Phenotypic Expression
Terms
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- Gene expression and the resultant phenotype can be modified through...
- the interaction between an individuals genotype and the external environment
- Penetrance
- The percentage of individuals that show at least some degree of expression of a mutant genotype
- How to calculate percent penetrance
- 100-[percent of mutant individuals showing wildtype phenotype]
- Expressivity
- reflects the range of expression of the mutant genotype
- what could be attributed to causing a phenotype variation if it is not the genetic background?
- environmental factors: temperature, humidity, nutrition
- Genetic Suppression
- the effect of a mutation on the phenotype may be reversed so that the wild type phenotype is expressed
- Position Effect
- region of chromosome is relocated or rearranged, normal expression of genes in that chromosomal region may be modified
- Heterochromatin
- gene is relocated to or near certain areas of the chromosome that are prematurely condensed and genetically inactive
- conditional mutations
- the expression of a mutation is affected by temperature
- Genetic Anticipation
- heritable disorders that exhibit a progressively earlier age of onset and an increased severity of the disorder. (the size of repeated segments increses)
- Genomic Imprinting
- a condition where the expression of a gene depends on whether the gene is inherited from the male or female parent
- Imprinting occurs...
- before or during gamete formation
- Can imprinting be erased?
- Yes, imprinting can eventually be erased through succeeding generations as genes pass from mother --> son --> grandchild
- Organelle Heredity
- organism's phenotype is affected by the expression of genes contained in DNA of mitochondria
- Maternal Effect
- phenotype is influenced by the genotype of the mother, not the individual. under control of gene products present in egg prior to fertilization.
- Extranuclear inheritance
- transmission of traits by genetic information contained in cytoplasmic organelles such as mitochondria and chloroplasts
- Homologous Chromosomes
- chromosomes that exist in pairs
- Chromosome
- Two sister chromatids connected by a common centromere
- Product of Meiosis
- 4 haploid gametes
- Product of Mitosis
- 2 genetically identical diploid gametes
- Crossing over occurs during
- Meiotic Prophase I
- Monosomy
- loss of a single chromosome
- Trisomy
- gain of a single chromosome
- Euploidy
- complete haploid sets of chromosomes are present
- Nondisjunction
- chromosomal variation originates as the result of an error during meiosis --> pairs of homologs fail to disjoin during segregation. causes monosomy & trisomy
- Downs Syndrome
- Nondisjunction of chromosome 21 during meiosis --> results in trisomy 21.
- amniocentesis
- procedure used to test for fetal defects in which fluid and fetal cells are withdrawn from the amniotic layer surrounding the fetus. more accurate than CVS
- Chorionic Villus Sampling (CVS)
- intravaginally recieves choronic fetal cells and uses them to detect cttigenetic and biochemical defects
- Aneupoloidy
- a condition in which the chromosome number is not an exact multiple of the haploid set
- Linkage
- Chromosomes that contain a very large number of genes. two or more nonallelic genes are inherited together. loci along same chromosome do not undergo independent assortment
- Crossing Over
- reciprocal exchange of chromosome segments between homologs that are paired. results in reshuffling or recombination of the alleles. Degree of crossing over between two loci is proportional to distance between them.
- Complete Linkage
- no crossing over 2 genetically different gametes are formed. produces only parental gametes.
- the number of recombinant gametes approaches 50% when
- the loci of 2 linked genes are far apart
- 50% recombination results in a phenotypic ratio of
- 1:1:1:1
- Close proximity, complete linkage and organisms are heterozygous at both loci result in
- unique F2 phenotypic ratio
- 1 map unit
- 1% recombination
- limit of observed recombination due to crossing over
- 50%
- linked genes that are more than 50mu apart can be expected to have crossing over ___% of the time
- 100