Genetics

1
Chapter 7

• Genetics

2
Mendels Experiments and Laws of Inheritance

• Hugo deVries 1830, Blending inheritance in
  Primrose.
• Mendel results refuted blending inheritance
  hypothesis When the F1 offspring were
  self-pollinated, the F2 generation showed a 31
  phenotypic ratio, with the recessive phenotype
  present in one-fourth of the offspring.
  Reappearance of the recessive phenotype refuted
  the blending hypothesis.

3
Mendels Experiments and Laws of Inheritance

• Because some alleles are dominant and some are
  recessive, the same phenotype can result from
  different genotypes.
• Homozygous genotypes have two copies of the same
  allele heterozygous genotypes have two different
  alleles. Heterozygous genotypes yield phenotypes
  showing the dominant trait.

4
Mendels Experiments and Laws of Inheritance
Monohybrid Cross

• Law of Segregation Mendel first law is that the
  units of inheritance (genes) are particulate,
  there are two copies (alleles) of each gene in
  every parent, and during gamete formation the two
  alleles for a character segregate from each
  other.

5
Mendels Experiments and Laws of Inheritance

• Mendels 2nd Law The Law of Independent
  Assortment From studies of the simultaneous
  inheritance of two characters, Mendel concluded
  that alleles of different genes assort
  independently.

6
Using Mendelian Genetics as a Predictor
7
Beyond Mendelian Inheritance
Incomplete Dominance

• Appears as blending inhertence
• Both alleles are expressed
• Results in intermediate phenotypes of
  heterozygotes

8
figure 10-14.jpg
Co-Dominance When alleles are both expressed in
the heterozygous form.
9
Gene Interactions

• Epistasis the products of different genes
  interact to produce a phenotype. One gene masks
  or otherwise affects the expression of another.

10
Alleles and Their Interactions

• Multiple Alleles lead to diversity of potential
  phenotypes
• New alleles arise by mutation, and many genes
  have multiple alleles.

5 phenotypes 10 genotypes
11
Gene Interactions

• Polygenic Inheritance the phenotype is the
  result of the additive effects of several genes.
• Produces a range of continuum in phenotypes

12
Sex Determination and Sex-Linked Inheritance

• In fruit flies and mammals, the X chromosome
  carries many genes, but the Y chromosome has only
  a few. Males have only one allele for most
  X-linked genes, so rare alleles appear
  phenotypically more often in males.

13
figure 10-26.jpg
Pedigree for red/green color blindness X-linkage

• Appears more often in males
• A male can pass only to daughters
• Females can be heterozygous carriers

Figure 10.26