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Humans produce hormones to control reproductive cycles and to control urine production - Edexcel - GCSE Biology - Question 3 - 2017 - Paper 1
Question 3
Humans produce hormones to control reproductive cycles and to control urine production. (a) After fertilisation an embryo is implanted in the lining of the uterus. ... show full transcript
Worked Solution & Example Answer:Humans produce hormones to control reproductive cycles and to control urine production - Edexcel - GCSE Biology - Question 3 - 2017 - Paper 1
Step 1
Describe how the sex of the embryo is determined at fertilisation.
Answer
The determination of the sex of the embryo occurs at fertilisation based on the combination of sex chromosomes contributed by the sperm and the egg. In humans, the mother provides an X chromosome from her egg, while the father contributes either an X or a Y chromosome from his sperm. If the fertilised egg receives an X chromosome from the sperm, the resulting genotype will be XX, which develops into a female embryo. Conversely, if the sperm contributes a Y chromosome, the genotype will be XY, leading to the development of a male embryo.
Step 2
Step 3
Use the Punnett square to calculate the probability that the child will be a male with haemophilia.
Answer
To find the probability, we set up a Punnett square:
X^H | Y
-----------------
X^h | X^H X^h | Y X^h
-----------------
X^h | X^H X^h | Y X^h
The possible genotypes from this cross are:
- X^H X^h (female carrier)
- X^H Y (normal male)
- X^h X^h (female with haemophilia)
- X^h Y (male with haemophilia)
From the Punnett square, there is 1 out of 4 chance (25%) of getting a male with haemophilia (the genotype X^h Y). Thus, the probability is 25%.