Moon pt.1 Flashcards by sophie courville

What is the blending theory?

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)

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What was Mendel’s experiment to disprove the blending theory

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What does it mean to be monohybrid?

Heterozygous of 1 gene

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

3 : 1

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What is a testcross?

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

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What is a loss of function mutation?

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

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What did Thomas Hunt Morgan’s experiments confirm?

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)

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

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

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

1/2 * 1/2 = 1/4

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

2^23

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

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

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

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

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What is the Chi-square test?

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

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How is the degree of freedom determined

The number of different phenotypes used in the calculation - 1

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What is a tetrad?

Four spores produced by meiosis of a haploid organism

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What is an ascus?

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

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

*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

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

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

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

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

What is a centimorgan?

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

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

50%

What is a molecular marker?

*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

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

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

What are Single Nucleotide Polymorphisms (SNPs) ?

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

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

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

What SNP is associated with Cystic Fibrosis?

Loss of Phe508 → 3 nucleotide deletion

What is a haplotype?

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

How can the mutations be qualified in a haplosufficient gene?

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

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

Haploinsufficient *often gain of function mutations, hyperactive

How does the p53 mutant allele affect health?

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)

What is incomplete/partial dominance?

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

What is codominance?

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

What is the dominance class of sickle cell anemia?

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

How are recessive lethal alleles maintained in the population?

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)

What are examples of conditional alleles?

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

What are auxotroph organisms?

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

What is expressivity?

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

Give an example of conditional allele temperature controlled phenotype

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

What is the complementation test?

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)

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

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

What is recesive epistasis?

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

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

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 -/-)

What are suppressors?

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

What is a modifier?

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

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

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

What is the ratio for a dominant epistasis relation?

12 : 3 : 1