ch12: mendels experiments and heredity Flashcards
why did gregor mendel pick pea plants to experiment on (4 bullets)
- many pea varieties (“mutants”) available
- short generation times
- many offspring per plant (each individual pea is one offspring)
- peas can self-fertilize OR be cross-fertilized
true-breeding strains
has been “inbred” for many generations; offspring has identical phenotypes to parent
female part of a flower
stigma or carpel
male part of the flower
anther
how did mendel cross pollinate the pea plants
he took the anther of one plant (so it cant self pollinate) and added pollen from another plant
mendels experimental method (5 steps)
- produce true-breeding parental strains for each trait he was studying (P)
- cross-fertilize two true-breeding strains that have alternate forms of a trait to produce F1 generation (hybrid)
- also perform reciprocal crosses to make sure the results werent dependent on which variety came from male vs female parental (F1)
- allow the hybrid (F1) offspring to self-fertilization to produce the F2 generation and count the number of offspring showing each for of the trait (F2)
- allow the F2 generation to self-fertilize to produce F3 generation and count number of offspring with each trait (F3)
monohybrid cross
cross to study only two variations of a single trait; mendel produced true-breeding pea strains for seven different traits
F1 generation
first filial generation; produced by crossing two true-breeding strains; dominant trait
F2 generation
second filial generation; results from the self-fertilization of F1 plants; recessive trait
what was the ratio of dominant to recessive traits
3:1
F3 generation
third filial generation; F2 plants self-fertilize;
recessive F2 plants were always true-breeding;
1/3 of F2 dominant plants were true-breeding;
2/3 of F2 plants were not (acted like the F1 generation)
how many categories of plants were in the F2 generation
three (true-breeding dominant, non-true breeding dominant, true-breeding recessive)
mendel’s observations (5 bullets)
- parents transmit genes for particular traits
- not all copies of a gene are identical (homozygous and heterozygous)
- presence of allele does not guarantee expression (dominant and recessive)
- each individual receives one copy of a gene from each parent (child receives one set of chromosomes containing genes from each parent)
- alleles segregate randomly to form gametes for next generation-no blending
phenotype
physical appearance of an individual
genotype
total set of alleles an individual contains
allele
alternate form of a gene (homozygous vs heterozygous)
dominant allele
expressed gene; capitol letter
recessive allele
hidden by dominant allele; lowercase letter
homozygous
two copies of the same allele; “true-breeding”
heterozygous
two different alleles
progeny
another word for offspring
physical basis for allele segregation is the behavior of
chromosomes during meiosis
punnett square
technique developed to easily visualize and anticipate genotypes for the various crosses
which shape represents which sex in a pedigree analysis
squares represent men, circles represent women
if you see an affected child with a recessive trait and both parents are unaffected
both parents must be carrier/heterozygous
how do you know if a disease is dominantly inherited
the disease will not skip a generation, at least one person will always be affected
autosomal dominant
affected males and females appear in each generation of the pedigree; affected mothers and fathers transmit the phenotype to both sones and daughters (huntington disease)
autosomal recessive
the disease appears in male and female children of unaffected parents (cystic fibrosis)
dihybrid crosses
examination of two separate traits in a single cross; traits sort independently on different chromosomes
dihybrid cross ratio for an F2 generation
9:3:3:1
rule of addition
the probability of any combination of results is the sum of their individual probabilities
rule of multiplication
probability of two independent events occurring at the same time is the product of their individual probabilities
how to perform a test cross (also known as a back cross)
cross an unknown dominant (P__) with a homozygous recessive (pp)
-if the dominant was homozygous (PP), all offspring will be dominant (Pp)
-if the dominant was heterozygous (Pp), half of the offspring will be recessive (pp)
what does chi squared determine
sum of the deviations between observed and predicted frequencies
P value of 0.5
critical values (maximum difference between observes and expected) that would occur by chance 95% of the time
degree of freedom
number of phenotypes - 1
if X^2 is GREATER than the critical value, that means that…
the distribution of phenotypes is greater than expected by chance 95% of the time, meaning you would reject the hypothesis
if X^2 is LESS than the critical value, that means that…
the distribution of phenotypes is within the expected by chance 95% of the time, meaning you would accept the hypothesis
chi squared equation
x^2 = “the sum of” (observed-expected)^2 / expected
mendel’s model of inheritance only works if the following criteria are met:
1) each trait is controlled by a single gene
2) each gene only has two alleles
3) there is a clear dominant/recessive relationship between the two alleles
polygenic inheritance
occurs when multiple genes are involved in controlling the phenotype of a trait; these traits show continuous variation and are referred to as quantitive traits (eye color or height)
pleiotropy
when an allele has more than one effect on the phenotype; difficult to predict because a gene that affects one trait often performs other unknown functions (cystic fibrosis)
multiple alleles
each individual can only have 2 alleles (2n), but may be more than 2 alleles for a gene IN A POPULATION
(Ex. ABO blood types -> 3 alleles)
incomplete dominance
-heterozygote is intermediate in phenotype between the two homozygotes
ex. red flower+white flower= pink flower
-written as an exponent (C^R C^R or C^W C^W)
codominance
-each allele has its own effect, and heterozygote shows some aspect of the phenotypes of both homozygotes
ex. blood type: A, B, AB, O
-written as “I” + superscript
- I^A I^A = A blood type
-I^B I^B = B blood type
-I^A I^B = AB blood type
-ii= O blood type
