1. KA 4: Ante- and postnatal screening
(a) Antenatal screening
(c) Pedigree charts
(b) Postnatal screening

2. Learning Outcomes State 2 reasons pedigree charts are used
Name the 4 patterns of inheritance that a pedigree chart can show
Identify characteristics for each pattern of inheritance
Draw, analyse and interpret pedigree charts over 3 generations
Be able to use standardised human pedigree nomenclature and symbols
sex, matings, siblings, affected individuals, twins, heterozygotes, carrier of sex-linked allele and deceased
Calculate probability of outcomes in single genes inherited conditions
Identify genotype for potential offspring and for parents

4. Key Words (revision!)
Gene: a sequence of DNA that codes for a particular protein
Allele: a different form or different version of a gene
Phenotype: the physical appearance of an organism
Genotype: The genes an organism possesses
Dominant: an allele that is always expressed even if only one dominant allele is present
Recessive: an allele that is always masked by the dominant allele, unless paired with another recessive allele
Homozygous: 2 alleles that are identical (BB or bb)
Heterozygous: 2 alleles that are not identical (Bb)
A human cell contains 23 pairs of chromosomes.
The first 22 chromosome pairs are called AUTOSOMES
The last pair of chromosomes are called SEX CHROMOSOMES (X or Y)

5. In order to be successful at Genetics based questions:
Fore-warning:
In order to be successful at Genetics based questions:
It’s all about PRACTICE!
The more examples you do, the better you will be at them!
Do your working!
Do not just guess. Some questions may require you to do 4 punnet squares – SO DO THEM!

6. Pedigree Charts: Why use them?
A pattern of inheritance about one characteristic can be obtained and used to construct a pedigree chart.
Once the phenotypes are determines, the genotypes can also be found.
Construction of a pedigree chart is carried out by genetic councillor who can advise the a couple of the chances of them passing a genetic disorder on to their children

7. Pedigree Charts Types of inheritance (single gene disorders):
Autosomal recessive
Cystic fibrosis / Thalassaemia
Autosomal dominant
Huntington’s chorea
Autosomal incomplete dominance
Sickle cell disease & sickle cell trait
Sex-linked recessive
Haemophilia / Duchenne Muscular Dystrophy
Females who carry 2 recessive alleles suffer from the disease.
Females who carry 1 recessive alleles are known as carriers.
Males need only 1 recessive allele to suffer from the disease.

8. Another sex-linked disorder…

9. Different types of colour-blindness
Normal colour vision uses all three types of light cones correctly and is known as trichromacy
reduced sensitivity to green light
reduced sensitivity to red light
reduced sensitivity to blue light

11. Sex-linked genes
Genes that are found on the X chromosome but have no homologous allele on the Y chromosome are called SEX LINKED genes
Sex linked genes always show in the phenotype as there are no genes on the Y chromosome to counteract them.
Sex-linked genes
Missing area
X Y

12. Pedigree Charts - Patterns
Autosomal recessive
Rare / may skip generations / trait expressed amongst cousins
Autosomal dominant
Appears in every generations / each sufferer also has an affected parent / males and females express trait equally / if 1 branch does not express the trait, it will not reappear in future generations
Autosomal incomplete dominant
Fully expressed form of disorder occurs rarely / partly expressed form occurs more frequently / each fully expressed sufferer has 2 parents that shows partial expression / males and females express trait equally
Sex-linked recessive
More males are affected than females / none of the sons of an affected male show the trait

13. Nomenclature &Symbols
Normal female
Normal male
Affected female
Affected male
Carrier

14. Nomenclature &Symbols

15. Task:
Use the previous notes on “Pedigree charts - patterns” to help you answer the MCQ exam questions…

16. Pedigree Charts - Patterns
Answer = B

17. Pedigree Charts - Patterns
Answer = C

18. Pedigree Charts - Patterns
Answer = B

19. To determine GENOTYPES:
Some Nat 5 examples 
To determine GENOTYPES:
Fill in the recessive alleles first
Then complete the dominant alleles by looking at the CHILDREN

20. What is the genotype for R? What is the genotype for S?
The allele for free earlobes (E) is dominant to the allele for fixed earlobes (e)
What is the genotype for R?
What is the genotype for S? Ee ee

21. Hh HH/Hh The allele for red hair (h) is recessive to non-red (H)
Work out what genotype the dad must be.
What 2 possible genotypes will the sister have? Hh
HH/Hh

22. Now Higher Levels Qs!

23. Autosomal recessive
Answer = A

24. Autosomal dominant
Answer = B

25. Autosomal dominant
Answer = C

26. Autosomal Incomplete Dominance
Answer = A

27. Blood groups Phenotype Possible Genotype Blood group A AA or AO
Blood group B
BB or BO
Blood group O OO
Blood group AB AB

28. Autosomal Incomplete Dominance
Answer = A

29. Sex-linked recessive Question 1:
What are chances of a normal female and a colour-blind male having a colour blind daughter?
Question 2:
If the daughter of the above cross had a child with a normal, what are the chances of having a colour-blind son?

30. normal female x colour-blind male
Sex-linked recessive
normal female x colour-blind male
XnY
XNXN P
Gametes
XN or XN
Xn or Y XN Xn
XN Xn Y
XN Y
F1 genotype
Carrier girl: Carrier girl: Normal boy: normal boy
F1 phenotype

31. carrier female x normal male
Sex-linked recessive
carrier female x normal male
XNY
XNXn F1
Gametes
XN or Xn
XN or Y XN Xn
XN XN
XN Xn Y
XN Y
Xn Y
F2 genotype
Normal girl: Carrier girl: Normal boy: affected boy
F2 phenotype

32. Sex-linked recessive
Answer = D

33. Sex-linked recessive
Answer = C

34. Task: Pedigree Charts Collect a pedigree chart sheet
Complete the chart by filling in the genotypes for every family member
Identify the type of pedigree chart, using your notes
You have 15 minutes!
All answers can be found in the textbook (pages )

35. Learning Outcomes State 2 reasons pedigree charts are used
Name the 4 patterns of inheritance that a pedigree chart can show
Identify characteristics for each pattern of inheritance
Draw, analyse and interpret pedigree charts over 3 generations
Be able to use standardised human pedigree nomenclature and symbols
sex, matings, siblings, affected individuals, twins, heterozygotes, carrier of sex-linked allele and deceased
Calculate probability of outcomes in single genes inherited conditions
Identify genotype for potential offspring and for parents