Basic Genetic Principles Flashcards
Pedigree symbols to note
Square - male; circle - female. Diamond - unknown.
Pregnancy convention
Write P on the symbol.
Pedigree stillbirth
Note SB and weeks.
Spotaneous miscarriage symbol
Triangle - note sex and week.
Termination of pregnancy
Triangle with line through it, note sex and week
Adoption in family
show with dotted line. Or if adopted out, show with brackets
How to show there are problems in a relationship
with two diagonal lines - might not get much about them
Twins
diagonal lines. DZ = fraternal; MZ = paternal, connect line between. ? for unknown.
No children
Single diagonal line at bottom; or double for endometriosis.
Consanguinity
double line b/w parents that are closely related
Degree for a relative
1st - parent or sibling; 2nd - cousin, or grandparent or uncle. Etc.
Hemizygote
Only got one copy of allele, ie male with one X and one Y. Only one copy on the X.
Compound heterozygote
Both alleles don’t work properly due to mutation. Shade differently?
Autosomal dominant
Appears in each generation, both sexes affected.
How could a autosomal dominant just pop up brand new?
New mutation; Variable expression (some show the trait more than other who also have it); Penetrance (all or nothing); Age of onset; Heterogeneity (many genes that can result in same thing); Phenocopy (produced by environment); Sex influenced traits; Mosaicism: somatic or germ line (only in part of body)
Autosomal recessive
Not every generation since the normal dominates it. More common in consanguinity. Equal chance for boy and girl. 2 heterozygous parents have 25% chance of a child getting affected.
X linked recessive
Mostly only affects males because they only have one X, passed to them by mother only. Females with the mutation are generally carriers, sometimes middy affected. Daughters will be carriers. Lyonization is a factor
Lyonization
One X chromosome is inactivated in a cell, so manifestation can be different ratio throughout the body.
X linked dominant
Rare, Affected males have affected daughters, no sons. Female carrier: sons and daughters affected. Affected females x2 more common. If lethal to males, many miscarriages for male children
Multifactorial inheritance
most common pattern; genes + environment; polygenic (many genes, less environment); multifactorial; threshold traits (enough factors); twin studies. Examples like diabetes, hypertension, folic acid intake, cleft pallet.
Liability
If you have a 1st degree relative (or more), your chance increases greatly compared to population. Can reach a threshold.
Features of multifactorial
Risks increased but less than single gene; “familial” appearance; risk drops off sharply for 2’ relative; severity (if severe in first child, higher chance for second); sex difference (just how it is); number affected; the rarer the condition the higher the risk; empiric figures (look at studies); consanguinity
