Exam 2 Flashcards
What is incomplete dominance
Only one allele is expressed; the other allele is nonfunctional, such as creating a pink flower from red and while
What is codominance?
Both alleles are expressed such as blood types
What is penetrance?
The percentage of individuals having a particular genotype that express the expected phenotype
What is expressivity
The degree to which a character is expressed
What is a lethal allele?
Causes death at an early stage of development, and so some genotypes may not appear among the progeny
What is epistasis?
One gene masks the effect of the other gene
What is the masking gene and the masked gene called for epistasis
Epistatic gene: gene that does the masking
Hypostatic gene: gene whose effect is being masked
What is recessive epistasis?
Epistatic gene is recessive (only masks when there are two copies of the epistatic allele)
What is dominant epistasis?
Only a single copy of the epistatic allele is required to mask the phenotype of the hypostatic gene
What is duplicate recessive epistasis?
Two recessive alleles at either of two loci are capable of suppressing a phenotype
What is complementation
Test that determines whether mutations are at the same locus or at different loci
What are sex influenced characteristics?
Autosomal genes that are expressed differently in males vs female
- higher penetrance in one of the sexes
What are sex-limited characteristics
Autosomal gene only expressed in one sex
What is cytoplasmic inheritance
Usually one gamete (egg) contributes all the cytoplasm to progeny. Can lead to phenotypic variation since no mechanisms ensure mitochondria are evenly distributed
What is LHON?
Leber Hereditary Optic Neuropathy
- Mitochondrially inherited
What is the pedigree for mitochondrial disease?
The mother infects all children, but the father doesn’t infect anyone
What are maternal effect genes
Phenotype of the offspring is determined by the genotype of the mother
What are temperature sensitive alleles
An allele whose product is functional only at certain temperatures
What is continuous characteristics ?
Exhibit continuous distribution of phenotypes, the phenotype is usually determined by interaction between many genes
What is pleiotropy
One gene affects multiple characteristics.
How do I determine the frequency of one allele?
What is the allele frequency for XA and Xa
What are the Hardy-Weinberg law assumptions
- Infinity large population
- Mating is random
- No natural selection
- No mutations
- No migration
What are effect of non random mating
positive assortative mating
negative assortative mating
What is positive assortative mating
Mating with someone who is phenotypically similar
Reduces frequency of heterozygotes
What is negative assortative mating
Mate with someone who is phenotypically dissimilar
Increases frequency of heterozygotes
What is inbreeding
Mating with an indiviudal who is genetically related
What is outcrossing?
Avoidance of mating with a genetically related individual
What is allele by the same descent
Two copies of the allele are descended from the same copy in a common ancestor, so they are identical by descent (inbreeding)
What is alleles are identical by state
Two copies of the A allele are the alike in structure and function but are descended from two different copies in different ancestors
What is the inbreeding coefficient
A measure of the probability that two alleles are identical by descent
- ranges from 0 to 1
- 0 is random mating
- 1 is identical descent
How does the proportion of homo and heterozygosity change with inbreeding
What is inbreeding depression?
Increase of lethal and deleterious traits caused by inbreeding
What is genetic drift?
Change in allele frequency due to sampling error
What are the causes of genetic drift
- SAmpling error in small populations: only few gametes are used for reproduction. Can skew data
- Founder effect: establishment of a population by a small number of individuals
- Bottleneck: occurs when most of the population is destroyed
How is fitness calculated
To calculate fitness for each genotype, we take the mean number of offspring produced by a genotype and divide it by the mean number of offspring produced by the most prolific genotype
What is genetic recombination?
The sorting of alleles into new combinations
What are linkage group
Genes that are close together on a chromosome and often get inherited together. Genes that are farther apart are more likely to recombine due to crossing over.
What is complete linkage
Genes on the same chromosome that are so close that there is no crossing over between the two genes
What is incomplete linkage
Genes on the same chromosome that are far enough away that crossing over can happen between the two genes
What is coupling conformation
Where a wild type allele is found on one chromosome and mutant alleles are found on the other chromosome
What is the repulsion conformation
Each chromosome contains one wild type and one mutant allele
How do you determine if its coupling or repulsion?
You have to look at the nonrecombinants progeny, which is the highest number progeny. Look at their genotype
Who confirmed the chromosomal theory of inheritance
Barbara McClintock using maize
What are Genetic maps
based on recombination frequencies between different gnee on a chromosome
What are physical gene maps
Does not reply on recombination frequencies. Often correlation between phenotype and a chromosomal landmark (deletion)
If a linkage group’s recombination frequency is greater than 50% what does that mean?
They belong to different linkage groups either on different chromosomes or far apart on the same chromosome
What are the 3 point testcross?
- Single crossover
- Single crossover
- Double crossover (creates the least progeny)
How do we determine how many classes of progeny are possible
2^n
n = number of genes
How do you determine gene order?
- Identify the recombinant progeny
- Identify the double crossover progeny
- Compare the two, they should be different in one
- The one that differs is the middle
How do you determine map distance
After determining the gene order, find the progeny that are recombinant for the first segment and divide by the total progeny, then do it for the second segment.
What is interference
One crossover physically interferes with the formation of a second crossover
Interference = 1 - CofC
How do you determine coefficient of coincidence?
Determine the probability of crossover occuring by multiplying the probability of the two segments happening time the total progency. This give you the expected.
C of C = observed/expected
Why is the recombination frequency vs actual map distance not linear
Recombination rates underestimate the true physical distance between genes at higher map distances
