PedigreesPedigrees
GraphGraph of genetic inheritance of genetic inheritance Similar to a Similar to a family treefamily tree
SymbolsSymbols Square – normal Square – normal malemale Circle – normal Circle – normal femalefemale ShadedShaded square – male showing trait square – male showing trait ShadedShaded circle – female showing trait circle – female showing trait Half-shaded square – male Half-shaded square – male carriercarrier Half-shaded circleHalf-shaded circle – female carrier – female carrier
Simple Recessive HereditySimple Recessive Heredity
Most genetic disorders are Most genetic disorders are recessiverecessive
Must be inherited from Must be inherited from bothboth parentsparents
Common to certain Common to certain ethnicethnic groupsgroups
Cystic fibrosis – CaucasianCystic fibrosis – Caucasian Tay-Sachs Disease – Tay-Sachs Disease –
Ashkenazic JewsAshkenazic Jews Phenylketonuria (PKU) – Phenylketonuria (PKU) –
Norwegian or SwedishNorwegian or Swedish Sickle-cell anemia – African Sickle-cell anemia – African
AmericansAmericans
Simple Dominant HereditySimple Dominant Heredity
Only need a Only need a singlesingle dominant allele that is dominant allele that is inherited from inherited from oneone parent parent Tongue rollingTongue rolling Unattached earlobesUnattached earlobes Brown eyesBrown eyes Hitchhiker’s thumbHitchhiker’s thumb Thick lipsThick lips Almond-shaped eyesAlmond-shaped eyes Huntington’s diseaseHuntington’s disease
Incomplete DominanceIncomplete Dominance
The result of The result of blendingblendingPhenotype is Phenotype is intermediateintermediateExample: Example:
Red snapdragon (R’R’) Red snapdragon (R’R’) x White snapdragon (R”R”) x White snapdragon (R”R”) = Pink snapdragon (R’R”) = Pink snapdragon (R’R”)
CodominanceCodominance
The expression of both The expression of both alleles alleles equallyequally
Two Two differentdifferent uppercase uppercase letters are usedletters are used
Example: white chicken Example: white chicken x black chicken = x black chicken =
black black andand white chicken white chicken (BB x WW = all (BB x WW = all BWBW))
Multiple Phenotypes from Multiple Phenotypes from Multiple AllelesMultiple Alleles
Traits controlled by more than Traits controlled by more than two allelestwo allelesAn organism still only An organism still only has 2 has 2 allelesalleles, BUT , BUT manymany alleles alleles existexistExample: coat color in rabbitsExample: coat color in rabbits
Dark gray (C) is Dark gray (C) is dominantdominant to all to all other colorsother colors
Chinchilla (CChinchilla (Cchch) is dominant to ) is dominant to HimalayanHimalayan and and whitewhite
Himalayan (CHimalayan (Chh) is dominant only to ) is dominant only to whitewhite
white (c) is white (c) is recessiverecessive to all other to all other colorscolors
Blood TypeBlood Type A, B, AB, OA, B, AB, O
Sex DeterminationSex DeterminationAutosomesAutosomes are all are all chromosomes that do chromosomes that do notnot determine sex of individual.determine sex of individual.
2222 pairs pairs
Sex chromosomes Sex chromosomes chromosomes that determine the chromosomes that determine the
sexsex of an individual of an individual make up the make up the 23rd23rd pair of pair of
chromosomes in chromosomes in humanshumansFemales – Females – XXXXMales – Males – XYXY
Sex-linked TraitsSex-linked TraitsTraits that are Traits that are carriedcarried on the sex chromosomes on the sex chromosomesX-linkedX-linked traits can be transferred to males or females traits can be transferred to males or femalesY-linked traits can only be passed down to Y-linked traits can only be passed down to malesmalesExample: color-blindness and hemophilia are Example: color-blindness and hemophilia are X-linkedX-linked
Polygenic TraitsPolygenic TraitsInheritance pattern controlled by Inheritance pattern controlled by 22 or more or more genesgenesMay be on the May be on the samesame or or differentdifferent chromosomes chromosomesEach Each genegene may have may have 22 or more alleles or more allelesUpper and lowercase letters used, but Upper and lowercase letters used, but uppercase does uppercase does notnot indicate indicate dominancedominanceAll All heterozygotesheterozygotes are intermediate are intermediateContinuous Continuous rangerange of variability of variability
ExamplesExamplesheightheight skin colorskin colorEye colorEye color
Environmental InfluencesEnvironmental InfluencesExternal environmentExternal environment: can affect gene : can affect gene expression or expression or phenotypephenotype
Examples: temperature, nutrition, light, and Examples: temperature, nutrition, light, and chemicalschemicals
Internal EnvironmentInternal Environment: absence or : absence or presence of particular presence of particular hormoneshormones, can , can affect the expression of a trait in males affect the expression of a trait in males and femalesand females
Examples: male-pattern baldness, horn size Examples: male-pattern baldness, horn size in sheep, feather color in peacocks in sheep, feather color in peacocks