bzyct-137-solved-assignment-2024-ss-020cab3d-1c01-486f-9bdf-7506d86b97ee

1. a) Explain dihybrid cross and Mendel’s Law of independent assortment.

• 9/16 will be yellow and round (YYRR, YYRr, YyRR, YyRr)
• 3/16 will be yellow and wrinkled (YYrr, Yyrr)
• 3/16 will be green and round (yyRR, yyRr)
• 1/16 will be green and wrinkled (yyrr)

1. Recessive Epistasis:
   • In recessive epistasis, the presence of two recessive alleles at one locus masks the expression of alleles at a second locus. A common example is the 9:3:4 phenotypic ratio seen in Labrador retriever coat color, where the presence of two recessive alleles for pigment deposition (ee) masks the expression of the B locus that determines black or brown coat color.
   • Example Ratio: 9:3:4
2. Dominant Epistasis:
   • In dominant epistasis, a single copy of an allele at one locus masks the expression of alleles at a second locus. An example is the 12:3:1 ratio seen in fruit color in certain squash varieties, where a dominant allele for white color (W) masks the expression of color alleles at another locus.
   • Example Ratio: 12:3:1
3. Duplicate Recessive Epistasis:
   • In this type of epistasis, two genes are required for the expression of a phenotype, and the presence of recessive alleles at either locus masks the expression of the dominant phenotype. An example is the 9:7 ratio seen in the flower color of certain plants, where both genes are required for pigment production.
   • Example Ratio: 9:7
4. Duplicate Dominant Epistasis:
   • In duplicate dominant epistasis, the dominant allele of either of two genes is sufficient to produce the same phenotype, resulting in a 15:1 phenotypic ratio.
   • Example Ratio: 15:1
5. Dominant-Recessive Epistasis:
   • In this type of epistasis, the dominant allele at one locus masks the expression of alleles at a second locus, but only if the second locus is homozygous recessive. An example is the 13:3 ratio seen in certain traits.
   • Example Ratio: 13:3
6. Polymeric (Cumulative) Epistasis:
   • This occurs when two or more genes contribute additively to a single phenotype, often resulting in a continuous range of phenotypes rather than discrete classes.