Basic Genetic Principles

Question 1

Pedigree symbols to note

Answer 1

Square - male; circle - female. Diamond - unknown.

Question 2

Pregnancy convention

Answer 2

Write P on the symbol.

Question 3

Pedigree stillbirth

Answer 3

Note SB and weeks.

Question 4

Spotaneous miscarriage symbol

Answer 4

Triangle - note sex and week.

Question 5

Termination of pregnancy

Answer 5

Triangle with line through it, note sex and week

Question 6

Adoption in family

Answer 6

show with dotted line. Or if adopted out, show with brackets

Question 7

How to show there are problems in a relationship

Answer 7

with two diagonal lines - might not get much about them

Question 8

Twins

Answer 8

diagonal lines. DZ = fraternal; MZ = paternal, connect line between. ? for unknown.

Question 9

No children

Answer 9

Single diagonal line at bottom; or double for endometriosis.

Question 10

Consanguinity

Answer 10

double line b/w parents that are closely related

Question 11

Degree for a relative

Answer 11

1st - parent or sibling; 2nd - cousin, or grandparent or uncle. Etc.

Question 12

Hemizygote

Answer 12

Only got one copy of allele, ie male with one X and one Y. Only one copy on the X.

Question 13

Compound heterozygote

Answer 13

Both alleles don’t work properly due to mutation. Shade differently?

Question 14

Autosomal dominant

Answer 14

Appears in each generation, both sexes affected.

Question 15

How could a autosomal dominant just pop up brand new?

Answer 15

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)

Question 16

Autosomal recessive

Answer 16

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.

Question 17

X linked recessive

Answer 17

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

Question 18

Lyonization

Answer 18

One X chromosome is inactivated in a cell, so manifestation can be different ratio throughout the body.

Question 19

X linked dominant

Answer 19

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

Question 20

Multifactorial inheritance

Answer 20

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.

Question 21

Liability

Answer 21

If you have a 1st degree relative (or more), your chance increases greatly compared to population. Can reach a threshold.

Question 22

Features of multifactorial

Answer 22

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