Exam 2 Flashcards
a priori
where you get the observation from, “the earlier”
a posteriori
“from the later”
what are important parts of the experimental design?
controls and treatments
parts of formulating a hypothesis using prior knowledge
- a priori (“from the earlier)
- a posteriori (“from the later”)
Mendel’s hypothesis
the observed traits and hypothesized they were due to some hereditary factor
what were the controls of Mendel’s experimental design?
purebred lines
Fo
the initial, base generation, the parents
F1
the first generation, the offspring of the parents/base generation
F2
the second generation, the offspring of the F1 generation
Mendels Laws:
First Law: _________________
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Second Law: ______________
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First Law: Segregation
- each individual organism possesses two alleles encoding a trait (diploid)
- alleles separate when gametes are formed
- alleles separate in equal proportions
Second Law: Independent Assortment
- alleles at different loci separate independently
Mendel’s first law
segregation
Mendel’s second law
independent assortment
gene
inherited factors that determine a characteristic
allele
alternative forms of a gene
locus
specific location on a chromosome
genotype
combination of alleles
homozygote
2 identical alleles at locus
heterozygote
2 different alleles at locus
intergenic
non coding region (region between genes)
phenotype
manifestation or appearance of a characteristic
how does a phenotype arise?
a phenotype arises from the effects of genes that develop within a particular environment
__________ and _________ are dominant and recessive, NOT __________
PHENOTYPES and TRAITS are dominant and recessive, NOT ALLELES
monohybrid cross
between 2 lines that breed true for ONE trait
dihybrid cross
breeds true for TWO traits
backcross
breed offspring back to the parental generation
when does segregation occur during cell division?
before meiosis and anaphase 1 of meiosis
when does independent assortment occur during cell division?
anaphase 1
probability
probability expressed the likelihood of the occurrence of a particular event
conditional probability
a probability that is modified by additional information that another event has occurred
multiplication or addition rule: this AND this
multiply
multiplication or addition rule: this OR this
addition
multiplication rule
the probability of 2 or more independent events occurring together is calculated by multiplying the probabilities of each of the individual events
addition rule
the probability of any of two or more mutually exclusive events is calculated by adding the probabilities of the individual events
testcross
cross between an individual with an unknown genotype and an individual with the homozygous recessive genotype
wild type
the trait or allele is most commonly found in natural (wild) populations (denoted with a +)
subscripts and superscripts
added to distinguish between genes
slash (/)
distinguish two alleles present in an individual genotypes
underscore ( _ )
in a genotype, indicates that any allele is possible
dihybrid cross
2 – heterozygous at both loci
(cross between two individuals that differ in 2 chromosomes)
phenotypic ratio: Tt x tt
1:1
phenotypic ratio: Tt x Tt
3:1
F2 generation ratio: RRYY x rryy
9:3:3:1
What causes an F2 generation of a dihybrid cross to have a 9:3:3:1 ratio?
this is due to independent assortment, the alleles at each locus separate independently to produce 4 types of gametes, all outcomes are possible and create a 9:3:3:1 ratio
For a 9:3:3:1 ratio what two things have to be true for this to work?
- loci must be independent
- there must be complete dominance
chi-square goodness of fit test
statistical test used to evaluate how well a set of observed values fit the expected value
what does the chi-square test indicate?
indicates the probability that the difference between the observed and the expected value is due to chance and provides information about how well observed values fit expected values
what can the chi-square test NOT tell us?
- whether a genetic cross has been correctly carried out
- whether the results are correct
- whether we have chosen correct genetic explanation for the results
Null Model (Ho)
the data will fit ________________
Alternate Model (Ha)
the data does not fit our model
you can either ________ or __________________ the null model, you cannot accept the model
reject or fail to reject
Type 1 Error
incorrectly reject the null
Type 2 Error
incorrectly fail to reject the null
on the chi squared test: greater than 0.05
fail to reject the null
on the chi squared test: less than 0.05
reject the null
equation for degrees of freedoms
number of classes - number of parameters estimated - 1
mechanisms of sex determination
- chromosome (XX-XO, XX-XY, ZZ-ZW)
- environmental (order, temperature)
sex (noun)
refers to sexual phenotypes
sex determination
the mechanism by which sex is established
phenotype
physical manifestation of a trait
biological sex
refers to the anatomical and physiological phenotype of an individual
hemaphrodite
both sexes present in the same organism
monoecious
individual having both male AND female reproduction female reproductive structures (latin: one house, a hemaprodite)
dioecious
individuals have either male OR female reproductive structures (latin: two houses, chromosomal, genetic or environmental)
examples of environmental sex determining systems
- stacks of slipper limpets determines sex
- temperature of certain reptiles and birds eggs
sex determination systems: chromosomal
chromosomal theory of heredity states that genes are present on chromosomes
we don’t transmit ________ to the next generation, we transmit _____________
alleles, chromosomes
1/2 of sperm have an ___ chromosome, 1/2 sperm have an ___ chromosome, all eggs carry a ___ chromosome
X, Y, X
heterogametic
different sex chromosome complement (ex: XY, ZW)
homogametic
same sex chromosome complement (ex: XX, ZZ)
male vs female: XX vs XO
- XX = female
- XO = male
male vs female: XX vs XY
- XX = female
- XY = male
pseudoautosomal region (PAR)
regions where the sequence is the same (homologous gene sequence), where X and Y pair
male vs female: ZZ vs ZW
- ZZ = male
- ZW = female
Turner Syndrome
- XO
- a single X chromosome in each cell
- female
mosaic / mosaicism
some cells have XX and other cells have XO
there are no known cases in which a person is missing both X’s, what does this mean?
it is an indication that at least one X chromosome is needed for human development
Kleinfelter Syndrome
- XXY
- cells with one or more Y chromosomes and multiple X chromosomes
- male
Poly X Females
- XXX
- triple X syndrome
sex determining region Y
- SRY gene
- encodes a transcription factor that promotes differentiation of the testes
Why do males have SRY gene?
mammals early development have undifferentiated gonads, the default is to go female, but the cascade started by SRY causes gonads to develop as male
hemizygosity
possession of a single allele at a locus
males are homozygous for genes on the _______ chromosomes
X
dosage compensation
females have 2 copies of the X and males have 1 X, the amount of proteins produced is often due to the number of copies present, so females would produce double the amount of proteins than males, to compensate for this one of the X’s inactivates in each cell
Lyon Hypothesis
within the female cell, one of the X chromosomes is inactivated
when does X inactivation occur?
happens in early development, at random
Barr body
inactive X chromosome
if there are excess X’s only one is active - how many barr bodies are pressent in each example? XX, XXX, XXXY
- XX = 1 barr body
- XXX = 2 barr bpdies
- XX = 2 barr bodies
_______ are dominant or recessive
TRAITS
complete dominance
- the same phenotype is expressed in homozygotes (AA) and in heterozygotes (Aa)
- only the phenotype of the dominant allele is expressed in a heterozygote
incomplete dominance
the phenotype of the heterozygote is intermediate between the phenotypes of the 2 homozygotes
codominance
type of allelic interaction in which the heterozygote simultaneously expresses traits of both homozygotes
dominance affects the way that genes are __________ (the phenotype), but not the way genes are _________
expressed, inherited
Dominance
is a result of interactions of alleles within the same locus
Allelic interactions that characterize dominance are
interactions between the products of the genes
The nature of the ________________ is relative to the level at which the phenotype is examined
dominance
penetrance
percentage of individuals with a particular genotype that express the phenotype expected of that genotype
incomplete penetrance
a case in which some individuals possesses the genotype for a trait but do not express the expected phenotype
expressitivity
degree to which a trait is expressed
multiple alleles
presence of more than 2 alleles at a locus in a group of diploid individuals; however each individual of the group has only two of the possible alleles
equation for the number of genotypes possible
n(n+1) / 2
lethal allele
allele that causes death of an individual organism, often easy in development, so that the organism does not appear in the progeny of a genetic cross.
a ____________ lethal allele kills individual that are homozygous for the allele; a ____________ lethal allele kills both heterozygous and homozygotes
recessive, dominant
a lethal allele typically has a ___:___ ratio
2:1
a dihybrid cross typically has a __:__:__:__ ratio
9:3:3:1
what is an example of a dihybrid cross?
YYRR x yyrr or YyRr x YyRr
gene interaction
interaction between genes at different loci that affect the same characteristic
epistasis
type of gene interaction in which a GENE at one locus masks or suppresses the effects of a GENE at a DIFFERENT locus
epistatic gene
gene that masks or surpasses the effect of a gene at a different locus
recessive epistasis
the recessive genotype at one locus masks the phenotype at a second locus
hypostatic gene
gene that is masked or suppressed by the action of a gene at a different locus
dominant epistasis
a single copy of an allele at one locus masks the phenotype of a second locus
duplicative recessive epistasis
two recessive alleles at EITHER of two loci are capable of suppressing a phenotype
sex-influenced
characteristic encoded by AUTOSOMAL genes that are more readily expressed in one sex
example of sex-influenced characteristic
an autosomal dominant gene may have higher penetrance in males than in females, or an autosomal gene may be dominant in males but recessive in females
sex-limited
characteristic encoded by AUTOSOMAL genes and expressed in only one sex
cytoplasmic inheritance
inheritance of characteristics encoded by genes located in the cytoplasm. Because the cytoplasm is usually contributed entirely by one parent, most cytoplasmically inherited characteristics are inherited from only one parent.
genetic maternal effect
determination of the phenotype of an offspring not by its own genotype, but by the nuclear genotype of its mother
genomic imprinting
differential expression of a gene that depends on the sex of the parent that transmitted the gene
traits have dominant and recessive inheritance not alleles, why?
traits are said to have dominant and recessive inheritance because the terms “dominant” and “recessive” describe the relationship between different alleles of a gene, which ultimately determine the expression of a trait
what are 2 examples of levels a genotype may manifest as a phenotype
molecular and organismal level
