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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 sex of the embryo is determined by the type of sperm that fertilizes the egg. Sperm carry either an X or a Y chromosome:
- If the sperm contributes an X chromosome, the resulting genotype will be XX, leading to a female embryo.
- If the sperm contributes a Y chromosome, the resulting genotype will be XY, leading to 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 determine the probability, we can set up a Punnett square using the alleles for the mother (carrier) and father (normal).
Mother: X^H X^h (carrier) Father: X^H Y (normal male)
The Punnett square is arranged as follows:
| X^H | Y
-----------------
X^H | X^H | X^h
-----------------
X^h | X^H | X^h
Offspring Genotypes:
- X^H X^H (Normal female)
- X^H X^h (Carrier female)
- X^h Y (Male with haemophilia)
- X^H Y (Normal male)
Probability:
Out of the four possible outcomes:
- 1 X^h Y (Male with haemophilia)
Thus, the probability of the child being a male with haemophilia is: rac{1}{4} = 25\%.