Photo AI
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 combination of sex chromosomes contributed by the parents during fertilisation. Males contribute either an X or a Y chromosome from the sperm, while females provide an X chromosome from the egg. If the sperm carries an X chromosome, the resulting genotype will be XX, leading to a female embryo. Conversely, if the sperm carries a Y chromosome, the genotype will be XY, resulting in 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 calculate the probability using the Punnett square, we represent the female carrier with genotype X^H X^h and the non-haemophiliac male with genotype X^H Y.
The Punnett square will look like this:
| X^H | Y
------------------
X^H | X^H X^H | X^H Y
------------------
X^h | X^H X^h | X^h Y
The possible genotypes for their children are:
- X^H X^H (female, normal)
- X^H Y (male, normal)
- X^H X^h (female, carrier)
- X^h Y (male, haemophiliac)
From this, there are two males (X^H Y and X^h Y) and out of the four offspring, one (X^h Y) is a male with haemophilia. Thus, the probability of having a male child with haemophilia is:
P(X^h Y) = rac{1}{4}
This can also be expressed as 25%.