Inheritance Patterns Inheritance patterns Whether a trait is

Inheritance Patterns

Inheritance patterns • Whether a trait is dominant or recessive DOES NOT have anything to do with how common it is.

Inheritance patterns • Whether a trait is dominant or recessive DOES NOT have anything to do with how common it is. • Eg – straight hair is the most common type in Asia, but it is a recessive genotype.

Inheritance patterns • Whether a trait is dominant or recessive DOES NOT have anything to do with how common it is. • Eg – straight hair is the most common type in Asia, but it is a recessive genotype. • In inheriting a trait: - Two recessives crossed can produce only recessive offspring.

Inheritance patterns • Whether a trait is dominant or recessive DOES NOT have anything to do with how common it is. • Eg – straight hair is the most common type in Asia, but it is a recessive genotype. • In inheriting a trait: - Two recessives crossed can produce only recessive offspring. - Two dominants crossed can produce both dominant and recessive offspring if both parents are heterozygous.

Inheritance patterns • Whether a trait is dominant or recessive DOES NOT have anything to do with how common it is. • Eg – straight hair is the most common type in Asia, but it is a recessive genotype. • In inheriting a trait: - Two recessives crossed can produce only recessive offspring. - Two dominants crossed can produce both dominant and recessive offspring if both parents are heterozygous. • Complete activity 2 D

Test cross • Individuals which are heterozygous may be called carriers, because they carry the recessive allele which is masked by the dominant allele so is not expressed in the phenotype.

Test cross • Individuals which are heterozygous may be called carriers, because they carry the recessive allele which is masked by the dominant allele so is not expressed in the phenotype. • For breeding purposes, heterozygotes are not desirable because the recessive can pair up and create a recessive offspring – therefore they are NOT pure breeders

Test cross • Individuals which are heterozygous may be called carriers, because they carry the recessive allele which is masked by the dominant allele so is not expressed in the phenotype. • For breeding purposes, heterozygotes are not desirable because the recessive can pair up and create a recessive offspring – therefore they are NOT pure breeders • Animal breeders often need to find out whether an individual showing the dominant phenotype is homozygous (pure-breeder) or heterozygous.

Test cross • Individuals which are heterozygous may be called carriers, because they carry the recessive allele which is masked by the dominant allele so is not expressed in the phenotype. • For breeding purposes, heterozygotes are not desirable because the recessive can pair up and create a recessive offspring – therefore they are NOT pure breeders • Animal breeders often need to find out whether an individual showing the dominant phenotype is homozygous (pure-breeder) or heterozygous. • To find this out, the individual is crossed with a homozygous recessive individual.

Example of a test cross • Rabbits may have brown hair or white hair. Brown is dominant (therefore may be BB or Bb) – but we can’t tell. White hair is recessive (therefore bb)

Example of a test cross • Rabbits may have brown hair or white hair. Brown is dominant (therefore may be BB or Bb) – but we can’t tell. White hair is recessive (therefore bb) • Firstly we cross Bb x bb B b b Bb bb • This shows that 50% will be brown and 50% white so parent is not pure breeding.

Example of a test cross • Now we try again • Cross BB x bb B B b Bb Bb • All offspring are brown = this parent can be used for breeding. *Now complete 2 E*