(a) List four characteristics which can be genetically transmitted in humans. (b)(i) Name two sites eac• in plants and animals where meiosis occurs. (ii) St...

Answer Details

(a) Four characteristics that can be genetically transmitted in humans

• Blood group (ABO / Rhesus).
• Skin (and eye) colour.
• Ability to roll the tongue.
• Height (and shape of the nose, hair type, colour blindness, sickle-cell trait).

(b)(i) Two sites each where meiosis occurs

In plants: the anther (in the pollen sacs) and the ovule (embryo sac) of the flower.

In animals: the testes (in males) and the ovaries (in females).

(b)(ii) Two differences between meiosis and mitosis

(c) Blood-group paternity test

The ABO blood groups are controlled by three alleles: I^A and I^B (co-dominant) and i (recessive). Group O is ii.

Genotypes given:

• Woman: blood group A, heterozygous = I^Ai
• Son: blood group O = ii
• Mr James: blood group A, homozygous = I^AI^A

For the son to be group O (ii), he must receive an i allele from each parent. The mother (I^Ai) can supply an i allele. The alleged father must therefore also supply an i allele.

Cross: mother I^Ai \( \times \) Mr James I^AI^A

(i) Conclusion: All possible children of this cross are blood group A (I^AI^A or I^Ai). None can be group O. Therefore the woman's claim is disproved: Mr James cannot be the father of the group O son.

(ii) Reason: Mr James, being homozygous group A (I^AI^A), can only pass on an I^A allele. A group O child must receive an i allele from both parents, so a homozygous group A man cannot father a group O child.