Transcript Mendel’s Laws of Heredity

Chapter 20:2 NOTES
pages 599-605
Genetics- The Study of
Inheritance
Heredity
 The way traits are passed to you from your
parents
 Traits are physical characteristics
 􀂋 Eye Color 􀂋 Hair Color
 􀂋 Height 􀂋 Weight
 􀂋 Body Structure
 􀂋 Facial Features
 􀂋 Skin Color
Genetics

Genetics= the study of how traits are
passed form parent to offspring
A GENE is a section on DNA
on a chromosome that has
the trait information

Genes
Humans have thousands of
different genes arranged on 23
pairs of chromosomes.

• Genes control all of the traits of organisms—even traits
that can’t be seen, such as the size and shape of your
stomach and your blood type.

Genes provide all of the information needed for growth
and life.
What determines traits?
 One
pair of chromosomes can
contain genes that control many
different traits.
 Each gene on one chromosome of the pair
has a similar gene on the other
chromosome of the pair.
 Each gene of a gene pair is called an allele
(uh LEEL)
 The
genes that make up a gene pair might
or might not contain the same information
about a trait.
 If a pair of chromosomes contains different
alleles for a trait, that trait is called a
hybrid .
 When a trait has two identical alleles, it’s
called pure.
Dominant and Recessive
 Capital
letters are called Dominant alleles.
 When these alleles are present, they take over or show.
They are the “stronger” alleles
 Lower
case letter are recessive alleles and are the “weaker”
of the alleles.
Dominant Alleles
 Dominance
means that one allele covers over or masks
another allele of the trait.


Purple is the dominant flower color in pea plants.
For instance, if a pea plant has one purple-flower allele
and one white-flower allele or two purple-flower alleles, its
flowers will be purple.
 The
dominant allele (purple) is seen
when the trait is hybrid (Dr) or dominant
pure (DD)
Recessive Alleles
• Recessive alleles are seen only when a trait is recessive
pure (rr)
Passing Traits to Offspring
Variation
 Variation-
different ways a trait appears
 Several gene pairs control some traits
 EX- height…..it varies in families
Mutations
A
change in a gene
 Can

happen because an error during meiosis or mitosis
or because of something in the environment
 Whether
a mutation is beneficial, harmful, or neutral, all
mutations add variation to the genes of a species.
Beneficial, Neutral, or Harmful
Beneficial mutation example: resistance to AIDS or to heart
disease
Neutral mutation example: 4 leaf clover
Harmful mutation example: a deformed foot
Selective Breeding


Sometimes, a mutation produces a different version
of a trait that many people find attractive.
To continue this trait, selective breeding is
practiced.
 Examples: 1.
Breeding fast racehorses
2. breeding cattle based on milk production
Homework
 Page 605