Patterns of Heredity Patterns of Heredity Can Be ComplexCan Be Complex

Section 8-4Section 8-4

Most Traits Are Not Controlled Most Traits Are Not Controlled by Simple Dominant-Recessive by Simple Dominant-Recessive

AllelesAlleles►Some traits display more complex Some traits display more complex

patterns of heredity than the simple patterns of heredity than the simple dominant-recessive patterns discusseddominant-recessive patterns discussed

Traits Influenced by Several Traits Influenced by Several GenesGenes

►Polygenic traitPolygenic trait – when several genes – when several genes influence a traitinfluence a trait

►The genes for a polygenic trait may be The genes for a polygenic trait may be scattered along the same chromosome or scattered along the same chromosome or located on different chromosomes.located on different chromosomes.

►Determining the effect of any one of Determining the effect of any one of these genes is difficult. Due to these genes is difficult. Due to independent assortment and crossing-independent assortment and crossing-over, many combinations appear in over, many combinations appear in offspring.offspring.

►Human polygenic traits – eye color, height Human polygenic traits – eye color, height , weight, hair color, and skin color, weight, hair color, and skin color

Intermediate TraitsIntermediate Traits

► Incomplete Dominance – when an Incomplete Dominance – when an individual displays a trait that is individual displays a trait that is intermediate between two parentsintermediate between two parents

Ex: Red snapdragon crossed with Ex: Red snapdragon crossed with white snapdragon – not red nor white, white snapdragon – not red nor white, but pinkbut pink

Traits with Two Forms Displayed Traits with Two Forms Displayed at the Same Timeat the Same Time

►CodominanceCodominance – when two dominant – when two dominant alleles are expressed at one timealleles are expressed at one time

►Different from incomplete dominance in Different from incomplete dominance in that both traits are displayed, not the that both traits are displayed, not the two traits being mixedtwo traits being mixed

►Ex: Roan color in horses: Red hair Ex: Roan color in horses: Red hair parent and white hair parent, offspring parent and white hair parent, offspring has red and white hair or roan color has red and white hair or roan color hairhair

Traits controlled by Genes with Traits controlled by Genes with Three or More AllelesThree or More Alleles

►Multiple Alleles – genes with three or Multiple Alleles – genes with three or more allelesmore alleles

►Ex: ABO blood groups/blood typesEx: ABO blood groups/blood typesDetermined by 3 alleles – IDetermined by 3 alleles – IAA, I, IBB, i, i

Letters A and B refer to a carbohydrate Letters A and B refer to a carbohydrate on the surface of the red blood cell. The on the surface of the red blood cell. The letter i means there is no carbohydrate letter i means there is no carbohydrate present. A and B are dominant over i, but present. A and B are dominant over i, but neither A nor B is dominant over the neither A nor B is dominant over the other. When they are both present, they other. When they are both present, they are codominant. Only 4 blood types – A, are codominant. Only 4 blood types – A, B, AB, OB, AB, O

Traits Influenced by the Traits Influenced by the EnvironmentEnvironment

►Phenotype can be influenced by the Phenotype can be influenced by the environmentenvironment

►Hydrangeas – blue if in acidic soil, pink Hydrangeas – blue if in acidic soil, pink if in basic soilif in basic soil

►Arctic Fox – changes coat color in Arctic Fox – changes coat color in seasons (temperature)seasons (temperature)

Some traits are Caused by Some traits are Caused by MutationsMutations

► In order for a person to develop and In order for a person to develop and function normally, the proteins encoded by function normally, the proteins encoded by his or her genes must function precisely.his or her genes must function precisely.

►Sometimes genes are damaged or copied Sometimes genes are damaged or copied incorrectly, resulting in faulty proteins.incorrectly, resulting in faulty proteins.

►Changes in genetic material are called Changes in genetic material are called mutationsmutations..

►Mutations are rare because most of the Mutations are rare because most of the time the body can correct them, but time the body can correct them, but sometimes they may have harmful effects.sometimes they may have harmful effects.

►The harmful effects produced by The harmful effects produced by inherited mutations – inherited mutations – genetic genetic disordersdisorders

►Many mutations are carried by Many mutations are carried by recessive allelesrecessive alleles

►Two phenotypically normal people who Two phenotypically normal people who are heterozygous carriers of a are heterozygous carriers of a recessive mutation can produce recessive mutation can produce children who are homozygous for the children who are homozygous for the recessive allele.recessive allele.

Sickle Cell AnemiaSickle Cell Anemia

►Condition caused by a mutated allele Condition caused by a mutated allele that produces a defective form of the that produces a defective form of the protein hemoglobinprotein hemoglobin

►Causes red blood cells to bend into a Causes red blood cells to bend into a sickle shapesickle shape

►Red blood cells that are sickle rupture Red blood cells that are sickle rupture easilyeasily

►Results in less oxygen being carried by Results in less oxygen being carried by the bloodthe blood

►Tend to get stuck in blood vessels, so Tend to get stuck in blood vessels, so can cut off supply of blood to organscan cut off supply of blood to organs

Sickle Cell AnemiaSickle Cell Anemia

►The recessive allele that causes sickle-The recessive allele that causes sickle-shaped RBC also helps protect cells of shaped RBC also helps protect cells of heterozygous individuals from effects heterozygous individuals from effects of malaria.of malaria.

►Cause death of the parasite that Cause death of the parasite that causes malariacauses malaria

HemophiliaHemophilia

►A condition that impairs the blood’s A condition that impairs the blood’s ability to clotability to clot

►Sex-linked traitSex-linked trait

Huntington’s DiseaseHuntington’s Disease

►Caused by a dominant allele located Caused by a dominant allele located on an autosomeon an autosome

►Begins in thirties and forties with mild Begins in thirties and forties with mild forgetfulness and irritabilityforgetfulness and irritability

►Causes loss of muscle control, Causes loss of muscle control, uncontrollable physical spasms, severe uncontrollable physical spasms, severe mental illness, and eventually deathmental illness, and eventually death

Detecting and Treating Genetic Detecting and Treating Genetic DisordersDisorders

►Most genetic disorders cannot be Most genetic disorders cannot be cured, although progress is being cured, although progress is being mademade

►Can undergo genetic counseling – form Can undergo genetic counseling – form of medical guidance that informs of medical guidance that informs people about genetic problems that people about genetic problems that could affect them or their offspringcould affect them or their offspring

Phenylketonuria (PKU)Phenylketonuria (PKU)

►Lack an enzyme that converts the Lack an enzyme that converts the amino acid tyrosineamino acid tyrosine

►Phenylalanine builds up in the body Phenylalanine builds up in the body and causes severe mental retardation and causes severe mental retardation

► If newborn is diagnosed soon after If newborn is diagnosed soon after birth, the newborn is placed on a low-birth, the newborn is placed on a low-phenylalanine diet, ensuring that the phenylalanine diet, ensuring that the baby will get enough phenylalanine to baby will get enough phenylalanine to make proteins, but not enough to make proteins, but not enough to cause enough damage.cause enough damage.