Chapter 2 Flashcards
Gregor mendel gen info
- priest
- was gonna be a teacher but didn’t finish exam
- interested in natural science
Blending theory of inheritance
pre gregor mendel era
offspring traits are an intermediate mixture of the parental traits
black + white cat = grey cat
Mendel pea dom/rec traits
how many traits researched?
7 researched
dom:
1. yellow seed
2. round seed
3. green pod
4. inflated pod
5. purple flower
6. axial
7. tall
5 awesome features of Mendel’s experiment
- controlled breeding (artificial cross-fertilization)
- Pure breeding strains
- Dichotomous traits
- Quantification of results
- Used replicate, reciprocal and test crosses
GG x gg phenotypic ratios for F1 and F2
F1: 4:0
F2: 3:1
Mendel’s first law
Law of segregation
- 2 alleles for a trait separate during gamete formation
- equal probability (50/50) of being passed on
- random unions in predictable proportions
Test cross
first cross homo homo to get hetero for sure
AA x aa = Aa
then cross hetero with homo recessive
Gg x gg phenotypic ratios for F1 and F2
F1: 1:1
F2: 1:1
Mendel’s second saw
Law of independent assortment
for UNLINKED genes, the segregation of alleles at one gene is independent of the segregation of alleles at another gene
9:3:3:1 result (3:1 for each trait)
GGAA x ggaa phenotypic ratios for F1 and F2
F1: GgAa
F2: 9:3:3:1 (phenotypically)
Product rule
probability of two events occurring SIMULTANEOUSLY or CONSECUTIVELY
“AND” rule
multiplication
Sum rule
events that CANNOT occur at the same time
probability of one event or the other occurring
“OR” rule
addition
Conditional probability
The probability of an event occurring with a previous outcome modifying the result
you know the pod is green, what are the genotype odds
Binomial probability
combination or sequence of events
two parts
1. number of combination outcomes that can occur
2. calculating the probability of each event
Binomial equation
- number of combination outcomes that can occur
n! / r!(n-r)! - calculating the probability of each event
p^r q^(n-r)
Phenotypic ratios for 2 genes
AaBb x AaBb
9:3:3:1
AaBb x aabb
1:1:1:1
Chi-square test (X^2)
a way to test whether observed data significantly differs from expected data
X^2 = sum (O-E)^2/E
P value
Chi-square tests result in a probability value
high p values (>0.05) suggest any differences observed in data are NOT statistically significant
so we CAN’T reject the null hypothesis
low p values (<0.05) suggest any differences observed in data ARE statistically significant
so we CAN reject the null hypothesis
Null hypothesis
there is no difference between observed and expected data
expected data represents the outcome from random chance
Three things P value depends on
- X^2 value
- higher values mean the null hypothesis is less likely and P value will be lower - Degrees of freedom
- number of independent values in the data
- higher df means the X^2 value must be higher to reject null
df = # outcomes - 1 - alpha value
- threshold for P to be considered significant
- often 0.05
One gene-one enzyme hypothesis
- gene is a unit encoding a polypeptide
- mutations often involve a “blockage” in a biochemical pathway
ex. inhibiting enzyme function
= retain an immature colour
Human karyotype
23 pairs of chromosomes
22 pairs are autosomal
- usually follow mendelian
1 pair is sex chromosomes
Pedigrees
aka family trees
a way of tracing inheritance of traits
generations indicated by roman numerals
Autosomal patterns of inheritance (gen.)
Dom traits
- similar frequency m/f
- if individual has the trait, at least one parent will too
- if neither parent has, offspring won’t have
- parents with trait may produce children who don’t have it
Recessive traits
- similar frequency m/f
- if both parent have, all offspring will have, often skips generations
- if one parent has and child has, other parent hetero
