The mutation that causes cystic fibrosis diminished

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The mutation that causes cystic fibrosis diminished the function of this Cl transporter, affecting several parts of the body in different ways. Thick mucus in the lungs. Excessively salty sweat. Sterility in homozygous recessive males. Multiple effects of the sickle-cell gene include: breakdown of red blood cells, clumping of cells and clogging of small blood vessels, physical weakness, anemia, heart failure, pain and fever, brain damage, paralysis, kidney failure, etc.
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9 Gene Interactions General information A gene interaction indicates that the phenotype is determined by the contribution of two or more genes. According to Mendelian inheritance, a cross involving two heterozygous individuals for two genes that obey the laws of segregation and independent assortment should produce a 9:3:3:1 ratio of phenotypes. Deviations from this ratio are a good indication of gene interactions. When the alleles of one gene mask the phenotypic effects of the alleles of another gene, the phenomenon is called epistasis. A cross involving a two-gene interaction can produce four distinct phenotypes due to epistasis. The first indication of gene interactions was provided in 1906 by Bateson and Punnett, who were studying comb morphology in chickens (Figure 4.19). Their dihybrid cross (heterozygous/heterozygous x heterozygous/heterozygous) produced four distinct phenotypes in a 9:3:3:1 ratio, rather than the four combinations of two phenotypes in a 9:3:3:1 ratio expected from a simple Mendelian dihybrid cross: R (rose comb) is dominant to r P (pea comb) is dominant to p R and P (walnut comb) are codominant rrpp produces a single comb Dominant/Dominant ( R_P_ ) – walnut comb Dominant/Recessive ( R_pp ) – rose comb Recessive/Dominant ( rrP_ ) – pea comb Recessive/Recessive (rrpp) – single comb A cross involving a two-gene interaction can produce two distinct phenotypes due to epistasis. This was first described by Bateson and Punnett in their work with flower colors in the sweet pea, Lathyrus odoratus (Figure 4.20). Their dihybrid cross produced a 9:7 (purple-flowered : white-flowered) phenotypic ratio.
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10 This phenomenon is the result of independent genes (gene C and gene P ) encoding enzymes that control a single biochemical pathway: Enzyme A Enzyme P Colorless precursor colorless intermediate purple pigment A plant that is homozygous recessive for either allele will develop white flowers regardless of the genotype of the other gene because the purple pigment does not get produced in either case. A cross involving a two-gene interaction can produce three distinct phenotypes due to epistasis. The coat color for rodents is controlled by two genes, A (for agouti) and C (for colored). The dihybrid cross produces agouti, black, and albino offspring in a 9:3:4 ratio (Figure 4.21).
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  • Spring '08
  • SAXENA
  • Genetics, red blood cells, Sex linkage

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