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Sagot :
Let's analyze the genetics of cleft chin versus no-cleft chin in humans using Mendel's method of crossing two true breeding parents.
### P Generation
We start with two true-breeding parents:
- One parent with a cleft chin has the genotype CC (homozygous dominant).
- The other without a cleft chin has the genotype cc (homozygous recessive).
### F1 Generation
When these two parents are crossed (CC x cc), all offspring (F1 generation) will receive one allele from each parent resulting in the genotype Cc. Since the cleft chin trait (C) is dominant, all F1 offspring will exhibit a cleft chin.
### F2 Generation
The F1 generation (Cc) is then self-crossed (Cc x Cc) to produce the F2 generation. Using a Punnett Square for the cross:
```
C c
C CC Cc
c Cc cc
```
This gives us:
- 1 CC (cleft chin)
- 2 Cc (cleft chin)
- 1 cc (no cleft chin)
Hence, the phenotype ratio in the F2 generation is:
- 3 with cleft chins
- 1 with no-cleft chin
### Conclusions and Checking Options
1. The [tex]$P$[/tex] generation, [tex]$F_1$[/tex] generation, and [tex]$F_2$[/tex] generation will have all cleft chins.
- False. The F2 generation will have a 3:1 ratio of cleft chin to no-cleft chin.
2. The [tex]$P$[/tex] generation, [tex]$F_1$[/tex] generation, and [tex]$F_2$[/tex] generation will have all no-cleft chins.
- False. The P generation and F1 generation will have cleft chins, while the F2 generation will show a 3:1 ratio.
3. The [tex]$P$[/tex] generation and [tex]$F_1$[/tex] generation will have all cleft chins.
- True. The P generation has true-breeding cleft chins, and the F1 generation will be heterozygous with all cleft chins.
4. The [tex]$F_1$[/tex] generation will have all cleft chins.
- True. All F1 individuals are heterozygous (Cc) and will exhibit the dominant trait (cleft chin).
5. The [tex]$P$[/tex] generation and [tex]$F_2$[/tex] generation will have all no-cleft chins.
- False. The P generation doesn’t have all no-cleft chins, and the F2 generation shows a mix (3:1 ratio).
6. The P generation and [tex]$F _2$[/tex] generation will have cleft chins and no-cleft chins.
- False. The P generation only has cleft chins, the F2 generation has both cleft chins and no-cleft chins but the P does not have both traits.
7. The P generation, [tex]$F _1$[/tex] generation, and [tex]$F _2$[/tex] generation will have cleft chins and no-cleft chins.
- True. This correctly captures the diversity across all generations: the P generation has both true-breeding parents (one with cleft chin and one without), the F1 is all with cleft chin, and the F2 generation has both cleft and no-cleft chins.
Therefore, the correct options are:
- The P generation and F1 generation will have all cleft chins.
- The P generation, [tex]$F _1$[/tex] generation, and [tex]$F _2$[/tex] generation will have cleft chins and no-cleft chins.
Thus, our final answer is:
```
[2, 5]
```
### P Generation
We start with two true-breeding parents:
- One parent with a cleft chin has the genotype CC (homozygous dominant).
- The other without a cleft chin has the genotype cc (homozygous recessive).
### F1 Generation
When these two parents are crossed (CC x cc), all offspring (F1 generation) will receive one allele from each parent resulting in the genotype Cc. Since the cleft chin trait (C) is dominant, all F1 offspring will exhibit a cleft chin.
### F2 Generation
The F1 generation (Cc) is then self-crossed (Cc x Cc) to produce the F2 generation. Using a Punnett Square for the cross:
```
C c
C CC Cc
c Cc cc
```
This gives us:
- 1 CC (cleft chin)
- 2 Cc (cleft chin)
- 1 cc (no cleft chin)
Hence, the phenotype ratio in the F2 generation is:
- 3 with cleft chins
- 1 with no-cleft chin
### Conclusions and Checking Options
1. The [tex]$P$[/tex] generation, [tex]$F_1$[/tex] generation, and [tex]$F_2$[/tex] generation will have all cleft chins.
- False. The F2 generation will have a 3:1 ratio of cleft chin to no-cleft chin.
2. The [tex]$P$[/tex] generation, [tex]$F_1$[/tex] generation, and [tex]$F_2$[/tex] generation will have all no-cleft chins.
- False. The P generation and F1 generation will have cleft chins, while the F2 generation will show a 3:1 ratio.
3. The [tex]$P$[/tex] generation and [tex]$F_1$[/tex] generation will have all cleft chins.
- True. The P generation has true-breeding cleft chins, and the F1 generation will be heterozygous with all cleft chins.
4. The [tex]$F_1$[/tex] generation will have all cleft chins.
- True. All F1 individuals are heterozygous (Cc) and will exhibit the dominant trait (cleft chin).
5. The [tex]$P$[/tex] generation and [tex]$F_2$[/tex] generation will have all no-cleft chins.
- False. The P generation doesn’t have all no-cleft chins, and the F2 generation shows a mix (3:1 ratio).
6. The P generation and [tex]$F _2$[/tex] generation will have cleft chins and no-cleft chins.
- False. The P generation only has cleft chins, the F2 generation has both cleft chins and no-cleft chins but the P does not have both traits.
7. The P generation, [tex]$F _1$[/tex] generation, and [tex]$F _2$[/tex] generation will have cleft chins and no-cleft chins.
- True. This correctly captures the diversity across all generations: the P generation has both true-breeding parents (one with cleft chin and one without), the F1 is all with cleft chin, and the F2 generation has both cleft and no-cleft chins.
Therefore, the correct options are:
- The P generation and F1 generation will have all cleft chins.
- The P generation, [tex]$F _1$[/tex] generation, and [tex]$F _2$[/tex] generation will have cleft chins and no-cleft chins.
Thus, our final answer is:
```
[2, 5]
```
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