Test 1 Genetics

Front 1

likelihood of independent events
occurring simultaneously = product of the
individual probabilities [ex., =P(1)xP(2) ]

Back 1

Product rule

Front 2

likelihood of mutually
exclusive events occurring
simultaneously is sum of individual
probabilities [e.g., = P(1)+P(2) ]

Back 2

Sum rule

Front 3

“There is no difference
between the real and predicted data.”

Back 3

null hypothesis

Front 4

test difference
between real and expected data

Back 4

Chi-squared test

Front 5

Probability that observed variation from predicted
values due to chance
• The lower the P-value the likelier the null
hypothesis (“no difference between real and
predicted data”) should be rejected
Common threshold: P≤0.05 -- suggests should
reject null hypothesis

Back 5

P-value

Front 6

# of categories -1

Back 6

Degrees of freedom

Front 7

Complete loss of gene function:
• Usually recessive
• Some genes need two functional copies to have wild type
phenotype: “haplo-insufficient”

Back 7

Null (amorph) (LOF) mutations

Front 8

• Usually recessive, but can also show haplo-insufficiency

Back 8

Partial LOF (hypomorph)

Front 9

Increase in normal gene
function:
• Usually dominant
• Effects ameliorated by combining with a LOF allele

Back 9

Gain of function (“GOF”) mutations– Hypermorph

Front 10

Gene acquires novel function
• Usually dominant
• May or may not retain normal function

Back 10

Neomorph Gain of function (GOF)

Front 11

Antagonize or interfere with wild-type gene
function
• Usually dominant
• Phenotypic effects ameliorated by combining with a
hypermorph (increased function)
• Effects worsened by combining with a LOF allele

Back 11

Antimorph (dominant negative)

Front 12

The complete set of
chromosomes in a cell

Back 12

Karyotype

Front 13

cell grows
– prepares for
chromosome
replication

Back 13

G1 phase

Front 14

– DNA replication
– each
chromosome
duplicated to
form two sister
chromatids

Back 14

S phase

Front 15

postsynthesis gap

Back 15

G2

Front 16

– mitosis
– sister
chromatids
separate
– one goes
to each
daughter
cell

Back 16

M phase

Front 17

Cross mutants and examine
phenotype of progeny
determine whether two mutations are alleles
of same or different genes

Back 17

Complementation test

Front 18

Allele pair where
heterozygote phenotype is
intermediate between
homozygote phenotypes

Back 18

Incomplete dominance

Front 19

Allele pair where heterozygote exhibits both
homozygote phenotypes (“sum of phenotypes”)

Back 19

Codominance

Front 20

the action of one gene masks or
modifies the phenotypic effects of the other

Back 20

Epistasis
The gene that masks is the “epistatic” gene
The gene that is masked is “hypostatic”

Front 21

– 9/16 A/- B/-
– 3/16 a/a B/-
– 4/16 { (3/16) A/- b/b +(1/16) a/a b/b }

Back 21

Recessive epistasis

Front 22

– 12/16 { (9/16) A/- B/- + (3/16) A/- b/b }
– 3/16 a/a B/-
– 1/16 a/a b/b

Back 22

Dominant epistasis

Front 23

– 9/16 A/- B/-
– 7/16 { (3/16) A/- b/b + (3/16) a/a B/- + (1/16) a/a b/b

Back 23

Duplicate recessive epistasis

Front 24

Frequency of a
dominant or recessive gene
manifesting its trait.
• Complete Penetrance: 100% of
individuals are affected
• Incomplete Penetrance: <100%
individuals affected

Back 24

Penetrance

Front 25

The degree to which
a dominant or recessive gene is
phenotypically expressed in an
individual.

Back 25

Expressivity

Front 26

phenotypic
severity highly consistent
between individuals

Back 26

Constant expressivity

Front 27

phenotypic
severity highly variable between
individuals

Back 27

Variable expressivity

Front 28

– Clear demarcations between phenotypic classes
– Phenotype is robust assay for genotype
– Example: comb shape, fruit and fur color

Back 28

Discontinuous traits

Front 29

– Continuous distribution of phenotypes across a range
of values
– Examples: height, weight...
– Continuous traits also known as “Quantitative traits”

Back 29

Continuous traits

Front 30

Combined action of alleles
for multiple genes (polygenes) determine
quantitative trait
• Each allele has small effect on final outcome

Back 30

Polygene hypothesis

Front 31

increase in one
variable correlated with
increase in other

Back 31

correlation coefficient If r>0

Front 32

increase in one
variable correlated with
decrease in other

Back 32

correlation coefficient r<0

Front 33

fraction of
variation attributable to genetic rather
than environmental factors
– HB
2= VG / VP

Back 33

Broad-sense heritability

Front 34

fraction of variation
attributable to additive genetic variance

Back 34

narrow-sense heritability

Front 35

segments of the genome associated
with phenotypic differences between
individuals

Back 35

QTLs: Quantitative Trait Loci