chapter 2 Flashcards
Mendel’s Blending Theory of Heredity
viewed the traits in offspring as an intermediate mixture of the parental traits (ex: black+white cat = gray kittens (black and white traits would never reappear if gray kittens crossed)
dichotomous states
each of the 7 traits Mendel studied had 2 states (a dominant and recessive phenotype)
5 features of Mendel’s breeding experiments that were critical to his success
- controlled breeding by artificial cross-fertilization
- used pure-breeding strains
- selection of dichotomous traits
- quantification of results
- used replicate, reciprocal and test crosses
what did Mendel’s controlled genetic crosses of pea plants reveal:
that phenotypic ratio varied in a repeatable way across generations
demonstrated segregation of alleles
Mendel’s first law: law of segregation
-2 alleles for each trait separate during gamete formation
-each allele has an equal probability of being passed on
-mendel further tested this law by doing a “test cross” (crossing a heterozygous individual w/a homozygous recessive individual) = he found a 1:1 genotypic and phenotypic ratio
what is a test cross
cross of an individual organism of dominant phenotype but unknown genotype and an organism with a homozygous recessive genotype (and phenotype).
Law of Independent assortment (Mendel’s second law) and what genes does it only apply to
inheritance of two or more traits simultaneously
-law states that during gamete formation the segregation of alleles at one gene is independent of the segregation of alleles at another gene
-generated 9:3:3:1 ratio in his dihybrid cross (within this he recognized two 3:1 ratios for each trait)
only applies to genes that are unlinked (seperate or far away on the same chromosome)
product rule (And)
if 2 or more events are independent, the probability of the first event and the second event occurring simultaneously/consecutively is the product of their individual probabilities
ex: the probability of rolling a 1 twice in a row using a die
(1/6)(1/6) = 1/32
sum rule (or)
if two or more events are independent, and cannot occur at the same time (mutually exclusive), the probability of one event OR the other event occurring is the sum of their individual probabilities
ex: the probability of rolling a 1 or a 3 in one tosses
(1/6) + (1/6) = (2/6)
conditional probability
probability of an event occuring with a previous outcome modifying or “conditioning” the result
binomial probability and 2 parts of it, plus variables
problems involving a combination or sequence of events that is more complex
ex: what are the chances of getting 2 tails and 1 head in three coin tosses?
part 1: the number of combinations that can occur (n choose r)
part 2: (p^r)(q^(n-r))
n = number of independent trials
r = number of outcome your interested in getting
p = probability
q = 1 - p
Mendel’s phenotypic ratios for one gene and two genes
one gene (A/a) :
3:1 (Aa Aa)
1:1 (Aa aa)
two genes (A/a B/b):
9:3:3:1 (AaBb AaBb)
1:1:1:1 (AaBb aabb)
chi-squared test
test whether observed data significantly differs from expected data
what is the p-value (probability value)
-high vs low
this value indicates the likelihood that the observed data differs from the expected data by random chance alone
-allows us to test against a null hypothesis
high P values (>0.05): any differences are not statistically significant. cannot reject null
low P values (<0.05) : any differences are statistically significant, can reject null
what 3 numbers does the P-value depend on:
1.the x2 value: higher values means the null hypothesis is less likely, and the P will be lower
- degrees of freedom: number of independent values in the data. Higher df means the x2 value must be higher to reject null.
- alpha value: a priori threshold for P value to be considered significant. By convention alpha is often 0.05.
how do mutations usually arise? and what do mutations do?
involve a blockage in a biochemical pathway (mutations inhibit enzyme function which leads to a different phenotype)
Human Karyotype contains:
23 pairs of chromosomes in total
( 22 pairs are autosomal and 1 pair is sex chromosome)
is autosomal inheritance consistent with mendelian principles
yes
Pedigree
used for tracing transmission of disease and other conditions through families
pattern of inheritance for autosomal dominant traits (pedigree)
-equal/similar frequency in males and females
-each individual with the trait has at least 1 parent that also shares the trait
-if neither parent has the trait, none of their offspring will
-parents that have the trait may produce children who do not have it
pattern of inheritance for autosomal recessive traits
-equal or similar frequency in males and females
- if both parents have the trait, all offspring will have it
- the trait often skips generations, but frequency is shared by siblings in the same generation
-if one parent has the trait, the child can only have it if the other parent is heterozygous
mendelian genetics
investigates transmission across generations
molecular genetics
investigates inheritance, expression and variation of nucleic acids and proteins
evolutionary genetics
examines origins and genetic relationships between organisms and the evolution of genes and genomes
