Test 2 Flashcards
What is incomplete dominance?
when the heterozygote (Aa) has a phenotype that’s in between the phenotypes of two homozygotes (AA or aa)
What is complete dominance?
• when the phenotype of Aa and AA are the same.
• only dominant allele is expressed in a heterozygote
What is the phenotypic ratio of two heterozygotes that exhibit incomplete dominance?
1:2:1
What is codominance?
when the heterozygote simultaneously expresses the phenotype of both homozygotes (AA and aa)
What is incomplete penetrance?
when a genotype doesn’t always produce the expected phenotype
What is penetrance?
the percentage of individuals having a particular genotype that express the expected phenotype
What is expressivity?
the degree to which a trait is expressed
Level in expression
What is a lethal allele?
an allele that cause death at an early stage in development
What is a recessive lethal allele?
it kills individuals that are homozygous for that allele
What is a dominant lethal allele?
the allele kills both heterozygote and homozygote
What is aurea?
It’s a recessive lethal allele in plant species that doesn’t allow them to photosynthesize
What are multiple alleles?
For a given locus, there are more than two alleles within a group of organisms
What does multiple alleles mean?
Each pair has a dominance relationship
How do you calculate the number of genotypes with multiple alleles (n) for diploids?
[(n)(n+1)]/2
How do you calculate the number of different homozygotes?
n
only one way to get a homozygote
How do you calculate the number of different heterozygotes possible for diploids?
[(n)(n-1)]/2
How many different alleles can diploid individual have?
Only two different alleles of a gene
What is gene interaction?
Interaction between genes at different loci that affect the SAME characteristic
What is epistasis?
When a gene at one locus masks or suppresses the effect of a gene at different locus
What is an epistatic gene?
The gene that does the masking in epistasis
What is a hypostatic gene?
the gene whose expression is being masked
What is recessive epistasis?
when the expression of the homozygous recessive (bb) of one gene is epistatic to the expression to the second gene
bb inhibits the expression of an allele
What is dominant epistasis?
when the dominant allele expression of a homozygous or heterozygote of one gene is epistatic to the second gene
What is duplicate recessive epistasis?
what two recessive alleles at either gene suppress a phenotype
What is duplicate dominant epistasis?
When a single dominant allele of either gene is sufficient to mask the second gene
What is dominant with recessive suppressor?
When the dominant allele of one gene combines with the suppressor from a second gene that restore the dominant phenotype of the first gene
Suppresses the expression of the first gene
What is the phenotypic ratio for recessive epistasis?
9:3:4
What is the phenotypic ratio for dominant epistasis?
12:3:1
What is the phenotypic ratio for duplicate recessive epistasis?
9:7
What is the phenotypic ratio for duplicate interaction epistasis?
9:6:1
What is the phenotypic ratio for duplicate dominant epistasis?
15:1
What is the ratio for dominant and recessive epistasis?
13:3
What is a sex-linked characteristic?
When genes located on the sex chromosomes
What are sex influenced characteristics?
when autosomal genes are more readily expressed in one gene. Expression in male and female is different
What is a sex limited characteristic?
Autosomal genes whose expression only appears in one sex. Each can carry the genes but is only expressed by one sex
What is genetic maternal effect?
When the genotype of the mother determines the PHENOTYPE of the offspring
What is cytoplasmic inheritance?
when characteristics are encoded by genes from the cytoplasm, which are inherited only from mom
What is a temperature sensitive allele?
an allele whose product function differently in various temperature ranges
What is genomic imprinting?
when a gene is expressed differently depending on whether it came from mom or dad
What is a phenocopy?
when environmental agent results in an individual of one genotype that mimics expected phenotype of a different genotype
THIS IS NON-HEREDITARY CHANGE
What are discontinuous characteristics?
When there are few distinguishable phenotypes. there is separation between the groups
(Round or wrinkled)
What are continuous characteristics?
Characteristics that display a large number of possible phenotypes that aren’t easily distinguishable
Ex: human height
What are polygenic characteristics?
characteristics that are encoded by genes at MANY LOCI
What is pleiotropy?
When one gene affects multiple characteristics
What are dizygotic twins?
Non identical twins. Coincidental fertilization of 2 eggs. 50% genetically related
What are monozygotic twins?
Identical twins. Single fertilization split of initial embryo. 100% genetically related
What is a concordant trait?
The trait shared by both twin members
Same phenotype
What are discordant twins?
Only one member has the trait
What is concordance?
The percentage of twin pairs that are concordant for a trait
What is an ultrasonography?
Ultrasound
High-frequency sound is beamed into uterus, sound waves detect dense tissue and bounce back to transform a picture
What is amniocentesis?
prenatal test that obtains a sample of amniotic fluid from the uterus
Weeks 15-18, cells are cultured
What is chorionic villus sampling?
Prenatal testing
A plastic tube comes in contact w the outer layer of the placenta. Suction is applied and a small piece of chorion is removed
What is a karyotype?
A picture of the complete set of chromosomes
What are maternal blood screening tests?
Exam level of certain substances in the mothers blood. Only indicates increased risk of a problem
What is noninvasive prenatal screening?
• cell-free fetal dna
• Tests that use maternal blood
• no risk to fetus or placenta
• ~ 9 weeks
What is preimplantation genetic diagnosis?
people who carry a genetic defect can avoid producing a child with the disorder
• use of in vitro fertilization
What is newborn screening?
when newborn infants are tested for genetic disorders
• mandatory bc early identification can lead to effective treatment
What is presymptomatic genetic testing?
Tests for healthy adults for genes that might predispose them to a genetic condition in the future
What is HETerozygote screening?
Test healthy members of a population to identify het carriers of a disease-causing allele but have the potential to produce children who have the disease
Their recessive allele can cause disease
What is pharmacogenetic screening?
• Tailored medicine
• look for alleles that cause positive or negative reaction to treatments
What are some complications in interpreting genetic tests?
• some diseases are caused by many mutations which are not easily detected with one test
• incomplete penetrance can cause individual phenotype to escape the genotypic expectations
Why are humans not an ideal genetic model?
- small numbers of offspring
- cannot make controlled matings
- long generation time
- difficult to maintain groups in a controlled or similar environment
What is a pedigree?
Pictorial representation of a family history that outline the inheritance of one or more characteristics
What are autosomal recessive traits?
- Appear in both sexes with equal frequency
- Tend to skip generations
- Affected offspring are often born to unaffected parents
- When parents are het (Aa), 1/4 of offspring will be affected
- Appears more in children of consanguineous mates
What are autosomal dominant traits?
- Appear in both sexes with equal frequency
- Both sexes transmit trait.
- Doesn’t skip generations.
- Affected offspring must have affected parent
- When one parent (affected) is HET and one parent is unaffected, 1/2 offspring will be affected
- Unaffected parents do not transmit trait
What are X-linked RECESSIVE traits?
- Usually more males than females are affected
- Affected sons are usually born from unaffected mothers; thus, the trait skips generations.
- Approximately half of a carrier (het) mother’s sons are affected.
- Never passed from father to son
- All daughters of affected fathers are carriers.
What are X-linked DOMINANT traits?
- Both males and females can be affected BUT usually more females
- Does NOT skip generations. Affected sons must have an affected mother
affected daughters must have either an affected mother or an affected father. - Affected fathers pass the trait to all their daughters.
- Affected mothers (if heterozygous) pass the trait to 1/2 of their sons and 1/2 of their daughters.
What is a Y-linked trait?
- Only males are affected
- Passed from father to all sons
- Does not skip generations
What is the principle of segregation?
States that alleles separate during meiosis
What is independent assortment?
When alleles at one locus assort independently of alleles at another locus
What is recombination?
When alleles of different genes can assort into new, non-parental combinations
What are linked genes?
Genes that are located close together on the same chromosome
What is a linkage group?
A group of linked genes
What are non recombinant gametes?
Gamete that contains only the original combinations of alleles that were present in the parents
What are cis/coupling genes?
When there are two dominant or two recessive alleles on the same chromosome
AB/ab
What are trans/repulsion genes?
When there are one dominant and one recessive allele on the chromosome
Ab/aB
What is the chiasma?
The physical position of where crossing over happens between non sister chromatids
How do you find the recombination frequency?
(# of recombinant progeny/total # progeny) x 100%
What did Walter Sutton discover?
that genes are physically located on chromosomes
the chromosome theory of inheritance
What did Nettie Stevens and Edmund Wilson discover?
That sex was associated with a specific chromosome in insects
What did Calvin bridges discover?
that non disjunction of X chromosomes was related to the inheritance of eye color in Drosophila
What did Creighton and McClintock discover?
That intrachromosomal recombination was the result of physical exchange between chromosomes
What is a three point cross?
A cross between a heterozygote at three loci and a homozygous recessive at the same three loci
How many classes of phenotypes are possible from a three point cross?
8
2^3=8
What is interference?
a second crossover event adjacent to the first is often less frequent than expencted
What is the coefficient of coincidence?
The ratio of observed double crossovers to expected crossovers
How do you calculate the coefficient of coincidence?
• # of observed dco/ # of expected dco
How do you find the expected dco?
Frequencies of cM between genes X total offspring
How do you calculate interference?
1- coefficient of coincidence
What does the number from the coefficient of coincidence actually mean?
That we are only viewing that percentage of double crossovers that we expected
0.6 —> 60% observed dco of expected
What does the interference value tell us?
The number will tell us that the dco progeny expected will not be observed bc of interference
1-0.6= 0.4
40% dco will not be observed
What are recombination hotspots?
Where recombination is at least 10 times as high as the average elsewhere in the genome
Where can levels of recombination vary?
• among species
• among chromosomes of a single species
• between males and females
What is mapping with molecular markers?
uses DNA sequences as locations instead of organisms or cellulite phenotypes of the alleles
What are genome wide-association studies?
Looking for nonrandom associations between the presence of a trait
What is haplotype?
A specific set of linked genetic variants or alleles
What is linkage disequilibrium?
The nonrandom association between alleles in a HAPLOTYPE
What does Giemsa dye reveal?
DNA rich in adenine and thymine
Known as G bands
What does Quinacrine mustard reveal?
The differences in cytosine-guanine and adenine-thymine base pairs
What is C banding?
It reveals DNA regions of occupied by centromeric heterochromatin
What is R bands?
Rich in cytosine-guanine base pairs
What is aneuploidy?
When the number of individual chromosomes is altered
What are the four types of chromosome rearrangements?
- Duplications
- Deletions
- Inversions
- Translocations
What is a chromosome duplication?
when part of the chromosome has been doubled
What’s a tandem duplication?
When the duplicated segment is right next to the original segment
AB•CDEFEFG
What is a displaced duplication?
When the duplicated segment is somewhere else on the chromosome or different chromosome
AB•CDEFGEF
What is the Bar mutation?
Small duplication on the X chromosome
More Bar region=smaller eyes
Why are duplications important in evolution?
• They are one way that genes evolve
• the extra copy from the duplication is free to undergo mutation and change
• may acquire enough mutations to assume a new function that benefits the organism
What is a chromosome deletion?
The loss of a chromosome segment
AB•CDEFG —> AB•CDG
What is cri-du-chat syndrome?
Heterozygous deletion on the short arm of chromosome 5
What is a chromosome inversion?
When a chromosome segment is inverted 180°
AB•CDEFG —> AB•CFEDG
What are paracentric inversions?
When the inversion doesn’t include the centromere
What’s are PERIcentric inversions?
Inversions that include the centromere
AB•CDEFG —> ADC•BEFG
What are translocations?
When chromosome segments moved from one chromosome to another or within the the same chromosome
What are non reciprocal INTRAchromosomal translocations?
When the segment moves to a different place on the SAMEEEE chromosome
What are non reciprocal INTERchromosomal translocations?
When the segments moves to a new place
What is polyploidy?
When there is an increase in the # of chromosome sets
What is nullisomy?
The los of both members of a homologous pair of chromosomes
Example: 2n=46 nullisomic=44 chromosomes
• 2n-2
What is monosomy?
The loss of a SINGLE chromosome
2n-1
What is trisomy?
GAIN of a single chromosome
2n+1
What is tetrasomy?
The gain of two homologous chromosomes
2n+1
What psi Prader-Willi syndrome?
The los is part of Chromosome 15q from one homolog
Compulsive eating
What is position effect?
If genes positions are altered, so will their expression
What is pseudodominance?
The expression of a normally recessive allele due to a deletion on the homologous chromosome
