Chapter 8- Mendel And Heredity

1
Chapter 8- Mendel And Heredity
2
I. The origins of Genetics

• A. The passing of traits from parents to
  offspring is called heredity.
•  
• 1. Mendel was a mathematician and looked at
  genetics differently than anyone in the past ever
  did.

3

• 2. Genetics is the branch of biology that
  focuses on heredity.
•  
• 3. Mendel counted the number of each kind of
  offspring and analyzed the data.
• 4. Quantitative approaches to science-those
  that include measuring and counting.

4
(No Transcript)
5
B. Useful features in peas

•   1. The garden pea is a good subject for
  studying heredity for several reasons.

6

• a. The garden pea has many traits that have
  two clearly different forms that are easy to tell
  apart.
•  
• b. The mating of the garden pea flowers can be
  easily controlled.
•  
• c. The garden pea is small, grows easily,
  matures quickly and produces many offspring.

7
(No Transcript)
8

• C. Mendel observed that traits are expressed as
  simple ratios
•  
• 1. Mendels initial experiments were
  monohybrid crosses. A cross with ONE pair of
  contrasting traits.
•  
• 2. Mendel allowed true breeding or
  self-pollination to occur.

9
(No Transcript)
10

• 3. These true-breeding plants served as the
  parental generation in Mendels experiments.
•  
• 4. The parental generation, or P generation are
  the first two individuals that are crossed.

11

• 5. Mendel crossed the P generation to get the
  F1 generation. First generation. He then
  examined each F1 plant and recorded the number of
  F1 plants and their traits.
•  
• 6. Mendel then mated the F1 generation to get a
  F2 generation. The second generation and then
  again examined each of their traits.

12

• Mendels results.
• 1. See page 162 figure 8.4

13
II. Mendels theory

• A. Mendels work became a theory of heredity.
•  
• 1. The four hypotheses Mendel developed were
  based directly on the result of his experiments.

14

• a. For each inherited trait, an individual
  has two copies of genes- one from each parent.
•  
• b. There are alternative versions of genes.
  These are called alleles.

15

• c. When two different alleles occur together,
  one of them bay be completely expressed, while
  the other may have no affect on the appearance.
  Mendel explained these to be dominant and
  recessive.
•  
• d. When gametes are formed, the alleles for
  each gene in an individual separate independently
  of one another.

16

• B. Mendels findings in modern terms
•  
• 1. If two traits are the same they are called
  homozygous.
•  
• 2. If two traits are different they are called
  heterozygous.

17

• 3. Dominant genes are expressed with capital
  letters.
•  
• 4. Recessive genes are expressed with lower
  caps.
•  
• 5. Example Brown is dominant B, blue is
  recessive b.
•  
• 6. A set of alleles that an individual has is
  called the genotype.

18

• 7. What the individual expresses is called the
  phenotype.
•  
• 8. Example BB, Bb and bb are genotypes.
•  
• 9. BB, and Bb would have brown eyes, and bb
  would have blue eyes. The colors are the
  phenotypes.

19

• B. Mendels Ideas gave rise to the laws of
  heredity.
•  
• 1. The first law, the law of segregation,
  states that the two alleles for a trait segregate
  or separate when gametes are formed.

20

• 2. The law of independent assortment states
  that the alleles of different genes separate
  independently of one another during gamete
  formation.

21
II. Studying heredity

• A. Punnet squares- see board.

22

• B. Probability on the board.

23
(No Transcript)
24

• C. Pedigrees on the board.

25

• D. Sex linked traits on board.

26
(No Transcript)
27
(No Transcript)
28
(No Transcript)
29
III. Patterns of Heredity can be complex

• A. Traits influenced by several genes
•  
• 1. When several genes influence a trait, the
  trait is said to be polygenetic.

30

• 2. In some traits there is neither dominant nor
  recessive genes. These are called incomplete
  dominance. Example Red flower RR and a White
  WW flower both with incomplete dominance will
  have pink flowers.

31
(No Transcript)
32

•  3. When two dominant alleles are expressed at
  the same time, both forms of the trait are
  displayed this is called co dominance. Example
  Coat colors in a horse.
• 4. Genes with three or more alleles are said to
  have multiple alleles. Example blood groups ABO.

33
1.      Genotypes Phenotypes IAIA A IAIo
A IBIB B IBIo BIAIB AB IoIo O
34

• 5. An individuals phenotype often depends on
  conditions in the environment.
• 6. Some traits are affected by the temperature,
  sunlight or seasons.
• 7. In humans the environment influences height.
  Height is influenced by nutrition, an internal
  environment conditions.

35

• B. Some traits are caused by mutations
•  
• 1.      Sickle cell anemia is a recessive genetic
  disorder caused by a mutated allele that produces
  a defected form of the protein hemoglobin.
•  
• 2.      Hemophilia is a recessive genetic
  disorder that impairs the bloods body to clot.

36

• 3. Huntingtons disease is a genetic disorder
  caused by a DOMINANT allele. The symptoms do not
  appear until the victim is in their 30s or 40s.
  This disease caused severe mental illness and
  eventually death.
•  
• 4. Most genetic disorders cannot be cured, but
  progress is being made

37

• 5. There is genetic testing to detect any bad
  genes.
•  
• 6. Gene technology may soon by replacing
  defected genes with copies of healthy ones this
  is called gene therapy.