Page 1 of 189
BIOD 210 Module 1-7 Exam Genetics LATEST
UPDATE THIS YEAR (2026-2027) ALL 300
QUESTIONS AND CORRECT ANSWERS WITH
RATIONALES
Question 1: A researcher is studying a family in which a particular disease appears in every
generation, affecting both males and females equally, and affected individuals always have at
least one affected parent. Which inheritance pattern is most consistent with these
observations?
A) Autosomal recessive
B) X-linked recessive
C) Autosomal dominant
D) Y-linked inheritance
Answer: C) Autosomal dominant
Rationale: Autosomal dominant traits appear in every generation with no skipped generations,
affect both sexes equally, and affected individuals have at least one affected parent. Autosomal
recessive traits can skip generations and require both parents to be carriers.
1
, Page 2 of 189
Question 2: During DNA replication, which enzyme is responsible for synthesizing the RNA
primers needed to initiate DNA synthesis?
A) DNA polymerase III
B) Helicase
C) Primase
D) Ligase
Answer: C) Primase
Rationale: Primase is a type of RNA polymerase that synthesizes short RNA primers
complementary to the DNA template. These primers provide the free 3'-OH group required by
DNA polymerase to begin adding deoxynucleotides.
Question 3: A plant breeder crosses two true-breeding pea plants—one with purple flowers
(dominant) and one with white flowers (recessive). All F₁ offspring have purple flowers. When
the F₁ plants are self-crossed, what phenotypic ratio is expected in the F₂ generation?
A) 1:1
B) 3:1
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, Page 3 of 189
C) 9:3:3:1
D) 1:2:1
Answer: B) 3:1
Rationale: This is a monohybrid cross between two heterozygotes (Pp × Pp). The genotypic ratio
is 1:2:1 (PP:Pp:pp), but since purple is dominant, the phenotypic ratio is 3 purple : 1 white.
Question 4: A karyotype reveals that a patient has 47 chromosomes with an extra copy of
chromosome 21. Which condition is most likely present?
A) Turner syndrome
B) Klinefelter syndrome
C) Down syndrome
D) Patau syndrome
Answer: C) Down syndrome
Rationale: Down syndrome (trisomy 21) is caused by an extra copy of chromosome 21, resulting
in 47 total chromosomes. Turner syndrome is monosomy X (45,X), Klinefelter is XXY, and Patau is
trisomy 13.
3
, Page 4 of 189
Question 5: Which of the following correctly describes the directionality of DNA synthesis
during replication?
A) 5' to 3' on the leading strand and 3' to 5' on the lagging strand
B) 3' to 5' on both strands
C) 5' to 3' on both strands
D) 5' to 3' on the leading strand only
Answer: C) 5' to 3' on both strands
Rationale: DNA polymerase synthesizes new DNA in the 5' to 3' direction on both the leading
and lagging strands. The lagging strand is synthesized discontinuously as Okazaki fragments,
but each fragment is still synthesized 5' to 3'.
Question 6: In a dihybrid cross between two individuals heterozygous for both traits (AaBb ×
AaBb), what proportion of offspring would be homozygous recessive for both traits?
A) 1/16
B) 1/8
4
BIOD 210 Module 1-7 Exam Genetics LATEST
UPDATE THIS YEAR (2026-2027) ALL 300
QUESTIONS AND CORRECT ANSWERS WITH
RATIONALES
Question 1: A researcher is studying a family in which a particular disease appears in every
generation, affecting both males and females equally, and affected individuals always have at
least one affected parent. Which inheritance pattern is most consistent with these
observations?
A) Autosomal recessive
B) X-linked recessive
C) Autosomal dominant
D) Y-linked inheritance
Answer: C) Autosomal dominant
Rationale: Autosomal dominant traits appear in every generation with no skipped generations,
affect both sexes equally, and affected individuals have at least one affected parent. Autosomal
recessive traits can skip generations and require both parents to be carriers.
1
, Page 2 of 189
Question 2: During DNA replication, which enzyme is responsible for synthesizing the RNA
primers needed to initiate DNA synthesis?
A) DNA polymerase III
B) Helicase
C) Primase
D) Ligase
Answer: C) Primase
Rationale: Primase is a type of RNA polymerase that synthesizes short RNA primers
complementary to the DNA template. These primers provide the free 3'-OH group required by
DNA polymerase to begin adding deoxynucleotides.
Question 3: A plant breeder crosses two true-breeding pea plants—one with purple flowers
(dominant) and one with white flowers (recessive). All F₁ offspring have purple flowers. When
the F₁ plants are self-crossed, what phenotypic ratio is expected in the F₂ generation?
A) 1:1
B) 3:1
2
, Page 3 of 189
C) 9:3:3:1
D) 1:2:1
Answer: B) 3:1
Rationale: This is a monohybrid cross between two heterozygotes (Pp × Pp). The genotypic ratio
is 1:2:1 (PP:Pp:pp), but since purple is dominant, the phenotypic ratio is 3 purple : 1 white.
Question 4: A karyotype reveals that a patient has 47 chromosomes with an extra copy of
chromosome 21. Which condition is most likely present?
A) Turner syndrome
B) Klinefelter syndrome
C) Down syndrome
D) Patau syndrome
Answer: C) Down syndrome
Rationale: Down syndrome (trisomy 21) is caused by an extra copy of chromosome 21, resulting
in 47 total chromosomes. Turner syndrome is monosomy X (45,X), Klinefelter is XXY, and Patau is
trisomy 13.
3
, Page 4 of 189
Question 5: Which of the following correctly describes the directionality of DNA synthesis
during replication?
A) 5' to 3' on the leading strand and 3' to 5' on the lagging strand
B) 3' to 5' on both strands
C) 5' to 3' on both strands
D) 5' to 3' on the leading strand only
Answer: C) 5' to 3' on both strands
Rationale: DNA polymerase synthesizes new DNA in the 5' to 3' direction on both the leading
and lagging strands. The lagging strand is synthesized discontinuously as Okazaki fragments,
but each fragment is still synthesized 5' to 3'.
Question 6: In a dihybrid cross between two individuals heterozygous for both traits (AaBb ×
AaBb), what proportion of offspring would be homozygous recessive for both traits?
A) 1/16
B) 1/8
4
