This set of Cytogenetics Multiple Choice Questions & Answers (MCQs) focuses on “Other Methods of Sex Determination”.
1. The XO system of sex determination is found in ______________
a) Insects
b) Birds
c) Reptiles
d) Mammals
View Answer
Explanation: Insects have this XO system of sex determination. Thus it can be seen in Grasshopper, cockroaches, bees etc. Other options here have different modes of sex determination other than XO.
2. In case of XO system if an organism has AA+XO it will be a _______
a) Male
b) Neuter
c) Female
d) Bisexual
View Answer
Explanation: In XO system presence of one copy of X chromosome produces a male, while there is no Y chromosome. Two copies give a female.
3. In XO system a male has a mother but not a _____________
a) Grand father
b) Father
c) Grand mother
d) Sibling
View Answer
Explanation: The males are produced by parthenogenesis, i.e. by mitosis. While fertilization only takes place in case of a female child, only the two X chromosomes come together. Thus, the male has a mother but no father; they do however have a grandfather.
4. We will see ZZ/ZW system in chicken; state true or false.
a) True
b) False
View Answer
Explanation: ZZ/ZW system is seen in birds, chicken being a bird also follows this system. Mammals and insects have other system of gene determination.
5. In ZZ/ZW system which of the following is true?
a) All organisms have ZZ chromosome
b) The chromosomes are shaped like Z
c) Females have ZW constitution
d) Male is heterozygous
View Answer
Explanation: ZZ/ZW sex determination system is much like XX/XY system. However, in this case male is homozygous ZZ and female is heterozygous ZW. In this case to avoid confusion different notation is used and not because of the shape.
6. In ZZ/ZW system if there is a recessive Z allele carrying a distinct phenotype, it will have greater probability of expression in ____________
a) Male
b) Female
c) Recessive genes will not be expressed
d) Both genders equally
View Answer
Explanation: Females being heterozygous will lack the compensating functional copy from other Z chromosomes will express it with greater probability. This is similar to the fact that X linked recessive disorder in mammals is expressed more in males.
7. Genic system of sex determination is seen in _______________
a) Yeast
b) Fishes
c) Reptiles
d) Mammals
View Answer
Explanation: Yeast and other eukaryotic microorganism have this genic system of sex determination. In this case there is no special sex chromosome.
8. In bees the males are produced by _________
a) Mitosis and then fertilization
b) Meiosis and then fertilization
c) Mitosis but no fertilization
d) Meiosis but no fertilizaton
View Answer
Explanation: Bees have XO system of sex determination. In it the males are produced by parthenogenesis i.e. here is mitosis occurring in the mother that gives the zygote for male offspring.
9. Parthenogenesis can also take place in human beings.
a) True
b) False
View Answer
Explanation: Although intriguing but parthenogenesis is not possible for human beings. This is because of imprinting where some genes from a particular parent are turned off in offspring depending on its gender.
10. Which of the following is true for a genic mode of sex determination?
a) It is seen in higher eukaryotes
b) Gene locus determines gender
c) XX will always give female in this case
d) It makes use of parthenogenesis for producing male offspring
View Answer
Explanation: Genic mode of sex determination is seen in eukaryotic microorganisms. In this case, there is no separate chromosome but allele at the gene locus determines sex.
11. In yeast the gene responsible for sex determination is ______________
a) SXL
b) XCE
c) MAT
d) XIST
View Answer
Explanation: In yeast, the genes at the MAT locus are responsible for determining the sex. Sex is mainly determined as mating factor and it alternates with every generation.
12. In yeast a MAT a type yeast can mate with __________
a) MAT alpha
b) MAT beta
c) MAT a
d) It can’t mate
View Answer
Explanation: There are two mating types in yeast, MAT a and MAT alpha. Only yeast cells of opposite mating types can mate. In this case MAT, a can thus mate with MAT alpha. There is no MAT beta.
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