Bio: Genetics and Evolution

Question 1

Griffith Experiment

Answer 1

Two strains of bacteria -> S (smooth) and R (rough)
S was virulent so killed mice, R didn’t
When heat killed S was added to R, the mouse died so they knew the cell extract of dead S was capable of conferring virulence to R strain

Question 2

Avery-MacLeod-McCarthy Experiment

Answer 2

Took the S strain extract from Griffith Experiment and see if mouse died if destroyed virus’ RNA, lipids, Polysaccharides, protein and DNA
When DNA destroyed mouse survived
This suggested that DNA was able to transform bacteria, and was the molecule of heritability that scientists has been looking for

Question 3

Hersey-Chase

Answer 3

Phage T2 was added to E. Coli in either radioactively labeled 32P or 35S
So ultimately the capsids of the 35S radioactive phages were labeled and the genome of the 32P phages were labeled
Then they allowed phages to infect bacteria and only the bacteria that were infected by 32P phages demonstrated genetic material with 32P -> Supports that DNA carries genetic information in the cell

Question 4

Diploid

Answer 4

Have two copies of genetic material in cell -> one from mom and one from dad

Question 5

Main similarities and differences between mitosis and meiosis? Product of each?

Answer 5

Sim -> both have replication of genome before (S phase) to make sister chromatids
Diff -> mitosis: one round of cell division, meiosis: 2 rounds of cell division (meiosis I and II), recombination b/w homologous chromosomes
Another diff = meiosis is terminal process, once you do it once you’re done
Mitosis product: 2 identical diploid autosomes
Meiosis: 4 haploid gametes

Question 6

Names steps of meiosis, describe process of prophase: (mention if haploid)
Bivalent
Tetrad

Answer 6

Prophase, metaphase, anaphase, telophase
Begin as diploid (like mitosis)
Prophase: longest phase, like mitosis, chromosomes condense, nuclear envelope breaks down.
Unlike mitosis, **homologous chromosomes pair during prophase I in synapsis with two copies of each gene on two different chromosomes brought closely together. The paired homologous chromosomes are called bivalent tetrad, genes can then be swapped by crossing over

Question 7

Synaptonemal complex (SC)

Answer 7

Synapsis is mediated by Synaptonemal complex (SC) which holds the chromosomes together, there is more specifics page 233

Question 8

Describe metaphase I
Independent assortment

Describe anaphase I

Telophase I (are the cells haploid or diploid?)

Then what happens/how does it relate to mitosis (sim and diff)? What do you get at the end?

Answer 8

Metaphase I:
alignment along metaphase plate, as in mitosis
Independent assortment = how homologous chromosomes line up
The difference: in mitosis sister chromatids lined up at plate but in meiosis tetrads are aligned at plate

Anaphase I: homologous chromosomes separate and sister chromatids remain together

Telophase I: the cell divides into into two cells, these cells are considered haploid, each cell has a single set of chromosomes and each chromosome is pair of sister chromatids, then cytokinesis

Then meiosis II begins and the movements of chromosomes are identical to those of mitosis with the sole difference being that in meiosis II there is haploid number of chromosomes, while in mitosis there is diploid number.
The sister chromatids are separated during anaphase II and after telophase II, you get four haploid cells produced from single diploid parent cell
each cell 1n1x

Question 9

Are the sister chromatids that separated during meiotic anaphase II identical in their DNA sequence?

Answer 9

No -> recombination

Question 10

True or false:
In meiosis recombination occurs between sister chromatids

Gametes normally contain how many copies of each chromosome?

What does recombination allow for?

Answer 10

FALSE
recombination occurs in meiosis only between homologous chromosomes

Gametes normally have one copy of each chromosome = haploid

Recombinaton produces new combinations
of alleles not found in parent and allow allows genes located on the same chromosome to assort independently

Question 11

Nondisjunction during meiosis I and II:

What do the gametes look like with nondisjunction during meiosis I and of one of the cells in meiosis II?

Answer 11

Nondisjunction during meiosis I = 2 gametes with no copies of chromosome and 2 gametes with 2 copies of chromosomes

Nondisjunction of one of the cells during during meiosis II = 2 normal gametes, 1 with no copies of chromosomes, 1 with 2 copies

Question 12

What can nondisjunction lead to?

Answer 12

Trisomy bc one of the bad gametes may have extra chromosome and fuse with normal one -> can get trisomy
or can fuse with gamete with no chromosomes and get monosomy (one chromosome)

Question 13

What is Mendel’s law of segregation, when does it occur?

What is independent assortment, when does it occur?

Answer 13

Law of segregation -> two alleles of an individual are separated and passed on to the next generation singly
anaphase I and anaphase II
Law of independent assortment -> How one pair of alleles separate is independent of how other pairs separate - prob bc line up in different ways (alleles of one gene will separate into gametes independently of alleles for another gene)
metaphase I

Question 14

True-breeding/pure-bred

testcross

Answer 14

= homozygous (identical alleles)
an organism that always passes down certain phenotypic traits (i.e. physically expressed traits) to its offspring of many generations
When a strain always produces the same trait when mated with itself, it is likely to be homozygous for the trait
ex. True breeding green plant GG
true breeding yellow plant gg

testcross -> cross something with homozygous (true-breeding) recessive genotype to determine its genotype

Question 15

Incomplete Dominance

Answer 15

If the phenotype of a heterozygote is a blended is blended mix of both alleles
red flower and white flower make pink flower

Question 16

Codominance

What is the main example and its alleles?

Answer 16

Two alleles are both expressed but are not blended. For example, the alleles of ABO blood group antigens that are found on the surface of red blood cells display codominance

IA, IB, i
IA and IB are codominant and will be expressed regardless of the second allele, while i is recessive to both IA and IB

There is also other main antigen in blood typing called rhesus = Rh
RhDRhD (also seen as RR) -> positive
RhdRhd (also seen as rr) -> negative
can also be heterozygous

Question 17

Codominance

What is the main example and its alleles?

Answer 17

Two alleles are both expressed but are not blended. For example, the alleles of ABO blood group antigens that are found on the surface of red blood cells display codominance

IA, IB, i
IA and IB are codominant and will be expressed regardless of the second allele, while i is recessive to both IA and IB

There is also other main antigen in blood typing called rhesus = Rh
RhDRhD (also seen as RR) -> positive
RhdRhd (also seen as rr) -> negative
can also be heterozygous

For Rh factor only, you have to be exposed to Rh first before make antibodies to it (unlike for blood type ex. b) but eventually anti-Rh AB form so this bad blood donation is not a horrible but if happens again, the recipient already have anti-Rh ab ready to attack and this is BAD
Rh + , Rh -
ex. hemolytic newborn: second baby if Rh+ the mom’s anti-Rh+ ab’s (If she is Rh-) can cross placental barrier (unlike anti-A, anti-B, etc bc too big to cross) and attack bc her body has already seen Rh+ before

Question 18

Pleiotropism

Answer 18

A gene that affects several traits ex. sickle cell

gene has pleiotropic effects if its expression alters many different, seemlingly unrelated aspects of the organism’s total phenotype. For example, a mutation in a gene may cause altered development of heart, bone, and inner ears.

Question 19

Polygenism

Answer 19

Trait that is determined by several genes ex. height
Complex traits that are influenced by many genes. These traits tend to display a range of phenotypes in a continuous distribution.
For example height is polygenic and is influenced by genes for growth factors, receptors, hormones, bone disposition, muscle development, E utilization, and so on. As a consequence there is a wide range of heights

Question 20

Epistasis

Answer 20

Expression of alleles for one gene is dependent on a different gene -> for example, a gene for curly hair cannot be expressed if a different gene causes baldness

Question 21

Epistasis

Answer 21

Dominance between completely different genes
Expression of alleles for one gene is dependent on a different gene -> for example, a gene for curly hair cannot be expressed if a different gene causes baldness

Question 22

Recessive lethal alleles

Answer 22

Some mutant alleles can cause death of an organism when present in a homozygous manner and typically code for essential gene products

Question 23

What pattern of expression will a recessive allele on the X chromosome display in males?

Answer 23

In males, recessive alleles on the X chromosome are always expressed, since no other allele is present that can mask the recessive allele

Question 24

What does a sex-linked trait mean?

What is linkage?

Answer 24

Traits that are determined by genes on X or Y chromosomes are called sex-linked traits bc of their unique patterns of expression and inheritance.

Genes that are located on the same chromosome may not display independent assortment, however. The failure of genes to display independent assortment is called linkage

Question 25

Is it possible to predict the possible gametes of a TTgg individual? Of a TtGg?

Answer 25

TTgg will be Tg regardless if linked or not

TtGg we don’t know unless they say which 2 alleles are present together on same chromosome

Question 26

What is one acception to linkage?

Answer 26

One exception is meiotic recombination b/w homologous chromosomes can separate alleles that were located on the same chromosome

Question 27

If it is known that two genes are located on the same chromosome but during a cross they assort completely randomly, how can this be?

Answer 27

Often in a cross involving genes on the same chromosome, the result will be intermediate between independent assortment and complete linkage. The reason for this is that recombination occurs between the genes during meiosis of some of the gametes but not all of the gametes -> if genes are on the same chromosome, but are far apart from one another, then recombination occurs frequently. The genes will assort randomly during meiosis and will not display any linkage even though they are on the same chromosome

Question 28

**Frequency of recombination equation
What us a recombinant? What does it tell you?
What recombination frequency indicates independent assortment?

Answer 28

RF = recombination frequency = number of recombinants/total number of offspring

We can see if two genes are linked, and how tightly, by using data from genetic crosses to calculate the recombination frequency.

Recombinant is combination of phenotypes not seen before in previous generations

When genes are on the same chromosome but very far apart, they assort independently due to crossing over (homologous recombination).

MEMORIZE: Expected recom freq if have independent assortment/ no linkage = 37.5% map units apart

Question 29

Hemizygosity

Answer 29

The individual only has one copy of the chromosomes in a diploid organism
This is true for X linked and Y linked traits
and mitochondrial traits which are ONLY contributed by the mother bc mother contributes egg which holds all the organelles

Question 30

Y-linked traits -> who can pass it on?
Would be possible for a father to pass a Y-linked trait to female children?
Can males be carriers of recessive Y-linked traits without expressing them?

Answer 30

Traits encoded by genes on the Y chromosome would only be passed from male parents to male children
question 1 -> no
Question 2 -> no bc only have 1 Y chromosome so doesn’t matter if trait is dom or rec, he will have disease

Question 31

X-linked traits
From which parent do males receive X-linked traits?

Can males have sex-linked recombination? If want practice pg. 253 great problems

Answer 31

Can be X-linked dom or rec
ex. hemophilia
Since men are hemizygous for X-linked traits; they have only one copy of genes on the X chromosome. As a result, males ALWAYS express recessive X-linked alleles

Males receieve X-linked traits from their mother
ex. colorblindness is recessive X-linked trait mostly found in men

Men CANNOT have sex linked recombination bc they have X and Y chromosomes

Question 32

Population

Answer 32

Members of a species that mate and reproduce with each other

Question 33

Hardy-Weinberg in Population Genetics
What does the Hardy-Weinberg law state? What are the assumptions? What is the equation?

What is the frequency of yellow allele for pea plants in the gene pool of progeny?

How does Hardy-Weinberg related to segregation, independent assortment, and recombination?

How long does it take a population to reach Hardy-Weinberg equilibrium

Answer 33

Describes gene pool (sum of all genetic material of pop) AND attempts to predict the gene pool of a population in the future

Hardy-Weinberg law states that the frequency of alleles in the gene pool of a population will not change over time, provided a number of assumptions are true:

a) no mutation
b) no migration
c) no natural selection
d) random mating
e) population sufficiently large to prevent random drift in allele frequencies

p + q = 1
p^2 + 2pq + q^2 =1

p -> frequency of dominant allele
q -> frequency of recessive allele

If dom allele was G and rec was g
then p^2 -> freq of GG
2pq -> freq of Gg
q^2 -> freq of gg

Question -> the frequency of the allele would be just like the parents bc not alleles destroyed

In terms of Harvey-Weinberg, segregation, independent assortment, and recombination can alter combinations of alleles but cannot change frequency of an allele in the gametes of one individual or the gametes of the pop as a whole

The F2 generation (and all generations after that) will have the same genotype frequencies as the F1
Takes 1 gen to reach harvey Weinberg equilibrium again once 20 new moose walk in and mess up allele frequency

Question 34

What 2 things need to happen for natural selection to occur?
Basis of evolution in species and pop?
What does good fitness mean?

Answer 34

natural selection occurs only if you survive AND reproduce
Changes in allele freq (not Hardy)
Natural selection only acts on heritable traits not things that happen to animal during lifetime ex. if it gets virus
Also natural selection only acts on phenotypes not genotypes (if someone heterzygous but disease rec, then the person won’t have disease)
If there is only one allele of a gene, then no variability that natural selection can act on
Natural selection cannot make more alleles, only act on existing ones

Good fitness means having more offspring that pass on their alleles to future generations of the population

Question 35

Two sources of genetic variation:

Random drift?

Answer 35

a) new alleles from mutations (could be deletion etc.)
b) new combo’s of alleles due to recombination, segregation, independent assortment

random drift is change in allele freq of pop

Question 36

Modes of natural selection:
Directional selection
Divergent selection
Stabilizing selection

Artificial selection
Sexual Selection
Kin Selection

Species

Answer 36

Think of those mice diagrams or pg. 259

Artificial selection -> Humans interfere in the mating of many animals and plants, using artificial selection to achieve desired traits through controlled mating
Sexual Selection -> Animals often do not choose mates randomly
Kin Selection -> natural selection does not always act on individuals ex. a female lion may sacrifice herself to save her sister’s children for sake of the alleles they share to be passed on

Species = group of organisms that can reproduce with each other sexually, can mate AND produce fit offspring (offspring ARE NOT STERILE/can reproduce)

Question 37

There are many factors of reproductive isolation which are either prezygotic or postzygotic, define each

What is Hybrid inviability, hybrid sterility, hybrid breakdown

Answer 37

prezygotic -> barriers prevent formation of zygote
All forms in book pg 260

Post-zygotic -> prevent development, survival, or reproduction of hybrid individuals

a) Hybrid inviability hybrid offspring do not develop or mature normally and die at embryonic stage
b) Hybrid sterility hybrid is born and develops normally but does not produce normal gametes and thus is incapable of breeding
c) Hybrid breakdown when two hybrids mate successfully to produce a hybrid offspring, but this second generation hybrid is somehow biologically defective

Question 38

Cladogenesis

Homologous structures
Analogous structures
Convergent evolution
Divergent evolution

Answer 38

is branching speciation where one species diversifies and becomes two or more new species
Homologous structures -> physical features shared by 2 diff species as a result of a common ancestor
Analogous structures -> serve the same function in two different species but NOT due to common ancestry ex. flagellum in sperm and bacterial flagella have diff structure but same motility function
Convergent evolution -> When two different species come to possess many analogous structures due to similar selective pressures
Divergent evolution -> the opposite

Question 39

Diagram: 
Anterior
Posterior
Dorsal 
Ventral
Superior 
Inferior
Cephalad 
Caudad

Answer 39

Anterior -> front facing (dog head) 
Posterior -> opposite (dog butt) 
Dorsal -> "on top" like sharks dorsal fin 
Ventral -> opposite (belly button of human when on their back)
Superior -> "toward the head"
Inferior -> "toward the feet" 
Cephalad -> "toward the head" 
Caudad -> opposite

Question 40

Young earth lacked _____ (gas)

Answer 40

O2

Question 41

*What is a tip that there is a sex linked gene?

Answer 41

A gender bias in the phenotype of a trait usually indicates that you’re working with a sex-linked trait

Question 42

What does it mean to backcross something?

Answer 42

Cross it back with something it had previously crossed with before

Question 43

What can gel electrophoresis do? What is SDS? What is needed to break disulfide bridges?

Answer 43

Running a gel can separate mixtures of DNA, RNA, or protein according to molecular size

SDS = sodium dodecyl sulfate -> a detergent that denatures proteins and coats them with a uniform neg charge

Need a reducing agent to break disulfide bonds (BME, DTT, etc)

Question 44

**What is the only requirement for when you think about recombinants? When can it happen?
How can you tell when genes are linked by looking at phenotype data?

Answer 44

There must be 2 different traits you’re talking about
Recombination can occur with linked genes (although depends on how close the alleles are on the chromosome) and unlinked genes (the 3:3 part of 9:3:3:1 are recombinants)

One tip for noticing linked genes is if you see groups of low numbers compared to others groups

Question 45

What does n and x mean?

Answer 45

n indicated if have mom and dad homologous chromosomes or just mom/dad
x indicates if have sister chromatids or not (looks like an x)

Question 46

Polymorphic

Answer 46

Trait that comes in several varieties ex. hair color
usually not critical for survival

A gene is said to be polymorphic if more than one allele occupies that gene’s locus within a population
Polymorphic genes were mutated but don’t result in death -> have variety of eye colors bc of these mutations, polymorphic traits usually NOT critical for survival
Sometimes these mutations are okay bc sickle cell can protect against malaria (parasite that atatcks the red blood cells) -> only reason why these mutations are around are bc they give you an advantage

Question 47

• Tip off that you are dealing with non-classical dominance

Answer 47

a) Two different uppercase letters ex. if red flowers RR crossed with white flowers WW and get RW pink flowers
b) blended phenotype

Question 48

Human ABO group genes
what do they code for?

Universal donor?
Universal recipient?

Answer 48

Codes for a protein on the surface of RBC
Ex. IA IA represents type A blood
a group A individual will have anti-B antibodies (make antibodies to the protein you don’t have)

Universal donor: O neg (no proteins to trigger a rxn in recipient)
Universal acceptor: ABpos (all proteins recognized as normal proteins)

Type O is from ii genotype
Type AB is codominance and from IAIB genotype

Question 49

*What to look for to determine in trait is dominant or recessive, sex-linked, mitochondrial inheritance

Answer 49

to determine in trait is dominant or recessive -> recessive traits often skip generations, but dominant traits do not
sex-linked -> tends to be unequal distribution of affected males vs females
mitochondrial inheritance -> affected females will have all affected children and affected males have no affected children

Question 50

Genomic imprinting

Follows mendelian pattern?

Answer 50

Expression of gene depends on whether it is inherited from the male or female parent
Do not follow mendelian pattern of inheritance - depending on how the genes are marked, either express maternally or paternally inherited genes NOT BOTH