Level 1 — RecognitionExtensions of Mendelian Genetics

Extensions of Mendelian Genetics

⏱ 20 minutes30 marksprintable — key stays hidden on paper

Level 1: Recognition Test

Time Limit: 20 minutes Total Marks: 30

Section A — Multiple Choice (1 mark each)

Choose the single best answer.

Q1. In a cross of red ( $C^RC^R$ ) × white ( $C^WC^W$ ) snapdragons, the F1 are all pink. This illustrates:

A) Codominance
B) Incomplete dominance
C) Epistasis
D) Pleiotropy

Q2. The ABO blood group system is a classic example of:

A) Incomplete dominance only
B) Codominance and multiple alleles
C) Polygenic inheritance
D) Sex linkage

Q3. A trait controlled by many genes, each with a small additive effect, producing a continuous range of phenotypes, is termed:

A) Pleiotropic
B) Epistatic
C) Polygenic
D) Codominant

Q4. A single gene affecting multiple, seemingly unrelated phenotypic traits describes:

A) Epistasis
B) Pleiotropy
C) Multiple alleles
D) Incomplete dominance

Q5. In humans, hemophilia and red–green colorblindness are examples of:

A) Autosomal dominant disorders
B) X-linked recessive disorders
C) Y-linked disorders
D) Polygenic disorders

Q6. When one gene masks or modifies the expression of another gene at a different locus, this is:

A) Codominance
B) Epistasis
C) Linkage
D) Incomplete dominance

Q7. Two genes located far apart on the same chromosome show a recombination frequency approaching:

A) 0%
B) 25%
C) 50%
D) 100%

Q8. In the XY sex-determination system of mammals, the sex of offspring is determined by the:

A) Egg
B) Sperm
C) Environment temperature
D) Number of X chromosomes only

Q9. Coat colour in Himalayan rabbits (dark at cooler extremities) demonstrates:

A) Polygenic inheritance
B) Environmental effect on phenotype
C) Codominance
D) Y-linkage

Q10. A gene with more than two allelic forms in a population is said to have:

A) Multiple alleles
B) Pleiotropy
C) Epistasis
D) Linkage

Section B — Matching (1 mark each, 5 marks)

Q11. Match each term (i–v) with its correct description (a–e).

Term	Description
(i) Incomplete dominance	(a) Genes on the same chromosome inherited together
(ii) Codominance	(b) Heterozygote shows a blended intermediate phenotype
(iii) Linkage	(c) One gene at one locus masks another gene at a different locus
(iv) Epistasis	(d) Both alleles fully and separately expressed in heterozygote
(v) Recombination frequency	(e) Proportion of offspring with new allele combinations

Section C — True/False WITH Justification

(2 marks each: 1 for correct T/F, 1 for a valid justification)

Q12. An AB blood-type individual can donate red cells to an O blood-type individual. (2)

Q13. In X-linked recessive inheritance, an affected father passes the disorder allele to all of his sons. (2)

Q14. A recombination frequency of 12% between two genes means they are 12 map units apart. (2)

Q15. Skin colour in humans being controlled by several genes explains why it shows a continuous range rather than distinct categories. (2)

Q16. Two genes showing 50% recombination frequency must be located on different chromosomes. (2)

End of paper.

Answer keyMark scheme & solutions

Section A (10 marks)

Q1 — B) Incomplete dominance. Heterozygote (pink) is intermediate between the two homozygotes; neither allele fully dominates. (1)

Q2 — B) Codominance and multiple alleles. Three alleles ( $I^A, I^B, i$ ) exist (multiple alleles); $I^A$ and $I^B$ are both expressed in AB individuals (codominance). (1)

Q3 — C) Polygenic. Many genes with small additive effects → continuous phenotype distribution. (1)

Q4 — B) Pleiotropy. One gene → many phenotypic effects. (1)

Q5 — B) X-linked recessive disorders. Recessive alleles carried on the X chromosome. (1)

Q6 — B) Epistasis. Gene interaction where one locus masks another. (1)

Q7 — C) 50%. Genes far apart behave as if unlinked; maximum RF = 50%. (1)

Q8 — B) Sperm. Males (XY) produce X- or Y-bearing sperm; egg always carries X. (1)

Q9 — B) Environmental effect on phenotype. Temperature-sensitive enzyme produces pigment only in cooler body regions. (1)

Q10 — A) Multiple alleles. More than two alleles for one gene in the population. (1)

Section B (5 marks)

Q11: (i)–(b); (ii)–(d); (iii)–(a); (iv)–(c); (v)–(e). 1 mark each correct match.

Q12 — FALSE (1). AB red cells carry both A and B antigens; an O recipient has both anti-A and anti-B antibodies, so the cells would be attacked. AB is the universal recipient, NOT universal donor. (O is universal donor.) (1)

Q13 — FALSE (1). A father passes his X to daughters and his Y to sons. Sons get his Y (no disease allele from father); so all his DAUGHTERS become carriers/affected, not his sons. (1)

Q14 — TRUE (1). 1% recombination frequency = 1 map unit (centimorgan); therefore 12% RF = 12 map units. (1)

Q15 — TRUE (1). Multiple genes each add a small effect, and their combined additive contributions plus environment produce a smooth continuous (bell-shaped) distribution rather than discrete classes. (1)

Q16 — FALSE (1). 50% RF can arise either from genes on different chromosomes OR from genes very far apart on the same chromosome; it does not uniquely prove different chromosomes. (1)

[
  {"claim":"RF of 12% equals 12 map units (1% = 1 cM)","code":"rf=12; map_units=rf; result = (map_units==12)"},
  {"claim":"Maximum recombination frequency between two loci is 50%","code":"max_rf=50; result = (max_rf==50)"},
  {"claim":"ABO gene has 3 alleles giving multiple-allele system","code":"alleles={'IA','IB','i'}; result = (len(alleles)==3 and len(alleles)>2)"},
  {"claim":"Snapdragon RxW gives pink F1 (incomplete dominance, intermediate)","code":"red=2; white=0; pink=(red+white)/2; result = (pink==1 and 0<pink<red)"}
]