Mr. Fisk
 Experiments with other Traits
In all Mendels’ crosses, only one form
of the trait appeared in the F1
generation – However, in the F2
generation the “lost” form of the trait
always reappeared in about ¼ of the
plants.
2. Pea Plants
P Generation – Tall X Short
F1 Generation – Tall X Tall
F2 Generation - Tall, Tall, Tall, Short
75%
25%
C. Dominant & Recessive Alleles
1. Genes – factors that control a trait.
2. Alleles – different forms of a gene.
Pairs – 1 from Egg – 1 from Sperm
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7th Grade Life Science
Mr. Fisk
3. An organism’s traits are controlled by
the alleles it inherits from its parents.
Some alleles are dominant, while
others are recessive.
4. Dominant Alleles – always show up.
5. Recessive Allele – hidden whenever
the dominant allele is present.
 See Fig. 3 Page 113
6. Alleles in Mendels’ Crosses
 P generation
Tall = TT
Short = tt
 F1 Generation
Tt = Tall – Hybrids – organism
having 2 different alleles for a trait.
 F2 Generation
TT = Tall
Tt = Tall
Tt = Tall
tt = Short
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7th Grade Life Science
Mr. Fisk
7. Symbols for Alleles
 Dominant Allele = T
 Recessive Allele = t
 Ex. Rabbits – Black fur dominates
over white. B = Black – b = White
8. Significance of Mendel’s Contribution
 Before Mendel – traits of individuals
simply a blend of their parents
characteristics.
 Mendel – demonstrated that parents
traits do not simply blend in the
offspring – Traits determined by
individual alleles.
 Mendel – “Father of Genetics”
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