Patterns of Heredity and Patterns of Heredity and Human GeneticsHuman Genetics

Chapter 11Chapter 11

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