Patterns of Heredity and Human Genetics Chapter 11

Pedigrees Graph of genetic inheritance Similar to a family tree Similar to a family treeSymbols Square – normal male Square – normal male Circle – normal female Circle – normal female Shaded square – male showing trait Shaded square – male showing trait Shaded circle – female showing trait Shaded circle – female showing trait Half-shaded square – male carrier Half-shaded square – male carrier Half-shaded circle – female carrier Half-shaded circle – female carrier

Simple Recessive Heredity Most genetic disorders are recessive Must be inherited from both parents Common to certain ethnic groups Cystic fibrosis – Caucasian Tay-Sachs Disease – Ashkenazic Jews Phenylketonuria (PKU) – Norwegian or Swedish Sickle-cell anemia – African Americans

Simple Dominant Heredity Only need a single dominant allele that is inherited from one parent Tongue rolling Tongue rolling Unattached earlobes Unattached earlobes Brown eyes Brown eyes Hitchhiker’s thumb Hitchhiker’s thumb Thick lips Thick lips Almond-shaped eyes Almond-shaped eyes Huntington’s disease Huntington’s disease

Incomplete Dominance The result of blending Phenotype is intermediate 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”)

Codominance The expression of both alleles equally Two different uppercase letters are used Example: white chicken x black chicken = black and white chicken (BB x WW = all BW)

Multiple Phenotypes from Multiple Alleles Multiple Phenotypes from Multiple Alleles Traits controlled by more than two alleles An organism still only has 2 alleles, BUT many alleles exist Example: coat color in rabbits Dark gray (C) is dominant to all other colors Dark gray (C) is dominant to all other colors Chinchilla (C ch ) is dominant to Himalayan and white Chinchilla (C ch ) is dominant to Himalayan and white Himalayan (C h ) is dominant only to white Himalayan (C h ) is dominant only to white white (c) is recessive to all other colors white (c) is recessive to all other colors Blood Type A, B, AB, O A, B, AB, O

Sex Determination Autosomes are all chromosomes that do not determine sex of individual. 22 pairs 22 pairs Sex chromosomes chromosomes that determine the sex of an individual chromosomes that determine the sex of an individual make up the 23rd pair of chromosomes in humans make up the 23rd pair of chromosomes in humans Females – XX Males – XY

Sex-linked Traits Traits that are carried on the sex chromosomes X-linked traits can be transferred to males or females Y-linked traits can only be passed down to males Example: color-blindness and hemophilia are X-linked

Polygenic Traits Inheritance pattern controlled by 2 or more genes May be on the same or different chromosomes Each gene may have 2 or more alleles Upper and lowercase letters used, but uppercase does not indicate dominance All heterozygotes are intermediate Continuous range of variability Examples Examplesheight skin color Eye color

Environmental Influences External environment: can affect gene expression or phenotype Examples: temperature, nutrition, light, and chemicals Examples: temperature, nutrition, light, and chemicals Internal Environment: absence or presence of particular hormones, can affect the expression of a trait in males and females Examples: male-pattern baldness, horn size in sheep, feather color in peacocks Examples: male-pattern baldness, horn size in sheep, feather color in peacocks