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Chapter 20:2 NOTES pages 599-605

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Chapter 20:2 NOTES pages 599-605 Genetics- The Study of Inheritance – PowerPoint PPT presentation

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Title: Chapter 20:2 NOTES pages 599-605


1
Chapter 202 NOTES pages 599-605
  • Genetics- The Study of Inheritance

2
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

3
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

4
Genes
  • Humans have thousands of
  • different genes arranged on 23
  • pairs of chromosomes.
  • Genes control all of the traits of organismseven
    traits that cant 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.

5
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)

6
  • 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, its
    called pure.

7
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.

8
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9
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)

10
Recessive Alleles
  • Recessive alleles are seen only when a trait is
    recessive pure (rr)

11
Passing Traits to Offspring
12
Variation
  • Variation- different ways a trait appears
  • Several gene pairs control some traits
  • EX- height..it varies in families

13
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.

14
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

15
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

16
Homework
  • Page 605
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