Same answer chain

Use this to connect the question's starting point to the final result.

Use parent genotypes to identify possible gametes

Combine gametes to derive offspring genotypes

Map each offspring genotype to the affected or unaffected phenotype

State a probability that matches the derived offspring outcomes

Current question

A man and a woman do not have CF. The man and the woman have a child who has CF. Draw a Punnett square diagram to find the probability that their next child will have CF. Use the symbols: T = dominant allele t = recessive allele Draw a ring around the genotype of any children with CF. Probability = Embryo screening for CF can be done by two methods. Method 1 • The woman becomes pregnant by sexual intercourse. • After 10 weeks of pregnancy a fine needle is inserted into the uterus. • A sample of the fluid surrounding the embryo is taken. • The DNA of the embryo is tested for CF. The screening is done free by specialist hospitals for couples who are at risk of having

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Why this earns marks

1 Use parent genotypes to identify possible gametes.
2 Combine gametes to derive offspring genotypes.
3 Map each offspring genotype to the affected or unaffected phenotype.
4 State a probability that matches the derived offspring outcomes.

Common weak answer: Names the topic but skips the middle reasoning links.