ls7b review
Imagine an instance where there are two parents, and both have polydactyly (i.e., six fingers on each hand), a trait which is determined in this example by a single gene. They have four children, none of whom have polydactyly. What is the probability their next child will have polydactyly?
0.75
Why can't we measure genetic variation in a population using observable traits (phenotypes)?
1) many traits are encoded by multiple genes 2) the environment can also affect phenotype
Consider a gene with four alleles: A1, A2, A3, and A4. If the cross A1A2 × A3A3 yields two offspring, what is the probability that both of them have the same genotype?
1/2
For most genes on the human X chromosome, what percent of XY males with a mutant allele on the X chromosome will express the mutant phenotype?
100%
A true‑breeding black rabbit is crossed with a true‑breeding white rabbit to produce an F1 generation of 16 individuals. If the black color trait is dominant, which of the outcomes represents the expected phenotype of an F1 generation cross?
16 black rabbits, 0 white rabbits, 0 gray rabbits
If a gene has two alleles, and allele A has a frequency of 83 percent, then allele a has a frequency of:
17%
If nondisjunction occurs in the first meiotic division, how many of the four possible gametes produced from meiosis will have the wrong number of chromosomes?
4
The maximum frequency of recombination between two genes is:
50% explain why
For a single-nucleotide polymorphism (SNP) with three alleles, how many different diploid genotypes are possible?
6 explain why
All of the following are similarities between the behavior of genes and the behavior of chromosomes EXCEPT: A. Alleles segregate in gamete formation, and homologous chromosomes separate in meiosis I B. Dominant alleles determine the individual's phenotype, and sister chromatids determine the individual's karyotype. C. An individual has two alleles of each gene and two chromosomes in each homologous pair D. Alleles of different genes segregate independently, and different homologous pairs separate independently in meiosis. E. Offspring receive one allele of each gene from each parent, and offspring receive one chromosome from each homologous pair in the sperm and egg.
B explain why each of the options is either true or false
True or False: A phenotype always refers to something that you can see with your eyes, like hair color or eye color.
False
True or False: Harmful mutations are always quickly weeded out of a population.
False
True or false: All organisms have either an X or Y chromosome, as these chromosomes are solely responsible for determining the sex of an individual.
False
True or false: During meiosis in female mammals, sex chromosomes segregate to produce two types of eggs: X‑bearing eggs and Y‑bearing eggs.
False
True or False: First‐division nondisjunction will only yield gametes with an extra chromosome, whereas second‐division nondisjunction will only yield gametes missing a chromosome.
False explain why
True or False: True‑breeding plants are typically heterozygous for most genes.
False; true breeding plants are typically homozygous for most genes
When the F1 plants are allowed to self fertilize, they produced both yellow and green peas in the next generation. How is this explained?
In the F1 heterozygotes, the alleles segregate from each other when gametes form and then combine to make homozygotes and heterozygotes offspring.
When Mendel crossed yellow peas with green peas, the next generation was all yellow. How is this explained?
The parental plants pass one of their two alleles on to the offspring which is heterozygous, and the A allele is dominant to the a allele.
When a 9:3:3:1 ratio of phenotypes is produced by a cross between two individuals, which phenotypes are present in the rarest class that is represented by only 1 of the 16 possible genotypes of offspring?
These offspring have the recessive phenotype of both traits.
True or False: Two genes, A and B, are found on the same chromosome. One chromosome has alleles A and B, while its homolog has alleles a and b. If genes A and B are so closely linked that the recombination frequency is 0 percent, only AB and ab gametes will be produced during meiosis.
True
True or false: For genes with incomplete penetrance some individuals can show the trait while others with the same genotype may not.
True
True or false: In humans, fruit flies, and many other organisms, most of the genes on the X chromosome are not found on the Y chromosome.
True
True or false: Most of the genetic variation seen in the human population is neutral.
True
True or false: The tips of the arms of the X and Y chromosomes share small regions of homology. Genes located in these regions are inherited in the same manner as the ones found in autosomes.
True
True or false: Without the SRY gene, humans and other mammals would develop and retain the female sex organs and phenotype.
True
True or false: homologous chromosomes usually have the same arrangement of genes along their length.
True
True or false:The genotype of a fetus can be screened for SNPs associated with some diseases.
True
True or False: A Punnett square can be used to interpret the results of a testcross.
True elaborate
The addition rule requires which option?
Two outcomes (such as having the genotype BB or Bb) are mutually exclusive in an organism
How do mutations arise? a. Mutations arise randomly and independent of other mutations in the cell. b. Mutations arise simultaneously, where whole sets of mutations occur in a single event. c. Mutations arise in a specific sequence where a mutation in one gene directly leads to a mutation in a specific second gene. d. Mutations in cancer cells arise because they need to divide faster.
a
Consider an A - T versus G - C single-nucleotide polymorphism (SNP) in the human genome. This means that the DNA molecules in the population at this site have which combinations of base pairs? a. A-T or G-C b. A-C or G-T c. A - T or G - T or G - C d. A - T or A - G or G - C e. A - T or A - C or G - T or G - C
a explain why
If all variation in height among humans was due to environmental influences alone, the mean height of offspring when graphed against the mean height of parents should be closest to which line in the graph? a. the population mean line b. the parental mean line
a explain why
The Y‑linked trait of hairy ears has been passed down for many generations in a certain family. A hairy‑eared male in this family would be expected to have: a. a paternal grandfather with hairy ears b. male and female grandchildren with hairy ears c. nephews with hairy ears d. uncles with hairy ears e. a maternal grandfather with hairy ears
a explain why
which is a characteristic of meiotic cell division? a. cell division results in the production of gametes b. the cells produced by meiosis are genetically identical c. results in the formation of two cells d. requires two rounds of dna replication
a explain why each other option is wrong
The principle of independent assortment states that: a. alleles of a gene pair assort independently of other gene pairs b. when gametes are formed, the two members of a gene pair will separate equally into gametes c. one set of alleles of a gene pair always assorts with the alleles of another gene pair d. when gametes are formed, the two members of a gene pair assort together in gametes
a explain why the other options are wrong
Which of the events is least likely to produce recombinant chromosomes? a. crossovers between sister chromatids b. crossovers between non-sister chromatids c. crossovers between homologous chromosomes
a explain why the other options are wrong
Which of the statements best reflects the extent to which we can distinguish the effects of genes and the environment on the expression of a complex trait? a. In a group of individuals of the same sex, about 80% of the variation in height among individuals is due to genetic differences and 20% is due to environmental differences. b. For identical twins raised in the same environment, height should not differ by more than 20%. c. About 80% of an individual's height is determined by genes and 20% by environment. d. If one individual is 60 inches tall and another is 70 inches tall, they differ in about 80% of their genes.
a explain why the other options are wrong
Which of the statements are true of both first- and second-division nondisjunction? Select all that apply. a. gametes are produced with missing chromosomes b. half of gametes produced are wild-type, whereas half are mutated c. sister chromatids fail to separate d. gametes are produced with extra chromosomes e. homologous chromosomes fail to separate
a and d explain why the other options are wrong
The actual offspring mean height in the graph lies between the parental mean line and the population mean because: Select all that apply. a. the phenotypes of the parents result from both their genes and their environment. b. during meiotic cell division segregation and recombination break up combinations of genes leading to extreme phenotypes (e.g., very tall or very short). c. the phenotypes of the offspring result from both their genes and their environment.
a, b, c explain why
Why might a phylogeny based only on molecular data show a different pattern of relationships than a phylogeny of the same taxa based only on morphological traits? Select all that apply. a) Gene sequence changes may not result in morphological changes. b) The molecular data may be based on the analysis of introns, which aren't expressed and don't contribute to the evolutionary history of a group of taxa. c) Some highly conserved genetic sequences can result in unrelated species appearing closely related in a molecular phylogeny, and do not reflect the same pattern as the morphologic phylogeny. d) Gene sequences always provide more data than morphological traits. e) Morphological analyses always provide more data, because each morphological trait is the result of the expression of many genes.
a, c
The gene for nose shape is found on the X chromosome. Round nose is dominant to pointed nose. Human individuals with XXY (an additional X chromosome) are designated male. Individuals with XO (only one X chromosome) are designated female. Identify the possible nondisjunction events (rare mistakes during meiosis) that could explain the phenotype of the offspring produced by an XY parent with a pointed nose and a XX parent with a round nose have an offspring with Klinefelter Syndrome (genotype XXY) with a pointed nose. Select all that apply. Nondisjunction could have occurred in meiosis 1 of the XX parent. Nondisjunction could have occurred in meiosis 2 of the XY parent. Nondisjunction could have occurred in meiosis 2 of the XX parent. Nondisjunction could have occurred in meiosis 1 of the XY parent.
all except meiosis 2 of the XY parent draw this out and explain
If an XY male carries a mutation on his X chromosome, ______ will receive the mutant X.
all of his daughters
Genes in different chromosomes ______ during meiosis. Genes that are very close together in the same chromosome are ______.
assort independently; linked
when do sister chromatids separate in meiosis? a. telophase i b. anaphase ii c. anaphase i d. metaphase ii
b
Which of the answer choices is a possible human genotype that could result from nondisjunction of the sex chromosomes in one of the parental gametes? a. XO b. all these choices are correct c. XXX d. XYY e. XXY
b explain
For an individual who is heterozygous for two genes, Aa and Bb, what does independent assortment predict? a. offspring inheriting the dominant allele (A) of the first gene will also inherit the dominant (B) allele of the second gene. b. offspring inheriting the dominant (A) allele of the first gene are equally likely to inherit either the dominant (B) or the recessive (b) allele of the second gene. c. offspring inheriting the recessive allele (a) of the first gene will inherit the dominant allele (B) of the second gene.
b explain why the other options are wrong
In Mendel's crosses: a. the F1 plants had a 3:1 ratio of yellow to green b. the plants he started with had two alleles of each gene c. the plants he started with were heterozygous
b explain why the other options are wrong
The principle of independent assortment holds that: a. in heterozygotes, the phenotype will be determined by the dominant allele. b. the pattern of inheritance of one trait does not influence the pattern of inheritance of another trait. c. during fertilization, haploid gametes join to create a diploid zygote d. in heterozygotes, half the gametes will get one allele, and the other half will get the second allele.
b explain why the other options are wrong
While doing a pedigree analysis of a European royal family, you notice a disease in a female child of two healthy parents. There are also some cousins with the same genetic disease. If this disease is controlled by a single gene, then the most likely explanation for these observations is the disease is: a. only seen in heterozygous individuals like the daughter b. recessive and only seen in homozygous recessive individuals like the daughter c. dominant and only seen in homozygous dominant individuals like the daughter d. a spontaneous mutation e. dominant and is seen in homozygous dominant or heterozygous individuals
b explain why the other options are wrong
why are women with the genotype XXX not phenotypically different from an XX female?
because of X-inactivation. only one X chromosome is active in each cell, regardless of how many X chromosomes there are in a cell
Single-nucleotide polymorphisms (SNPs) can be detected by microarrays, which are wafer-like substrates to which millions of short stretches of DNA are attached. A microarray consists of many different squares, each one containing a different sequence of single-stranded DNA to which fluorescently labeled strands of DNAs from patients with different SNPs can hybridize. If one square will hybridize with an SNP having a C-G base pair at a particular site, and an adjacent square will hybridize with an SNP having a T-A base pair at the same site, which of the genotypes will hybridize with both squares and make them fluoresce? a. All of the genotypes hybridize with both squares. b. the homozygous C-G/C-G genotype c. the heterozygous C-G/T-A genotype d. the homozygous T-A/T-A genotype
c
If all variation among individuals in a population is due to differing environments, heritability is _____, and the slope of the line used to measure it is _____. a. 100%; 1 b. 100%; 0.5 c. 0%; 0 d. 50%; 0.5 e. 50%; 1
c explain why
Diploid somatic cells of elephants have 56 chromosomes. If nondisjunction of one of an elephant's chromosomes occurs in meiosis I, the resulting sperm are expected to have the chromosome complement: a. 28, 28, 29, 27 b. 56, 56, 57, 55 c. 29, 29, 27, 27 d. 28, 28, 28, 28 e. 29, 29, 28, 28
c explain why the other options are wrong
Genes located along the X chromosome: a. are always recessive to genes located on the Y chromosome b. are contributed solely by the female parent c. are called X-linked genes d. have a full set of complementary alleles on the Y chromosome
c explain why the other options are wrong
In his cross, what did Mendel do? a. he used plants that were heterozygous in his initial crosses b. he did not use pure-breeding plants in his crosses c. he studied traits controlled by a single gene
c explain why the other options are wrong
Most complex traits are: Select all that apply. a. homozygous for all alleles affecting the trait. b. inherited in pedigrees showing simple Mendelian patterns. c. affected by interactions between genes and environmental factors. d. heterozygous for all alleles affecting the trait. e. affected by environmental factors. f. affected by multiple genes.
c, e, f
what do the nodes on a phylogenetic tree represent?
common ancestors
Which of the statements is true regarding a phylogenetic tree? a) Phylogenetic trees depict only the evolutionary relationships between different classes; relationships among different species within the same genus are not illustrated in such trees. b) Given the sheer number of prokaryotic and eukaryotic species on Earth, it is impossible to create a phylogenetic tree encompassing all of these organisms. c) Within a phylogenetic tree, the order of groups located at the tree tips—not the nodes within a tree—determines sister-group relationships. d) Phylogenetic trees could be considered physical representations of hypotheses that seek to establish the evolutionary relationships between different organisms. e) Phylogenetic trees are constructed based solely on the morphological characteristics of species; sequence similarities among different organisms are evaluated only by taxonomists.
d
How do most cancers arise? a. from multiple mutations arising simultaneously in a single cell b. from a single mutations arising simultaneously in a cluster of cells c. from mutations arising in a single cell that are then transmitted to other cells in the body d. from a series of mutations that arise in the descendants of a single somatic cell
d explain why
which statement is true about gametes? a. they have the same number of chromosomes as a somatic cell of the same individual b. they are genetically identical to other gametes formed during meiosis c. they are formed by mitotic cell division d. they fuse to form a new organism during fertilization e. they are found in animals but not plants
d explain why each other option is wrong
A researcher is creating pedigrees for a trait he suspects to be dominant in humans. What are some of the likely features of his pedigrees for families with this trait? a. only females will have this dominant trait b. all the offspring of a mating where one parent has the trait will be affected c. the occurrence of mating between individuals with this trait will be high, as all dominant traits are common within any given population d. none of the other answer options is correct
d explain why the other options are wrong
Imagine that a doctor sees a patient that is genotypically male, but is phenotypically female. How could this occur? a. This patient likely carries a mutation in the X chromosome that increases X chromosome‑associated protein levels. b. This patient likely carries a mutation in SRY that increases SRY protein levels. c. This patient likely carries a mutation in SRY that increases SRY protein levels, and a mutation in the X chromosome that decreases X chromosome‑associated protein levels. d. This patient likely carries a mutation in SRY that decreases SRY protein levels. e. This patient likely carries a mutation in the X chromosome that decreases X chromosome‑associated protein levels.
d explain why the other options are wrong
During meiosis crossing over takes place between: a. sister chromatids b. any two chromatids c. nonhomologous chromosomes d. non-sister chromatids e. nonhomologous chromatids
d. explain why the other options are wrong
Mammals are ______ and produce ______ gametes.
diploid; haploid explain what this means
You are examining a human pedigree for a trait. You notice that the trait appears in every generation, is equally likely to occur in males and females, and about half of the offspring are affected when one parent is affected. The trait is most likely: (recessive, dominant)
dominant explain
Sunlight exposure has stronger effect on skin cancer risk in fair‑skinned humans than in individuals with darker skin. This is an example of: a. differences in the norm of reaction. b. epistasis. c. pleiotropy. d. genotype‑by‑environment interaction. e. All of these choices are correct.
e explain why
Diploid somatic cells of elephants have 56 chromosomes. If nondisjunction of one of an elephant's chromosomes occurs in meiosis II, the resulting sperm are expected to have the chromosome complement: a. 28, 28, 28, 28 b. 29, 29, 28, 28 c. 56, 56, 57, 55 d. 29, 29, 27, 27 e. 28, 28, 29, 27
e explain why the other options are wrong
Which of the answer choices is true of a cross involving a sex-linked gene but not of a cross involving an autosomal gene? a. both parents have two copies of a sex-linked gene b. recombination/crossing over cannot take place between sex chromosomes c. only autosomal genes observe the law of segregation d. a punnett square cannot be used for illustrating the possible outcomes of a cross involving a sex-linked gene e. the phenotypic outcomes of females and males can be different
e explain why the other options are wrong
When one gene is able to modify the effect of a second gene, the phenomenon is known as:
epistasis
true or false: consider a population of killer whales. the gene pool of this population only contains alleles harboring beneficial or neutral mutations, as deleterious mutations are efficiently eliminated from the gene pool of a species.
false
True or false: An example of regression toward the mean occurs if the offspring of two short parents had an average height equal to the average height of the parents, not of the population as a whole.
false explain why
True or false: Similar to single gene traits, traits determined by multiple genes also show the expected 3:1 ratio of phenotypes in the progeny between two heterozygotes.
false explain why not
The ______ two loci are on a chromosome, the more likely they will be separated by crossover events during gamete formation, and thus the frequency of recombination between loci on a chromosome can be used to measure the ______ between those loci.
farther apart; genetic distance
all the alleles present in ALL individuals in a species are referred to as the ____ of that species.
gene pool
A normal female who carries a recessive X-linked allele for hemophilia will pass it on to:
half of her sons and half of her daughters
Prophase of meiosis I has some important differences from prophase of mitosis. These differences include: ______ pair, and ______ occurs.
homologous chromosomes; crossing over
A testcross involves crossing with a(n) ______ individual and is used to determine the ______ of the tested parent.
homozygous recessive; genotype
what does the ratio 9:3:3:1 represent?
in a cross between two individuals who are heterozygous for two traits determined by dominant and recessive alleles (Aa Bb), 9:3:3:1 is the ratio of phenotypes for the traits determined by both genes
what is the difference between a single nucleotide polymorphism (SNP) and a point mutation?
in a point mutation, one base is replaced with another one, but in a SNP, the base pair differs between individuals
what does it mean for an organism to have a heterozygous genotype for a given gene?
it has two different allelic variants of that particular gene
homologous chromosomes separate from each other in: a. mitosis b. meiosis ii c. they never separate d. meiosis i
meiosis i explain why each other option is wrong
A taxon that includes a single common ancestor and all its descendants is a _____ group.
monophyletic
what are the two sources of genetic variation?
mutation and recombination
In which type of nondisjunction could the two copies of a chromosome in a gamete be heterozygous? (which meiotic division)
nondisjunction in the first meiotic division. draw it out
Mutations that destroy or create a cleavage site for a restriction enzyme are the source of:
restriction fragment length polymorphisms
what does it mean if a female is a carrier for hemophilia?
she is heterozygous, with one mutant allele for that trait
Traits that are shared by more than one member of a group because of common ancestry are known as:
synapomorphies
what's the result of a mutation that occurs in somatic cells?
the mutation may be expressed in the individual, but will not be passed along to its offspring
Nondisjunction results in gametes that violate which principle?
the principle of segregation explain why
When heritability is 0%, genes play no role in ____
the variation of a trait between individuals
as a population geneticist, you find a species of snails with more genetic diversity than humans. what does this mean?
there is more variation in the gene pool of snails than humans
After doing PCR on the same region between two individuals, you notice that each person's DNA yielded pieces of different sizes. Which of the following is the MOST likely explanation?
this is an example of VNTRs
A chromosomal segment that breaks off and attaches to another chromosome is what type of mutation?
translocation
Imagine that a scientist discovers a new flying species of mammal that resembles a winged rabbit. true or false: If molecular sequence data show that bats and this new species share a common ancestor not shared by other mammals, the wings of these two species would be considered homologous.
true
True or false: A point mutation occurs when a single nucleotide gets replaced by a different one
true
True or false: Genetic variations in DNA sequences in human populations, such as single nucleotide polymorphisms (SNPs), have been used to map "disease genes" by determining whether the SNP is linked to the mutant gene.
true
True or false: The graph indicates that on average the offspring of short parents will be taller than their parents, and the offspring of tall parents will be shorter than their parents.
true
true or false: In a given population, all humans have the same blood type O. If no other alleles for blood type exist in this population, this population is "fixed" for the O allele.
true
true or false: Traditional levels of taxonomy are nested in categories from least to most inclusive. This same relationship is also represented on a phylogenetic tree by moving from the terminal (most recent) nodes to the earliest nodes.
true
true or false: class> order level > family in terms of inclusivity
true
True or false: A trait with high heritability responds strongly to selection, whereas a trait with low heritability responds slowly or not at all.
true explain why