Complex Patterns of Inheritance

Sickle-cell anemiaAutosomal recessive trait1 in 12 African Americans (black

Americans whose families originated in Africa) is heterozygous (carrier)

Common in white Americans whose families originated in the countries surrounding the Mediterranean Sea

• Person suffers from anemia (low # rbc)• Abnormally shaped cells slow blood flow,

block small vessels, and results in tissue damage and pain

• Have other serious health problems because of the impaired circulation

• Treatments – blood transfusion and drug therapy

Sex Determination

Sex chromosomes determine an individual’s gender.

•Humans have 23 pair (46 total) of chromosomes in each of somatic cells

•22 are autosomes•The 23rd pair are sex

chromosomesXX = femaleXY = male

Dosage Compensation

• The X chromosome carries a variety of genes that are necessary for the development of both females and males.

• The Y chromosome mainly has genes that relate to the development of male characteristics.

Chromosome InactivationChromosome Inactivation- random

inactivation of the X chromosome. Example – calico catOne X chromosome codes for orange fur

and one X chromosome codes for black fur.

Sex linked traits• Sex-linked traits (X-linked)- traits controlled by

genes located on the X chromosome.• X-linked inheritance - passed on by the female

– even if recessive, the trait is expressed because the male does not pass an X for a dominant allele.

Ex: Color blindness and hemophilia

Muscular dystrophy is a deadly disorder in which the muscles grow progressively weaker. The disease is caused by a recessive gene on the X chromosome

Polygenic Inheritance

Polygenic Inheritance- pattern of a trait that is controlled by two or more genes

Genes may be on the same chromosome or different chromosome

All heterozygotes are intermediate in phenotype

Polygenic InheritanceInheritance pattern of a trait that is controlled by

two or more genesSkin color, eye colorWill express a range of colors (intermediate)

Environmental InfluencesThe environment also has an effect on

phenotype. As organisms develop many factors influence how genes will be expressed

2 environmental influences• Internal environment-Male and females

express traits differently due to hormones-Horn size in rams, feather color in peacocks-Age affects how genes function

• External environment-Temperature, nutrition, light, chemicals, and infectious agents