Biology
In a homozygous pea plant, axial flowers (A) are dominant over terminal flowers (a).
(i) What is the phenotype and genotype of the F1 generation if a plant bearing pure axial flowers is crossed with a plant bearing pure terminal flowers?
(ii) Draw a Punnett square board to show the gametes and offsprings when both the parent plants are heterozygous for axial flowers.
(iii) What is the phenotypic ratio and genotypic ratio of the above cross shown in (ii).
(iv) State Mendel's Law of Dominance.
(v) Name two genetic disorders commonly seen in human males.
Genetics
ICSE 2017
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Answer
(i) Phenotype – All bear axial flowers
Genotype – All are heterozygous dominant for axial flowers.
(ii) Below is the Punnett square board showing the gametes and offsprings when both the parent plants are heterozygous for axial flowers:
| A | a | |
| A | AA | Aa |
| a | Aa | aa |
(iii) Phenotypic ratio — 3 : 1
Genotypic ratio — 1 : 2 : 1
(iv) Mendel's Law of Dominance — Out of a pair of contrasting characters present together, only one is able to express itself while the other remains suppressed. The one that expresses is the dominant character and the one that is unexpressed is the recessive. The recessive character can express only when the pair consists of both recessives (homozygous recessive).
(v) Two genetic disorders commonly seen in human males are:
- Colour blindness
- Haemophilia
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