Cytogenetics Questions and Answers – Lethal Alleles

«
»

This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Lethal Alleles”.

1. Lethal alleles can only be recessive.
a) True
b) False
View Answer

Answer: b
Explanation: Lethal alleles can be both dominant as well as recessive. In case of recessive, it only appears when the individual is homozygous for the gene.
advertisement

2. In Aurea, a type of snapdragon, only ______________ carrying dominant genes live.
a) Homozygous
b) Homozygote
c) Heterozygote
d) Heterozygous
View Answer

Answer: c
Explanation: In this case the heterozygote produces 2:1 ratio of yellow: green leaves. The homozygous dominant individual germinates but due to lack of chlorophyll fails to grow.

3. The ______________ mouse is lethal.
a) Homozygous white
b) Homozygous black
c) Heterozygous agouti
d) Homozygous yellow
View Answer

Answer: d
Explanation: The homozygous yellow mouse dies off as it carries the lethal gene in two copies. However in all other options the mouse likes.
advertisement
advertisement

4. Cross of two yellow mice will give _____________ normal mouse.
a) 1/4
b) 2/4
c) 1/3
d) 2/3
View Answer

Answer: c
Explanation: Homozygous condition of the yellow allele will lead to lethality thus the living yellow mouse are heterozygous. Their cross will give 1/4th of homozygous yellow allele mice which will die changing the proportion of normal mice to 1.3rd of the living ones.

5. Which of the following is not true for yellow mice?
a) The homozygous yellow mice die
b) A normal ice crossed to yellow mice will always give normal probabilities of F1
c) In yellow mice the yellow coloring allele is under control of Raly promoter
d) The homozygous mouse dies as the yellow allele is produced in excess
View Answer

Answer: d
Explanation: In homozygous condition the mice die not due to over expression of agouti, or yellow coloring gene but due to absence of expression of Raly gene.
advertisement

6. The lethal mutation that is seen in the yellow mice is due to _______________ mutation
a) Insertion
b) Deletion
c) Non-sense
d) Frame shift
View Answer

Answer: b
Explanation: The mutation seen in this case is deletion mutation. The raly gene and the agouti genes lie side by side. Deletion of the gene sequence of Rally and the promoter of Agouti gives this colour.

7. Tay Sach’s disease doesn’t agree with which of the following?
a) It causes death in heterozygotes
b) Death occurs within 2-3 years of life
c) HEXA gene is affected
d) Central nervous system is affected
View Answer

Answer: a
Explanation: Tay Sach’s disease occurs due to the homozygous condition of the lethal allele only. It is a recessive gene and not a dominant gene.
advertisement

8. A person homozygous for lethal allele______________
a) Always dies
b) Always expresses the phenotype
c) May not express the phenotype
d) They have severe abnormalities
View Answer

Answer: c
Explanation: A person with a lethal allele doesn’t always die, as in case of temperature sensitive mutant it is seen that the lethality only occurs at higher temperature.

9. Huntington’s disease affects individuals carrying the gene starting from the age of ____________
a) 10
b) 20
c) 30
d) Random
View Answer

Answer: c
Explanation: People carrying this dominant allele show the symptoms starting from their 30s. Thus, even with the presence of dominant allele, it is not expressed right from the start.
advertisement

10. Dominant lethal alleles are quickly removed from the pool while the recessive ones remain.
a) True
b) False
View Answer

Answer: a
Explanation: If the lethal allele is dominant it will be expressed even in heterozygotes. This will lead to the death of most individuals carrying the gene and if that is before the mating age the gene will gradually be eradicated from the gene pool.

Sanfoundry Global Education & Learning Series – Cytogenetics.

To practice all areas of Cytogenetics, here is complete set of 1000+ Multiple Choice Questions and Answers.

Participate in the Sanfoundry Certification contest to get free Certificate of Merit. Join our social networks below and stay updated with latest contests, videos, internships and jobs!

advertisement
advertisement
Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He is Linux Kernel Developer & SAN Architect and is passionate about competency developments in these areas. He lives in Bangalore and delivers focused training sessions to IT professionals in Linux Kernel, Linux Debugging, Linux Device Drivers, Linux Networking, Linux Storage, Advanced C Programming, SAN Storage Technologies, SCSI Internals & Storage Protocols such as iSCSI & Fiber Channel. Stay connected with him @ LinkedIn | Youtube | Instagram | Facebook | Twitter