Question

1. Haemophilia and red-green colour-blindness is usually observed in men. Why?
2. Perform a cross (or crosses) where haemophilic daughter(s) and haemophilic son(s) are
produced in the same ratio.

OR
1. Where do transcription and translation occur in bacteria and eukaryotes respectively?
2. Draw a labelled schematic sketch of replication fork of DNA.
3. A DNA segment has a total of 1000 nucleotides, out of which 240 of them are Adenine-containing nucleotides. How many pyrimidine bases does this segment possess?

Hint:

X-linked disorders affect males more due to the presence of a single X chromosome. Always use complementary base pairing logic when calculating nucleotide distribution in DNA.

Answer 1

Step 1 (A):

1. Haemoph ilia and red-green colourblindness are X-linked recessive disorders. Since men have only one X chromosome, the presence of a single defective gene leads to expression of the disorder. Women, having two X chromosomes, must inherit two defective copies to express the condition, which is less likely.
2. For equal production of haemophilic daughters and sons, the cross must be between a carrier female ($X^H X^h$) and a haemophilic male ($X^h Y$):
   
    

	$X^H$	$X^h$
$X^h$	$X^H X^h$ (Carrier Daughter)	$X^h X^h$ (Haemophilic Daughter)
$Y$	$X^H Y$ (Normal Son)	$X^h Y$ (Haemophilic Son)

1. This cross results in 1 haemophilic daughter and 1 haemophilic son out of 4 children.

Step 2 (B):

1. In bacteria, both transcription and translation occur in the cytoplasm. In eukaryotes, transcription occurs in the nucleus, and translation occurs in the cytoplasm.
2.  
3. DNA base pairing:
   • Adenine (A) pairs with Thymine (T)
   • Guanine (G) pairs with Cytosine (C)