Genetics 2450 Exam 1

Griffith's Transformation Experiment

1. 1928 - Frederick Griffith worked with Streptococcus pneumonia 2. Used two strains: the S strain which produces smooth, shiny colonies and is virulent; R strain which produces rough colonies and is non-virulent 3. Griffith worked with the IIS and IIIS strains which have type II and type III polysaccharide coats 4. Occassionally, S-type cells mutate into R-type and vice versa 5. Injected mice with different strains of the bacterium and observed their effects. When the mice were injected with IIR bacteria, the mice lived but when injected with IIIS bacteria, the mice died and living IIS bacteria could be isolated from their blood -If the IIIS bacteria were killed by heat before injection, the mice lived 6. The experiment showed that the bacteria had to be both alive and have the polysaccharide coat to be virulent and kill the mice 7. In his key experiment, Griffith injected mice with a mixture of living IIR bacteria and heat-killed IIIS bacteria - The mice died and living IIIS bacteria were present in the blood - These bacteria could not have arisen by mutation of the R bacteria because mutation would have produced IIS bacteria - He concluded that some IIR bacteria had been transformed into smooth, virulent IIIS bacteria by interaction with the dead IIIS bacteria - Genetic material from the dead IIIS bacteria had been added to the genetic material in the living IIR - Called the agent the transforming principle

Duplicate dominant epistasis

1. A is epistatic to B and b, and B is epistatic to A and a Ex: fruit shape in the shepherd's purse plant

Burkitt lymphoma

1. A virus-induced tumor that affects the cells of the immune system called B cells 2. Normally, B cells secrete antibodies (immunoglobin molecules) 3. 90% of the tumors in Burkitt lymphoma patients are associated with a reciprocal translocation involving chromosomes 8 and 14 4. A proto-oncogene becomes activated as a result of the translocation event: - The distal end of chromosome 8, starting with the MYC proto-oncogene, exchanges with the distal end of chromosome 14 - The MYC gene becomes positioned next to a transcriptionally active immunoglobin gene, resulting in overexpression of the MYC gene - The overexpressed MYC gene is the oncogene responsible for the uncontrolled cell growth and division that leads to the development of Burkitt lymphoma

Dominant epistasis

1. A/- B/- and A/- b/b individuals have the same phenotype so the phenotypic ratio of the F2 is 12:3:1 instead of 9:3:3:1 2. One gene when dominant is epistatic to the other gene

Avery's Transformation Experiment

1. Avery, MacLeod and McCarty attempted to identify Griffiths transforming principle by studying the transformation of R-type bacteria to S-type in the test tube 2. They lysed IIIS cells with a detergent and used a centrifuge to separate the cellular components from the cellular debris 3. Then they incubated the extract with a culture of living IIR bacteria and then plated cells on a culture medium in a Petri dish 4. Colonies of IIIS bacteria grew on the plate showing that the extract contained the transforming principle; the genetic material from IIIS bacteria capable of transforming IIR bacteria into IIIS bacteria 5. Avery and his colleagues knew that one of the macromolecular components in the extract - polysaccharides, proteins, RNA or DNA - must be the transforming principle - To determine which, they treated samples of the cell extract with enzymes that could degrade one or more of the macromolecules, then tested to see if transformation still occurred - They found that the extract failed to bring about transformation only when DNA had been degraded - These results showed that DNA must have been the transforming principle (the genetic material) - Removing DNA from the cell extract was the only change that could eliminate the ability of the extract to provide the IIR bacterium with genetic material

The effects of the environment: temperature

1. Biochemical reactions in the cell are catalyzed by enzymes 2. Some alleles of an enzyme-coding gene may give rise to an enzyme that is temperature sensitive; it may function normally at one temperature but be non-functional at another Ex: fur color in Siamese cats

The effects of the environment: chemicals

1. Certain chemicals can affect an organism significantly 2. The human disease phenylketonuria is an autosomal recessive trait with a defect in the biochemical pathway for the metabolism of the amino acid phenylaline 3. Individuals who are homozygous for the recessive allele have various symptoms but the most notable is mental retardation at an early age 4. Their diet determines how severe the symptoms of PKU will be

What occurs during prophase (mitosis)?

1. Chromatids condense so they gradually appear shorter and fatter under microscopy 2. By late prophase, each chromosome that was duplicated during the S phase of interphase can be seen to consist of two sister chromatids 3. While condensation is occurring, the nucleolus shrinks 4. The mitotic spindle assembles outside the nucleus 5. Centrioles (focal point for spindle assembly) are arranged in pairs and duplicated before the S phase 6. Each new centriole pair becomes the focus of an array of microtubules called the aster 7. Early in prophase, the two asters are next to one another and close to the nuclear envelope 8. By late prophase, the two asters have moved far apart along the outside of the nucleus and are spanned by the microtubular spindle fibers

Z-DNA

1. DNA with alternating purine and pyrimidine bases can organize into left-handed and right-handed helices 2. The left-handed helix has a zigzag arrangement of the sugar-phosphate backbone 3. Has 12.0 bp per complete helical turn 4. Thin and elongated with a deep minor groove 5. The major groove is near the surface of the helix, so is not very distinct

Two groups of modifier genes

1. Enhancers - intensify the phenotype controlled by the other gene 2. Reducers - decrease the phenotypic expression of the other gene

B-DNA

1. Forms under conditions of high humidity 2. Thinner and longer double helix than A-DNA 3. Wide major groove, narrow minor grooves of similar depths

What are the end products of two meiotic divisions?

1. Four haploid cells (gametes in animals) from one original diploid cell 2. Each of the four progeny cells has one chromosome from each homologous pair of chromosomes 3. Because of crossing-over, these chromosomes are not exact copies of the original chromosomes

Double tetrasomic

1. Has two chromosomes present in four copies each 2. The cell is 2N+2+2

Double monosomic

1. Has two separate chromosomes present in only one copy each 2. The cell is 2N-1-1

How has the environment played a role in determining height?

1. Human height has increased about 1 inch per generation over the past 100 years as a result of better diets and improved health care 2. Genes and the environment have interacted in determining human height

Anaphase I

1. In anaphase I, the chromosomes in each tetrad separate, so the chromosomes of each homologous pair disjoin and migrate towards opposite poles, the area where new nuclei will form 2. At this stage, each of the separated chromosomes is called a dyad 3. The migration assumes that maternally and paternally derived centromeres segregate randomly to each pole, and that at each pole there is a haploid complement of replicated centromeres with associated sister chromatids 4. At this time, homologous chromosomes have segregated from each other, but sister chromatids remain attached at their respective centromeres

Metaphase I

1. In metaphase I, the kinetochore microtubules align the tetrads on the metaphase plate 2. The pairs of homologs (the tetrads) are found at the metaphase plate 3. In mitosis, replicated homologous chromosomes (sister chromatid pairs) align independently of one another at the metaphase plate

Prometaphase I

1. In prometaphase I, the nucleoli disappear, the nuclear envelope breaks down, and the meiotic spindle that has been forming between the separating centriole pairs enters the former nuclear area 2. As in mitosis, kinetochore microtubules attach to chromosomes 3. The kinetochore microtubules from one pole attach to both sister kinetochores of one duplicated chromosome, and kinetochore microtubules from the other pole attach to both sister kinetochores of the duplicated chromosome in a tetrad

Telophase I

1. In telophase I, the dyads complete their migration to opposite poles of the cell and the spindle disassembles 2. In some species, new nuclear envelopes form around each haploid grouping 3. In most species, cytokinesis follows telophase I, producing two haploid cells

Relative-Sequence DNA

1. Include both moderately repetitive and highly repetitive DNA sequences 2. Can be arranged within the genome in one of two ways: dispersed repeated or interspersed repeated DNA, and tandemly repeated DNA 3. Dispersed repeated sequences consist of families of repeated sequences interspersed through the genome with unique-sequence DNA 4. Two types of dispersed repeated sequences: long interspersed elements (LINEs) in which the sequences in the families are about 1,000-7,000 bp long short interspersed elements (SINEs) in which the families are 100-400 bp long 5. Tandemly repeated DNA sequences are arranged one after the other in the genome in a head-to-tail organization

Monosomy (a monosomic cell)

1. Involves a loss of a single chromosome 2. The cell is 2N-1 3. Can arise if nondisjunction in meiosis in a parent produces a gamete with no copies of a particular chromosome and one copy of all other chromosomes in the set 4. Produce two kinds of haploid gametes: N and N-1

Nullisomy (a nullisomic cell)

1. Involves a loss of one homologous chromosome pair 2. The cell is 2N-2 3. Can arise if nondisjunction occurs for the same chromosome in meiosis in both parents producing gametes with no copies of that chromosome and one copy of all other chromosomes in the set

Trisomy (a trisomic cell)

1. Involves a single extra chromosome 2. The cell is 2N+1 3. The cell has three copies of a particular chromosome and two copies of all other chromosomes 4. Can arise if nondisjunction occurs for the same chromosome in meiosis in both parents producing gametes with two copies of that chromosome and one copy of all other chromosomes in the set

Chronic Myelogenous Leukemia (CML)

1. Involves chromosomes 9 and 22 2. Untreated can be an invariably fatal cancer involving the uncontrolled replication of myeloblasts 3. 90% of patients with CML have a chromosomal mutation called the Philadelphia chromosome in the leukemic cells

What are the three significant results of meiosis?

1. Meiosis generates haploid nuclei with half the number of chromosomes found in the diploid cell that entered the process 2. In metaphase I, each maternally and paternally derived chromosome has an equal chance of aligning on one or the other side of the equatorial metaphase plate 3. The crossing-over between maternal and paternal chromatid pairs during meiosis I generates still more variation in the final combinations

Meiosis in Animals

1. Most multicellular animals are diploid and produce haploid gametes 2. Fusion of two haploid gametes produces a diploid zygote when their nuclei fuse in fertilization and then the zygote divides by mitosis to provide the new diploid organism 3. In males, gametes are sperm produced through spermatogenesis 4. In females, gametes are eggs produced through oogenesis 5. In male animals, the sperm cells (spermatozoa) are produced within the testes which contain the primordial germ cells 6. Via mitosis, the primordial germ cells produce secondary spermatogonia which transform into primary spermatocytes (meiocytes) each which undergo meiosis I and gives rise to two secondary spermatocytes 7. Each secondary spermatocyte undergoes meiosis II 8. The results of these two divisions are four haploid spermatids that eventually differentiate into the male gametes 9. In female animals, the ovary contains the primordial germ cells (primary oogonia) that give rise to secondary oogonia through mitosis 10. These cells transform into primary oocytes which grow until the end of oogenesis 11. The diploid primary oocyte goes through meiosis I and unequal cytokinesis to give rise to two cells-a large one called the secondary oocyte and a small one called the first polar body 12. In meiosis II, the secondary oocyte produces two haploid cells-one is a very small cell called a second polar body and the other is a large cell that rapidly matures into the mature egg cell (ovum) 13. The first polar body may or may not divide during meiosis II 14. Only one mature gamete (the ovum) is produced by meiosis of a diploid cell in the female animal 15. In humans, all oocytes are formed in the fetus and one oocyte completes meiosis I each month in the adult female but does not progress unless stimulated to do so through fertilization by a sperm

What occurs during Meiosis II?

1. No DNA replication occurs between meiosis I and meiosis II 2. In prophase II, the chromosomes condense and a spindle forms 3. In prometaphase II, the nuclear envelopes (if formed in telophase I) break down and the spindle organizes across the cell 4. Kinetochore microtubules from the opposite poles attach to the kinetochores of each chromosome 5. In metaphase II, the movement of the kinetochore microtubules aligns the chromosomes on the metaphase plate 5. During anaphase II, the centromeres separate and the now daughter chromosomes are pulled to the opposite poles of the spindle 6. One sister chromatid of each pair goes to one pole and the other goes to the opposite pole 7. The separated chromatids are now considered chromosomes 8. In telophase II, the chromosomes begin de-condensing, a nuclear envelope forms around each set of chromosomes and cytokinesis takes place 9. After telophase II, the chromosomes continue de-condensing, eventually becoming invisible under the microscope

Trisomy-21

1. Occurs when there are three copies of 21 2. Frequency of about 2510/1 million conceptions and 1430/1 million live births 3. Individuals have Down syndrome, characterized by low IQ, epicanthal folds, short and broad hands, and below-average height 4. A direct relationship between maternal age and probability of giving birth to an individual with this disease

The effects of the environment: sex

1. Phenotypic expression associated with one allele may be influenced by the sex of the individual 2. In the case of sex-linked genes, differences in the phenotypes of the two sexes are related to different complements of genes on the sex chromosomes 3. In some cases, genes that are on autosomes affect a particular phenotype that appears in one sex but not the other, called sex-limited traits Ex: distribution of facial hair 4. Sex-influenced traits are often controlled by autosomal genes 5. Sex-influenced traits appear in both sexes, but either the frequency of occurrence in the two sexes is different or the relationship between genotype and phenotype is different Ex: pattern baldness, cleft lip/palate, clubfoot, gout, osteoporosis

Unique-Sequence DNA

1. Present in one to a few copies in the genome 2. Sometimes called single-copy sequences - they are sequences that are present as single copies in the genome (two copies per diploid cell) 3. Protein-coding genes are in the unique-sequence class of DNA 4. Make up approximately 55-60% of the genome in humans

Trisomy-18

1. Produces Edwards syndrome 2. Occurs in about 2.5 in 10,000 live births 3. About 80% of infants with Edwards syndrome are female 4. Small at birth and have multiple congenital malformations affecting almost every organ in the body 5. Clenched fists, an elongated skull, low-set malformed ears, mental and developmental retardation are associated with this syndrome

Trisomy-13

1. Produces Patau syndrome 2. Characteristics include cleft lip and palate, small eyes, polydactyly, mental and developmental retardation, and cardiac anomalies 3. Most infants die before the age of 3

Four main characteristics of extranuclear inheritance

1. Ratios typical of Mendelian segregation are not found because meiosis based Mendelian segregation is not involved 2. In multicellular eukaryotes, the results of reciprocal crosses involving extranuclear genes are not the same as reciprocal crosses involving nuclear genes because meiosis based Mendelian segregation is not involved 2a. Mitochondrial and chloroplast genes usually show uni-parental inheritance from generation to generation 2b. In uni-parental inheritance, all progeny have the phenotype of only one parent 2c. Multicellular eukaryotes usually exclusively inherit the phenotype of the mother 2d. Maternal inheritance occurs because the amount of cytoplasm in the female gamete usually greatly exceeds that in the male gamete resulting in the zygote receiving most of its cytoplasm from the female parent and a negligible amount from the male parents 2e. The results of reciprocal crosses between a wild-type and a mutant strain are identical if the genes are located on nuclear chromosomes 2f. One exception occurs when X-linked genes are involved, but even then the results follow nuclear chromosome segregation patterns and are distinct from those for extranuclear inheritance 3. Extranuclear genes cannot be mapped to the chromosomes in the nucleus 4. Extranuclear inheritance is not affected by substituting a nucleus with a different genotype

Genetic crosses of Drosophila done by Alfred Sturtevant in 1913 showed what?

1. Red (wild-type) eye color is dominant to eosin and to white 2. Eosin is recessive to the wild-type but dominant to white

Philadelphia chromosome

1. Results from a reciprocal translocation involving the movement of part of the long arm of chromosome 22 2. The reciprocal translocation converts a proto-oncogene to an oncogene 3. The ABL proto-oncogene, normally located on chromosome 9, is translocated to chromosome 22 in patients with CML 4. The translocation positions the ABL gene within the breakpoint cluster region (BCR) gene 5. The hybrid BCR-ABL gene is the oncogene responsible for CML - the hybrid gene expresses an activated tyrosine kinase 6. Activated tyrosine kinase is a kind of gene product that contributes to stimulating a cell to grow and divide, in this case resulting in too many white blood cells

3 Types of Duplications

1. Tandem duplication - when the mutation generates duplicated segments that are adjacent to each other, with the order of the genes in both segments the same as the order of the original 2. Reverse tandem duplication - when the order of genes in the duplicated segment is opposite of the order of the original 3. Terminal tandem duplication - when the duplicated segments are arranged in tandem at the end of a chromosome

The effects of the environment: age of onset

1. The age of the organism creates internal environmental changes that can affect the phenotypic expression associated with an allele 2. Not all genes are active all the time, rather programmed activation/deactivation of genes occurs as the organism develops and functions Ex: pattern baldness, Duchenne muscular dystrophy

Gene analysis

1. The dissection of the structure and function of the genetic material 2. In classic genetic analysis, progeny from crosses between parents with different genetic characters are analyzed to determine the frequency with which differing parental alleles are associated in new combinations

Prophase I

1. The important difference between prophase 1 of meiosis and prophase of mitosis is that homologous chromosomes pair with each other in meiosis, and crossing-over occurs only in meiosis 2. In leptonema (early prophase 1) the extended chromosomes begin to condense and become visible as long, thin threads 3. Once a cell enters leptonema it is committed to the meitoic process 4. In zygonema (early-middle prophase I) the chromosomes continue to condense 5. The homologous pairs of chromosomes actively find each other and align roughly along their lengths 6. Each pair of homologs undergoes synapsis-the formation along the length of the chromatids of a zipper-like structure called the synaptonemal complex which aligns the two homologs precisely 7. Telomeres of chromosomes play a key role in the initiation of synapsis-during meiosis I, telomeres are clustered on the nuclear envelope to produce an arrangement called a bouquet 8. Pachynema (middle prophase I) starts when synapsis is completed 9. Each synapsed set of homologous chromosomes consists of four chromatids called a bivalent or tetrad 10. During pachynema, crossing-over occurs 11. The physical exchange that occurs in crossing-over is facilitated by the alignment of the homologous chromosomes brought about by the synaptonemal complex 12. At the end of pachynema, the synaptonemal complex is disassembled and the chromosomes started to elongate 13. In diplonema (middle to late prophase I) the synaptonemal complex disassembles and the homologous chromosomes begin to move apart 14. The result of crossing-over becomes visible during diplonema as a cross-shaped structure called a chiasma 15. At each chiasma the homologous chromosomes are very tightly associated 16. In most organisms, diplonema is followed rapidly by the remaining stages of meiosis 17. In diakinesis (late prophase I) the chromosomes condense even more, making it impossible to see the four members of the tetrads, but the chiasmata are clearly visible

What occurs during anaphase (mitosis)?

1. The joined centromeres of sister chromatids separate, giving rise to two daughter chromosomes 2. Once the kinetochores on each chromosome separate, the sister chromatid pairs undergo disjunction and the daughter chromosomes move towards opposite poles 3. The daughter chromosomes are pulled toward the opposite poles of the cell by the shortening microtubules attached to the kinetochores 5. As they are pulled, the chromosomes assume characteristic shapes related to the location of the centromere along the chromosome's length 6. The movement continues until the separated daughter chromosomes have reached the two poles, at which point chromosome segregation has been completed 7. Cytokinesis usually begins in the latter stages of anaphase

What occurs during metaphase (mitosis)?

1. The kinetochore microtubules orient the chromosomes so that their centromeres become aligned at the metaphase plate, a plane halfway between the two spindle poles, with the long axes of the chromosomes oriented at 90 degrees to the spindle axis 2. Further chromosome condensation occurs just after the chromosomes have finished separating in the subsequent anaphase stage 3. This late condensations minimizes the potential problem of chromosome arms extending over the plane of division which could result in mechanical damage to the chromosomes

Meiosis in Plants

1. The life cycle of sexually reproducing plants typically has two phases-the gametophyte or haploid stage in which gametes are produced and the sporophyte or diploid stage in which haploid spores are produced by meiosis 2. In angiosperms (flowering plants) the flower is the structure in which sexual reproduction occurs 3. Stamens are the reproductive organs of males and pistils are the reproductive organs of females 4. Each stamen consists of a single stalk (the filament) on top of which is an anther 5. Pollen grains (immature male gametophytes) are released from the anther 6. The pistil (contains the female gametophytes) consist of the stigma, a sticky surface specialized to receive pollen; the style, a thin stalk down which a pollen tube grows from a pollen grain that adheres to the stigma; and the ovary at the base of the structure which contain the ovules 7. Each ovule encloses a female gametophyte (embryo sac) containing a single egg cell 8. When the egg is fertilized, the ovule develops into a seed 9. Among living organisms, only plants produce gametes from special bodies called gametophytes 10. Plant life cycles have two distinct reproductive phases called the alternation of generations 11. Meiosis and fertilization are the transitions between these stages 12. The haploid gametophyte generation begins with spores that are produced by meiosis

What occurs during prometaphase (mitosis)?

1. The nuclear envelope breaks down 2. The developing spindle enters the former nuclear area 3. Kinetochores (sites for the attachment of the chromosomes to spindle microtubules) bind to each centromere 4. For a pair of sister chromatids, one - many kinetochore microtubules from one pole attach to the kinetochore of one chromatid 5. An equivalent number of kinetochore microtubules from the other pole attach to the kinetochore of the other chromatid 6. Non-kinetochore microtubules originate from each spindle pore and overlap in the middle of the spindle

Two ways in which extranuclear inheritance differs from maternal effect

1. The phenotype in extranuclear inheritance is determined by an individual's organellar gene, whereas the phenotype in maternal effect is determined by a nuclear gene in the mother of the individual 2. An individual's phenotype in extranuclear inheritance matches its genotype, whereas an individual's phenotype in maternal effect does not match its own genotype, instead matching that of its mother

What occurs during telophase (mitosis)?

1. The two sets of daughter chromosomes are assembled into two groups at opposite ends of the cell 2. The chromosomes begin to uncoil and assume the elongated state characteristic of interphase 3. A nuclear envelope forms around each group of chromosomes, the spindle microtubules disappear, and the nucleolus or nucleoli reform 4. Nuclear division is complete and the cell has two nuclei

Duplicate recessive epistasis (complementary gene action)

1. a/a is epistatic to B and b, and b/b is epistatic to A and a ex: flower color in the sweet pea

A-DNA

1. seen only in conditions of low humidity 2. Right handed double helix 3. Double helix is short and wide with a narrow, very deep major groove and a wide, shallow minor groove

People of the blood type A (I^A/I^A or I^A/i) have only the ___ antigen(s) on their red blood cells

A

For a haploid (N) cell, chromosome duplication produces?

A cell in which each chromosome has doubled its content

For a diploid (2N) cell, chromosome duplication produces?

A cell in which each chromosome set has doubled its content, but has two sets of chromosomes

Deletions

A chromosomal mutation in which part of a chromosome is missing 1. Deletions begin where breaks occur in chromosomes 2. Breaks can be induced by agents such as heat, radiation, viruses, chemicals, and transposable elements, or by errors in recombination 3. Deletion mutations cannot revert to the wild-type since a segment of chromosome is missing 4. In diploid organisms, an individual heterozygous for deletion may be normal 5. If a homolog contains recessive alleles that have deleterious effects, consequences can be severe 6. If deletion involves the loss of a centromere, the result is an acentric chromosome which is usually lost during meiosis 6a. This deletion of an entire chromosome from the genome may have serious or even lethal consequences depending on the particular chromosome deleted and the organism 7. Deletions can be used to determine the physical location of a gene on a chromosome 8. Homozygotes for deletion usually die if the deletion is large Ex: A human disorder caused by a heterozygous deletion is cri-du-chat syndrome which results from an observable deletion of part of the short arm of chromosome 5 - one of the larger human chromosomes. Children with cri-du-chat syndrome are severely mentally retarded, have a number of physical abnormalities, and cry with a sound like the mew of a cat Another example is Prader-Willi syndrom which results from heterozygosity for a deletion of part of the long arm of chromosome 15.

Translocation

A chromosomal mutation in which there is a change in position of chromosome segments and the gene sequences they contain to a different location in the genome 1. No gain or loss of genetic material is involved in a translocation 2. Nonreciprocal intrachromosomal translocation - when a chromosome segment changes position within the same chromosome 3. Nonreciprocal interchromosomal translocation - when a chromosome segment is transferred from one chromosome to another 4. Reciprocal interchromosomal translocation - when a chromosome segment is transferred from one chromosome to another if an exchange of segments between the two chromosomes is involved In organisms homozygous for the translocations (both copies of the genome in the diploid have the translocation), the genetic consequence is an alternation in the linkage relationships of genes

Duplications

A chromosomal mutation that results in the doubling of a segment of a chromosome. 1. Duplications have played an important role in the evolution of multiple genes with related functions, called multigene families 2. Heterozygous duplications result in unpaired loops similar to those described for chromosome deletion and may be detected cytologically 3. Duplications of particular genetic regions can have unique phenotypic effects Ex: the Bar mutant on the X chromosome of Drosophila - In strains homozygous for the Bar mutation, the number of facets of the compound eye is less than that of the normal eye, giving the eye a bar-shaped (slit-like), rather than oval, appearance - Bar resembles an incompletely dominant mutation because females heterozygous for Bar have more facets and a somewhat larger bar-shaped eye than do females homozygous for Bar - Males hemizygous for Bar have very small eyes like those of homozygous Bar females - The Bar trait is the result of a duplication of a small segment of the X chromosome Ex of multigene families: hemoglobin molecules contain two copies of two different subunits - the α-globin polypeptide and the β-globin polypeptide -At different developmental stages, from embryo to adult, a human individual has different hemoglobin molecules assembled from different types of α- and β-globin polypeptides - The genes for each of the α-globin type of polypeptides are clustered together on one chromosome, while the genes for each of the β-globin type of polypeptides are clustered together on another - The sequences of the α-globin genes are all similar, as are the sequences of the β-globin genes

Inversions

A chromosomal mutation that results when a segment of a chromosome is excised and then reintegrated at an orientation 180⁰ from the original orientation 1. Two types of inversions: Paracentric inversions do not include the centromere, but pericentric inversions do 2. Genetic material typically is not lost when an inversion takes place, although there can be phenotypic consequences when the breakpoints (inversion ends) occur within genes or within regions that control gene expression 3. Homozygous inversions can be identified through the non-wild-type linkage relationships that result between the genes within the inverted segment and the genes that flank the inverted segment 4. The meiotic consequences of a chromosome inversion depends on whether the inversion occurs in a homozygote or heterozygote - If the inversion is homozygous, then meiosis is normal and there are no problems related to gene duplications or deletions - For an inversion heterozygote, there are no meiotic problems if crossing-over is absent in the inversion but serious genetic consequences ensue if crossing-over occurs in the inversion Ex: Paracentric - *ABCDEFG/*ABCDEFG with centromere (*) to the left of gene A - In meiosis, the homologous chromosomes attempt to pair such that the best possible base pairing occurs - Because of the inverted segment on one homolog, pairing of homologous chromosomes requires the formation of loops containing the inverted segments; called inversion loops

Meiosis I results in?

A reduction in the number of chromosomes in each cell from diploid to haploid

Fusion of gametes produces what?

A zygote

Recessive epistasis

A/- b/b and a/a b/b individuals have the same phenotype resulting in a phenotypic ratio in the F2 of 9:3:4 rather than 9:3:3:1 Ex: coat color in rodents

Two types of purines

Adenine (A) and Guanine (G)

Alternate Segregation

Alternate centromeres migrate to the same pole, producing two gametes, each of which is viable because it contains a complete set of genes One of these gametes has two normal chromosomes, and the other has two translocated chromosomes

Antibodies against the B antigen agglutinate any red blood cells that have ___ antigen(s) on them

B

People of blood type B (I^B/I^B or I^B/i) have the ___ antigen(s) on their red blood cells

B

The I^A allele encodes a glycosyltransferase enzyme that adds a particular type of sugar to the H antigen to produce the ____ antigen

B

The rare h/h individuals are similar to blood group O but are said to have what kind of blood type?

Bombay blood type

How are diploid eukaryotes produced?

By the fusion of two haploid gametes (mature reproductive cells)

Position Effect

Changes in the phenotypic expression of one or more genes as a result of a change in position i the genome 1. May be exhibited if a gene that is normally located in euchromatin is brought near heterochromatin by a chromosomal rearrangement 2. Gene transcription typically occurs in euchromatin but not in heterochromatin; the difference in chromosome condensation is responsible for the distinction Ex: X-linked white-eye locus in Drosophila

The phenomenon in which the heterozygote exhibits the phenotypes of both homozygotes is called what?

Codominance

The phenomenon in which one allele is dominant to another so that the phenotype of the heterozygote is the same as that of the homozygous dominant is called what?

Complete dominance

The phenomenon in which the recessive allele is phenotypically expressed only when homozygous is called what?

Complete recessiveness

What are the four common types of chromosomal mutations?

Deletions, duplications, inversions and translocations

_________ exert their effect in heterozygotes resulting in the death of the organism

Dominant lethals

The complementation test was developed by?

Edward Lewis to study genes in Drosophila

Chromatid bundles found in polytene chromosomes are created by what process?

Endoreduplication - the process of repeating cycles of chromosome duplication without nuclear or cell division

The interaction between alleles of two or more genes to control a single phenotype

Epistasis

Nondisjunction at meiosis I produces?

Four abnormal gametes: two with a chromosome duplicated and two with the corresponding chromosome missing

3 stages of interphase

G1 (gap 1), S and G2 (gap 2)

Syntentic genes

Genes that are on the same chromosome

Linked genes

Genes that do not appear to assort independently because they are located on the same chromosome

In an I^A/I^B heterozygote, both enzymes are produced and therefore some ____ antigen is converted to the A antigen and some to the B antigen

H

Most people produce a glycolipid called the ____ antigen

H

People who are homozygous for the i allele carry only the ____ antigen on their red blood cells

H

The H antigen is encoded by the dominant ___ allele of locus distinct from the ABO blood group gene

H

Eukaryotes

Have two copies of each type of chromosome in their nucleus, diploid, 2N

Individuals of blood group AB are?

Heterozygous I^A/I^B

Individuals of blood group A are either?

I^A/I^A or I^A/i

Individuals of blood group B are either?

I^B/I^B or I^B/i

The phenomenon in which the phenotype of the heterozygote lies in the range between the phenotypes of individuals that are homozygous for either allele occurs in what type of dominance?

Incomplete

The phenomenon in which one allele of a gene is not completely dominant to another allele of the same gene is called what?

Incomplete dominance or semidominance or partial dominance

Modifier genes

Interact with another non-allelic gene but modifies the phenotype associated with expression of the alleles of that gene in a milder way

The fragile X chromosome is inherited in what type of fashion?

Mendelian

Chromosomes are typically identified during which phase?

Metaphase

Nondisjunction

Occurs when homologous chromosomes in meiosis I or daughter chromosomes in meiosis II fail to move to opposite poles during anaphase

Two classes of nitrogenous bases

Purines - nine-membered, double-ringed structures Pyrimidines - six-membered, single-ringed structures

Testcross

The best cross to use for linkage - involves a cross between two individuals, one of which is homozygous recessive for all genes involved

The I^A allele of the ABO blood group gene encodes a product needed for what?

The biosynthesis of the A antigen but that is not involved in the biosynthesis of the B antigen

The I^B allele of the ABO blood group gene encodes a product needed for what?

The biosynthesis of the B antigen but is not involved in the biosynthesis of the A antigen

Meiosis II results in?

The separation of sister chromatids, resulting in each of the four nuclei (derived from two meiotic divisions) receiving one chromosome of each chromosome set

Three types of pyrimidines

Thymine (T), Cytosine (C) and Uracil (U)

Although a gene may have multiple alleles in a given population of individuals, a single diploid individual can have a maximum of ____ of these alleles

Two

Mitosis results in?

Two progeny haploid cells, each with one complete set of chromosomes

Fragile Sites

Unstained areas or narrowings that develop in chromosomes when human cells are grown in culture

Chromosomal mutations (chromosomal aberrations)

Variations from the normal (wild-type) condition in chromosome structure or number

Euploid

When an organism or a cell has one complete set of chromosomes or an exact multiple of complete sets Euakryotic organisms that are normally diploid and eukaryotic organisms that are normally haploid are euploids

There are ________ and ________ lethal mutations

X-linked, autosomal

In strains homozygous for reciprocal translocation, does meiosis occur normally?

Yes because all chromosome pairs can pair properly, and crossing-over does not produce any abnormal chromatids

Karyotype

a complete set of all the metaphase chromosomes in a cell

An allele that results in the death of an organism is called what?

a lethal allele

Epigenetics

a meiotically or mitotically heritable change in gene expression that does not involve a change in the DNA sequence of the affected gene(s)

Mitochondrial (mt)DNA contains information for what?

a number of mitochondrial components such as tRNAs, rRNAs, some polypeptide subunits of the proteins cytochrome oxidase, NADH-dehydrogenase, and ATPase

Antibody

a protein molecule that recognizes and binds to the foreign substance (antigen) introduced into the organism as part of the immune response to remove the foreign antigen from the body

Adjacent-1 segregation

adjacent non-homologous centromeres migrate to the same pole Both gametes produced contain gene duplications and deletions and are often inviable Occurs about as frequently as alternate segregation

The gene involved with lethal alleles is called what?

an essential gene

Aneuploid

an organism or cell that has a chromosome number that is not an exact multiple of the haploid set of chromosomes

People in the Bombay blood group produce _______ antibodies

anti-O

Antigen

any molecule that is recognized as foreign by an organism and that therefore stimulates the production of specific protein molecules called antibodies which bind to the antigen

People with blood type O produce neither A nor B antigens, so their blood can be transfused to what type of recipients?

any recipient, people of blood type A, B, AB or O

People of blood type AB (I^A/I^B) have ______ antigen(s) on their red blood cells

both A and B

For a trait such as height, genes set ________ or ______ for the phenotype

certain limits, specify a potential

Polytene chromosomes are composed of?

chromatid bundles

Autosomes

chromosomes that are not sex chromosomes

The genomes of mitochondria in many organisms are?

circular, double-stranded, supercoiled DNA molecules

The ________ determines whether two independently isolated mutants with the same phenotype have mutations in the same or different genes

complementation or cis-trans test

Penetrance is ______ when all the homozygous recessives show one phenotype, all homozygous dominant show another phenotype, and all heterozygotes are alike

complete, 100%

Centromeres

constrictions along the length of each chromosome that are important for the behavior of chromosomes during cellular division

When the centromeres separate, sister chromatids become?

daughter chromosomes

Adjacent-2 segregation

different pairs of adjacent homologous centromeres migrate to the same pole Both products have gene duplications and deletions and are always inviable

Mitosis occurs in what type of cells?

diploid and haploid

In all cases, chloroplast (cp)DNA is what?

double-stranded, circular and supercoiled

Homolog

each chromosomal member pair

A gene that masks the expression of another gene is said to be ______ and a gene whose expression is masked is said to be _______.

epistatic, hypostatic

The degree to which a penetrant gene or genotype is phenotypically expressed in an individual is called?

expressivity

Human height or stature is definitely influenced by what?

genes

The chloroplast genome contains what?

genes for the rRNAs of chloroplast ribosomes, tRNAs, and some proteins required for transcription and translation of the cp-encoded genes

Extranuclear genes

genes in mitochondrial and chloroplast genomes also known as extrachromosomal genes, cytoplasmic genes, non-Mendelian genes, or organellar genes

The ABO blood group gene encodes ___________, enzymes that add sugar groups to a pre-existing polysachharide that is combined with a lipid to form a glycolipid

glycosyltransferases

If a mutation of an essential gene is caused by a recessive lethal allele, _________ for that allele show the lethal phenotype

homozygotes

If a mutation of an essential gene is caused by a dominant lethal allele, ____________ and ________ for that allele show the lethal phenotype

homozygotes, heterozygotes

The ____ allele encodes no functional products involved in the biosynthesis of either the A or B antigen

i

Where is DNA found outside of the nucleus?

in mitochondria and chloroplasts

Polymers

large molecules that consist of many similar smaller molecules called monomers linked together; DNA and RNA are polymers

Essential genes are genes that can result in a __________ when mutated

lethal phenotype

Maternal effect occurs as the result of?

mRNA or proteins deposited in the oocyte before fertilization that direct early development of the embryo

The phenomenon in which a phenotype of the offspring is determined by the nuclear genotype of the mother is called what?

maternal effect

During meiosis, which division is reductional?

meiosis I

Mendel's law of independent segregation depends on the random positioning of centromeres at which meiotic division?

meiosis I

Which meiotic division is similar to mitosis?

meiosis II

Suppressor gene

modifier genes that shift the phenotype associate with a mutant allele of another gene towards the phenotype associated with the wild-type allele of that gene

Cytoplasm is inherited from the ______ in many organisms, so the inheritance of extranuclear genes in these organisms is strictly _______.

mother, maternal

People of blood type O (i/i) have ______ antigen(s) on their red blood cells

neither A nor B

People who are homozygous for the i allele produce _____ enzymes to convert the H antigen glycolipid

no

The other components found in mitochondria are encoded by what?

nuclear genes and are imported into the mitochondria

Polyploid zygotes

occurs when gametes with two chromosomes sets with a normal gamete fuse

In incomplete dominance with cases involving a loss-of-function allele, ____ allele(s) in a heterozygote is expressed to produce a product

one

In mitosis, ____ copy(s) of each duplicated chromosome segregates into both _______ cells.

one, daughter

Each gamete has ___ set of chromosomes and they are diploid/haploid?

one, haploid

Recombinants

progeny showing non-parental combinations of alleles

Parentals

progeny showing the parental combination of alleles

What are the five stages of Meiosis I?

prophase I, prometaphase I, metaphase I, anaphase I and telophase I

What are the five stages of mitosis?

prophase, prometaphase, metaphase, anaphase and telophase

The mitochondrial and chloroplast genes encode the _____ components of ribosomes of organelles

rRNA

People with blood type AB produce both the A and B antigens, so their blood can be transfused to what type of recipients?

recipients who do not have either anti-A or anti-B antibodies, people of blood type AB

People with blood type A produce the A antigen, so their blood can be transfused to what type of recipients?

recipients who do not have the anti-A antibody, people of blood type A or AB

People with blood type B produce the B antigen, so their blood can be transfused to what type of recipients?

recipients who do not have the anti-B antibody, people of blood type B or AB

Glycolipids associate with _______ membranes to form the blood group antigens

red blood cell

People who are homozygous for the recessive mutant allele, h, do not make the H antigen; therefore...?

regardless of the presence of I^A or I^B alleles at the ABO blood group gene, no A or B antigens can be produced

The four major processes that interact to constitute the complex process of development are?

replication of the genetic material, growth, differentiation of the various cell types and the arrangement of differentiated cells into defined tissues and organs

Polytene chromosomes

special kinds of chromosomes found in certain tissues of insects

The mitochondrial and chloroplast genes encode many of the ______ used in organellar protein synthesis

tRNAs

What occurs during the S phase in mitosis?

the DNA of each chromosome is replicated giving two exact copies called sister chromatids that are held together by the replicated but unseparated centromeres

What occurs during G1 in mitosis?

the cell prepares for DNA and chromosome replication

What occurs during G2 in mitosis?

the cell prepares for cell division

The length of the cell cycle depends on?

the duration of G1

Within the limits set by genes, the phenotype an individual develops depends on what?

the environment

Maternal effect genes

the genes that encode for the product produced by the mRNA or proteins deposited in the oocyte before fertilization

Penetrance depends on what?

the genotype and the environment

Homologous Chromosomes

the members of a chromosome pair that contain the same genes and pair during meiosis in diploid organisms

In proliferating somatic cells, the cell cycle consists of what two phases?

the mitotic phase (M) and the interphase between divisions

Nucleotides

the monomers that make up DNA and RNA - each nucleotide consists of pentose sugar, a nitrogenous base, and a phosphate group

The percentage of individuals with a given genotype who exhibit the phenotype associated with that genotype is called what?

the penetrance of the genotype

Genetic recombination

the process by which the recombinants are produced

People of blood group O are homozygous for?

the recessive i allele; ii

The quantity of product for an expressed allele produced by a homozygote in incomplete dominance has what?

two doses of the gene product resulting in full phenotypic expression

Nondisjunction at meiosis II produces?

two normal gametes and two abnormal gametes - a single gamete with two daughter chromosomes and one gamete with that same chromosome missing

People with blood type AB are _____ recipients

universal

People with blood type O are _____ donors

universal

Metacentric chromosome

when centromere is located at about the center of the chromosome giving the appearance of two equal arms

Telocentric chromosome

when centromere is located at the end of the chromosome giving the appearance of the chromosome having one arm

Acrocentric chromosome

when centromere location gives chromosome appearance of one arm containing a stalk with a "bulb" called a satellite on it

Submetacentric chromosome

when centromere location gives the appearance of chromosome having one arm longer than the other