Exam 1 Flashcards
Genes are the basic units of
heredity
What is heredity?
how genes transmit traits from parents to offspring
What is the study of biological information?
how organisms store, replicate, transmit, and utilize information that allows survival and reproduction
DNA –>
RNA –> Protein
__ was the first applied genetic technique
artificial selection
What is artificial selection?
the purposeful control of mating by choice of parents for the next generation
What are the crucial questions about selective breeding?
- What is inherited?
- How is it inherited?
- What is the role of chance in heredity?
Who discovered the basic principles of genetics?
Gregor Mendel
What are the four general themes of Mendelian Genetics?
- variation is widespread in nature and provides for continuously evolving diversity
- observable variation is essential for following genes from one generation to another
- variation is inherited by genetic laws, which can explain why like begets like and unlike
- Mendel’s laws apply to all sexually reproducing organisms
What were the keys to the success of Mendel’s experiments?
- pure-breeding lines of peas
- inheritance of alternative (or antagonistic) forms of traits
- experimental technique (controlled breeding)
Mendel performed __ crosses to control whether trait was passed on by sperm or egg
reciprocal
What is a phenotype?
an observable form of a given trait
What is a monohybrid cross?
mating of pure-breeding parental plants antagonistic for a single trait
In a monohybrid cross, both parental traits reappear in F2 progeny in a __ ratio
3:1
Mendel proposed that each plant carries
two copies of a unit of inheritance
Trait that appears in F1 progeny is the
dominant form
Trait that is hidden in the F1 progeny is the
recessive form
What are units of inheritance?
genes
What are alternative forms of a single gene?
alleles
Individuals with two different alleles for a single trait are
heterozygotes
Pure breeding individuals are
homozygotes
What does Mendel’s law of segregation state?
- the two alleles for each trait separate during gamete formation
- two gametes, one from each parent, unite at random at fertilization
What is a gamete?
specialized cells that carry genes between generations (egg/sperm)
What is segregation?
separation of alleles so that each gamete receives only one copy of each gene
In a F2 progeny
- 1/4 will breed true for the dominant trait
- 1/2 will be hybrids
- 1/4 will breed true for the recessive trait
What is probability?
a measure of how likely some event is to occur
-expresses a belief in future events, or outcomes
What are independent events?
the probability of event 1 does not affect the probability of event 2
What is the product rule?
probability of two independent events occurring together is the product of their individual probabilities
What is the sum rule?
probability of either of two mutually exclusive events occurring is the sum of their individual probabilities
What is an example of an ordered event?
What is the probability of flipping a heads, then a heads, then a tails?
What is an example of an unordered event?
What is the probability that in 3 tosses you will get two heads and a tail?
What is genotype?
a pair of alleles in an individual (e.g. YY or Yy)
Genotypes in F2 progeny are in a ___ ratio
1:2:1
Phenotypes in F2 progeny are in __ ratio
3:1
What can a test cross reveal?
an unknown genotype in an individual with a dominant phenotype
Mendel’s dihybrid crosses revealed the law of
independent assortment
The different types of germinal cells of a hybrid are produced on average in
equal numbers
The possible number of gamete genotypes from a hybrid =
2^n
n: number of heterozygous traits
What did Mendel’s work do?
- Explained reappearance of hidden traits
- disproved blended inheritance
- showed that parents contributed equally to next generation
- developed a testable model for making predictions about inheritance
A specific gene determines a __ , whose activity may affect phenotype
specific enzyme
A dominant allele usually determines
a normally functioning protein
A recessive allele usually does not
encode a functional protein
Why is it challenging to determine inheritance patterns in humans?
- long generation time (lives a long time)
- small numbers of progeny (so Mendel’s ratios rarely observed)
- no controlled matings
- no pure-breeding lines
What are the categories of inheritance?
- autosomal recessive
- autosomal dominant
- x-linked recessive
- x-linked dominant
- y’linked
- organelle (mitochondria or chloroplast)
What are pedigrees?
diagrams of a family’s genetic features that extends over multiple generation
How are male and female represented in a pedigree?
female: circle
male: square
How is an affected individual represented in a pedigree?
box is colored in
What is characteristic of a horizontal pattern of inheritance?
parents of affected individuals are unaffected but are heterozygous (carriers) for the recessive allele
What is characteristic of a vertical pattern of inheritance?
every affected person has at least one affected parent
What are the three key aspects of pedigrees with dominant traits?
- affected children always have at least one affected parent
- As a result, dominant traits show a vertical pattern of inheritance
- two affected parents can produce unaffected children, if both parents are heterozygotes
What are the four key aspects of pedigrees with recessive traits?
- affected individuals can be the children of two unaffected carriers, particularly as a result of consanguineous matings
- all the children of two affected parents should be affected
- rare recessive traits show a horizontal pattern of inheritance
- extremely common recessive traits might show a vertical pattern of inheritance
What are some of the most common single-gene traits caused by recessive alleles in humans?
- Thallassemia
- Sickle-cell anemia
- Cystic fibrosis
- Tay-Sachs disease
- Phenylketonuria (PKU)
- Hypercholesterolemia
- Huntington disease
Most traits in humans are due to the interaction of __ and do not show a simple Mendelian pattern of inheritance
multiple genes
Most single-gene Mendelian traits will be
recessive
What is pleiotropy?
one gene may contribute to several characteristics
The phenotype of the __ defines the dominance relationship of two alleles
heterozygote
What is complete dominance?
when the hybrid resembles one of the two parents
What is incomplete dominance?
when the hybrid resembles neither parent
Incomplete dominance is a blending of __ only, not the __
phenotype; genotype
Pink flowers in snapdragons are the result of
incomplete dominance
In codominance, the F1 hybrids display traits of
both parents
-neither phenotype dominant or recessive
When two alleles at a gene both produce functional protein products, they will often be
codominant
Dominance relations between alleles do not affect
transmission of alleles
Type of dominance (complete, incomplete, codominance) depends on the type of proteins encoded and their biochemical functions but have no effect on
allele segregation
Dominance and recessiveness are not inherent properties of different mutant alleles, but are
effects observed relative to other alleles at the same locus
What is allele frequency?
percentage of the total number of gene copies for one allele in a population
What is a wild type (+)?
most common allele
What is a mutant allele?
rare allele (new alleles that are generated by mutation)
What is a monomorphic gene?
has only one common allele
What is a polymorphic gene?
has more than one common allele
With some pleiotropic genes, an allele can be dominant for a trait when heterozygous, but when homozygous it can be
inviable
Novel phenotypes can arise from incomplete dominance and codominance in the F1 generation and will be
the most common phenotype in F2’s (1:2:1)
If you see crosses of various phenotypes at one trait and each cross gives you a 3:1 ratio, you have
1 gene with many alleles (allele series)
Lethal mutations are usually __ and can’t be homozygous
recessive alleles
Single traits arising from interaction of multiple genes are
multifactorial
Phenotype can be modified by interaction of genes with
environmental conditions (temp, diet, etc)
What is multifactorial inheritance?
most common traits arise from the action of 1 or more genes or interaction of genes with the environment
Two genes can determine
one trait
Novel phenotypes can result from
gene interactions
What is epistasis?
an allele at one locus masks the effects of an allele at another locus
In epistasis, the gene that does the masking is __ to the other gene
epistatic
In epistasis, the gene that is masked is __ to the other gene
hypostatic
Epistasis can be
recessive or dominant
For epistasis to be recessive, the epistatic gene must be
homozygous recessive
e.g. ee
For epistasis to be dominant, the epistatic gene must
have at lease one dominant allele present
e.g. E-
What is an example of recessive epistasis?
dog coat color
What is an example of dominant epistasis?
squash fruit color and chicken feather color
Dominant epistasis 1 produces a __ ratio in F2 progeny
12:3:1
Dominant epistasis 2 produces a __ ratio in F2 progeny
13:3
What is recessive epistasis?
homozygous recessive of one gene masks both alleles of another gene
What is dominant epistasis 1?
dominant allele of one gene hides effects of BOTH alleles of another gene
What is dominant epistasis 2?
dominant allele of one gene hides effects of DOMINANT ALLELE of another gene
What is complementary gene interaction?
one dominant allele of each of TWO genes is necessary to produce phenotype
What is the F2 phenotypic ratio of complementary gene interactions?
9:7
What is the F2 phenotypic ratio of recessive epistasis?
9:3:4
What is the F2 phenotypic ratio when there is no gene interaction?
9:3:3:1
Heterogeneous traits have the same recessive phenotype but are caused by
mutations in different genes
What is a genetic cross called?
a complementation test
Complementation testing is used to determine if
a particular RECESSIVE phenotype arises from mutations in the same or separate genes
T or F? Complementation testing can be used with dominant phenotypes
F
__ __ help us determine the inheritance of the trait
breeding studies
Phenotypic variation for some traits can occur because of
- differences in penetrance and/or expressivity
- effects of modifier genes
- effects of environment
- pure chance
What is penetrance?
the percentage of a population with a particular genotype that shows the expected phenotype
-can be complete (100%) or incomplete (<100%)
What is expressivity?
degree or intensity with which a particular genotype is expressed in a phenotype
-can be variable or unvarying
What do modifier genes do?
alter the phenotypes produced by alleles of other genes
-have a subtle secondary effect on phenotype controlled by major genes
__ can often have phenotypic effects
temp
__ __ mutations are lethal only under some conditions
conditional lethal
In permissive conditions, mutant allele has __ function
wild-type
In restrictive conditions, mutant allele has __ functions
defective
What is a phenocopy?
a phenotype arising from an environmental agent that mimics the effect of a mutant gene
What is characteristic of phenocopy?
- genetically “normal” individuals show abnormal phenotype due to environmental influence
- not heritable
- can be deleterious or beneficial
What are discontinuous traits?
“either-or” phenotypic differences between alternative alleles
What are continuous traits determined by?
segregating alleles of many genes that interact together and with with the environment
What is characteristic of continuous traits?
- appear to “blend” and “unblend”
- also called quantitative traits because the traits vary over a range that can be measured
- usually polygenic- controlled by multiple genes
The more genes or alleles, the more
phenotypic classes and the greater the similarity to continuous variation
Metaphase chromosomes can be classified by
centromere position
Why are chromosomes studied in metaphase?
chromosomes are most visible at this point just before nucleus divides
Following duplication, chromosomes have 2 identical halves (__ __) attached at centromere
sister chromatids
What is characteristic of a metacentric chromosome?
centromere is in the middle
What is characteristic of an afrocentric chromosome?
centromer is near one end
Homologs contain the same set of genes, but have different __ for each gene
alleles
Non homologs carry
completely unrelated sets of genes
What is characteristic of human chromosomes at metaphase?
2n = 46, n = 23
In a karyotype, each homologous pair is arranged in order of
decreasing size
What is mitosis?
the mechanism that parcels out chromosomes into daughter cells, and maintains genetic integrity during cell division
Mitosis __ chromosome number in cells between divisions
preserves
The cell cycle is a repeating pattern of
cell growth and division
Nuclear division during mitosis apportions chromosomes
equally to two genetically identical daughter cells
What are the three parts of interphase?
gap 1 (G1) phase, synthesis (S) phase, and gap 2 (G2) phase
What is interphase?
a period of cell growth and chromosome duplication between divisions
What is formed during interphase?
microtubules in cytoplasm
Are chromosomes duplicating or dividing in the G1 phase of interphase?
no
What happens during the S phase of interphase?
duplication of chromosome into sister chromatids
- remain joined at centromere
- considered 1 chromosome as long as they remain joined at centromere
What happens during the G2 phase of interphase?
synthesis of proteins required for mitosis
What happens during prophase of mitosis?
- chromosomes (consisting of 2 sister chromatids) condense and become visible
- centrosomes move apart toward opposite poles
- nucleoli begin to dissolve
- nuclear envelope remains intact
What happens during pro metaphase of mitosis?
- nuclear envelope breaks down
- microtubules invade the nucleus and connect to kinetochores in centromere of each chromatid
- sister chromatids attach randomly to microtubules from opposite poles
What are kinetochores?
specialized structure at centromere of each chromatid that function in conveyance of chromatids along microtubules
What occurs during metaphase of mitosis?
- chromosomes align on the metaphase plate with sister chromatids facing opposite poles
- forces pushing and pulling chromosomes to or from each pole are in balanced equilibrium
What occurs during anaphase of mitosis?
- centromeres of all chromosomes divide simultaneously (chromosomes doubled during this stage)
- kinetochore microtubules shorten and pull separated sister chromatids to opposite poles (characteristic V shape) (identical gene info heads to each pole)
What happens during telophase of mitosis?
- nuclear envelope forms around each group of chromatids
- nucleoli re-form
- spindle fibers disperse
- chromosomes decondense
What is the final stage of cell division?
cytokinesis
Cytokinesis begins during __ but is not completed until after __
anaphase; telophase
What happens during cytokinesis?
parent cells split into two daughter cells with identical nuclei
What is fertilization?
the union of haploid gametes to produce diploid zygotes
Fertilized eggs carry matching sets of chromosomes, one set from __ and one set from __
maternal gamete; paternal gamete
Gametes are haploid (n), which means
they carry only a single set of chromosomes
Zygotes are diploid (2n), which means
they carry two matching sets of chromosomes: 1 from each parent
What does mitosis ensure?
that all cells of developing individuals have identical 2n chromosome sets
What does meiosis ensure?
that each zygote only receives one copy of each homologous chromosome from each parent
__ make up vast majority of cells in the organism
somatic cells
__ are precursors to gametes
germ cells
__ are set aside from somatic cells during embryogenesis
germ cells
__ becomes incorporated into reproductive organs
germ cells
In germ cells, only cells that undergo meiosis produce
haploid gametes
How many rounds of meiosis are there?
2
In meiosis, when do chromosomes duplicate?
once at start of meiosis 1
In meiosis, nuclei divide
twice
In meiosis, nuclei divide twice, in both __ and __
meiosis 1 and meiosis 2
Why do gametes contain 1/2 the amount of chromosomes found in somatic cells?
because in meiosis the nuclei divide twice
The end product of meiosis is
4 haploid cells
Give an overview of meiosis 1
- homologs pair, exchange parts, and then segregate
- sister chromatids remain intact at centromere throughout meiosis 1
- recombination occurs between maternal and paternal homologs (non-sister chromatids)
- after recombination, homologous chromosomes (not chromatids) segregate to different daughter cells (chromatids still attached at centromere)
What are the first three substages of prophase 1?
leptotene, zygotene, and pachytene
What occurs during leptotene?
- chromosomes thicken and become visible, but the chromatids remain invisible
- centrosomes begin to move toward opposite poles
What occurs during zygotene?
- homologous chromosomes enter synapsis
2. the synaptonemal complex forms
What occurs during pachytene?
- synapsis is complete
2. crossing-over, genetic exchange between non sister chromatids of a homologous pair, occurs
What are the last two substages of prophase 1?
diplotene and diakinesis
What occurs during diplotene?
- synaptonemal complex dissolves
- a tetrad of four chromatids is visible
- crossover points appear as chiasmata, holding non sister chromatids together
- meiotic arrest occurs at this time in many species
What occurs during diakinesis?
- chromatids thicken and shorten
2. at the end of prophase 1, the nuclear membrane (not shown earlier) breaks down, and the spindle begins to form
In metaphase 1 and anaphase 1 (of meiosis 1), homologs move to
opposite poles
What occurs during metaphase 1 of meiosis 1?
- tetrads line up along the metaphase plate
- each chromosome of a homologous pair attaches to fibers from opposite poles
- sister chromatids attach to fibers from the same pole
What occurs during anaphase 1 (of meiosis 1)?
- the centromere does not divide
- the chiasmata migrate off chromatid ends
- homologous chromosomes move to opposite poles
Meiosis 1 is a
reductional division
What occurs during telophase 1 (of meiosis 1)?
- the nuclear envelope re-forms
2. resultant cells have half the number of chromosomes, each consisting of two sister chromatids
What occurs during interkinesis (of meiosis 1)?
- this is similar to interphase with one important exception: NO CHROMOSOMAL DUPLICATION TAKES PLACE
- in some species, the chromosomes decondense; in others, they do not
- each daughter cell has 1/2 chromosomes of parent; no replication
During meiosis 2, sister chromatids
separate and move to opposite poles
How is metaphase 2 (of meiosis 2) distinct from mitosis metaphase?
- number of chromosomes is 1/2
- chromatids not identical because of recombination
What occurs in anaphase 2 (of meiosis 2)?
the sister chromatids separate
What occurs in prophase 2 (of meiosis 2)?
- chromosomes condense
- centrioles move toward the poles
- the nuclear envelope breaks down at the end of prophase 2
What occurs in metaphase 2 (of meiosis 2)?
- chromosomes align at the metaphase plate
2. sister chromatids attach to spindle fibers from opposite poles
Meiosis 2 is an
equational division
What occurs in telophase 2 (of meiosis 2)?
- chromosomes begin to uncoil
2. nuclear envelopes and nucleoli re-form
What occurs in cytokinesis (of meiosis 2)?
- the cytoplasm divides, forming four new haploid cells
Behavior of chromosomes __ the behavior of genes
parallels
Separation of homologs during meiosis 1 ensures that gametes obtain either __ or __ for each gene on each chromosome in a __ ratio
1 maternal allele, 1 paternal allele; 1:1
How does meiosis contribute to genetic diversity?
- independent assortment of non homologs at metaphase 1 creates different combinations of alleles
- crossing over between homologs creates different combos of alleles within each chromosome and ensures each gamete is unique
Mitosis is a __, while meiosis involves __
conservative mechanism that preserves genetic identity; combinations associated with independent assortment and recombination alter variation
The chromosome theory is confirmed and validated by the fact that:
- inheritance of genes and chromosomes correspond
- transmission of particular chromosome coincides with transmission of traits other than for sex determination
- the inheritance of particular traits linked to inheritance of particular chromosome
T.H. Morgan made major advancements to confirm chromosome theory with his work with
drosiphila
Gene symbol is identifies by
abnormal phenotype
Wild-type allele denoted with
superscript (+)
Recessive mutant allele denoted with __; dominant mutant allele denoted with __
lower case; upper case
Give a summary of chromosome theory
- assigns locations of Mendel’s genes within cells
- meiosis ensures that matching parts of homologous chromosomes segregate to different gametes (accounts for law of segregation)
- each homolog pair aligns independently at metaphase 1 (accounts for law of independent assortment)
- mutations on chromosomes (new alleles) can get transmitted if they occur in germ cells
- through mitotic division, each cell receives the same set of chromosomes
A black mouse is crossed to a brown mouse. All of the F1 progeny (there are many of them) are black. One of
the F1 mice is crossed to a brown mouse. What proportion of the F2 mice will be brown?
A. none of them
B. all
C. 1/4
D. 1/2
E. 3/4
D
In cats, unlinked autosomal genes control the presence of striped/solid coat and hair length. Striped coat is
dominant to solid coat, and short hair is dominant to long hair. A striped, short hair female cat that is
heterozygous for both traits mates with a solid, long hair male. What fraction of the progeny will have striped
coat and short hair?
A. none of them
B. 1/8
C. 1/4
D. 1/2
E. 9/16
C
In tomatoes red fruit (R) is dominant to yellow fruit (r), and cut leaf (C) is dominant to potato leaf (c). The
genes that control these traits are on different chromosomes. The progeny of one mating were:
305 red, cut leaf; 312 red, potato leaf;
101 yellow, cut leaf; 97 yellow, potato leaf.
What were the genotypes of the parents that produced these progeny?
A. Rr Cc x Rr cc
B. RR Cc x rr Cc
C. Rr cc x Rr cc
D. Rr CC x RR cc
E. RR CC x rr Cc
A
In the following cross, what fraction of the progeny will have the same phenotype as the first parent? AA Bb cc x aa Bb cc A. All of them B. 3/4 C. 1/2 D. 3/8 E. 1/4
B
Allele D is completely dominant to d, and allele E is completely dominant to e. In the cross Dd Ee x Dd Ee,
what fraction of the progeny show both dominant traits?
A. none of them
B. 1/8
C. 1/4
D. 1/2
E. 9/16
E
Two genes are responsible for purple flower color in sweet peas; recessive alleles at either or both genes
result in white flowers. A cross between two true-breeding white-flowered plants produces only purple F1s.
These F1s are self-crossed. What fraction of the F2s will have white flowers?
A. 1/4
B. 1/2
C. 7/16
D. 9/16
E. none of them
C
Two genes control comb shape in chickens, producing four different phenotypes. A cross between two
dihybrids (each with a walnut comb) produces the following results: 9/16 walnut, 3/16 pea, 3/16 rose, 1/16
single. In a cross between a true-breeding rose and a true-breeding pea chicken, what will be the phenotypes
of the progeny?
A. 9:3:3:1 walnut:pea:rose:single
B. 1:1:1:1 walnut:pea:rose:single
C. all walnut
D. 1/2 pea, 1/2 rose
C
Feather color in chickens in controlled by a gene C: C- individuals have colored feathers while cc individuals are
white. The dominant allele of a second gene A (unlinked to C) inhibits color production and is epistatic to C (Aindividuals
are always white, but aa individuals have colored or white feathers depending on the C genotype).
A cross between a colored chicken and a white chicken produces 3/4 white and 1/4 colored progeny. What
were the genotypes of the underlined chickens?
A. cc Aa x cc Aa
B. Cc aa x Cc aa
C. Cc aa x cc Aa
D. Cc aa x cc aa
C
Tay-Sachs is a rare autosomal recessive disease that causes deterioration of the central nervous system early
in life. John and Mary visit you, a genetic counselor, and ask you to determine the probability that they will
have a child affected by the disease. John’s brother died of the disease. Mary’s sister has a child with the
disease. The disease-causing allele is rare, so assume individuals with unknown genotypes are homozygous for
the wildtype allele unless there is reason to believe otherwise. The probability that the couple’s first child will
have Tay-Sachs is:
A. 1/36
B. 1/12
C. 1/9
D. 1/8
E. 1/4
B
A phenotypically normal couple has a son who has hemophilia, an X-linked recessive trait. What is the
probability that the couple’s daughter is a carrier of the trait?
A. absolutely certain
B. 2/3
C. 1/2
D. 1/4
E. not possible
C
Rabbit coat color is determined by a gene C with three alleles, C (agouti, the wildtype tan color), cCH (chinchilla, a mottled grey) and cH (Himalayan, mostly white with black paws and ears). These alleles form the following 4 dominance series: C > c^CH > c^H . In the following cross: C c^CH x c^CH c^H what fraction of the offspring will have a chinchilla phenotype? A. all of them B. 3/4 C. 1/2 D. 1/4 E. none of them
C
In snapdragons tall is dominant to short. Flower color shows incomplete dominance: homozygotes are either
red or white, but heterozygotes are pink. A red tall plant from a pure-breeding strain is mated to a pink short
plant. What fraction of the progeny will be pink tall?
A. 1/4
B. 3/8
C. 1/2
D. 3/4
E. 9/16
C
The tortoiseshell / calico coat pattern in cats results from an X-linked gene with orange and black alleles, and
the effect of X-inactivation in female cats. A tortoiseshell female and a black male mate – what fraction of
their progeny will have a tortoiseshell coat?
A. All of them
B. 3/4
C. 1/2
D. 1/4
E. None of them
D
Crimson argoweed plants isolated from the wild have two phenotypes, tall and short. A cross between two
short plants produces only short progeny. A cross between two tall plants produces 2/3 tall and 1/3 short. Not
believing the latter result you carry out the same cross several more times, between two tall plants taken from
the wild whose parentage and genotypes are not known. The same result is obtained every time: 2/3 tall and
1/3 short. Which is the likely explanation?
A. Short plants are homozygous for one allele and tall plants are homozygous for the other allele.
B. Tall plants are heterozygous and short plants are homozygous. One of the homozygous genotypes is
lethal.
C. The gene for plant height resides on a sex chromosome. More careful investigation will likely reveal
that tall and short phenotypes correlate with gender.
D. This result is indicative of three alleles forming a dominance series.
B
Huntington disease is a rare neurodegenerative disease that is inherited as an autosomal dominant trait. Joe
has just learned that his father has HD. A genetic test on Joe’s mother reveals that she is not at risk for HD.
What is the probability that Joe will develop the disease?
A. zero
B. 1/8
C. 1/4
D. 1/2
E. 100% (absolutely certain)
D
Which of the following is always true of a test cross?
A. One of the individuals is homozygous for the recessive allele for the gene(s) of interest.
B. One of the individuals is homozygous for the dominant allele for the genes(s) of interest.
C. Male and female gametes are obtained from the same individual, or from two individuals that are
genotypically identical to each other.
D. All of the above.
A
In a classic series of experiments, geneticists analyzed the ability of several mutants of the fungus Neurospora
to grow on defined media that lacked the amino acid arginine or some of the precursors to arginine. The
conclusion from this series of experiments was that:
A. genes encode enzymes.
B. messenger RNAs are intermediates between gene and protein.
C. DNA is the genetic material.
D. introns must be removed from RNAs before protein synthesis can occur.
E. mutations are changes in DNA sequence
A
Two mutations that do not complement each other:
A. produce F1 hybrid progeny with the mutant phenotype.
B. produce F1 hybrid progeny with the wildtype phenotype.
C. produce F1 hybrid progeny with a novel phenotype not observed in either single mutation alone.
D. are alleles of different genes.
A
A leucine auxotrophic mutant would …
A. grow on both minimal medium and on minimal medium supplemented with leucine.
B. grow on minimal medium, but die on minimal medium in which leucine is the only energy source
C. die on minimal medium, but grow on minimal medium supplemented with leucine
D. die on both minimal medium and minimal medium supplemented with leucine
C
A particular cross produces a 1:2:1 genotypic ratio and a 1:2:1 phenotypic ratio. This indicates:
A. a cross between two heterozygotes for a trait with a normal dominant:recessive relationship
B. a cross involving more than two alleles with a dominance series
C. a cross between two heterozygotes for a trait with incomplete dominance
D. a cross in which one of the genotypes is lethal
C
A cross between two heterozygotes produces progeny genotypes in the ratio of: A. 1:0 B. 1:1 C. 1:2:1 D. 3:1 E. 1:1:1:1
C
The human diploid chromosome number is: A. 12 B. 23 6 C. 34 D. 46 E. 78
D
How many genetically-distinct gametes are produced by an individual of genotype Aa Bb CC DD Ee? A. 2 B. 4 C. 8 D. 16 E. 32
C
How many genetically distinct gametes (sperm) are produced by a male fruit fly that is heterozygous for one autosomal gene? A. 2 B. 3 C. 4 D. 6 E. 8
C
In a plant in which the diploid chromosome number is 18, how many chromatids are present during prophase I of meiosis? A. 18 B. 24 C. 36 D. 54 E. 72
C
Which of the following is true of homologous chromosomes?
A. They carry alleles for the same genes in the same relative positions.
B. They exchange segments at meiosis by crossing over.
C. They physically pair at meiosis.
D. All of the above.
E. None of the above.
D
The phenomenon of crossing over occurs… A. during prophase of mitosis B. during prophase I of meiosis C. during anaphase II of meiosis D. during metaphase I of meiosis E. two or more of the above
B
Drosophila has a diploid chromosome number of 8. At the end of meiosis I, each daughter cell contains \_\_ chromosomes and \_\_ chromatids. A. 8, 16 B. 4, 16 C. 4, 8 D. 8, 8
C
A 2:1 phenotypic ratio is characteristic of
recessive lethality
Which of the following best describes meiosis?
cell divisions where the chromosomes replicate once and the nucleus divides twice
T or F? An individual that is pure breeding for two traits must either be homozygous for the dominant allele at both traits or homozygous for the recessive allele at both traits
F
If a plant of genotype Aa Bb CC is test crossed, what proportion of the progeny would be aa Bb Cc?
1/4
In a trihybrid cross AA BB CC x aa bb cc parents, what proportion of homozygotes across all genes is expected among the F2 offspring?
1/8
How many different progeny genotypes can result from a cross of Aa Bb Cc dd Ee with Aa Bb cc DD Ee?
54
Assuming complete dominance and no gene interactions, in the cross Aa Bb Cc dd Ee x Aa Bb cc DD Ee, how many distinct phenotypes are possible for the offspring?
16
During which of the stages of meiosis would homologous chromosomes be paired?
both prophase of meiosis 1 and metaphase of meiosis 1
A diploid organism with 10 chromosomes in each somatic cell undergoes mitosis. How many cells will result from this meiotic event, and how many chromosomes will be present in each?
4 cells with 5 chromosomes each
In labs, the E gene is __ to the B gene
recessively epistatic
A pure breeding brown Lab and a pure-breeding yellow Lab were crossed and produced both black and brown puppies. What is the genotype of the yellow parent?
Bbee
In the question above involving the brown and yellow dogs, what proportion of the puppies are expected to be black?
1/2
A couple is concerned that their child will have a very rare dominant autosomal disease that has a penetrance of 25%. The woman and her father were both affected by the disease, but there is no history of the disease allele on her mother’s side of the family. The husband has no history of the disease allele in his family. What is the probability that the child will be affected by the disease?
1/8
Several genes code for different types of antigens on the surface of red blood cells. These include the ABO that gives rise to the A, B, AB, and O blood types, as well as MN and Rh. The Rh locus can contain either a positive or negative allele, with positive being dominant to negative. M and N are codominant alleles of the MN gene. Which individual could not father a child with the blood type A M Rh(neg) if the mother has the O M Rh(pos) phenotype?
O M Rh(pos)
Coat color in a certain species of rabbit is governed by multiple alleles. The dominance series for these alleles is as follows: colored (c+), himalayan (ch), and albino (c). Give the phenotypes and ratios of the cross c + c x ch c
2 colored: 1 himalayan: 1 albino
Which stage of cell division best explains Mendel’s law of segregation?
movement of homologous chromosomes to opposite poles at anaphase of meiosis 1
Chromosomes in the same cell that carry the same sets of genes are known as
homologous
A female fruit fly with deformed bristles was mated with a male from a true-breeding wild-type stock with long bristles. All of the F1 females had wild-type bristles and all of the F1 males had deformed bristles. If the F1 flies are intercrossed, the expected ratio of long to deformed bristles in the F2 flies is
1:1 in both sexes
Pea plants possess a number of characteristics that aided Mendel in the discovery of the laws of segregation and independent assortment. Which is not correct?
a. peas possess numerous traits with discrete antagonistic forms that could be easily studied in Mendel’s crosses
b. pure breeding lines could be easily generated
c. pea plants contain a large number of continuous forms at the traits Mendel selected, which provided the needed variation for experiments
d. peas produce large numbers of offspring
e. peas are amiable to carefully controlled experimental crosses
C
A and B are dominant alleles of two independently assorting genes. Each gene produces an enzyme that catalyzes the conversion of one pigment to another, and a and b are recessive alleles, both are nonfunctional. A fully homozygous yellow eyed frog of genotype AA bb is crossed with a white eyed frog of genotype aa BB. The F1 progeny are allowed to mate. What proportion would you expect in the F2 progeny?
9 red: 4 white: 3 yellow
