4A Flashcards
A couple of (problematic) theories of __________ from the mid 1800s:
* _______ inheritance: offspring have traits that are intermediate to their parents’
* Lamarck: “_______ __ ______ ____” – in other words,________ traits acquired by
parents are passed on to offspring
– _______ evolution
A couple of (problematic) theories of inheritance from the mid 1800s:
* Blending inheritance: offspring have traits that are intermediate to their parents’
* Lamarck: “inheritance of acquired traits” – in other words, favourable traits acquired by
parents are passed on to offspring
– directed evolution
If _________ inheritance was the mechanism,
variation will be ________ over time.
Inheritance
Does not reflect the ______ presence of
variation observed in _
If blending inheritance was the mechanism,
variation will be reduced over time.
Inheritance
Does not reflect the constant presence of
variation observed in p
GREGOR MENDEL
-tested hypothesis of __________vs_______inheritance
* used ___________ varieties of peas
* always give the same phenotype when ________________________________
* many varieties with different characters
* Published Versuche über Pflanzenhybriden (_________ ___ ______ _____) in 1866, not translated to English
until 1901
-tested hypothesis of blending vs. particulate inheritance
* used true-breeding varieties of peas
* always give the same phenotype when self-crossed
* many varieties with different characters
* Published Versuche über Pflanzenhybriden (Experiments
on Plant Hybridization) in 1866, not translated to English
until 1901
Determine whether statistical patterns in the occurrence
of the contrasting traits persisted by means of crossing
Three important distinctions:
1) ______________ strains (“____” phenotypes)
2) Focused on ________ ______ at a time
3) __________: counted the ________
1) True-breeding strains (“good” phenotypes)
2) Focused on single trait at a time
3) Quantitative: counted the progeny(offspring)
Often the __________ allele codes for a __________ protein whereas the ________
allele does not. Pea colour is determined by the presence of a __________
enzyme that breaks down _________
Often the dominant allele codes for a functional protein whereas the recessive
allele does not. Pea colour is determined by the presence of a functional
enzyme that breaks down chlorophyl
Good nomenclature -
gene symbols reflect mutations or recessive traits
P generation (parental)
cross two true-breeding varieties with a
different phenotype
F1 gen
generation seeds (Filial): F1 “self-fertilize”
F2 generation seeds: what is the outcome? What phenotype are observed
the ratio of 3:1
-always more dominant than recessive
-aLWAYS SEE 3 times more dominant than recessive
Expected ratio of dominant to recessive
phenotypes?
Expected ratio of A/A : A/a : a/a genotypes?
* What are the alleles here? What are the
genotypes?
-3:1
-1:2:1 genotypic ratio
-phenotype and genotype ratios
Seeds in the F2 generation showing the
recessive green phenotype should be
________ _________ ___
* The A/A and A/a genotypes: distinguished by
seeds produced________ ___ ________
* Can we distinguish A/A plants? A/a plants?
Seeds in the F2 generation showing the
recessive green phenotype should be
homozygous recessive a/a
* The A/A and A/a genotypes: distinguished by
seeds produced when F1 is self-fertilized.
* Can we distinguish A/A plants? A/a plants?
No, not phenotypically in the case of complete dominance by phenotype alone
Mendel’s hypothesis:
versus smooth peas)
* If an individual’s pair of genes consists of __________ _____________, one allele is _______ over the other
(_______ trait masks _________ one).
* The pair of alleles that control a character separate as
gametes (______); half of the gametes (_______) carry
one allele and the other half carry the other
allele (Mendel’s Principle of Segregation)_); ______
organisms get one allele from each parent
Mendels hypothesis: Adult plants carry two copies of factors (genes) that
govern the inheritance of a character (e.g., wrinkled
versus smooth peas)
* If an individual’s pair of genes consists of different
alleles, one allele is dominant over the other
(dominant trait masks recessive one).
* The pair of alleles that control a character separate as
gametes (meiosis); half of the gametes (haploid) carry
one allele and the other half carry the other
allele (Mendel’s Principle of Segregation); diploid
organisms get one allele from each parent
Product rule
Probability of two independent events occurring in
succession
* Individual (independent) probabilities are multiplied
* Example: Coin flip probabilities
Sum Rule
Probability of an outcome that can be achieved by two or
more mutually exclusive events is the sum of their
individual probabilities.
* Individual probabilities are added
* Probability of a heads and a tails in two tosses:
* First possibility: heads then tails
* Heads = ½, Tails = ½ (½ × ½ = ¼)
* Second possibility: tails then heads
* Tails = ½, Heads = ½ (½ × ½ = ¼)
* Total probability: ¼ + ¼ = ½
Consider: In the mating A/a × A/a, what is the probability that, (i) the pea nearest
to the stem is green and (ii) among four seeds in a pod, exactly one is green?
* Each seed results from
________ fertilization
* Note: Use of word “and”
____ possible ways that one
seed can be green (outcomes
are _________ ________
Consider: In the mating A/a × A/a, what is the probability that, (i) the pea nearest
to the stem is green and (ii) among four seeds in a pod, exactly one is green?
* Each seed results from
independent fertilization
* Note: Use of word “and”
Four possible ways that one
seed can be green (outcomes
are mutually exclusive
Monohybrid cross:
*Probability of a gamete inheriting one of
the two alleles during meiosis is _______
(____________ _________- of chromosomes at
the _________ plate)
*Probability of a genotype in a cross is
determined by the product of the
probabilities of acquiring each gamete
from the mother and father
Monohybrid cross: a cross between two
heterozygotes (for a single gene)
*Probability of a gamete inheriting one of
the two alleles during meiosis is random
(random alignment of chromosomes at
the metaphase plate)
*Probability of a genotype in a cross is
determined by the product of the
probabilities of acquiring each gamete
from the mother and father
Mendels principle of segragation is
Each organism is diploid: has two alleles
*Homozygous: the two alleles are the same,
therefore produce only one type of gamete
*Heterozygous: the two alleles are different,
therefore produces two types of gametes
How to determine a hetezygote
A test cross is a mating to an individual with
the homozygous recessive genotype
Highly informative: tester individuals carry only
the recessive allel
Test cross: to determine whether the dominant
phenotype is a homozygote or heterozygote
-Procedure: cross individual with dominant
phenotype to a homozygous recessive
* If heterozygous (P/p), then see 1:1 of
dominant and recessive phenotypes
* If homozygous (P/P), then see all dominant
phenotyp
The principles of transmission genetics have a physical basis
in the process of meiosis
- 1903 Walter Sutton was grad student studying
________ and ______ in grasshoppers - noticed:
- chromosomes occur in ______ in ________ organisms
- chromosomes of each pair _________ in _________
- separation of each pair of chromosomes is
___________ of other pairs - Chromosomal Theory of Inheritance
- confirmed by Thomas Hunt Morgan in 1910
he realized that what he was observing was the separation of things that ended up forming the gametes, and if we we were to stick alleles onto those things being sepatrated it would explain this process of segregation that mendel was observing .
The principles of transmission genetics have a physical basis
in the process of meiosis
* 1903 Walter Sutton was grad student studying
fertilization and meiosis in grasshoppers
* noticed:
* chromosomes occur in pairs in diploid organisms
* chromosomes of each pair separated in gametes
* separation of each pair of chromosomes is
independent of other pairs
* Chromosomal Theory of Inheritance
* confirmed by Thomas Hunt Morgan in 1910
he realized that what he was observing was the separation of things that ended up forming the gametes, and if we we were to stick alleles onto those things being sepatrated it would explain this process of segregation that mendel was observing .
Gene pairs carried on
_________ chromosomes
_________ of alleles observed
by Mendel corresponds to the
____________ of chromosomes that
takes place in _________ _
Gene pairs carried on
homologous chromosomes
Segregation of alleles observed
by Mendel corresponds to the
separation of chromosomes that
takes place in anaphase I
Dominance is not universally observe
-in simple Mendelian inheritance, dominant traits always mask recessive ones
* not all traits follow this
* incomplete dominance: intermediate phenotype
* codominance : both traits expresse
incomplete dominance
-One allele is not completely dominant to
the other allele
* Heterozygote exhibits an intermediate
phenotype compared to the homozygous
phenotypes
* Uses superscript to label the alleles
instead of uppercase and lowercase
letter
Incomplete dominance:
CR allele:…
* CW allele: _________ enzyme
* Heterozygote plants produce some ….
* The selfing of F1 plants produces F2 flowers with what ratio?
CR allele: functional enzyme produces red pigment
* CW allele: nonfunctional enzyme
* Heterozygote plants produce some functional
enzyme but not full amount, producing intermediate
phenotype
* The selfing of F1 plants produces F2 flowers with
what ratio? 1:2:1
Incomplete dominance
* The result of ___________ can be observed directly
* Ratio of red:pink:white phenotypes is _______, which
reflects the ratio of CR/CR: CR/CW: CW/CW
* Note genotype ratio and phenotype ratio are both
_______, since each genotype has a distinct _________
(maybe Mendel should have started with these!
- The result of segregation can be observed directly
- Ratio of red:pink:white phenotypes is 1:2:1, which
reflects the ratio of CR/CR: CR/CW: CW/CW - Note genotype ratio and phenotype ratio are both
1:2:1, since each genotype has a distinct phenotype
(maybe Mendel should have started with these!
Codominant alleles -
Codominant alleles have equal effects (dominant alleles fight for expression)
- heterozygote exhibits both homozygote phenotype
> 2 alleles
How many different alleles for a given gene?
* _______ ________ ________(MHC) cell surface molecules controlling
part of _______ _______
* Two alleles of each MHC gene are expressed __________ in each
individual.
* MHC genes are highly ________ : some genes contain over ____ alleles.
* Highly unlikely for two individuals to carry the exact two alleles for all MHC
genes.
* What is evolutionary consequence of polymorphism
How many different alleles for a given gene?
* Major histocompatibility complex (MHC) cell surface molecules controlling
part of immune system
* Two alleles of each MHC gene are expressed co-dominantly in each
individual.
* MHC genes are highly polymorphic : some genes contain over 1000 alleles.
* Highly unlikely for two individuals to carry the exact two alleles for all MHC
genes.
* What is evolutionary consequence of polymorphism
they have a huge number of possible combos with these that are making up the major Histocompatibility complex: why this is importamt bcs every version of this allele is going to alter the shape of this protein just a lil bit. Your body immune system is going to recognize all of your self hypes based on the shape of the protein of MHC. and its going to recgnize it as your own tissue, if u r someone who has to have an organ transplant the complication is that you are taking this organ from someone else as a diff combo of alleles of those MHCs your immune system may attack that as an entity ansd thats why it could get rejected (thats why its always better go get transplant ffrom some relative of urs bcs its more likely theres gonna be a chance that we r going to share some of those MHc alleles with a fam memebr
Mendelian segregation preserves
genetic variation
Darwin’s conundrum resolved
* A mechanism for inheritance
* But did not explain observations in a population
Discrete traits (“Mendelian”
more exception than a rule
complex traits vary continiously
he reality is that most traits we are looking at we would describe asd complex traits -
coplext traits have phenotypes that exist on some sort of spectrum where we are looking more at distribution of the traits rfatrher than just yellow vs green, tall vs short etc
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