Human Genetic Analysis
Complex inheritance of traits does not follow inheritance patterns described by Mendel.
Several genes can influence a trait- polygenic trait. Determining the effect of these genes is difficult.
Example: A horse with red hair mates with a horse with white hair, and their offspring has both red and white hair. How can this be?
CodominanceWhen two dominant alleles are expressed at the same time, both forms of the trait are displayed.Different from incomplete dominance because both traits are displayed.
Example: red flower x white flower = red and white flowered offspring equal number of red and white flowers
Example: Black horse x white horse = roan coatequal number of black and white hairs
Intermediate TraitsIncomplete dominance - an individual displays a trait that is intermediate between the two parents.Example: red flower x white flower = pink flowerNeither the red nor the white allele is completely dominant
X-Linked TraitsThe trait is carried by females on the X chromosome through a recessive allele. Males will have the disorder because they only have one X chromosome.
Traits influenced by the EnvironmentAn individuals phenotype often depends on conditions in the environment.Example: fur color in Siamese catsDark fur around cooler parts of the body- ears, nose, paws, and tails.Example: skin tone in humansExposure to the sun alters the color of the skin.
MutationsChanges in genetic material.
The harmful effects produced by inherited mutations are called genetic disorders.
Many mutations are carried by recessive alleles in heterozygous individuals. carriers
Genetic CounselingGenetic counseling is a form of medical guidance that informs people about genetic problems that could affect them or their offspring.
1. Genetic AbnormalityRare, uncommon version of a trait.
2. Genetic DisorderAn inherited condition that sooner or later will cause mild to severe medical problems.
3. SyndromeA recognized set of symptoms that characterize a given disorder.
4. DiseaseIllness caused by infectious, dietary, or environmental factors, NOT by inheritance of mutant genes.
P Point mutation, or any insertion/deletion entirely inside onegeneD Deletionof a gene or genesC Whole chromosome extra, missing, or bothT Trinucleotide repeat disorders: gene is extended in length
DisorderMutationChromosomeColor blindnessPXCystic fibrosisP7qDown syndromeC21HemophiliaPXKlinefelter syndromeCXSickle-cell diseaseP11pTaySachs diseaseP15
Karyotypesmicrograph in which the pairs of homologous chromosomes are arranged in decreasing size22 autosomes are matched together with one pair of nonmatching sex chromosomesUsed to study chromosomes in hopes of identifying genetic abnormalities or disorders.
PEDIGREE CHARTS 2007 Paul Billiet ODWS
What is a pedigree chart?a chart of the genetic history of a family over several generations.
used to study the transmission of hereditary conditions 2007 Paul Billiet ODWS
Constructing a PedigreeFemale
Connecting Pedigree SymbolsMarried Couple
Symbols used in pedigree charts AffectedX-linked
CarrierDeceased 2007 Paul Billiet ODWS..
Symbols used in pedigree charts Normal maleAffected maleNormal femaleAffected female 2007 Paul Billiet ODWS
Organizing the pedigree chart A pedigree chart of a family showing 20 individuals 2007 Paul Billiet ODWS
Organising the pedigree chartGenerations are identified by Roman numerals. 2007 Paul Billiet ODWS
Organising the pedigree chartIndividuals in each generation are identified by Arabic numerals numbered from the leftTherefore the affected individuals are II3, IV2 and IV3 2007 Paul Billiet ODWS
Interpreting a Pedigree ChartDetermine if the pedigree chart shows an autosomal or X-linked disease.
If most of the males in the pedigree are affected, then the disorder is X-linked. If it is a 50/50 ratio between men and women the disorder is autosomal.
Example of Pedigree ChartsIs it Autosomal or X-linked?
Determine whether the disorder is dominant or recessive.
If the disorder is dominant, one of the parents must have the disorder.If the disorder is recessive, neither parent has to have the disorder because they can be heterozygous.
Example of Pedigree ChartsDominant or Recessive?
Example of Pedigree ChartsDominant or Recessive?
*********Take a minute and try to decide if this slide is autosomal or X-linked.*It is autosomal because it is 50/50 men to women with the disorder, if it was X-linked most of the men in the diagram would have the disorder.Make sure you count the number of men with the disorder and the number of women with the disorder. In this pedigree, 3 men and 3 women have the disorder.*Is this pedigree dominant or recessive?*It is dominant because a parent in every generation have the disorder. Remember if a parent in every generation has the disorder, the disorder has not skipped a generation. If the disorder has not skipped a generation the disorder is dominant.
*Is this pedigree dominant or recessive?
*It is recessive because a parent in every generation does not have the disorder. Remember the disorder can skipped a generation if the disorder is recessive. The parents can be heterozygous and be carriers of the disorder but not have the symptoms of the disorder.