Laboratory Notes on Protein Pigments and Genetic Testing Techniques

A set of flashcards covering key concepts related to protein pigments, chi-square tests, genetic crosses, and inheritance patterns from laboratory notes.

Pteridines

Red pigment found in wild type or brick-eyed organisms.

Ommachrome

Brown pigment found in specific eye color phenotypes.

Transporting Pigment Precursors

Genes that transport precursor substances for pigments to the eye.

Mutated Transporters

Results in white eye phenotype due to lack of pigment transport.

Enzymes in Pigment Pathways

Catalysts required for pigment synthesis; one missing enzyme prevents pigment formation.

Chi Square Test

A statistical test used to determine whether observed results differ from expected results.

Null Hypothesis (H0)

The hypothesis stating that no significant difference exists between observed and expected results.

Alternate Hypothesis (H1)

The hypothesis stating that a significant difference exists between observed and expected results.

Degrees of Freedom

Calculated as the number of phenotype classes minus one.

Epistatic Interactions

Gene interactions that alter the expected Mendelian ratios.

Mendelian Ratios

Expected ratios of phenotype occurrence from simple inheritance patterns.

White-1 Mutation

A sex-linked mutation causing white eyes due to disrupted pigment transport.

Genotypes of Males with White Eyes

Xw+ Y for red eyes and Xw Y for white eyes; hemizygous condition.

Genotypes of Females with White Eyes

Xw+Xw+ for red eyes, Xw+Xw as carriers, and XwXw for white eyes.

What are the two classes of protein pigments?

Pteridines (red pigment) and Ommachrome (brown pigment).

What phenotype is associated with the (w) gene mutation?

White eyes.

What does the (bw) gene transport?

GTP to produce pteridine precursor, resulting in brown eyes.

What does the (st) gene transport?

Tryptophan to produce ommachrome precursor, resulting in scarlet eyes.

What happens if the ommachrome enzyme is missing?

No (bw) pigment is produced, only pteridines remain, resulting in st phenotype.

What is the effect of a missing pteridine enzyme?

Less or no red pigment, leading to either (bw) or (se) phenotype.

What is the eye color associated with the white mutation?

White eyes (no pigment transport).

What eye color is associated with a brown mutation or pteridine enzyme mutation?

Brown eyes (bw).

What eye color results from a scarlet mutation or ommachrome enzyme mutation?

Scarlet eyes (st).

What is the chi-square test used for in genetics?

To determine whether observed offspring match expected Mendelian ratios.

What is the null hypothesis (H0) in a chi-square test?

Observed results do not differ from expected results.

What does a small chi-square value indicate?

Data fits the prediction.

What is the expected Mendelian ratio for a monohybrid cross?

3:1.

What is the expected Mendelian ratio for a dihybrid cross?

9:3:3:1.

What does a chi-square value larger than the critical value indicate?

Reject the null hypothesis; observed results differ from expected results.

What is the formula for calculating chi-square?

X^2 = \sum\frac{(O - E)^2}{E}.

What are epistatic interactions?

Interactions that cause ratios to deviate from Mendelian ratios.

What does a linked gene indicate?

It does not follow Mendelian ratios.

What is the significance of recombinant frequencies in gene mapping?

They determine gene order and map distance (cM).

What is the molecular basis of the white mutation (w)?

Insertion of Doc-retroposon disrupts transcription, preventing pigment transport.

What is the genotype for male flies with red eyes?

Xw+ Y.

What is the genotype for female flies that are carriers of the white eye trait?

Xw+ Xw.

What is the phenotype for females homozygous for the white eye trait?

White eyes (Xw Xw).

What is population genetics?

The study of the amount and distribution of genetic variation in populations, and the evolutionary forces that drive this variation (mutation, selection, genetic drift, etc.).

What is a gene pool?

The total amount of alleles and their distribution in a population at any time.

How can genotype frequencies be calculated?

By dividing each genotype’s number by the total amount of flies in the population.

What are the frequencies of the genotypes in the Drosophila population given?

Frequency of AA = 0.16, Frequency of Aa = 0.48, Frequency of aa = 0.36.

What should the genotype frequencies add up to?

They should add up to 1 (e.g., 0.16 + 0.48 + 0.36 = 1).

How is the total amount of alleles calculated in a diploid population?

The total amount of alleles is calculated as 2N, where N is the number of individuals in the population.

What is the total number of alleles in a Drosophila population of 100 individuals?

200 alleles (2 x 100).

How is the frequency of allele A (p) estimated?

By calculating the total number of A alleles and dividing by the total number of alleles in the population.

How many A alleles are there in the given Drosophila population?

There are 32 A alleles, as 16 individuals are AA, producing 16 x 2 = 32 A alleles.