Crossing OverCrossing OverSuma Gondi and Kathryn Addabbo

CQ1: Imagine you are a member of the CQ1: Imagine you are a member of the committee assigned to determine whether committee assigned to determine whether Santhi is female. Here are possible results of Santhi is female. Here are possible results of the initial tests (we don’t know the real the initial tests (we don’t know the real results):results):

Female genitalia: Yes

Breasts and pubic hair: Yes

Regular menstrual cycle: Never

From this information, you conclude that Santhi is:

A: Male B: Female

The answer is B, Santhi is female.

CQ2: A karyotype was performed on an athlete. Here CQ2: A karyotype was performed on an athlete. Here are the results:are the results:

From these results, the athlete is:A: Male B: Female

The answer is A, because Santhi possesses both an X and Y chromosome.

CQ3: So if Santhi is a normal CQ3: So if Santhi is a normal female, her karyotype would be:female, her karyotype would be:

A: XXB: XYC: YYD: XXY

The answer would be A, females possess two X

chromosomes.

CQ4: Assume that this is one of Santhi’s CQ4: Assume that this is one of Santhi’s chromosomes. This chromosome is composed chromosomes. This chromosome is composed of two chromatids joined by a centromere.of two chromatids joined by a centromere.

A: These chromatids make up a diploid chromosome.

B: The cell that contains these sister chromatids must be diploid.

C: The sister chromatids were formed by replicating a single chromatid.

D: The sister chromatids were joined by fertilization, bringing together a maternal and paternal chromatid.

The answer is C, because the

chromatids are identical.

CQ5: What is true after Meiosis CQ5: What is true after Meiosis I?I?A: Four cells have been produced.B: The cells are haploid.C: The DNA will be replicated once more.D: The cells are ready to perform as

gametes.E: Each chromosome consists of a single

strand of DNA.

The answer is B.

CQ6: During Meiosis II:CQ6: During Meiosis II:

A: Homologous chromosomes separate.

B: The DNA is replicated.C: Gametes fuse.D: Sister chromatids separate.E: All of the above.

The answer is D. Sister chromatids are pulled apart.

CQ7: How many possible combinations CQ7: How many possible combinations of maternal chromosomes are possible of maternal chromosomes are possible in a human ovum due to independent in a human ovum due to independent assortment during meiosis?assortment during meiosis?

A: 23 combinations.B: 46 combinations.C: 232 = 529 combinations.D: 223 = ~ 8 million combinations.

The answer is D. There are many different combinations.

CQ8: Could Santhi have an CQ8: Could Santhi have an XX karyotype and be male?XX karyotype and be male?

A: No, an XX individual is always female.

B: Yes, this is common.C: Yes, if a male-determining control

gene is carried on one of her X chromosomes.

The answer is C.

CQ9: During crossover, all of CQ9: During crossover, all of the following happen EXCEPT:the following happen EXCEPT:

A: The homologous chromosomes line up in pairs.

B: The homologous chromosomes swap pieces with their adjacent partners.

C: Crossing over decreases the genetic variability in the gametes.

D: Each chromatid is unique after it has crossed over.

The answer is C.

CQ10: If you were a member of the CQ10: If you were a member of the Asian Games medal committee and Asian Games medal committee and Santhi’s karyotype revealed that she Santhi’s karyotype revealed that she is XY and is XY and SRY+SRY+, what would you do?, what would you do?

A: She has female genitalia, allow her to keep her medal.

B: She is genetically male, take her medal away.

C: Perform additional tests.

Our personal choice is A.

CQ11: What do you think about CQ11: What do you think about requiring gender testing for female requiring gender testing for female athletes in international competition?athletes in international competition?

A: It should be banned because gender determination is so complex.

B: It is necessary to ensure an even playing field.C: It is necessary, but needs to include a large

number of genetic tests to ensure fairness.D: It should be required for all athletes, both

male and female.

Our personal answer is both A and C. Gender determination is very complex, as the possibilities are endless. Yet if testing continues, it should be so fairly.