Other Patterns of Other Patterns of InheritanceInheritance

Think About It!Think About It!

What is a pattern? What is a pattern? Give an example.Give an example.

What is inheritance?What is inheritance?

Cross TypesCross Types

A cross represents the transfer of A cross represents the transfer of genetic material from one organism to genetic material from one organism to another.another. This an be illustrated by a Punnett squareThis an be illustrated by a Punnett square

The square is used to The square is used to predictpredict the results of a the results of a cross.cross.

Is named for the British geneticist Reginald Is named for the British geneticist Reginald Punnett.Punnett.

Show all the possible gamete combinations.Show all the possible gamete combinations.

Cross TypesCross Types

Monohybrid crossesMonohybrid crosses Focuses on only Focuses on only

one trait.one trait. The Punnett The Punnett

square for this square for this type of cross has type of cross has four boxes.four boxes.

Cross TypesCross Types

The ratio of a The ratio of a homozygous homozygous monohybrid monohybrid cross is 100% cross is 100% KEY:KEY:B- black coatB- black coatb- brown coatb- brown coat

BB BB

bb BbBb BbBb

bb BbBb BbBb

Cross TypesCross Types

The ratio of a The ratio of a heterozygous heterozygous monohybrid monohybrid cross is 3:1.cross is 3:1.KEY:KEY:B- black coatB- black coatb- brown coatb- brown coat

BB bb

BB BBBB BbBb

bb BbBb bbbb

Cross TypesCross Types

Dihybrid crossesDihybrid crosses Focus on two Focus on two

traits.traits. The Punnett The Punnett

square for this square for this type of cross has type of cross has sixteen boxes.sixteen boxes.

The ratio of a The ratio of a heterozygous heterozygous dihybrid cross is dihybrid cross is 9:3:3:1.9:3:3:1.

Other Patterns of InheritanceOther Patterns of Inheritance

Many genes do not follow Mendel’s Many genes do not follow Mendel’s patterns of inheritance.patterns of inheritance.

Factors that can influence heredity includeFactors that can influence heredity include Incomplete dominanceIncomplete dominance Co-dominanceCo-dominance Multiple AllelesMultiple Alleles Polygenic traitsPolygenic traits Environmental conditionsEnvironmental conditions

Incomplete DominanceIncomplete Dominance

The offspring The offspring exhibits a trait that exhibits a trait that is an intermediate is an intermediate form of the parent’s form of the parent’s traits.traits.

The phenotype is a The phenotype is a blend of the two blend of the two homozygous homozygous phenotypes.phenotypes.

Co dominance Co dominance

Two traits in a Two traits in a heterozygote are heterozygote are fully expressed.fully expressed.

Co dominance Co dominance

Multiple AllelesMultiple Alleles

Some traits are Some traits are controlled by genes controlled by genes that have two or that have two or more alleles.more alleles.

Multiple allele traits Multiple allele traits are hair and eye are hair and eye color.color.

Polygenic TraitsPolygenic Traits

Are traits that are controlled by more Are traits that are controlled by more than one pair of genes.than one pair of genes.

Examples include height, weight, and Examples include height, weight, and skin color.skin color.

Polygenic TraitsPolygenic Traits

Environmental conditionsEnvironmental conditions

An individual’s An individual’s phenotype often phenotype often depends on the depends on the surrounding surrounding environment.environment.

Examples: arctic fox Examples: arctic fox and hareand hare