Exam 1
Assume that long earlobes in humans are an autosomal dominant trait that exhibits 30% penetrance. A person who is heterozygous for long earlobes mates with a person who is homozygous for normal earlobes. What is the probability that their first child will have long earlobes?
.15
In a hypothetical mouse species, brown fur (B) is completely dominant to white fur (b), and long fur (L) is completely dominant to short fur (l). If two mice heterozygous for both traits mate and produce a litter of pups, what is the probability that an individual pup will have white, short fur?
1/16
A fruit fly has 4 pairs of chromosomes, whereas the house fly has 6 pairs of chromosomes. How many different combinations are possible in the gametes of fruit flies?
16
In pea plants, plant height is controlled by a single autosomal dominant gene. Tall plants (H) are dominant to short plants (h). In a cross of two heterozygous tall plants, which phenotypic ratio is expected in the resulting offspring?
3:1
What is the end result of meiosis?
4 gametes
Suppose Jonathan breeds flowers and wants to optimize the production of offspring with both short stems and white flowers, which are coded for by two genes with the recessive alleles t and p, respectively. In flowers T codes for tall stems and P codes for purple flowers. Jonathan crosses two heterozygotes that produce 656 offspring. How many of these 656 offspring are expected to have both short stems and white flowers?
41
A fruit fly has 4 pairs of chromosomes, whereas the house fly has 6 pairs of chromosomes. How many different combinations are possible in the gametes of house flies?
64
What is a gene?
A small section of functional DNA
locus
A specific place along the length of a chromosome where a given gene is located.
Cell theory began to develop in 1839, following the research of Matthias Schleiden and Theodor Schwann into plant and animal tissues. Both the botanist Schleiden and the physiologist Schwann noticed that every organism they viewed under a microscope, whether plant or animal, was composed of cells. Their observations that all living species are made up of one or more cells led to the early formation of cell theory. Which tenet of cell theory is described by the paragraph about the historical observations of cells?
All organisms are composed of one or more cells
A cell has a circular chromosome and histone proteins associated with its DNA, but lacks a nuclear membrane. What domain does this cell belong to?
Archaea
What do prokaryotes and eukaryotes have in common?
Both contain DNA and use ribosomes to synthesize proteins.
quantitative characteristics
Characteristics that vary along a continuum, usually due to influence of two or more genes.
dihybrid crosses
Cross or mating between organisms involving two pairs of contrasting traits
Color blindness is a sex linked recessive trait. A female is colorblind in one eye, and not both. Explain why this can happen.
Different X chromosomes are being silenced
what types of cell is categorized by it's nuclear membrane surrounding the DNA of the cell?
Eukaryotes
Which idea of Mendel requires at least 2 genes to be demonstrated?
Genes assort independently in diploids
A fruit fly has 4 pairs of chromosomes, whereas the house fly has 6 pairs of chromosomes. Based on chromosome number, in which species would you expect to more genetic variation among the progeny?
House fly
secondary oocytes
One of the products of meiosis I in female animals; receives most of the cytoplasm.
first polar body
One of the products of meiosis I in oogenesis; contains half the chromosomes but little of the cytoplasm.
Model Genetic Organisms
Organisms with characteristics that make them useful for genetic analysis
What happens during anaphase 2 of meiosis?
Sister chromatids separate from each other and migrate to opposite ends of the cell.
spermatogonia
The diploid cells in a testis that can give rise to primary spermatocytes.
How is a true breeding yellow-seeded pea plant different from a hybrid yellow-seeded pea plant?
They have the same phenotypes but different genotypes
XX-XO sex determination
This is seen in some insects. In this system females are XX and males are XO; there is no O chromosome the O just mean there is no additional chromosome.
what pattern of inheritance does color blindness follow?
X-linked recessive
Is it possible for a man to have different color-blindness phenotypes in each eye?
Yes, in an XXY male with a different active X in each eye.
The Talmud, an ancient book of Jewish civil and religious laws, states that if a woman bears two sons who die of bleeding after circumcision (removal of the foreskin from the penis), any additional sons that she has should not be circumcised. The bleeding is most likely due to the X‑linked disorder hemophilia. Furthermore, the Talmud states that the sons of her sisters must not be circumcised, whereas the sons of her brothers should be. Is this religious law consistent with sound genetic principles?
Yes, the woman is a carrier and half of her sons will be affected. Her sisters may also be carriers, but her brothers sons will get their X chromosomes from their mothers, who are unlikely to be carriers of the allele.
Autosome
a chromosome that does not determine sex
genomic imprinting
a phenomenon in which expression of an allele in offspring depends on whether the allele is inherited from the male or female parent
Crossing over
a process in which homologous chromosomes exchange genetic information. generates genetic variety
Suppose there is a vial containing a single generation of flies from a cross. There is an interesting phenotype where many individuals have abnormally long hairlike bristles, sensory organs extending from the dorsal thorax, as opposed to the short wirelike wild‑type bristles among the other siblings. References state that this mutant has a dominant mutation called Suave (Su) and that the phenotype of flies that are heterozygous or homozygous for Su appear phenotypically identical. Which fly should be crossed to a Suave male from this vial in order to generate progeny that help determine the male's genotype?
a wild type female sibling
Phenylketonuria (PKU) is a disease that results from a recessive gene. Two normal parents produce a child with PKU. a. What is the probability that a sperm from the father will contain the PKU allele? b. What is the probability that an egg from the mother will contain the PKU allele? c. What is the probability that their next child will have PKU? d. What is the probability that their next child will be heterozygous for the PKU allele?
a. 1/2 b. 1/2 c. 1/4 d. 1/2
In watermelons, bitter fruit (B) is dominant over sweet fruit (b), and yellow spots (S) are dominant over no spots (s). The genes for these two characteristics assort independently. A homozygous plant that has bitter fruit and yellow spots is crossed with a homozygous plant that has sweet fruit and no spots. The F1 are intercrossed to produce the F2. a. What are the phenotypic ratios in the F2? b. If an F1 plant is backcrossed with the bitter, yellow-spotted parent, what phenotypes and proportions are expected in the offspring? c. If an F1 plant is backcrossed with the sweet, nonspotted parent, what phenotypes and proportions are expected in the offspring?
a. 9/16 bitter fruits, yellow spots; 3/16 bitter fruit, no spots; 3/16 sweet fruit, yellow spots; 1/16 sweet fruit, no spots b. All bitter fruit with yellow spots c.1/4 bitter fruits, yellow spots; 1/4 bitter fruit, no spots; 1/4 sweet fruit, yellow spots; and 1/4 sweet fruit, no spots
In cats, curled ears result from an allele, Cu, that is dominant over an allele, cu, for normal ears. Black color results from an independently assorting allele, G, that is dominant over an allele for gray, g. A gray cat homozygous for curled ears is mated with a homozygous black cat with normal ears. All the F1 cats are black and have curled ears. What phenotypes and proportions are expected from the two crosses? a. Two of the F1 cats mate b. An F1 cat mates with a stray cat that is gray and possesses normal ears
a. 9/16 black cats, curled ears; 3/16 black cats, normal ears; 3/16 gray cats, curled ears, 1/16 gray cats normal ears b. 1/4 black cats, curled ears; 1/4 black cats, normal ears; 1/4 gray cats, curled ears; 1/4 gray cats, normal ears
In humans, oculocutaneous (OCA) albinism is a collection of autosomal recessive disorders characterized by an absence of the pigment melanin in skin, hair, and eyes. That is, normal pigmentation (A) is dominant over albinism (a). For this question, assume it is a single gene with two alleles. If both parents display the albino phenotype, what possible phenotypes may be observed in their offspring?
albinism only
homologous pair
alike in structure and size and each carries genetic information for the same set of hereditary characteristics
cell theory
all life is composed of cells, cells only arise from preexisting cells, and the fundamental unit of structure and function in living organisms is the cell.
checkpoints
allow or prohibit a cell's progression to the next stage of mitosis
Allele
alternate forms of the same gene
Define Barr body
an inactive x chromosome
lethal allele
causes death at an early stage of development, causes some genotypes to not appear among progeny. can alter genotypic ratio of progeny. 2:1 is almost always produced by recessive lethal allele
What are the functions of mitotic cell division?
cell regeneration, asexual reproduction, and growth of multicellular organisms
haploid
cells containing a single set of chromosomes
germ-plasm theory
cells in the reproductive organs carry a complete set of genetic information that is passed to the egg and sperm
telophase
cells start pulling apart
diploid
cells that carry two sets of genetic info
polyploid
cells that contain more than two sets of genetic information
oogonia
cells that produce primary oocytes by mitotic division
cytoplasmic inheritance
characteristics are encoded by genes located in cytoplasm, always maternally passed down, never inherited from father.
polygenic characteristics
characteristics encoded by genes at many loci
continuous characteristics
characteristics that exhibit a continuous distribution of phenotypes: many possible phenotypes
discontinuous characteristics
characteristics that have a few easily distinguished phenotypes
Suppose a man is heterozygous for heterochromia, an autosomal dominant disorder which causes two different colored eyes in an individual, produced 25 offspring with his normal-eyed wife. Of their children 16 were heterochromatic and 9 were normal. Calculate the chi square value for this observation.
chi square= 1.96
What are the sturctures in a cell that group genes together, are composed of chromatin (DNA and protein) and become visible under the light of a microscope during mitosis?
chromosomes
telophase 1
chromosomes arrive at the spindle poles and the cytoplasm divides
telophase 2
chromosomes arrive at the spindle poles and the cytoplasm divides
prophase
chromosomes become visible under a light microscope, spindles move to chromosomes
Prophase 1 of meiosis
chromosomes form homologous pairs and crossing over takes place
prophase 2
chromosomes recondense
Molecular genetics
concerns the chemical nature of the gene itself: how genetic information is encoded, replicated, and expressed
anaphase
connection between sister chromatids breaks down and they separate. Chromosomes move towards opposite ends of the cell
multifactorial characteristics
continuous characteristics that are both polygenic and influenced by environmental factors
backcross
cross between an f1 and a p
monohybrid cross
crosses between parents that differed in a single characteristic
cytokinesis
cytoplasmic division
expressivity
degree to which a trait is expressed
G2/M checkpoint
detection of DNA damage after replication
sex-influenced characteristics
determined by autosomal genes and inherited according to Mendel's principles, but are expressed differently in males and females.
primary spermatocyte
diploid cell that has gone through meiosis 1 and entered prophase 1
primary oocyte
diploid cells that complete meiosis 1 and divide to produce secondary oocytes
microsporocytes
diploid reproductive cells ( male, plants)
megasporocytes
diploid sex cells (female, plants)
prometaphase
disintegration of the nuclear membrane begins thisphase. Spindle microtubules enter nuclear region, each chromosome becomes attached to microtubules from opposite poles of the spindle
In Drosophila melanogaster, the level of expression of genes on the X chromosome in males is doubled. What phenomenon is this an example of?
dosage compensation
The principle of segregation
each individual diploid organism possesses two alleles for any particular characteristic, one from the maternal parent and one from the paternal parent. these alleles segregate when gametes are formed, one allele going into each gamete
epistasis
effect of a gene interaction in which one gene masks the effect of another gene at a different locus
sex-limited characteristics
encoded by autosomal genes that are expressed in only one sex
Transmission genetics
encompasses the basic principles of heredity and how traits are passed on from one generation to the next.
Spindle assembly checkpoint
ensures that each chromosome is attached to spindle fibers from opposite poles
phenocopy
environmental factors produce a phenotype that is the same as the phenotype produced by a genotype
Population genetics
explores the genetic composition of groups of individuals of the same species and how that composition changes over time and space.
XX-XY sex determination system
females are xx, males are xy
turner syndrome
females who have underdeveloped secondary sex characteristics. XO chromosomes
interphase
first stage of the cell cycle, in which the cell grows, develops and functions
microspores
four haploid cells produced by microsporocytes undergoing meiosis
spermatids
four haploid cells that are formed when a diploid reproductive cell divides meiotically
megaspores
four haploid cells, produced by megasporocytes undergoing meiosis
incomplete penetrance
genotype does not always produce expected phenotype
genic sex determination
genotypes at one or more loci determine the sex of an individual
Cohesin
holds sister chromatids together
anaphase 1
homologous chromosomes separate and are pulled to opposite poles
metaphase 1
homologous pairs of chromosomes line up in the middle
metaphase 2
individual chromosomes line up in the middle
preformationism
inside the egg or sperm there exists a fully formed miniature adult, a homunculus, which simply enlarges in the course of development
anaphase 2
kinetochores of sister chromatids separate and chromatids are pulled to opposite sides
Chromosome
long dna molecules visible during mitosis; large genetic element that carries genes essential to cellular function
G1/S checkpoint
maintains cell until necessary enzymes for replication are synthesized
zz-zw sex determination
males are zz, females are zw (sneks, butterflies, some amphibians)
dosage compensation
mechanisms that equalize the amount of protein produced by single X and two autosomes in heterogametic sex.
M phase
mitotic phase. the period of active cell division
Telomeres
natural ends or tips of a linear chromosome
Pleitropy
one gene affects multiple characteristics
testcross
one individual of unknown genotype is crossed with another individual with a homozygous recessive genotype for the trait in question
penetrance
percentage of individuals with a particular genotype that express the expected phenotype
interkinesis
period between meiosis one and two
incomplete dominance
phenotype of a heterozygous individual falls somewhere between the dominant and recessive phenotypes.
codominance
phenotype of heterozygote is not intermediate between the phenotypes of homozygotes, but rather simultaneously expresses teh phenotypes of BOTH homozygotes
genetic maternal effect
phenotype of offspring is determined by the genotype of the mother.
oogenesis
production of gametes in female organisms
spermatogenesis
production of sperm
What type of cell is categorized by its size (less than 10 um in size) and the fact that it lacks a true cytoskeleton?
prokaryote
blending inheritance
proposed that offspring are a blend of parental traits, suggests that the genetic material itself blends.
histones
protein molecules around which DNA is tightly coiled in chromatin present in eukarya and archaea
Common characteristics of model organisms
short generation time, production of numerous progeny, and the ability to be reared in a laboratory environment.
Origins of replication
sites where DNA synthesis begins; not easily observed by microscopy
second polar body
smaller cell, incapable of being fertilized
principle of independent assortment
states that alleles at different loci separate independently of one another
addition rule
states that the probability of any one of two or more mutually exclusive events is calculated by adding the probabilities of these events. Either or
multiplication rule
states that the probability of two or more independent events taking place together is calculated by multiplying their independent probabilities. And rule
Pangenesis
suggested that specific pieces of information travel from various parts of the body to reproductive organs, from which they are passed to the embryo
chi square test
sum of (observed-expected)^2/expected, tells how likely it is that results happened because of coincidence and not a miscalculation
What common features must all genomes have, no matter where they exist?
the ability to store the entire set of information the organism needs for reproduction and development, and the ability to replicate the genetic information accurately for the next generation.
ovum
the cell that received most cytoplasm that is now an egg
Metaphase
the chromosomes arrange in the middle
mitosis
the process of nuclear division
How does the structure of DNA encode genetic information?
the sequence of bases
What is the product of mitosis?
two cells genetically identical to the original cell
secondary spermatocyte
two haploid cells yielded from meiotic division of primary spermatocytes
Sister chromatids
two identical copies of a chromosome held together at a centromere
Synapse
very close pairing association
concept of dominance
when two different alleles are present in a genotype, only the trait encoded by one of them (the dominant allele) is observed in the phenotype
Lyon Hypothesis
within each female cell one of the two x chromosomes is inactivated, which is random