1. Higher Human Biology Subtopic 12 (b) Genetic Screening and Counselling
Physiology and Health
Higher Human Biology
Subtopic 12 (b)
Genetic Screening and Counselling

2. Learning Intentions To revise key terms which relate to genetics
To explain what a pedigree chart is and how it is used to analyse patterns of inheritance
To discuss the use of these charts in counselling

3. 2015 Exam Essay Title
A Describe hormonal control of the menstrual cycle under the following headings:
events leading to ovulation; 6
events following ovulation

6. Reminder Can you remember the key words about genetics? Haploid
Diploid
Gene
Alleles
Recessive
Dominant
Homozygous
Heterozygous
Genotype
Phenotype

7. Reminder
Genetic Crosses!

8. Pedigree Charts (family trees)
These can be used to analyse patterns of inheritance.
Phenotypes for a characteristic help construct the tree then the genotype can be worked out.

9. Pedigree Chart

10. Patterns of Inheritance
Conditions linked to the sex chromosomes (X and Y) are called sex linked
Conditions linked to all other chromosomes are called autosomal.
There are 4 main patterns to remember :
Autosomal recessive
Autosomal dominant
Autosomal incomplete dominance
Sex linked recessive

11. Autosomal recessive E.g. cystic fibrosis Rarely shows up
Skips generations
Shows up in couples who are closely related
Equally shows in male and females
E.g. cystic fibrosis

12. Outcomes Sufferers All homozygous recessive (cc) Non Sufferers
Homozygous dominant (CC)
Heterozygous (Cc)

13. Page 152

14. Page 152

15. Page 152 – What would the councillor think?
Cystic fibrosis is known in Sandra’s family and the counsellor has worked out she has a 2 in 3 chance of being a carrier. Ian’s family has no history of cystic fibrosis. Outcome Low risk of producing a child with CF

16. Autosomal dominant E.g. Huntington’s Trait appears in every generation
Each sufferer has an affected parent
Equal in males and females
If a branch of the tree is missed then the trait is gone
E.g. Huntington’s

17. Outcomes Sufferers Homozygous dominant (HH) Heterozygous (Hh)
Non Sufferers
- All homozygous recessive (hh)

18. Page 153

19. Page 153

20. Page 153 – What would the councillor think?
Both are still too young to know if they have received the mutant allele from their parents, however they both have a 1 in 2 chance of having the allele. Outcome They have a high chance of passing on the allele. 1 in 2 chance if one is a carrier. 3 in 4 chance if both are!

21. Autosomal incomplete dominant
Full condition rarely expressed
(both parents must be partial sufferers)
Part condition much more common
Equal in males and females
E.g. sickle cell

22. Outcomes Sufferers Non Sufferers Part sufferer = heterozygous (HS)
Full sufferers = homozygous for the
incompletely dominant allele (SS)
Non Sufferers
- Homozygous dominant (HH) for the other
incompletely dominant allele

23. Page 154

24. Page 155

25. Page 155
Both Chika and Sabato are heterozygous for the trait and so carry the incomplete allele for sickle cell.
Outcome
They have a 1 in 4 chance of their child fully expressing the trait, a 1 in 2 of part expression and a 1 in 4 of their child being unaffected.

26. Sex-linked recessive More males than females
Sons of affected males don’t show the condition as the get the Y chromosome from their father
Females are the carrier of the gene
E.g. haemophillia

27. Outcomes Sufferers Non Sufferers
Homozygous recessive ( XhY and rarely XhXh )
Non Sufferers
Homozygous dominant ( XHY or XHXH )
Heterozygous female carrier ( XHXh )

28. Page 155

29. Page 156

30. Page 156
Jane’s family has a history of haemophilia but Hamish’s does not. A counsellor would conclude that Jane has a 1 in 2 chance of being a carrier since her mother and sister are carriers. Outcome There would be a 1 in 4 chance of the child having haemophilia

31. Learning Intentions To revise key terms which relate to genetics
To explain what a pedigree chart is and how it is used to analyse patterns of inheritance
To discuss the use of these charts in counselling