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101 Cards in this Set

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Mendel's pea plant experiment
easy to mate- self pollination/cross pollination

studdied characteristics clearly distinguishable between true-breeding lines

in his first crosses followed outcome of single traits (MONOHYBRIDIZATION)
Outcome of monoybrid experiment
Particulate theory of inheritance- genetic determinants unaltered as hey pass from perent to offspring (genes don't "blend")

green, tall- dominant
yellow, dwarf- recessive
Mendel's law of segragation
Genes with determinant traits exist in 2 or more alleles.

if 2 alleles followed- 3:1 ratio

if 4 alleles followed- 9:3:3:1 ratio

different traits INDEPENDANTLY ASSORTED

Different ALLELES, same gene
Independant assortment
DIfferent GENES sort independently
Mendelian Inheritance
applies to many organisms; not just pea plants

for humans, a pedigree analysis used to understand pattern of inheritance of trait/inherited disease
Probability
likelihood an event will happen in the future

*probability=# of individuals with certain trait/total # of individuals

NOT an absolute value- there is random sampling error

*the smaller the sample, the greater the error
Sum Rule
probability of two or more MUTUALLY EXCLUSIVE events is equal to the sum of their individual probabilities

*mutually exclusive- one prevents the other from occuring

*key word- OR
Product Rule
predict individual events that occur in a particular order.

*multiply probabliities of each individual event
Binomial expansion equation
predict unordered combination of events

used to predict number of offspring from a genetic cross, but not in any specified order

P=n!/a!b!c! (p^a)(q^b)(r^c)
n-total number in sample
a-#of event one
b-#of event two (etc.)
p-probablility of a
q-probability of b (etc)
Chi-square test
test validity of genetic hypothesis

determine if expected and actual data are significantly different from each other

If event will occur less than 5% of the time hypothesis is considered incorrect

X^2= sum of (observed-expected)^2/expected
Chromosomes
contain genetic information in the form of PROTEINS

46 (23 pairs) in humans

~1,000 genes per chromosomes

cytogenetics-microscopic examination of chromosomes
Chromosome theory of inheritance
Accounts for laws of segregation and indepentant assortment.

*SEX CHROMOSOMES-determine gender
humans: Male XY, female XX
insects: male X, female XX
birds: male ZZ, female ZW
bees: male haploid, female diploid
Inheritance of Sex Chromosomes
Morgan's Drosophilia Experiment- white eyes are linked to the X gene

region at tip of X and Y chromosomes homologous (causes pairing)
Hemizygous
single copy of X-linked gene in a male
Sex linkage
genes found on one of the two sex chromosomes, but not both.

X-linked genes common, only a few Y-linked known
Pseudoautosomal Inheritance
inheritance pattern genes follow in homologous regios of sex chromosomes same as inheritance pattern of autosomal genes, but genes actually on sex chromosomes
Moleular explination of heterozygous cross
even though heterozygotes only produce 50% of the protein, they still produce enough to show the dominant trait phenotypically. (homozygous dominant individuals produce more than enough protien)
Wild type alleles
most prevalent allele in a population and usually encodes a functionally active protein.
Mutant alleles
wild type alleles that have been altered by mutation
Essential gene
gene that is necessary for survival
Lethal allele
allele that causes the death of an orginism
Nonessential genes
not absolutely required for survival, although they are likely to be beneficial to an organism.

loss of function is not lethal- only becomes lethal if mutated.
Condititional lethal alleles
only cause lethality under a given set of circumstances
Incomplete dominance
heterozygote exhibits phenotype that is intermediate between corrisponding homozygous individuals.
*under a microscope things appear incopletely dominant that appear dominant with the naked eye

Ex. red flower x white flower= pink flower

Molecular explination: 50% of wild type protein is not enough to produce normal phenotype
Multiple Alleles
many alleles encode for one gene.
Ex. Rabbit coat color:
4 alleles for the same gene- some temperature sensative: the protein produced only able to function at certain temperatures
*rabbit fur color determine by effectiveness of tyrosine
Codominance
heterozygote expresses both alleles simultaneously.

Ex. blood typing
working enzyme in blood type attaches sugar to protein in type A and B. Type O blood is a loss of function of the enzyme

Molecular explination: codominant alleles encode proteins that function slightly differently from each other, and the function of each protein, in the heterozygote, affects the phenotype uniquely
Gene dosage effect
two copies of the allele provide more color than one copy of the allele.

analogous to incomplete dominance
Overdominance/heterozygote advantage
heterozygotes may display characteristics that are more beneficial to their survival and reproducion than either corresponding homozygote

Ex: sickle cell anemia (heterozygotes less prone to malaria)
cistic fibrosis (heteros less susceptible to diarrheal diseases)

some heterozygotes make enzymes that function at greater temp. ranges
Sex influenced inheritance
alleles that are dominant in one gender but recessive in the opposite gender.
Ex: baldness in humans
Bb-male bald, female not bald

Molecular explination: sex hormones may regulate the molecular expression of the genes which can impact phenotypic effect of alleles
Sex limited traits
certain traits are only found in one of the two genders.
Ex: breast developement in humans

molecular explination: sex hormones may regulate the molecular expression of genes. This can have an impact on the phenotypic effects of alleles
Incomplete Penetrance
dominant alleles are not phenotypically expressed.

ex: POLYDACTYLISM- one dominant allele is sufficient to cause the condition, but some individuals carry the dominant allele and do NOT exhibit the trait.

*gene does not always "penetrate" the phenotype of the individual
Expressivity
Degree of expression of a trait.

Ploydactylism- person with several extra digits would show high expressivity and a person with a single extra digit would show a low expressivity.
Trait expression influenced by environment
-some traits determined by environmental conditions (temp, sunlight)

-Ex: PKU in humans- autosomal recessive disease is caused by a defect in a gene that encodes the enzyme phenylalanine hydroxylase. Homozygous individuals with this defective allele are unable to metabolize the amino acid phenylalanine. If diagnosed early and diet kept free of phenylalanine, they develope normally.
Epistasis
ccPP is white- the cc is masking the ability of the PP to show its phenotype.

(ccPP white, CCpp white, CcPp purple)

*must have one copy of enzyme from each gene to show the color
Two gene interaction cross
when trait is governed by two genes that exist in both dominant and recessive alleles, and when there are four possible phenotypes, a cross between two individuals that are heterozygous for both genes will produce a 9:3:3:1 ratio.

Ex: ccPPwhite, CCppwhite, CcPp purple
Epistatic two gene cross
when a trait is governed by two gnees exisiting in both dominant and recessive alleles, and when the recessive alleles (in homozygous condition) are epistatic to the other gene, a 9:7 ratio is observed in a cross between two heterozygous individuals.

epistatic interactions are usually explained by different proteins participating in an enzymatic pathway leading to the formation of a single product.
Bridges 8:4:3:1 Ratio in fruit flyes
cream allele is autosomally located and acts as a modifier of the eosin allele.
Linkage
two or more genes on the same chromosome.

*physically linked to each other because eukaryotic chromosome contains a single, continuous, linear peice of DNA.

*when genes are linked, F2 offspring have phenotype more commonly like PARENTAL GENERATION.

*recombinant offspring must be due to a crossover
Map Distance
(# of recombinant offspring/total number of offspring) X 100

*% of offspring due to crossing over

*can't have more than 50%- if more than 50% genes must be on separate chromosomes
Bivalent
composed of two pairs of sister chromatids.

in prophase I, a sister chromatid of one pair may crossover with a sister chromatid from the homologous pair
Genetic Recombination
crossovers that result in rearrangement of linked genes.

Resulting offspring called nonparental/recombinant offspring.
Bateson and Punnett
discovered two traits that did not assort indepentantly:
pruprle flowers with long pollen, and red flowers with round pollen.
Crossing over between X chromosomes
Morgan found in fruit flys that gray bodies, red eyes, normal wings, and yellow bodies, white eyes, and miniature wings occured more often than any other combinations.

Proved all three genes are located on the X chromosome and therefore tend to be transmitted together as a unit.

1.Homologous X chromosomes (in the female) can exchange pieces of chromosomes and create new nonparental combinations of alleles.
2. Likelihood of crossing over depends on the distance between two genes.
Chi Squared Analysis in linkage
Objectively decide whether two genes are linked or independently assorted in a dihybrid cross.

1. must begin with hypothesis that genes are not linked so an expected number can be found and the chi square can be applied.

2. Based on hypothesis, calculate the expected values of each of the four phenotypes

3. apply chi square formula, using the data for the observed values and expected values that have been calculated in step 2.

4. Interpret the calculated chi squared value
Creighton and McClintock Experiment
Purpose was to obtain direct experimental evidence that the formation of nonparental offspring involving linked genes is really due to crossing over.

First made crosses involving two linked genes to produce parental and recombinant offspring. Second, they used a microscope to view the structures of the chromosomes in the parents and in the offspring.

becuase the parental chromosomes had some unusual sturctural features, they could microscopically distinguish the two homologous chromosomes within the pair.

This allowed them to correlate the occurance of recombinant offspring microscopically.
Mitotic Recombination
When crossing over occurs during mitosis.

Occurs much less frequently than in meiosis

If occurs during an early stage of development, daughter cells containing the recombinant chromosomes continue to divide many times to produce a patch of tissue in the adult different from all the other tissue
Genetic mapping
use of crosses as a method to determine the linear order of genes that are linked to each other along the same chromosome.
Testcross
used to determine the number of offspring that can only be explianed by crossing over.

usually heterozygote X homozygous recessive

*goal is to find out if recombination has occured.

Alfred Sturtevant used the frequency of crossing over between two genes to produce the first genetic map
Trihybrid crossess
used to determine the order of and distance between three genes.

analysis of data is similar to dihybrid cross
Interference
using data from trihybrid crosses, its possible to calculate the distances between genes and determine the expeccted likelihood of a double crossover based on the product rule.
Posititve Interference
when a crossover occrus in one region of a chromosome, it often decreases the probability that another crossover will occur nearby.
Maternal Effect
the genotype of the mother directly determines the phenotypic traits of her offspring

*inheritance pattern for certain NUCLEAR GENES

*Explained by the process of oogenesis:
Nurse cells (diploid) produce gene products that are transported into the oocyte. The gene pro-ducts of the nurse cells thereby influence the early developmental stages of the embryo.

*Often play a role in cell division, body plan cleavage pattern, and body axis orientation

*Nurse cells produce mRNA and Proteins for D and d in heterozygous cells, so there are proteins for each allele in every egg.
Nuclear Genes
genes that are located on chromosomes found in the cell nucleus
Epigenetic Inheritance
Pattern in which modification occurs to a nuclear gene or chromosome that alters gene expression, but the expression is not permanently changed over the course of many generations.
Dosage Compensation
the level of expression of many genes on the sex chromosomes (particularly the X) are similar in both genders, even though males and females have different numbers of sex chromosomes.

PLACENTAL MAMMALS:
one of the X chromosomes in the somatic cells of females is inactivated. In humans, either maternal or paternal chromosome can be silenced. BARR BODIES- inactivated X chromosomes

MARSUPIAL MAMMALS:
Paternally derived X chromosome is inactivated in the somatic cells of females

DROSOPHILA MELANOGASTER:
level of expression of genes on the X chromosome in males is increased 2-fold.

CAENORHABDITIS ELEGANS:
level of expression of genes on both X chromosomes in hermaphrodites is decreased to 50% levels compared to males.
X Inactivation
Mary Loyn proposed dosage compensation in mammals is aquired due to random X inactivation

Inactivated X chromosome turns into a BARR BODY that is remembered by the rest of the cells, and is inactive throughout the organism.
Calico Cats
Epithelial skin cells are derived from this embryonic cell that had the Xb chromosome inactivated will produce a patch of white fur. Other embryonic cells may have the other chromosome inactivated (Xw). Epithelial cells that are derived from this embryonic cell will produce a patch of black fur. This produces a veriegated; phenotype fro heterozygous females.
Experiment to support Lyon hypothesis
Female adult epithelial cells had both enzymes, but the clones all had only one which proves one of the X chromosomes had been inactivated.
X-Inactivation Center (Xic)
Contains a gene that encodes and RNA called Xist. This RNA is transcribed from the inactivated X chromosome and coats it. The coating of the X chromosome with Xist RNA leads to compaction.

*During early embryonic developement, the NONinactivated X chromosome expressses the TsiX gene. This gene encodes an anitisense RNA that inhibits the effects of the Xist on the RNA.
Counting Human X chromosomes
1. Initiation: one of the X chromosomes is targeted to remain active and the other is inactivated.

2.Spreading: condensation occurs

3. Maintenance: Inactive X chromosome is maintained as the inactive X chromosome
Genomic Imprinting
gene or chromosome is only expressed depending on the gender of the parent from which it was inherited.

Only one parent's allele is transcribed- offspring remember who allele came from by marking the DNA by methylation of the genes during oogenesis and spermatogenesis*the methylated gene is usually SILENCED

If mother's gene is silenced, male offspring unsilence the gene when they produce sperm

*in mice: Igf gene-
imprinting occurs so the paternal allele is expressed and the maternal allele is silenced. The gene causes dwarfism

Cellular level:
1. establishment of imprinting during gametogenesis
2. maintenance of the impring during embryogenesis and in adult somatic cells
3. erasure and reestablishment of the imprinting in the germ cells
Prader-Willi Syndrome and Angelman Syndrome
Linked genes on chromosome 15

PWS:
inactivated by mother and inherited from father. If father's gene is inactive, offspring will have PWS

AS:
Inactivated by father and passed on by mother. If mother's gene is inactivated, offspring will have AS
Extranuclear Inheritance
Genetic material in cellular organelles found in cytoplasm of cells

Mitochondria and plastids contain their own DNA that contains genes that encode proteins that function within the organelles
Mitochondrial DNA
maternally inherited in humans

genetic material located in nucleoid inside mitochondria

Human:
called mtDNA
Each copy contains circular DNA that is 17,000 bp in length. Contains genes that encode ribosomal RNA, transfer RNA, and thirteen genes encoding polypeptides that are synthesized and function within the mitochondrion.

*most mitochondrial proteins encoded for in the nucleous
Chloroplast DNA
larger than mitochondrial genomes and have more genes

called cpDNA.

tobacco plant:
circular DNA
156,000 bp and 110-120 different genes that encode ribosomal RNA, transfer RNA, and proteins for photosynthesis

*many protiens encoded for in the nucleous
Reciprocal Cross
an experimenter investigates the relationship between the transmission of a trait and the gender of the parents.

in most cases, reciprocal crosses involving traits that are cytoplasmically inhehrited do not produce the same outcome becuase organelles do not segragate the same way in oogenesis as in spermatogenesis

EX: Plant chloroplast inheritance
Father does not transmit chloroplasts, so the plants only inherit the color from the mom. (green if all working chloroplasts, white if chloroplasts carry mutant allele that diminishes green pigment, and variegated if some of both)
Plants only get color trait from MOTHER
Petite Mutants
Segregational petite mutants- mutations in genes located in the nucleus.

Vegetative petite mutants- mutations in the mitchondrial genome itself. Two types:
1.Neutral: lack most mitochondrial DNA
2.Suppressive: lack small segments of the mitochondrial genetic material

*smr trait in Chlamydomonas is inherited from the mt+ parent, but not from the mt- parent. this trait is due to a gene located in the chloroplast genome
Mitochondria and Plastid Inheritance patterns
May be maternal, paternal, or piparental
Mitochondrial Mutations
Can cause human diseases
Endosymbiosis theory
the ancient origin of plastids occurred when a bacterium took up residence within a primordial eukaryotic cell.

over the course of evolution characteristics of the intracellular bacterial cell were gradually changed to become a plastid.

*applies in a similar way to mitochondia

During evolution of eukaryotes, most organnellular genes have been transferred from the organelles to the nucleus frequently, so mitochondria and chloroplasts have lost most of the genes that are still found in present day purple bacteria and cyanobacteria
Karyotype
a photograph a cytogeneticist microscopically examines in which all of the chromosomes vary considerably in size and shape.

three features most commonly used to identify chromosomes:
1. size
2. location of centromere
3. banding patterns when chromosomes treated with stain
Centromere location
can be:
metacentric-roughly in the middle
submetacentric- slightly off center
acrocentric- near one end
telocentric- at the end

Because of varying centromere location, each chromosome has a long arm (q) and a short arm (p)

To identify chromosomes of similar size and to map regions of specific chromosome, the chromosomes are TREATED WITH DYE that yields characteristic banding patterns. (also used to detect changes in chromosome structure)
Chromosome mutations
change the amount of material or rearranging the material

DEFICIENCY: segment of chromosomal material is missing

DUPLICATION: Genetic material is repeated compared to the normal parent chromosome

INVERSION: change in the direction of the genetic material along a single chromosome

TRANSLOCATION: one segment of a chromosome breaks off and becomes attached to a different chromosome.
*simple- single peice of chromosome attached to another chromosome
*reciprocal- interchange of material between two different chromosomes
Deficiency
phenotypic consequences of a chromosomal deficiency depend on the size of the deletion and whether it includes genes or portioins of genes that are vital for the development of the organism.

When deletions have a phenotypic effect, they are usually detramental.

Larger deletions tend to be more harmful because a greater number of genes are missing.
Duplications
Less harmful than deletions

Phenotypic consequences tend to correlate with size

Can add more genes to a genome and promote the formation of gene famalies

Often caused by uneaven crossig over

Positioning effect: three of the same genes on one chromosome has a more dramatic effect than three of the same genes between the two chromosomes.
Gene Families
two or more genes that are similar to each other

When two or more genes derrived from single ancestral gene, genes are said to be homologous to each other.
EX: Globin Gene Family
differences in the expression of the globin genes reflect the differences in the oxygen transport needs of humans during the embryonic, fetal, and postpartum stages of life
Inversions
chromosomal fragment has been flipped in the opposite orientation.

When centromere is found outside the inverted region- PARACENTRIC INVERSION

When centromere lies within inversion-PARICENTRIC INVERSION
(In parIcentric)
Inversion Heterozygotes
One normal and one inverted chromosome- yield unusual crossover products during meiosis. Whether or not abnormal chromosomes are produced depends on the location of the crossover and whether the inversion is paricentric or paracentric

***FIGURE 8.12
Translocations
UNBALANCED translocations usually have detrimental effects

Two ways to get a reciprocal cross:
1. two pieces break off from separate chromosomes and join
2. two nonhomologous chromosomes trade

BALANCED translocations usually have no phenotypic effect because individual has correct amount of genetic material

***FIGURE 8.15
during gamete formation, homologous chromosomes attempt to synapse with each other but because of translocations, pairing of homologous regions leads to the formation of an unusual sturcture that contains four pairs of sister chromatids- TRANSLOCATION CROSS

*alternate and adjacent-1 segragation are the likely outcomes when an individual carries a reciprocal translocation.
Aneuploidy
cell or organism does not have an exact multiple of a chromosomal set.

generally regarded as an abnormal condition.

*creates an imbalance in the level of gene expression between the majority of chromosomoes found in pairs vs. those not in pairs

In HUMANS:
aneuploidies generally involve small chromosomes or sex chromosomes.
Trisomies and monosomies of the other chromosomes usually lethel and lead to early abortion of pregnancy.

*can be influenced by the age of the parent- chance of aneuploidy increases with age.
Euploidy
A few examples of naturally occuring variations in euploidy are known.
EX:
Male bees are produced from unfertalized eggs and only have one set of chromosomes (haploid) Female bees diploid

A few polyploid species also discovered.
Endopolyploidy
in a diploid individual, some somatic cells may become polyploid

EX: Polytene chromosomes found in salivary cells of Drosophila and a few other insects
number of chromosomes increase nearly 1,000 fold.
During this process each of the four types of chromosomes aggregate to form a single stucture with several polytene arms.
Polyploidy
having three or more sets of chromosomes

very common in plants

polyploids having an uneven number of chromosome sets may be seedless, which is desireable in agriculture
Meiotic Nondisjuction
can produce aneuploidy or polyploidy

Complete nondisjunction could produce a diploid gamete and thereby a polyploid offspring
Mitotic Nondisjunction
Can produce patch of tissue with aleted chromosome number (aneuploid/polyploid cells)

Organism with mix of genetically different cells is said to be a MOSAIC
Autoploidy
nondisjunction can produce an individual with one or more sets of chromosomes- Occurs within a single species
Alloploidy
change in chromosome number due to interspecies matings
Allopolyploidy
combination of autoploidy and alloploidy; contains two or more sets of chromosomes from two or more species
Allodiploids
OFTEN STERILE: do not have chromosomes that are found in homologous pairs. Becomes difficult to evenly separate during meiosis

*Exception:
allodiploids of closely related species- chromosomes are homEologous and will pair with each other during mieosis I.
Allotetraploids
more likely to be fertile
Treatments that promote polyploidy
abrupt temp changes during initial stages of seedling growth, and the treatment of plants with chenical agents to interfere with the formation of the spindle apparatus.

*Colchicine is a common chemical used to produce polyploidy
Cell fusion
used to produce an allopolyploid:
prior to fusion, the plant cells from two species were treated with agents that gently digested the cell wall (without rupturing the plasma membrane) to create PROTOPLASTS. These are mixed together and treated with agents that cause fusion initially creating a HETEROKARYON that will eventually go through a nuclear fusion process to create a HYBRID CELL with a single nucleus.

*hybrid cells can be cultured and grown into individual plants
Anther Culture
monoploid plants can be produced directly from pollen (haploid male). Monoploids eventually converted to diploids by colchicine treatment.

*These diploids are homozygous for all of their genes because they were produced from monoploids.
Autoploidy
nondisjunction can produce an individual with one or more sets of chromosomes- Occurs within a single species
Alloploidy
change in chromosome number due to interspecies matings
Allopolyploidy
combination of autoploidy and alloploidy; contains two or more sets of chromosomes from two or more species
Allodiploids
OFTEN STERILE: do not have chromosomes that are found in homologous pairs. Becomes difficult to evenly separate during meiosis

*Exception:
allodiploids of closely related species- chromosomes are homEologous and will pair with each other during mieosis I.
Allotetraploids
more likely to be fertile
Treatments that promote polyploidy
abrupt temp changes during initial stages of seedling growth, and the treatment of plants with chenical agents to interfere with the formation of the spindle apparatus.

*Colchicine is a common chemical used to produce polyploidy
Cell fusion
used to produce an allopolyploid:
prior to fusion, the plant cells from two species were treated with agents that gently digested the cell wall (without rupturing the plasma membrane) to create PROTOPLASTS. These are mixed together and treated with agents that cause fusion initially creating a HETEROKARYON that will eventually go through a nuclear fusion process to create a HYBRID CELL with a single nucleus.

*hybrid cells can be cultured and grown into individual plants
Anther Culture
monoploid plants can be produced directly from pollen (haploid male). Monoploids eventually converted to diploids by colchicine treatment.

*These diploids are homozygous for all of their genes because they were produced from monoploids.