Chapter 5

• What is epistasis?


  one gene masks (hides) the effect of another gene at a different locus
• What is an epistatic gene?

  gene that masks or suppresses the effect of a gene at a different locus
• What is a hypostatic gene?

  gene that is masked or suppressed by the action of a gene at a different locus
• What is recessive epistasis?

  The presence of two recessive alleles masks the expression of an allele at a different locus.
• What is dominant epistasis?

  A dominant allele inhibits the expression of an allele at a different locus
• What is duplicate recessive epistasis?

  two recessive alleles at different loci can mask the expression of a phenotype
• 9:3:4 ratio is seen for recessive epistasis
• 12:3:1 ratio is seen for dominant epistasis
• 9:7 ratio is seen for duplicate recessive epistasis
• The A or B antigen for blood types are only produced when dominant H allele is present
• If the genotype is hhI^AI^A, there would be no A or B antigen
• People with type O blood can only get type O blood because their anti-A and anti-B antibodies would attack any donor blood with A or B antigens
• Since type O has no antigens, anyone of any blood type can receive type O blood.
• Dog coat color is recessive epistasis
• Squash color is dominant epistasis
• The B alleles in dogs produces black color
• bb in dogs produce brown color
• If the second locus for dog coat color has homozygous recessive alleles, there will be no melanin which results in a yellow color
• Alleles at one locus that has a dominant allele for squash will produce yellow color
• Alleles at one locus that has homozygous recessive alleles for squash will produce green color
• Alleles at the second locus that has a dominant allele for squash will produce no pigment so the color would be white
• complete dominance is the type of dominance in which the same phenotype is expressed in homozygotes and heterozygotes; only the dominant allele is expressed in a heterozygote
• codominance is when both alleles are expressed in a heterozygote
• Incomplete dominance is the type of dominance in which the phenotype of the heterozygote falls in between the phenotypes of the two homozygotes.
• sex-influenced characteristics are determined by autosomal genes and are inherited according to Mendel’s principles but are expressed differently in males and females
• sex influenced traits have a higher penetrance in one of the sexes compared to the other
• In genetic maternal effect, the genotype of the maternal parent determines the phenotype of the offspring
• sex limited characteristic is encoded by autosomal genes that are expressed in only one sex, and has zero penetrance on the other sex
• cytoplasmic inheritance is the inheritance of characteristics encoded by genes located in the cytoplasm
• most cytoplasmically inherited characteristics are inherited from only one parent as the cytoplasm is usually contributed entirely by the mother
• cytoplasmically inherited traits can exhibit extensive phenotypic variation, even within a single family.
• genomic imprinting is the differential expression of a gene depending on whether it is inherited from the male or female parent
• genomic imprinting is the gene whose expression is affected by the sex of the transmitting parent
• epigenetics is the phenomena due to alterations in DNA that does not include changes in the base sequence
• some traits are determined by modifications to DNA or chromatin that affects the way in which DNA sequences are expressed
• anticipation is when a genetic trait becomes more strongly expressed or is expressed at an earlier age as it is passed from generation to generation
• anticipation occurs due to expansion of an unstable region of DNA from generation to generation
• temperature sensitive allele is an allele whose product is functional only at a certain temperature, or whose product is inactive at a certain temperature
• incomplete penetrance is when the genotype does not always produce the expected phenotype
• expressivity is the degree to which a trait is expressed.