Moon pt.1

Question 1

What is the blending theory?

Answer 1

• Traits of parents get mixed like fluid
• Results in a NEW trait that is a mixed middle of both parents
• The original parent traits are lost in the blend (can’t be recovered)

Question 2

What was Mendel’s experiment to disprove the blending theory

Question 3

What does it mean to be monohybrid?

Answer 3

Heterozygous of 1 gene

Question 4

What is the phenotypical result/ratio of a monohybrid cross of a completely dominant trait?

Answer 4

3 : 1

Question 5

What is a testcross?

Answer 5

The cross of an individual to a fully recessive individual
Useful for determining the genotype of the gametes a testee can produce

ex: cross a purple heterozygous (purple dominant, white recessive) with full white → 50% purple, 50% white

Question 6

What is a loss of function mutation?

Answer 6

Often recessive (phenotype) because a single WT copy can be enough for normal function/phenotype → happens when the gene is haplosufficient →

Question 7

What did Thomas Hunt Morgan’s experiments confirm?

Answer 7

Some genes are not simply inherited in a 50/50 segregation manner
Ex: flie eyes are inherited following the X chromosomes sorting during meiosis

Mendel’s experiment only works for traits encoded by 1 autosomal gene

Confirmed the Chromosomes theory of inheritance → genes are stored in chromosomes inside the cell nuclei, also discovered the crossover phenomen (different chromosomes can trade places with one another)

Question 8

What is the result of an independent assortement of a dihybrid during meiosis?

Answer 8

Equal ratio of the four different genotypes of a gamete
Start with an AaBb cell → meiosis → gametes = AB, Ab, aB, ab

Question 9

During meiosis, what is the probability that the paternal chromosomes 1 and 2 are transmitted to a single gamete in a human?

Answer 9

1/2 * 1/2 = 1/4

Question 10

How many different genotypes of a gamete a human can produce during meiosis via independent assortement alone?

Answer 10

2^23

Question 11

If you cross 2 dihybrid peas (R/r; Y/y) together, what phenotypic ratio will you get?
*Complete dominance

Answer 11

4 phenotypes: 9:3:3:1 = YR:Ry:rY:ry (FOR THE PHENOTYPE), 16 different genotypes

Question 12

What does a dihybrid testcross produce when there is independent assortement?

Answer 12

Equal number of parental and recombinant type
*Parental = parents of the F1 dihybrid
1:1:1:1 ratio of parental and recombinant

Question 13

What is the Chi-square test?

Answer 13

x^2 = Σ (O-E)^2 /E
Used to determine if the degree of deviation from the expected valiue in significant → used 95% confidence level
p = 0.05 → you have 5% chance that rejecting the hypothesis independent assortement is wrong
If p <= 0.05, you can reject the hypothesis with confidence level of 95% or greater

Question 14

How is the degree of freedom determined

Answer 14

The number of different phenotypes used in the calculation - 1

Question 15

What is a tetrad?

Answer 15

Four spores produced by meiosis of a haploid organism

Question 16

What is an ascus?

Answer 16

Physical structure (ascus wall) keeps the tetrad together → can be isolated to study a single meiotic event

Question 17

What are the different options for crossover between 2 haploid AB x ab

Answer 17

*Crossing over between chromatids, not chromosomes (chromatid = 1/2 of a replicated chromosome)

2-chromosome stage (before replication):
2x Ab and 2x aB
4-chromatid stage (after replication):
AB, Ab, aB, ab

Question 18

What are the possible results for a multiple crossover between 2 haploids: ABC x abc (ABC are on the same chromosome)

Answer 18

2 chromatids → ABC, AbC, aBc, abc
3 chromatids → ABc, AbC, aBC, abc
4 chromatids → ABc, Abc, aBC, abC

Question 19

How does distance between 2 genes on a chromosome affect crossover likelyness?

Answer 19

The farther apart the genes are, the more likely they are to crossover and produce recombinants

Relative distance between 2 genes reflected by recombinant frequency

Question 20

What is a centimorgan?

Answer 20

1 genetic map unit = frequency at which 1% meiosis produce a recombinant

Question 21

What is the maximal relative frequency of crossover for 2 genes?

Answer 21

50%

Question 22

What is a molecular marker?

Answer 22

*Good approach to map a gene

Small DNA sequence differences (polymorphisms) within a specie that are presen at specific chromosomal locations

• Present through out the genome
• Most don’t have biological functions, no phenotype
• Molecular markers are often seen as bands on a gel
• Can be used to map a gene (ex: disease causing gene) by determining the linkage between the gene of interest and a molecular marker

Question 23

What is the utility of Simple sequence length polymorphisms (SSLPs)?

Answer 23

• Human genomes contain a lot of repetitive DNA sequences
• Unrelated people likely have different numbers of repeats
• A child has 1 set of paternal and 1 set of maternal SSLPs
• The lengths of SSLP regions can be quantified by PCR amplification using primers binding to flanking sequences → resolve in DNA gel

Length of the segment is associated with the personne, not with phenotype

Question 24

What are Single Nucleotide Polymorphisms (SNPs) ?

Answer 24

• The genomic sequences or 2 unrelated people ~ 99.9% identical
• SNP found in at least 1% of any population (common), if not, variant may be a mutation
• Some SNPs are more common in a specific population/ethnicity
• Can be found in intergenic region, within a gene or in regulatory region near a gene
• Most of time, has no effect on health, but some may play a role in susceptibility of a disease or sensitivity to an external factor

Question 25

How can mapping of disease gene can be done using SNP?

Answer 25

Some SNP always inherit with a disease gene (not same as SSLP that are related with the person, not the disease gene)

Question 26

What SNP is associated with Cystic Fibrosis?

Answer 26

Loss of Phe508 → 3 nucleotide deletion

Question 27

What is a haplotype?

Answer 27

Physical grouping of genomic variants (or polymorphisms) that tend to be inherited together, as a single group

Question 28

How can the mutations be qualified in a haplosufficient gene?

Answer 28

Recessive → if 1 copy has a loss-of-function mutation → WT phenotype

Question 29

How can we qualify a gene that has a dominant mutation?

Answer 29

Haploinsufficient
*often gain of function mutations, hyperactive

Question 30

How does the p53 mutant allele affect health?

Answer 30

p53 is a TF that binds DNA as a homotetramer
Dominant mutation → affects DNA binding domain → the mutant p53 can teramerize → the tetramer can’t bind DNA → no transcription (dominant-negative effect)

Question 31

What is incomplete/partial dominance?

Answer 31

Phenotype of heterozygous = halfway between the 2 homozygous
ex: white and red → pink

Question 32

What is codominance?

Answer 32

Phenotype of the heterozygous shows the presence of both homozygous fully
ex: blood types → A and B are codominant and dominant over O

Can see both bands separatly in the gel

*Dominance is determined by the phenotype

Question 33

What is the dominance class of sickle cell anemia?

Answer 33

HbA and HbS are codominant → both alleles can be clearly discerned at the protein level
Some RBC are sickled and some a normal

Question 34

How are recessive lethal alleles maintained in the population?

Answer 34

Maintained as heterozygous in haplosufficient genes

Homozygous mutation causing lethality can be recessive or dominant mutations
Ex: homozygous yellow = lethal, yellow is dominant
Yy = yellow, vital, yy = dark coat, YY = yellow, lethal
Yellow x Normal = Yy x yy → 1:1
Yellow x Yellow = Yy x Yy → 2:1 (Yellow : normal)

Question 35

What are examples of conditional alleles?

Answer 35

Alleles that depend on external factors:
Temperature sensitive mutants → low temp functions like WT, high temp is lethal
Auxotrophs → minimal media + arginine function like WT, minimal media is lethal

Question 36

What are auxotroph organisms?

Answer 36

organisms that lost ability to synthesize certain substances required for their growth → conditional alleles

Question 37

What is expressivity?

Answer 37

The degree to which a given allele is expressed at the phenotypic level, intensity of the phenotype

Question 38

Give an example of conditional allele temperature controlled phenotype

Answer 38

Tyrosine kinase that is active at a lower temperature → extermitis of the rabbit are colder so appear black id raised in colder temperature

Question 39

What is the complementation test?

Answer 39

To assess the presence of recessive mutations
When you can get a mutant crossing to organisms that apear ar WT (to know if both heterozygous)

Question 40

What does it indicate on the genotypes if you get a 9:7 phenotypic ratio?

Answer 40

2 genes act on the same pathway → if on of them is homozygous recessive → recessive phenotype
Ex: Interaction between a regulator gene and a target gene (TF and the gene it affects)

9: R/- ; A/-
3: r/r ; A/-
3: R/- ; a/a
1: r/r ; a/a
3+3+1 = 7 recessive phenotypes

Question 41

What is recesive epistasis?

Answer 41

Epistasis = when phenotypic manifestation of an allele is dependent on the genotype of a different gene

w is epistatic to m if recessive genotype of gene w masks phenotype associated with gene m
Ex: sequence of enzymes for flour → white → E1 (gene w) → pink → E2 (gene m) blue
Without w, no way to have the m phenotype

Question 42

What ratio is associated with a dihybrid cross in the context of recessive epistasis?

Answer 42

9:3:4
Ex: sequence of enzymes for flour → white → E1 (gene w) → pink → E2 (gene m) blue
9 blue (W/- ; M/-) : 3 pink (W/- ; m/m) : 4 white (w/w ; r/r + w/w -/-)

Question 43

What are suppressors?

Answer 43

mutant allele of another gene that REVERSES the effect of an original mutation of a 1st gene
Mutation + Supressor → WT

Question 44

What is a modifier?

Answer 44

a second mutation that changes the degree of expression of a mutated gene (phenotype)
Ex: in regulatory sequences
B code for transcription factor/is in regulatory sequence, A is the actual gene of the protein
A/B → WT
A/b → defective (low transcription)
a/B → defective (defective protein A)
a/b → extremely defective

Question 45

What does it mean for a gene interaction to be synthetic lethal?

Answer 45

Mutations in 2 genes, indivudally have weak mutant phenotype, together → lethality
Ex: multiprotein complexes

Question 46

What is the ratio for a dominant epistasis relation?

Answer 46

12 : 3 : 1