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Biology
Principles of Inheritance and Variation
198 questions from 38 papers, each with its answer.
- 198 questions
- 38 papers
- 5.62% of Biology
Polygenic Inheritance
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What is the pattern of inheritance for polygenic trait?
Polygenic inheritance shows continuous phenotypic variation and follows a non-Mendelian inheritance pattern.
Polygenic traits are controlled by three or more genes with cumulative additive effects showing continuous bell-shaped phenotypic variation (e.g. human skin colour, height), deviating from typical Mendelian monogenic ratios, hence following a non-Mendelian inheritance pattern.
Dihybrid Cross and Law of Independent Assortment
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Genes R and Y follow independent assortment. If RRYY produce round yellow seeds and rryy produce wrinkled green seeds, what will be the phenotypic ratio of the F2 generation?
A standard Mendelian dihybrid cross with independent assortment yields a 9:3:3:1 phenotypic ratio in F2.
Crossing homozygous parents $RRYY \times rryy$ gives dihybrid $RrYy$ in $F_1$. Self-fertilization of $F_1$ yields 16 combinations in $F_2$ with the classic 9:3:3:1 ratio (9 Round Yellow, 3 Round Green, 3 Wrinkled Yellow, 1 Wrinkled Green).
Pedigree Analysis
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With the help of given pedigree, find out the probability for the birth of a child having no disease and being a carrier (has the disease mutation in one allele of the gene) in $F_{3}$ generation.
Probability of a carrier female child ($X^C X$) from a carrier mother ($X^C X$) and normal father ($XY$) is 1/4.
The pedigree shows X-linked recessive inheritance. In $F_2$, the mother is a carrier female ($X^C X$) and the father is unaffected ($XY$). The offspring genotypes are: $X^C X$ (carrier female, 1/4), $XX$ (normal female, 1/4), $X^C Y$ (affected male, 1/4), $XY$ (normal male, 1/4). The probability of an unaffected child being a carrier is 1/4.
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