2. pedigree diagrams

Question 1

what are the 3 types of genetic disorders

Answer 1

1. single gene (alleles are single locus)
2. chromosomal (translocations, monosomy, trisomy)
3. complex (most common, both genetic and environmental, like cancer and CVS disease)

Question 2

2 types of genetic sequencing

Answer 2

WGS (whole genome sequencing) - along entire genome, both coding and non coding regions

WES (whole exome sequencing) - sequencing of coding regions, specifically focusing on protein encoding regions

Question 3

Pedigree def + function

Answer 3

Chart of the genetic family history over several generations –> able to characterise single gene disorders and hence derive their patterns of transmission.

!! the patterns of inheritence observed can also help distinguish between diseases of similar presentations

Question 4

steps to construct pedigree

Answer 4

1. identify consultand (person who asks for advice) and proband (affected individual who brings family to medical attention)
2. Collect family history (+ write date and person who provided info)
3. Model the history with the correct symbols and notation

!! AT LEAST 3 DEGREES OF RELATIVES ARE NECESSARY:
-1st degree are parents, siblings and children
-2nd degree are aunts, uncles, nieces, nephews, grandparents
-3rd degree are first cousins

Question 5

2 types of collection methods for pedigree family history

Answer 5

1. COMPREHENSIVE: general collection of medical concerns, conditions, hospitalisations, birth defects
2. TARGETED: specialised clinical setting for the evaluation of specific concerns + info is collected about that specific desired condition

Question 6

what are consaguinity relationships and what do they denote

Answer 6

consaguinity –> blood relations between two family members with children (denoted by double line). Specify their relation on the diagram (eg second cousins)

!! consanguinity relationships imply autosomal recessive inheritence patterns

Question 7

Autosomal dominant inheritence pattern

Answer 7

-only one allele needed to cause phenotype
-affects both sexes equally
-since its dominant it does not skip generations, hence meaning that every affected individual has at least 1 affected parent (unless imcomplete penetrance)

EX: marfan’s, achondroplasia, porphyria

Question 8

Autosomal recessive inheritence pattern

Answer 8

-both alleles need to be present to cause phenotype
-affects all sexes equally
-skips generations (ie 2 unaffected parents can be carriers and hence have an affected child)
-increased chance of this mode of inheritence in the case of consanguinity

EX. CF, sickle cell, PKU, galactosemia

Question 9

Xlinked recessive inheritence pattern

Answer 9

-affected females are XrXr, males XrY
-more males affected bcos they dont have a second X chromosome to compensate for the recessive allele.
-Hence only females can be carriers
-No male to male transmission (bcoe fathers pass their Y chromosome to sons)
-All affected daughters have affected fathers

EX. hemophelia, red/green colour blindness (diagnosed with the ishihara test with numbers in circles), favism, duchenne muscular dystrophy

Question 10

X linked dominant inheritence pattern

Answer 10

-affected females have XRXR or XRXr, males have XRY
-more affected females than males
-an affected male will have 100% of his daughters be affected (bcos he always passes down XR)

EX. hypophosphatemia (low levels of Pi)

Question 11

Y linked inheritence pattern

Answer 11

-only males affected (females dont have X chromosome)
-100% of affected sons have affected fathers
-affected fathers have 100% of their sons be affected

EX. hairy ears (rare bcos Y chromosome doesnt contain a lot of genes)