Sex Determination in Humans_Unsolved Paper
Chapter: Heredity and Evolution | Topic: Sex Determination in Humans
SEX DETERMINATION IN HUMANS_UNSOLVED PAPER
Topic: Sex Determination in Humans
Q1. In humans, the sex of a child is determined by the combination of:
- Only autosomes
- Sex chromosomes
- Blood groups
- Body cells only
Q2.Which pair of sex chromosomes is generally found in a human female?
- XY
- XX
- YY
- XO
Q3. Which pair of sex chromosomes is generally found in a human male?
- XX
- XY
- YY
- XO
Q4. A human sperm can normally carry:
- Only an X chromosome
- Only a Y chromosome
- Either an X or a Y chromosome
- Both X and Y chromosomes together
Q5. A human ovum normally carries:
- Only an X chromosome
- Only a Y chromosome
- Either X or Y chromosome
- Both X and Y chromosomes
Q6. If a sperm carrying a Y chromosome fertilises an ovum carrying an X chromosome, the resulting zygote will generally have:
- XX chromosomes
- XY chromosomes
- YY chromosomes
- XO chromosomes
Short questions
Q1. What are sex chromosomes? How are they different from autosomes?
Q2. State the sex-chromosome combinations generally found in human males and females.
Q3.Why can a sperm cell carry either an X chromosome or a Y chromosome, whereas a human ovum normally carries only an X chromosome?
Q4.What happens to the sex chromosomes when a sperm fuses with an ovum during fertilisation?
Q5. During a classroom activity, students are given two types of sperm cards-X and Y-and one type of ovum card-X.
What possible combinations can students form after fertilisation?
Q6. In some families, people incorrectly blame the mother for the sex of a baby.
Using the basic mechanism of human sex determination, explain why this belief is scientifically incorrect.
Q1. Explain the mechanism of sex determination in humans. Include the sex chromosomes present in males and females and the types of sex chromosomes carried by their gametes.
Q2. Describe how fertilisation can result in either an XX or XY chromosome combination in humans. Use a suitable genetic diagram or cross to explain the process.
Q3. A family celebrates the birth of a child, but relatives wrongly claim that the mother is responsible for whether the child is male or female. Explain scientifically why this claim is incorrect. Also describe the role of the sperm and ovum in determining the chromosome combination of the child.
Q1. Assume that X- and Y-bearing sperm are produced in equal proportions and that each has an equal chance of fertilising an ovum.
a) What is the theoretical probability of an XX chromosome combination?
b) What is the theoretical probability of an XY chromosome combination?
Q2. In a hypothetical sample of 200 fertilisations, assume equal probability of X-bearing and Y-bearing sperm fertilising the X-bearing ovum.
a) Calculate the expected number of XX combinations.
b) Calculate the expected number of XY combinations.
Q3. A teacher places 50 X-bearing sperm cards and 50 Y-bearing sperm cards in a box. Each student randomly picks one sperm card and combines it with an X-bearing ovum card.