Exam 1 Flashcards
The two types of experiments Mendel carried out (explain)
- Self fertilization: pollen and egg from the same plant, naturally occurs in peas
- Cross fertilization: pollen and egg from two different plants, produces hybrids (offspring)
Describe how Mendel carried out crosses
- Remove anthers from flower 1
- Transfer pollen from anthers of flower 2 to the stigma of flower 1
- Plant the seeds
define
Characters
observable characteristics of an organism
eye color
define
Trait
specific properties of a character
blue eyes
What approach did Mendel use and what does it mean?
Emperical approach
* no hypothesis
* quantitative analysis of crosses would provide mathematical relationships that govern traits
* used to deduce empirical laws
define
Single factor cross
crossing two variants of the same characteristic
Describe Mendel’s single factor cross process
- Cross two true breadding plants (Parental generation)
- The offspring (F1) self fertilize
- The offspring (F2) are analyzed for their traits
Parental: TT x tt
F1: Tt x Tt
F2: TT + 2Tt + tt
result and conclusion of Mendel’s single factor cross
- F2 generation had a phenotype of 3:1
- he concluded that this mean that a trait must exist in a dominant and recessive form, not a blended form
- genes are inherited as discrete units
- Law of segregation
define
Genes
inheritable units that reman unchanged
define
Alleles
different versions of the same gene
explain
Law of Segregation
- two copies of a gene seperate from each other during meiosis
- each gamate carries a single allele of a given gene
Results/Conclusion of Mendel’s 2 factor crosses
- Law of independent assortment
- F2 generation had seeds with new combinations that were not present in the parental generation
Law of independent assortment
two different genes will randomly assort during meiosis
Mendel’s 2 factor crosses has a phenotype ratio of
9:3:3:1
Pedigree basic symbols
- circle = female
- square = male
- filled in = affected
Cystic fibrosis
basic facts
- recessive disorder
- gene encodes a protein CFTR regulating ion transport
- mutant causes altered CFTR
random sampling error
define
- deviation b/w observated and expected
- large for small samples
Product rule
how to and what it gives
- gives the probability that two or more independent events will occur
- multiple probabilities of the independent events
Two hetrozygotes for a disease want to start a family, what is the chance their first 3 kids will have the disease (recessive)
1/4 * 1/4 * 1/4 = 1/64
0.016
1.6%
Binomial expansion equation
what it is and what it gives
- gives all possibilities for a given set of unordered events
- P = [n! ÷ (x!(n-x)!)] p x qn-x
- P = prob of outcome
- n = total events
- x = events in one category
- p = probability of x
- q = probability of other event
Two brown eyes heterozygotes (Bb) have 5 children. What is the probability that 2 of the cuples 5 children will have blue eyes?
P = [5! ÷ (2!)(3!)] (1/4)2 (3/4)3
P = 0.26 or 26%
Chi squared
explained
- shows goodness of fit aka how close the observed is to the hypothesis prediction
- does not prove hypothesis is correct
x2 = SUM OF (O - E)2 ÷ E
High chi square vs low
- High indicates low probability that deviations in observed are due to random chance (reject hypothesis)
- low indicates deviations due to random chance (do not reject hypothesis)
Process of making a karyotype
- sample of blood centrifuged after stopping cells in mitosis
- put in hypotonic solution causes blood cells to enlarge
- Put on slide to see karyotype (organized representation of cell)
Humans are _ and have _ number of chromosomes
Diploid, 46 total chromosomes (23 pairs)
Homologs
facts
- form a homologous pair (chromosome)
- nearly identical in size
- have same bandng pattern and genes
- Not necessarily the same alleles
Chromosomal theory of inheritants
general concepts
DNA in chromosomes and the chromosomes seperate to make gametes so each parent gives one sent of chromosomes to offspring
Explain how Meiosis relates to laws of segregation and independent assortment
- Seperation of homologs during Meiosis shows the law segregation because alleles are seperated
- Lining up on homologs in meiosis explains independent assortment because hetrozygotes can seperate their chromosomes in random ways
In fruit flies, sex is determined by
ratio of x chromosomes and number of autosomes
- if X/A = 0.5 male
- = 1 female
in bees, sex is determined by
number of autosomes
* males are haploid (1 set)
* females are diploid
Simple mendelian
patterns and molecular explanations
- obey mendel’s laws
- dominant/recessive
- 50% of protein from dominant allele is enough for dominant trait
Incomplete penetrance
patterns and molecular explanations
- dominant phenotype is not completely expressed
- dominant allele is present but protein not showing effects
- could be because of other genes or enviroment
Incomplete dominance
patterns and molecular explanations
- phenotype in hetrozygotes is a mix of the two alleles
- 50% of the protein from each alleles is not enough to make same trait as 100% of that protein
Overdominance
patterns and molecular explanations
- hetrozygotes have a trait that makes reproductive sucess higher than of either homozygote
- cells may have increased resistance, may produce more protein dimers & increase function, proteins may be produced in more conditions
Codominance
patterns and molecular explanations
- hetrozygote has BOTH phenotypes (not a mash/intermediate)
- example is AB blood type
- alleles encode slightly different proteins so function of each exist together
x-linked
patterns and molecular explanations
- genes are linked to x-chromosome
- 50% of the protein in males is enough for dominant trait but not necessarily in females
sex-influenced
patterns and molecular explanations
- effect of sex on phenotype is different for alleles
- recessive in one sex but dominant in others
- sex hormones may regulate expression of genes
sex-limited inheritance
patterns and molecular explanations
- trait occurs in only 1 sex
- sex hormones may regulate expression of genes
lethal alleles
patterns and molecular explanations
- causes death
- lose of function alleles usually
Most recessive mutants are loss of function because
- 50% of the functional protein is enough for the phenotype
- hetrozygote may upregulate normal gene to make up for the loss
3 explanations for dominant mutants
- Gain of function new or abnormal function of protein
- Dominant negative protein acts against normal protein
- Haploinsufficiency mutant is loss of function but 50% of protein is not enough for phenotype of wild type
Expressivity
degree to which trait is expressed
Incomplete dominance
outcome of single factor cross
- F1: 50% of protein not enough so phenotype is inbetween two alleles
- F2 has 1:2:1 phenotype rather than 3:1 since the heterozygotes have different phenotype
Overdominance
outcome of single factor cross
- hetrozygouse advantage
- genotype AND phenotype of F2 is 1:2:1
- more hetrozygous offspring survive
Sickle cell anemia
explained
- Homozygous for normal hemoglobin are just normal, homozygous for mutant have disease
- Hetrozygotes have adavantage because they do not suffer from sickle cell anemia and are more resistant to malaria
Blood type
explained
- 3 alleles for antigens
- i recessive to A and B
- A and B are codominant
- A & B = AB blood type
- Ai = A blood type
- Bi = B blood type
- ii = O blood type
X linked traits
outcome of single factor cross
F1 phenotpe depends on which parent has mutant/recessive allele
* if father has defective allele, no offspring will be affected but all women will be carriers
* if mother has 2 defective alleles (homozygous) then all daughters will be carries and all sons will be affected
Y linked traits
outcome of single factor cross
- transfered only from father to son
Sex-influences traits are …
chromosome type
autosomal
Lethal alleles
outcome of single factor cross
Hetrozygoous cross between F1 generation has F2 generation of 1:2 genotypes
* Lethal allele causes death of homozygous alleles for mutant so ratio is not mendelian
conditional lethan alleles…
only kill when certain enviromental conditions occur
pleiotropy
definition and causes
multiple effects of a single gene on the phenotype
* gene product can affect cells in multiple ways
* expressed in different cell types
* expressed at different times
White spotting phenotype occurs because
alleles that cause decrease in number of precursor cells during development as cells migrate
Gene interactions
definition
occur when two or more different genes influence the outcome of a single trait
Epistasis
definition
the alleles of one gene mask the phenotypic effect of the alleles of a different gene
Complementation
definition
two parents that express same or similar recessive phenotypes produce offspring with the wild type phenotype
Gene modifier effect
definition
allele of one gene modifies the phenotype of the alleles on a different gene
Gene redundancy
definition
a pattern in which the loss of function of one gene has no effect but loss of two has an effect, the genes are reduntant and only 1 is required
Epistatic interactions often arise
because 2 or more different proteins may have a common cellular function
Epistatis
F2 generation
F2 would have a different ratio due to masking
* like if gene C and P are both responsible for color
* a dominant C and P allele are both required for purple
* so having a cc or pp allele masks the other gene, even if the other gene has a dominant allele
* CcPp, CCPp, CcPP, CCPP = purple
* ccpp, ccPp, ccPP, Ccpp,CCpp = white
Gene redundant
F2 outcome
15:1 ratio
* Only double recessive genotype has a different phenotype
True-breeding tall plants with purple flowers are crossed to true-breeding dwarf plants with white flowers. The F1 plants were tall with purple flowers. The genes that affect these traits independently assort. If the F1 plants were crossed to dwarf plants with white flowers, the expected ratio of the F2 generation would be
1 tall/white flowers : 1 tall/purple flowers : 1 dwarf/white flowers : 1 dwarf/ purple flowers
A fruit fly with a diploid set of autosomes has one X chromosome but no Y chromosome. This fly would be _ because _.
male, the ratio of X chromosomes to autosomes is 0.5
Two different strains of plant exhibit a recessive phenotype of white flowers. When crossed, they produce offspring with wild-type purple flowers. The outcome of this cross is called _ and it indicates that _
complementation/the recessive alleles are in two different genes
Mendelian inheritance pattern rules
4 rules
- Expression of the genes influences traits
- Genes are passed down unaltered
- Law of segregation
- Law of Independent assortment
Maternal effect definition
genotype of the mother effects the phenotype of the offspring
Maternal effect for shell orientation cross:
Mother DD x Father dd
F1 Genotype: Dd
F1 phenotype: All dextral
Maternal effect shell orientation hetrozygous (F1) cross:
Dd x Dd
Genotype F2: 1 DD, 2 Dd, 1 dd
Phenotype: all dextral
Molecular mechanism of Maternal effect inheritance
- nurse cells are diploid while oocyte becomes haploid
- nurse cells give their mRNA/protein right after fertilization
- sperm allele too late to express and change development
- these genes play important role in early embryogenesis
Epigenetic inheritance definition
- modification alters gene expression
- not permanently changed over generations
- reversible and no change in DNA
Dosage compensation purpose and definition
changing gene expression to compensate for differences in sex chromosomes
Dosage compensation in mammals general
- inactive x chromosome is condensed down into a barr body
- happens during early development
- X chromosome inactivation passed down to somatic cells
X chromosome inactivation in mammals mechanism
- Nucleation: the number of X-inactivation centers (Xics) counted and chosen
- Spreading: inactivation starts and Xic and progresses until barr body
- Maintenance: barr body stays bar body
define/explain
Pseudoautosomal genes
- genes that are on barr body X chromosome but are expressed
- may involve loosening of chromatin
Genomic imprinting
definition
a segment of DNA is marked to express either maternal or paternal ingerited allele
Stages of imprinting
- Establishment of the imprint
- Maintenance of the imprint
- Erasure and reestablishment: the germ line cell (reproductive) is erased of imprinting to reestablish imprinting based on sex of species (will they pass on silenced alleles or not)
Molecular mechanism of imprinting
- imprinting control region (ICR) near gene
- methylation in genes silences them
Maternal inheritance
Genes that are encoded by mitochondrial DNA so only mother passes them down
How does variegated phonotype occur in leaves?
- Color of the leaves in in the chloroplast which are maternal inherited
- speices can have cells with different type chlorplasts so they have different colors
How does variegated phonotype occur in leaves?
- Color of the leaves in in the chloroplast which are maternal inherited
- species can have cells with different type chloroplasts so they have different colors
endosymbiosis theory
chloroplasts and mitochondria were primordial eukaryotic organisms that got endocytosis by an archaea
When two different genes are close together on the same chromosome and tend to be transmitted together from parent to offspring, this phenomenon is called
linkage
Crossing over occurs during
meiosis
_ is needed to produce recombinant offspring.
Crossing over
Two genes in Drosophila are found on the X chromosome. A true-breeding fly with white eyes and a gray body was crossed to a true-breeding fly with red eyes and a yellow body. All F1 offspring had red eyes and gray bodies. The F1 female offspring were crossed to male flies with white eyes and yellow bodies. Which F2 offspring is/are recombinant?
Those having white eyes with yellow bodies and red eyes with gray bodies
Let’s suppose that two genes are linked to each other along the same chromosome and they are 14 map units apart. A true-breeding AAbb individual is crossed to a true-breeding aaBB individual. The F1 offspring are mated to aabb individuals. If this testcross produces 1000 offspring, how many of them would you expect to be aabb?
70
In Chi square what hypothesis used and why?
An independent assortment hypothesis is proposed because it allows you to calculate expected numbers of offspring.
How to calculate % of recombinant offspring from map distance
map distance = % of recombinant offspring
A maternal effect gene exists in a dominant, normal head (N) allele and a recessive, small head (n) allele. A mother with a normal head has a bunch of offspring with small heads. What are the possible genotypes of the mother, maternal grandmother, and offspring
- Mother: nn;
- Maternal grandmother: Nn
- Offspring: Nn or nn
With regard to a maternal effect gene, a mother is DD and her haploid oocyte (D is fertilized by a sperm carrying the d allele. Which gene products would be found in this fertilized oocyte?
Only D gene products
Genomic imprinting is a type of _
epigenetic inheritance
The Igf2 gene that is inherited from the mother is silenced due to imprinting. A mutation, which we will call Igf2—, is a loss-of-function mutation. If an Igf2—Igf2 mother is crossed to a father that is Igf2—Igf2, what is the predicted outcome?
Half of the offspring would be normal, and half would be dwarf.
Due to imprinting, the gene(s) affecting Prader-Willi syndrome is silenced during egg formation, and the gene affecting Angelman syndrome is silenced during sperm formation. A person named Lynn has Prader-Willi Syndrome due to a deletion that encompasses genes involved with both Prader-Willi syndrome and Angelman syndrome. As an adult, Lynn has child with Angelman syndrome. Lynn is a ______ and the child is _______.
female, male or female
What inheritance pattern causes a variegated coat color, such as the Calico cat
X-chromosome inactivation
Let’s suppose a trait in dogs involves a gene that affects the shape of the spine. This gene exists as the wild-type allele that causes a normal spine and mutant allele that causes a crooked spine. A true-breeding female with a normal spine is crossed to a true-breeding male with a crooked spine. All of the F1 offspring have normal spines. The F1 female offspring are then crossed to true-breeding males with a crooked spine. All of the F2 offspring have normal spines. These are observations are consistent with
maternal inheritance and maternal effect
recombinant offspring definition
offspring that have been produced from a crossover event in at least one of the parent’s gametes
Genes that are _ have a higher probability of crossing over
far apart
if there are a small number of recombinant offspring with two genes, those two genes are (far or close)
close to each other
chi square formula
x2 = ((observed - expected)2) / expected
If reject hypothesis that genes independently assort,
then accept hypothesis that genes are linked
genetic mapping purpose
to determine the linear order of linked genes along a chromosome
Genes that are far apart result in…
many recombinant offspring
map distance equation
mu = (# recombinants / total offspring) * 100
test cross definition
individual that is a double (or triple) heterozygote crossed to a homozygous recessive individual
multiple cross overs set a quantitative limit on
measurable recombination frequencies as physical distance increases
accuracy of recombination frequency calculations from test crosses & map distance
as the map distance approaches 50mu, the number of recombinant offspring is underestimated as a test cross is only expected to yield a max of 50% recombinant offspring always
the probability of a double cross over is predicted by…
the product rule
product rule equation for probability of double cross over
= (probability of single cross over between genes 1 and 2) * (probability of a single cross over between genes 2 and 3)
positive interference
the first crossover between genes decreases the probability that another crossover will occur nearby
karyotype features
- location of the centromere
- size
- banding patterns
how does staining show banding patterns?
dark bands bind dye very heavily while light bands do not
banding pattern is useful because…
- distinguishes individual chromosomes
- detects changes in chromosome structure
- shows evolutionary relationships
4 types of centromere locations
- metacentric: in the middle
- submetacentric: slightly off center
- acrocentric: close to the end of chromosome
- telocentric: at the end of chromosome
G banding numbering convention
each side of the chromosome (p & q) is split into sections (with 1 being the sections closer to the centromere) and each section is divided into bands that are labelled in the same way
ex.
p-2-3
on the p side of the chromosome (above), section 2 third band
4 types of changes that can occur in chromosome structure
- deletions
- duplications
- inversions
- translocations
_ and _ change the total amount of genetic material in a chromosome
deletions and duplications
_ and _ do NOT change the total amount of genetic material in a chromosome
inversions and translocations
inversion definition
change in direction of a section of the chromosome
translocation 2 types and definitions
- simple: a piece of chromosome gets attached to another chromosome
- reciprocal: two different chromosomes exchange pieces that make two abnormal chromosomes
nonallelic homologous recombination
repetitive sequences cause a misalignment of homologous chromosomes which results in a misaligned cross over. results in duplication or deletion
a chromosomal deletion occurs when…
- a chromosome breaks and a piece is lost
terminal deletion definition
chromosome is broken into two pieces and the part without the centromere is lost
interstitial deletion
chromosome breaks in two places and the two outer pieces reattach and the central fragment is lost
duplication usually caused by…
abnormal events during recombination/crossing over
gene family definition
two or more genes in a single species that are derived from the same ancestral gene
how are gene families formed?
an abnormal event causes a gene duplication, and over generations there are mutations so the two duplicated genes become slightly different
paralogs
homologous genes within a species, carry out different but similar functions
copy number variation
a segment of DNA that varies in copy number among individuals
copy number variation can be caused by
- nonallelic homologous recombination
- proliferation of transposable elements
- errors in DNA replication
segmental duplication
one segment of DNA has multiple copies of the same gene
comparative genomic hybridization can be used to
detect deletions and duplications
how to interpret data from genomic hybridization
- look at the ratio of green to red fluorescence in the hybrid chromosome
- a ratio of 2 indicates a duplication in “green” (cancer cells usually)
- ratio of 0.5 indicates a deletion in green
Pericentric inversion
inversion that includes centromere
paracentric inversion
inversion not with centromere
two ways inversions can alter the phenotype of an individual (very rare)
- breakpoint effect: an inversion breakpoint is in the middle of a vital gene
- position effects: a gene is repositioned in a way that alters its gene expression
crossover betwee a pericentric inverted chromosome and a normal chromosome
results in 2 normal chromatin and 2 chromatin with a deletion and a duplication in each
crossover between a paracentric inverted chromosome and a normal chromosome
results in an acentric fragment and a dicentric chromosome
reciprocal translocations arise from (and examples)
- chromosome breakage and DNA repair (ex. reactive ends broken by external factors but DNA repair improperly attaches them back)
- abnormal crossovers (nonhomologous chromosomes do crossing over)
_ translocations are more lethal/problematic than _ translocations
unbalanced than balanced
in familial down syndrome
- the majority of chromosome 14 gets attached to chromosome 21
- offspring could have 3 copies of genes on chromosome 21 so exhibit similar characteristics of down syndrome
balanced carriers of familial down syndrome often have
reduced fertility
Robertsonian translocations
- breakage near centromeres of acrocentric chromosomes causes loss of small fragments and fusion of large segments into one chromosome
- most common rearrangement in humans
individuals with balanced translocations…
have a larger chance of producing gametes with an unbalanced combination of chromosomes
mechanism of gamete formation in individuals with balanced translocations
translocation cross forms where homologous line-up and form a octet
* alternate segregation: 2 normal gametes, 2 balanced gametes
* adjacent-1 segregation: 4 unbalanced gametes
* adjacent-2 segregation: 4 unbalanced gametes rare one
type of segregation where one cell gets both normal chromosomes and another cell gets both translocated chromosomes after meiosis 1
alternate segregation
type of segregation where all four cells have one normal and one translocated chromosome
adjacent-1 segregation
semisterility
having fewer variable gametes so individuals fertility is lower
euploidy
- variation in the number of complete sets of chromosomes
- organisms with 3 or more sets of chromosomes are also called polyploid
aneuploidy
- variation in the number of particular chromosomes within in a set
- organism can be trisomic for that chromosome or monosomic
aneuploidy causes an _ phenotype
abnormal
why does aneuploidy have a bad effect on phenotype
- genes on that chromosome are expressed 1.5x more
- for trisomy 21 (sex gene) pseudoautosomal genes are expressed imbalanced
down syndrome is caused by
- failure of chromosome 21 to segregate properly in meiosis 1
- 5% of the time it is paternal nondisjunction (X and Y not separated in sperm)
polyploidy in animals is
lethal usually
endopolyploidy
when certain tissues or cells are polyploid in an organism
* enhances the ability of a cell to produce specific proteins
polytene chromosomes
a bundle of chromosomes together, aggregate in the chromocenter
polyploids with an odd number
are usually sterile as they produce highly aneuploid gametes (chromosome sets don’t segregate equally)
lgf2 gene is silenced in
sperm
leber hereditary optic neuropathy is passed down in what pattern
maternal inheritence
gene in mitochondrial DNA
