Observing Patterns in Inherited Traits Chapter 7

Skin Color

Terms Used in Modern Genetics Heredity- characteristics passing from parents to offspring through genes Heredity- characteristics passing from parents to offspring through genes Genes Genes Each gene has a specific locus on a chromosome Each gene has a specific locus on a chromosome Heterozygous (Aa or Bb) Heterozygous (Aa or Bb) Homomzygous (AA or BB) Homomzygous (AA or BB)

Gregor Mendel

Genetics An allele is dominant if its effect masks the effect of a recessive allele paired with it An allele is dominant if its effect masks the effect of a recessive allele paired with it

Mendel’s Law of Segregation Only one of the 2 alleles gets put into each gamete Only one of the 2 alleles gets put into each gamete

Fig. 11-5, p. 172 homozygous dominant parent homozygous recessive parent (chromosomes duplicated before meiosis) meiosis I meiosis II (gametes) fertilization produces heterozygous offspring Segregation of Alleles at a Gene Locus

genotype phenotype

Construction of a Punnett Square  Punnett square

Dihybrid Cross 2 loci 2 loci AABB x aabb AABB x aabb F 2 phenotype ratio is 9:3:3:1 F 2 phenotype ratio is 9:3:3:1

Mendel’s Law of Independent Assortment Mendel’s law of independent assortment Mendel’s law of independent assortment One trait does not influence the inheritance of the other One trait does not influence the inheritance of the other Exception: linked genes Exception: linked genes

Fig. 11-9a, p. 175 parent plant homozygous for purple flowers and long stems parent plant homozygous for white flowers and short stems AABB aabb AB x ab

Fig. 11-9b, p. 175 What gametes will they form? AaBb F 1 generation

Fig. 11-9c, p. 175 AB Ab aB ab ABAABBAABbAaBBAaBb Ab AABbAAbbAaBbAabb aB AaBBAaBb aaBB aaBb ab AaBbAabbaaBbaabb D Out of 16 possible genetic outcomes of this dihybrid cross, 9 will result in plants that are purple-flowered and tall; 3, purple-flowered and short; 3, white-flowered and tall; and 1, white-flowered and short. The ratio of phenotypes of this dihybrid cross is 9:3:3:1.

Codominance Two nonidentical alleles of a gene are both fully expressed in heterozygotes, so neither is dominant or recessive Two nonidentical alleles of a gene are both fully expressed in heterozygotes, so neither is dominant or recessive Multiple allele systems Multiple allele systems

Incomplete Dominance One allele is not fully dominant over its partner One allele is not fully dominant over its partner

Epistasis Epistasis Epistasis Two or more gene products influence a trait Two or more gene products influence a trait Typically, one gene product suppresses the effect of another Typically, one gene product suppresses the effect of another

Epistasis in Coat Colors

Pleiotropy Pleiotropy Pleiotropy One gene product influences two or more traits One gene product influences two or more traits Example: Marfan syndrome Example: Marfan syndrome

Genes and the Environment Expression of some genes is affected by environmental factors such as temperature, altitude, or chemical exposure Expression of some genes is affected by environmental factors such as temperature, altitude, or chemical exposure