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Biology · 2024 · 5 marks
CBSE 2024 · Region 1 · Set 1 · Q32
(a) Stability, as one of the properties of genetic material, was very evident in one of the very early experiments in genetics. Name the scientist…
(a)
Stability, as one of the properties of genetic material, was very evident in one of the very early experiments in genetics. Name the scientist and describe his experiment. State the conclusion he arrived at.
OR
(b)
A tall pea plant bearing violet flowers with unknown genotype is given. Find the genotype by working out different crosses only by selfing the plants. Write the genotypic and phenotypic ratios of each cross shown by you.
Marking-scheme solution
-Frederick Griffith
Took two strains of Streptococcus pneumoniae bacteria and inject them into mice
R strain – Rough and Non–virulent
-S strain – Smooth and virulent (with mucous coat)
S strain → Inject into mice → Mice die
R strain → Inject into mice → Mice live
S strain (heat-killed) → Inject into mice → Mice live
S strain (heat-killed) + R strain (live) → Inject into mice → Mice die
·
Conclusion :
• -R–strain bacteria had been transformed by heat killed S – strain.
• -‘Transforming principle’ transferred from heat killed S-Strain and enabled R–
strain to synthesise a smooth polysaccharide coat. This must be due to the transfer of the genetic material.
• -Heat which killed bacteria did not destroy some of the properties of genetic
material which shows stability of genetic material.
Tall Pea plant with violet flowers can have $\displaystyle 4$ types of genotypes
TTVV , TtVV , TtVv , TTVv
Case I-
TTVV × TTVV
↓
Genotype TTVV
Phenotype All will be tall and violet.
Case II-
Tt VV × Tt VV
↓
Gametes
TV
tV
TV
TTVV Tall Violet
TtVV Tall Violet
tV
TtVV Tall Violet
ttVV Dwarf Violet
Phenotypic ratio Tall Violet : Dwarf Violet
$\displaystyle 3$ : $\displaystyle 1$
Genotypic ratio TTVV:TtVV : ttVV
$\displaystyle 1$ : $\displaystyle 2$ : $\displaystyle 1$
Case III-
Tt Vv × Tt Vv
↓
Gametes
TV
Tv
tV
tv
TV
TTVV
Tall violet
TTVv
Tall Violet
TtVV
Tall Violet
TtVv
Tall Violet
Tv
TTVv
Tall Violet
TTvv
Tall white
TtVv
Tall Violet
Ttvv
Tall white
tV
TtVV
Tall violet
TtVv
Tall Violet
ttVV
dwarf violet
ttVv
dwarf Violet
Tv
TtVv
Tall violet
Ttvv
Tall white
ttVv
dwarf violet
ttvv
dwarf white
Phenotypic ratio - Tall Violet : Dwarf violet:Tall white: dwarf white
$\displaystyle 9$ : $\displaystyle 3$ : $\displaystyle 3$: $\displaystyle 1$
Genotypic ratio- TTVV: TTVv:TtVV:TtVv:TTvv:ttVV: ttVv: Ttvv: ttvv
$\displaystyle 1$ : $\displaystyle 2$ : $\displaystyle 2$ : $\displaystyle 4$ : $\displaystyle 1$ :$\displaystyle 1$ :$\displaystyle 2$ :$\displaystyle 2$ : $\displaystyle 1$
Case IV
TTVv X TTVv
↓
Gametes
TV
Tv
TV
TTVV
Tall Violet
TTVv
Tall Violet
Tv
TTVv
Tall Violet
TTvv
Tall White
Phenotypic ratio- Tall violet Tall white
$\displaystyle 3$ : $\displaystyle 1$
Genotypic ratio- TTVV : TTVv : TTvv
$\displaystyle 1$ : $\displaystyle 2$ : $\displaystyle 1$
All Principles of Inheritance and Variation questions2024 question paperNCERT solutions: Principles of Inheritance and VariationPractice Principles of Inheritance and Variation →
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