Question 1: Define sex determination in biological terms.

Answer: Sex determination is the biological process that decides the sexual characteristics of an organism, typically resulting in male or female phenotypes, based on genetic or environmental factors.

Question 2: Explain how the presence of the Y chromosome influences male development in humans.

Answer: The Y chromosome contains the SRY gene, which triggers testes development and initiates pathways leading to male sexual characteristics during embryonic development.

Question 1: Describe how the XY chromosome system determines sex in humans.

Answer: In the XY system, males have one X and one Y chromosome, while females have two X chromosomes. The presence of the Y chromosome in males triggers male development.

Question 2: In some species, sex is determined by environmental factors. Name one such factor and describe its effect.

Answer: Temperature during incubation can determine sex; for example, in some reptiles, higher temperatures produce females, while lower temperatures produce males.

Question 1: Calculate the probability of a couple having a son if both parents are carriers of the sex-linked trait on the X chromosome, assuming the trait is recessive. Use Punnett square analysis.

Answer: The probability is 25%. (Punnett square: 50% chance of male offspring, with 50% of males inheriting the trait if the mother is a carrier.)

Question 2: If the chance of a fertilisation resulting in a female in a species with XY sex determination is 0.5, what is the probability that in 4 independent fertilisations, exactly 2 result in females? Use binomial probability formula.

Answer: Using P = (n choose k) * p^k * (1-p)^(n-k), P = (4 choose 2) * (0.5)^2 * (0.5)^2 = 6 * 0.25 * 0.25 = 0.375 or 37.5%.

Question 1: Design a simple experiment to investigate the effect of temperature on sex ratio in reptiles. List the key variables and safety precautions.

Answer: The experiment involves incubating reptile eggs at different temperatures. Independent variable: incubation temperature. Dependent variable: sex of hatchlings. Control variables: egg species, incubation duration. Safety precautions include handling eggs carefully to prevent damage and avoiding extreme temperatures that could harm researchers or eggs.

Question 1: In a population of 200 reptiles incubated at a certain temperature, 150 hatchlings are female and 50 are male. What is the observed sex ratio? What could this suggest about the influence of temperature?

Answer: The sex ratio is 3 females to 1 male. This suggests that the incubation temperature favoured female development, indicating environmental sex determination.

Question 1: Discuss how knowledge of sex-linked inheritance can be used in genetic counselling for hereditary diseases.

Answer: Genetic counselling can identify carriers of sex-linked disorders, such as haemophilia, allowing couples to understand the risks of passing on the condition and make informed reproductive choices.

Question 2: Explain how advances in genetic technology could potentially manipulate sex ratios in agriculture or conservation efforts.

Answer: Genetic techniques like gene editing or manipulation of sex-determining genes can influence the proportion of males and females in populations, aiding in pest control, breeding programmes, or conservation of endangered species.