Complex Patterns of Complex Patterns of HeredityHeredity

Advanced Biology Advanced Biology

DNHSDNHS

Complex Inheritance Complex Inheritance PatternsPatterns

Sometimes the laws and principles of Sometimes the laws and principles of genetics established by Gregor genetics established by Gregor Mendel do not always explain the Mendel do not always explain the inheritance patterns seen in an inheritance patterns seen in an organism.organism.

Incomplete DominanceIncomplete Dominance

The heterozygous or hybrid The heterozygous or hybrid individual will show an intermediate individual will show an intermediate phenotype between the two phenotype between the two homozygous individualshomozygous individuals

Example – Snap Dragons flower color Example – Snap Dragons flower color red crossed with white = red crossed with white = pinkpink

R = redR’ = white

R R

R’R’

R’ R

R’R

RR’

RR’RR’ RR’

RR’ RR RR’

R’R’

Genotype: Genotype:

Phenotype: Phenotype:

All RR’ hybrid

All pink

¼ RR; ½ RR’; ¼ R’R’¼ red; ½ pink; ¼ white

CodominanceCodominance The heterozygous individual will show the The heterozygous individual will show the

phenotypes of each of the homozygous phenotypes of each of the homozygous individualsindividuals

Example – chickens, Example – chickens, black+white=checkered (black and black+white=checkered (black and white)white)

Multiple AllelesMultiple Alleles Situation wherein there exists more Situation wherein there exists more

than two alleles for a specific trait.than two alleles for a specific trait. Example – Blood type in humans (A, Example – Blood type in humans (A,

B, O alleles)B, O alleles)

Sex Linked TraitsSex Linked Traits When a trait is seen in one sex more When a trait is seen in one sex more

often than another due to a gene often than another due to a gene that is carried on one of the sex that is carried on one of the sex chromosomeschromosomes

Examples – eye color in fruit flies and Examples – eye color in fruit flies and hemophilia and color blindness in hemophilia and color blindness in humanshumans

Polygenic InheritancePolygenic Inheritance

When a trait is influenced by many When a trait is influenced by many genesgenes

Tends to be a wide range of Tends to be a wide range of phenotypic variationphenotypic variation

Examples: skin color, hair color, Examples: skin color, hair color, height in humansheight in humans

A situation in which there is an A situation in which there is an individual of unknown genotype individual of unknown genotype

To determine the genotype you To determine the genotype you would cross it with a pure recessive would cross it with a pure recessive individualindividual

Test CrossesTest Crosses

PedigreePedigree A graphic A graphic

genetic genetic family tree family tree that follows that follows a trait a trait through through several several generationsgenerations

AneuploidyAneuploidy

A condition of having an abnormal A condition of having an abnormal chromosome numberchromosome number

Example – Down’s Syndrome, Sex Example – Down’s Syndrome, Sex Chromosome Aneuploidies (Turner Chromosome Aneuploidies (Turner Syndrome)Syndrome)