MDCAT Biology chapter 10: Biology · Inheritance MCQs with answers
By Team Megalecture · Updated 4 Nov 2026
46 exam-style questions on Biology · Inheritance, each with the answer and a short explanation. Ten of them are below to try. The chapter test draws ten fresh questions each time and is marked the moment you finish, with your score by topic.
Try each one, then open the answer. These ten stay the same; the test draws new ones every time.
1. In a certain squash, a dominant allele W of one gene gives white fruit whatever the alleles of a second, unlinked gene. Plants that are ww are yellow if they carry a dominant Y allele and green if they are yy. What fraction of the offspring of WwYy × WwYy is expected to be white?
A
3/4
B
1/4
C
9/16
D
15/16
Show answer
Answer: A. Any plant with at least one W allele is white, and W_ makes up 3/4 of the offspring (12/16); the ww plants are yellow (3/16) or green (1/16). This is epistasis: the W gene hides the effect of the Y gene. The fraction 9/16 counts only W_Y_ plants.
2. Considering the ABO system only, a patient of blood group B can safely receive red blood cells from donors of groups
A
B and AB
B
AB and O
C
A and O
D
B and O
Show answer
Answer: D. Group B plasma contains anti-A antibodies, so donor red cells must lack the A antigen: groups B and O. Red cells of group A or AB carry the A antigen and would be agglutinated.
3. Mendel's law of segregation states that
A
alleles of different genes are inherited independently of one another
B
in a heterozygote only the dominant allele is expressed in the phenotype
C
genes lying on the same chromosome are usually inherited together
D
the two alleles of a gene separate so that each gamete receives one
Show answer
Answer: D. The law of segregation: the two alleles of each gene separate during gamete formation, so a gamete carries only one allele of each gene. Independent inheritance of different genes is the second law (independent assortment).
4. A pea plant with round yellow seeds is crossed with a plant with wrinkled green seeds (rryy). The offspring are round yellow, round green, wrinkled yellow and wrinkled green in roughly equal numbers. The round yellow parent was
A
homozygous for both genes (RRYY)
B
heterozygous for seed shape only (RrYY)
C
heterozygous for both genes (RrYy)
D
heterozygous for seed colour only (RRYy)
Show answer
Answer: C. Four classes in a 1 : 1 : 1 : 1 ratio need four kinds of gamete (RY, Ry, rY, ry) in equal numbers, so the parent was heterozygous for both genes. RRYY would give only round yellow offspring, and RRYy only round ones.
5. A girl has red-green colour blindness, which is X-linked and recessive. What must be true of her parents?
A
her father is colour blind, and her mother is colour blind or a carrier
B
her mother is colour blind, but her father may have normal vision
C
her father may have normal vision, if her mother is a carrier
D
both her parents are colour blind
Show answer
Answer: A. The girl is XcXc, so she received an Xc from each parent. A father has one X, so he must be colour blind; her mother must be a carrier or colour blind. A normal father would have passed her a normal X.
6. Non-disjunction is the
A
exchange of segments between non-sister chromatids of homologues
B
failure of paired chromosomes or chromatids to separate
C
loss of a segment from a broken chromosome
D
pairing of homologous chromosomes in prophase I
Show answer
Answer: B. Non-disjunction is the failure of homologous chromosomes (meiosis I) or sister chromatids (meiosis II) to separate, so gametes get an extra or a missing chromosome. Exchange between non-sister chromatids is crossing over.
7. Which event in meiosis provides the basis of Mendel's law of segregation?
A
separation of homologous chromosomes into different gametes
B
crossing over between non-sister chromatids in prophase I
C
replication of every chromosome during the preceding interphase
D
pairing of non-homologous chromosomes at metaphase I
Show answer
Answer: A. The two alleles of a gene sit at the same locus on a pair of homologous chromosomes; when the homologues separate in meiosis, each gamete gets one allele. Crossing over reshuffles alleles of linked genes instead.
8. In peas, round seed (R) is dominant to wrinkled seed (r). Two heterozygous round plants are crossed and 800 seeds are produced. How many of the seeds are expected to be round and heterozygous?
A
200
B
300
C
600
D
400
Show answer
Answer: D. Rr × Rr gives 1 RR : 2 Rr : 1 rr, so heterozygotes are 2/4 of 800 = 400. 600 counts all the round seeds (RR and Rr), and 200 is the homozygous round ones.
9. Down syndrome is caused by
A
the loss of one X chromosome
B
an extra copy of chromosome 21
C
an extra X chromosome in a male
D
an extra Y chromosome in a male
Show answer
Answer: B. Down syndrome is trisomy 21 (47 chromosomes). Loss of an X gives Turner syndrome (45, XO) and an extra X in a male gives Klinefelter syndrome (47, XXY).
10. From the cross RrYy × RrYy in peas (round and yellow dominant), 160 F2 plants are raised. How many are expected to have round yellow seeds and breed true for both traits?
A
90
B
30
C
40
D
10
Show answer
Answer: D. Breeding true needs RRYY, which is 1/4 × 1/4 = 1/16 of the offspring: 160 ÷ 16 = 10. 90 counts all round yellow plants (9/16), most of which are heterozygous for at least one gene.
46, each with the answer and a short explanation, across 3 topics: Mendelian inheritance, Beyond simple dominance, Sex linkage and chromosomes. Every chapter test draws ten of them, so you can take it many times.
Is the MDCAT Biology chapter 10 test free?
Yes. The test, the answers and the explanations are free and need no sign-up. Sign in only if you want your scores kept across devices.
How is the chapter test marked?
The moment you press Finish: your score, the right answer and an explanation for every question, and the ones you got wrong saved in My mistakes to retry.
