Lecture 3 Flashcards
What are the phenotypic and genotypic ratios of a true breeding monohybrid cross for a diploid organism (assume mutation is recessive)?
Example: bb x BB F1 phenotype: All WT F1 genotype: Bb F2 phenotype: 3 WT: 1 mutant F2 genotype: 1/4 BB, 1/2 Bb, 1/4 bb
What are the phenotypic and genotypic ratios of a monohybrid cross for a diploid organism (assume mutation is dominant)?
Example: cc x Cc F1 phenotype: 1/2 WT, 1/2 mutant F1 genotype: 1/2 Cc, 1/2 cc F1 WT x WT: all WT F1 WT x mutant: 1/2 WT, 1/2 mutant F1 mutant x mutant: 3 mutant: 1 WT
What is the phenotypic ratio for a dihybrid cross for a diploid organism?
9:3:3:1
What is the phenotypic ratio for a monohybrid cross for a haploid organism?
1:1
What is the phenotypic ratio for a dihybrid cross for a haploid organism?
1:1:1:1
What are the two ways a mutant can be dominant?
Haploinsufficiency and dominant negative
What is haploinsufficency?
WT phenotype not expressed because there is not enough WT protein activity. Organism doesn’t have enough protein to get the job done so it’s like having no copies of the WT gene at all
What is dominant negative?
The mutant protein interferes with the function of the good copy by blocking it’s activity
What is incomplete dominance?
An intermediate phenotype seen in heterozygote. There are not enough doses of the protein in the heterozygote so the organism isn’t fully red.
Example: F1 is pink when mom was red and dad was white (assume red is dominant)
What is co-dominance?
When both parent phenotypes are expressed in the heterozygote, example: blood types
Explain dominance at the phenotypic level, biochemical level, and molecular level
Phenotypic: one allele may be dominant, incompletely dominant, or co-dominant
Biochemical: alleles are incompletely dominant (see the effect of both alleles)
Molecular: alleles are co-dominant (two alleles means two different proteins)
What is polygenic inheritance?
When the phenotype is determined by multiple copies of a SINGLE gene. Example is pigmentation –> overall color is determined by how many loci have a pigment allele. Produces bell shaped curve. Environment also has effects.
What are lethal/sterile mutations?
A mutation is lethal or sterile in homozygous condition. Can never get a true-breeding line of mutant. Mutant allele persists through heterozygote, could be dominant or recessive. Phenotypic ratio is 2:1 because homozygous is lethal so never seen.
What is special about mitochondria and chloroplasts?
They exist in the cytoplasm and have small circular chromosomes
- They divide independent of nuclear events
- Maternal inheritance: they are inherited with cytoplasm through the egg cell
- The cytoplasm mitochondrias or chloroplasts can contain a mix of mutant and normal organelles –> results in variegated plants
What is the X-Y sex system?
Homogametic sex (XX) can only contribute one type of sex chromosome (X), heterogametic sex (XY) can contribute two types of chromosomes (X or Y). Both sexes are diploid. Ex. Humans/fruit fly, bird/butterfly
