BIOLOGY TEST 2
What is the set of alleles that an individual possesses?
(A. A gene) B. A genotype C. A genome D. A genus
When do chiasmata form in meiosis?
(A. During prophase I )B. During metaphase I C. During anaphase I D. During prophase II
Which of the following statements about homologous chromosomes is correct?
(A. Each gene is at the same locus on both chromosomes.) B. They are two identical copies of a parent chromosome which are attached to one another at the centromere. C. They always produce identical phenotypes. D. They are chromosomes that have identical genes and alleles.
What is the relationship between Mendel's law of segregation and meiosis?
(A. Only one of a pair of alleles appears in a gamete.) B. The separation of "paternal" and "maternal" chromosomes shows no pattern. C. Gametes contain all dominant or all recessive alleles. D. Variation only results from two divisions
Which of the following chemicals is a component of eukaryotic chromosomes?
(A. Protein) B. Triglyceride C. Fatty acid D. RNA
What kind of inheritance does skin colour represent?
(A. Sex-linked (X-linked) )B. Multiple alleles C. Systemic D. Polygenic
A human cell has between 20 000 and 25 000 genes whereas an E. coli cell has approximately 4000 genes. Which of the following statements is true?
(A. The human genome is larger than the E. coli genome.) B. There are more genes on each human chromosome than on the E. coli chromosome. C. The human cell and the E. coli cell produce approximately the same variety of proteins. D. The DNA in both organisms is associated with histones (proteins).
Which processes involved in cloning an animal are indicated by the letters X and Y?
(A. differentiated cell removed from animal nucleus removed from unfertilized egg cell ) B. sex cell removed from animal nucleus removed from differentiated animal cell C. sex cell removed from animal nucleus removed from unfertilized egg cell D. differentiated cell removed from animal nucleus removed from differentiated animal cell
Comparison of genome size in T2 phage,Escherichia coli, Drosophila melanogaster, Homo sapiens and Paris japonica
- T2 phage: 0.18 millions of base pairs - Escherichia coli: 5 - Drosophila melanogaster: 140 - Homo sapiens: 3000 - Paris japonica: 150000
Consequences of radiation after nuclear bombing of Hiroshima and accident at Chernobyl.
-Chernoblyn which was a thing released that could cause genetic mutation.
Genes
-Genes are inherited from your parents -23 chromosomes from each parent -23 pairs in the end 3.1.U1 A gene is a heritable factor that consists of a length of DNA and influences a specific characteristic. 3.1.U2 A gene occupies a specific position on a chromosome. 3.1.U3 The various specific forms of a gene are alleles. 3.1.U4 Alleles differ from each other by one or only a few bases. 3.1.U5 New alleles are formed by mutation. [Deletions, insertions and frame shift mutations do not need to be included.] 3.1.U6 The genome is the whole of the genetic information of an organism. 3.1.U7 The entire base sequence of human genes was sequenced in the Human Genome Project
What type of enzyme could be used to cut a DNA molecule as indicated by the dotted line on the diagram below?
. DNA ligase B. DNA polymerase C. Helicase D. (Restriction enzyme)
Which processes result in recombination?
.) Independent assortment of Chromosomes: Chromosomes line up randomly on the metaphase plate. 2.) Crossing Over: Segments of DNA on the chromatids can switch with that of other chromatids, usually when the chromosomes are in tetrads. 3.) Random Fertilization: A random egg matches with a random sperm
Meiosis
1.U1 Chromosomes replicate in interphase before meiosis. 10.1.U2 Crossing over is the exchange of DNA material between non-sister homologous chromatids. 10.1.U3 Crossing over produces new combinations of alleles on the chromosomes of the haploid cells. 10.1.U4 Chiasmata formation between non-sister chromatids can result in an exchange of alleles. 10.1.U5 Homologous chromosomes separate in meiosis I. 10.1.U6 Sister chromatids separate in meiosis II. 10.1.U7 Independent assortment of genes is due to the random orientation of pairs of homologous chromosomes in meiosis I.
More inheritance
10.2.U1 Gene loci are said to be linked if on the same chromosome. 10.2.U2 Unlinked genes segregate independently as a result of meiosis. 10.2.U3 Variation can be discrete or continuous. 10.2.U4 The phenotypes of polygenic characteristics tend to show continuous variation. 10.2.U5 Chi-squared tests are used to determine whether the difference between an observed and expected frequency distribution is statistically significant
Chromosomes
3.2.U1 Prokaryotes have one chromosome consisting of a circular DNA molecule. 3.2.U2 Some prokaryotes also have plasmids but eukaryotes do not. 3.2.U3 Eukaryote chromosomes are linear DNA molecules associated with histone proteins. 3.2.U4 In a eukaryote species there are different chromosomes that carry different genes. 3.2.U5 Homologous chromosomes carry the same sequence of genes but not necessarily the same alleles of those genes. 3.2.U6 Diploid nuclei have pairs of homologous chromosomes. 3.2.U7 Haploid nuclei have one chromosome of each pair. [The two DNA molecules formed by DNA replication prior to cell division are considered to be sister chromatids until the splitting of the centromere at the start of anaphase. After this, they are individual chromosomes.] 3.2.U8 The number of chromosomes is a characteristic feature of members of a species. 3.2.U9 A karyogram shows the chromosomes of an organism in homologous pairs of decreasing length. [The terms karyotype and karyogram have different meanings. Karyotype is a property of a cell—the number and type of chromosomes present in the nucleus, not a photograph or diagram of them.] 3.2.U10 Sex is determined by sex chromosomes and autosomes are chromosomes that do not determine sex
Meiosis
3.3.U1 One diploid nucleus divides by meiosis to produce four haploid nuclei. 3.3.U2 The halving of the chromosome number allows a sexual life cycle with fusion of gametes. 3.3.U3 DNA is replicated before meiosis so that all chromosomes consist of two sister chromatids. 3.3.U4 The early stages of meiosis involve pairing of homologous chromosomes and crossing over followed by condensation. [The process of chiasmata formation need not be explained.] 3.3.U5 Orientation of pairs of homologous chromosomes prior to separation is random. 3.3.U6 Separation of pairs of homologous chromosomes in the first division of meiosis halves the chromosome number. 3.3.U7 Crossing over and random orientation promotes genetic variation. 3.3.U8 Fusion of gametes from different parents promotes genetic variation.
Inheritance
3.4.U1 Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed. 3.4.U2 Gametes are haploid so contain only one allele of each gene. 3.4.U3 The two alleles of each gene separate into different haploid daughter nuclei during meiosis. 3.4.U4 Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles. 3.4.U5 Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects. 3.4.U6 Many genetic diseases in humans are due to recessive alleles of autosomal genes, although some genetic diseases are due to dominant or co-dominant alleles. 3.4.U7 Some genetic diseases are sex-linked. The pattern of inheritance is different with sex-linked genes due to their location on sex chromosomes. [Alleles carried on X chromosomes should be shown as superscript letters on an upper case X, such as Xh.] 3.4.U8 Many genetic diseases have been identified in humans but most are very rare. 3.4.U9 Radiation and mutagenic chemicals increase the mutation rate and can cause genetic diseases and cancer.
Genetic Modification
3.5.U1 Gel electrophoresis is used to separate proteins or fragments of DNA according to size. 3.5.U2 PCR can be used to amplify small amounts of DNA. 3.5.U3 DNA profiling involves comparison of DNA. 3.5.U4 Genetic modification is carried out by gene transfer between species. 3.5.U5 Clones are groups of genetically identical organisms, derived from a single original parent cell. 3.5.U6 Many plant species and some animal species have natural methods of cloning. 3.5.U7 Animals can be cloned at the embryo stage by breaking up the embryo into more than one group of cells. 3.5.U8 Methods have been developed for cloning adult animals using differentiated cells.
The genes described above form a linkage group. Define linkage group.
A linkage group is a group of genes whose loci are on the same chromosome and therefore do not follow the law of independent assortment ◾Linked genes will tend to be inherited together - the only way to separate them is through recombination (via crossing over during synapsis
If an organism that is homozygous recessive for a trait is crossed with a heterozygote, what is the chance of getting a homozygous recessive phenotype in the first generation?
A. 0% B. 25% (C. 50%) D. 100%
A cell with a diploid number of 12 chromosomes undergoes meiosis. What will be the product at the end of meiosis?
A. 2 cells each with 12 chromosomes (B. 4 cells each with 6 chromosomes) C. 2 cells each with 6 chromosomes D. 4 cells each with 12 chromosomes
What is the usual cause of Down's syndrome?
A. 21 pairs of chromosomes (B. Trisomy 21) C. Non-disjunction of sex chromosomes D. Fertilization of the egg by two sperm
A cell in the testis of a male chimpanzee (Pan troglodytes) contains 48 chromosomes. It is about to undergo meiosis. How many molecules of DNA will be present in the nucleus of the sperm cells just after meiosis?
A. 96 B. 48( C. 24) D. 12
Which of the following conclusions did Mendel make from his experiments?
A. Dominant genes are more frequent than recessive genes. B. Genes are composed of DNA. (C. Genes for two different characteristics are inherited separately.) D. Segregation occurs through meiosis.
A small amount of a suspect's DNA is obtained from a crime scene. What techniques would be used to carry out DNA profiling?
A. Gel electrophoresis and paternity testing (B. Paternity testing and the polymerase chain reaction (PCR) )C. Polymerase chain reaction (PCR) and gel electrophoresis D. Test crossing and pedigree analysis
What does a karyogram show?
A. Gel electrophoresis bands from DNA (B. The number and appearance of chromosomes) C. A pair of alleles controlling a specific character D. All the genes possessed by a living organism
Why can DNA profiling be used to determine paternity?
A. Genes of children are exactly the same as their father's. (B. Half the genes of children are the same as their father's.) C. The father passes on all of his genes to each of his children. D. The father passes on a fraction of his genes equal to the number of his children.
What do all human males inherit from their mother? I. An X chromosome II. A Y chromosome III. Mitochondrial DNA
A. I and II only B. II only (C. I and III only) D. I, II and III
What are the fundamental structural units of eukaryotic chromosomes?
A. Nucleosomes B. Centromeres (C. Histones) D. Nucleoids
Male flies, heterozygous for both grey body and normal wings, were mated with black-bodied, vestigial-winged females. 2000 offspring were counted. The resulting percentage of each type of offspring is shown in the table below. Resulting offspring Frequency Grey body, normal wings 40% Black body, vestigial wings 40% Grey body, vestigial wings 10% Black body, normal wings 10%
A. The genes assort independently. B. A mistake has been made. (C. The genes are linked.) D. The genes are on separate chromosomes.
A parent organism of unknown genotype is mated in a test cross. Half of the offspring have the same phenotype as the parent. What can be concluded from this result?
A. The parent of unknown genotype is heterozygous. B. The parent of unknown genotype is homozygous dominant. (C. The parent of unknown genotype is homozygous recessive.) D. The parent of known genotype is heterozygous.
What is the difference between the alleles of a gene?
A. Their position on the chromosome (B. Their amino acid sequence ) C. Their pentose sugars D. Their base sequence
Which process is used in polymerase chain reaction (PCR)?
A. Transcription B. Translation C. (Replication D. Mutation)
Boys can inherit the recessive allele (c) that causes red-green colour blindness from their mother, not from their father. The allele for normal red and green vision is C. Which of the following genotypes are possible in men?
A. c only B. C or c only C. CC or cc only D. CC, Cc or cc only
Morgan's discovery of non-Mendelian ratios in Drosophila.
After breeding millions of Drosophila in his laboratory at Columbia University, in 1910 Morgan noticed one fruit fly with a distinctive characteristic: white eyes instead of red. He isolated this specimen and mated it to an ordinary red-eyed fly. Although the first generation of 1,237 offspring was all red-eyed but for three, white-eyed flies appeared in larger numbers in the second generation. Surprisingly, all white-eyed flies were male.
Explain, using an example, how females but not males can be carriers of some recessive alleles.
Because females have two X genes that only women can carry because the men do not have the two x's
Using a named example, discuss the benefits and harmful effects of genetic modification.
Benefits Harmful Effects Since there is less damage to the maize crops, there is a higher crop yield which can lessen food shortages. We are not sure of the consequences of humans and animals eating the modified crops. The bacterial DNA or the Bt toxin itself could be harmful to human as well as animal health.
46.) What are homologous chromosomes?
C.) Non-identical chromosomes with the same genes in the same sequence but not necessarily the same alleles
48.) What type of inheritance is shown in this pedigree chart?
C.) X-linked recessive
Explain how meiosis results in great genetic variety among gametes.
Crossing over
State the name of the technique that is used to separate fragments of DNA according to their size, during DNA profiling
Gel electrophoresis is a technique which is used to separate fragments of DNA according to size ◾Samples of fragmented DNA are placed in the wells of an agarose gel ◾The gel is placed in a buffering solution and an electrical current is passed across the gel ◾DNA, being negatively charged (due to phosphate), moves to the positive terminus (anode) ◾Smaller fragments are less impeded by the gel matrix and move faster through the gel ◾The fragments are thus separated according to size ◾Size can be calculated (in kilobases) by comparing against a known industry standard
State two general types of enzymes used in gene transfer.
Gene transfer involving plasmids, a host cell (bacterium, yeast or other cell) restriction enzymes (endonucleases) and DNA ligase. It involves all of these reactions. soon!
Homologous Chromosomes
Homologous chromosomes are similiar but not identical. Each carries the same genes in the same order, but the alleles for each trait may not be the same.
Explain how the recombinants are formed during meiosis.
In prophase 1, Recombinants form during Prophase of the first meiotic division when the homologous chromosomes pair up and chromatids cross over, break, and recombine, often to another chromosome of the homologous pair.
Mutations
Non-disjunction can cause Down syndrome and other chromosome abnormalities. 3.3.A2 Studies showing age of parents influences chances of non-disjunction.
Comparison of diploid chromosome numbers of Homo sapiens, Pan troglodytes, Canis familiaris, Oryza sativa, Parascaris equorum
Parascaris-4 diploid number (Horse) oryza- rice 24 homosapiens/humans-46 canis familiaris-dogs (78)
Describe, with the aid of a diagram, the behaviour of chromosomes in the different phases of meiosis.
Prophase I - homologous chromosomes join together to form a tetrad in a process called synapsis. • Metaphase I - homologous pairs line up along the central axis of the cell. • Anaphase I - homologous chromosomes are separated and pulled toward the nearest pole; sister chromatids move together. • Telophase I - the chromosomes have formed two groups; one group at each pole. • At cytokinesis, when the diploid parent cell divides, each daughter cell has only 1 of each kind of chromosome.
Cairns' technique for measuring the length of DNA molecules by autoradiography
Semi-conservative mode of replication of bacterial chromosome was also demonstrated by-J. Cairns •Using the technique of autoradiography Cairns first supplied the cells with suitable radioactive material like tritiated thymidine (H3-TdR) •H3 is heavy isotope of hydrogen and it replaces normal hydrogen in thymidine to give rise to tritiated thymidine). •This used because this will selectively label only DNA and will not label RNA, since the thymine base is absent in RNA. The tritiated thymidine gets incorporated into DNA and replaces ordinary thymidine. •The cellular material is then sectioned or else the cells may be broken down to release the intact bacterial chromosomes on slides. These slides are then covered by photographic emulsion and stored in dark. •During this storage the particles emitted by tritiated thymidine will expose the film, which can be developed. This photograph will then show the regions of the presence of tritium and thus indirectly show the presence of labelled DNA. •The results showed that autoradiographs from this replicating material prepared at regular known intervals demonstrated semi-conservative mode of replication. • In the figure below, one of the two strands in the daughter DNA molecules is derived from the parent molecule and the other is newly synthesized. In θ shaped figure, which is obtained in the second cycle of replication in presence of label, two arcs in the split region would never be equally labelled. For instance, one arc would be twice as heavily labelled as the other arc. This is what was actually observed by Cairns. The observations thus clearly supported the semi-conservative nature of replication.
Production of cloned embryos produced by somatic-cell nuclear transfer
Somatic cell nuclear transfer (SCNT), also called nuclear transfer, uses a different approach than artificial embryo twinning, but it produces the same result: an exact genetic copy, or clone, of an individual. This was the method used to create Dolly the Sheep. What does SCNT mean? Let's take it apart: Somatic cell: A somatic cell is any cell in the body other than sperm and egg, the two types of reproductive cells. Reproductive cells are also called germ cells. In mammals, every somatic cell has two complete sets of chromosomes, whereas the germ cells have only one complete set. Nuclear: The nucleus is a compartment that holds the cell's DNA. The DNA is divided into packages called chromosomes, and it contains all the information needed to form an organism. It's small differences in our DNA that make each of us unique. Transfer: Moving an object from one place to another. To make Dolly, researchers isolated a somatic cell from an adult female sheep. Next they removed the nucleus and all of its DNA from an egg cell. Then they transferred the nucleus from the somatic cell to the egg cell. After a couple of chemical tweaks, the egg cell, with its new nucleus, was behaving just like a freshly fertilized egg. It developed into an embryo, which was implanted into a surrogate mother and carried to term. (The transfer step is most often done using an electrical current to fuse the membranes of the egg and the somatic cell.) The lamb, Dolly, was an exact genetic replica of the adult female sheep that donated the somatic cell. She was the first-ever mammal to be cloned from an adult somatic cell.
Define the term polygenic inheritance.
The determination of a particular characteristic, e.g. height or skin colour, by many genes (polygenes), each having a small effect individually. Characteristics controlled in this way show continuous variation.
Genes in humans with other creaters
There are certain animsals that share human DNA sequences -Apes -Monkey's
Inheritance of cystic fibrosis and Huntington's disease.
They are both genetic conditions Cystic fibrosis is recessive but Huntington's is dominant Cystic fibrosis causes symptoms starting in childhood or even as a baby but Huntington's doesn't normally show until adulthood. Both are often lethal; until recently cystic fibrosis was lethal in adolescence but new treatments are greatly extending lifespan, because Huntington's comes on in adulthood some people die of other causes even though showing symptoms. Cystic fibrosis is a physical illness while many patients with Huntington's have mental deterioration including mood and personality changes. Both conditions can now be diagnosed by genetic testing.
Use of DNA profiling in paternity and forensic investigations.
They can now tell who did the crime by testing there DNA some times of the child.
Explain the consequences of a base substitution mutation in relation to the processes of transcription and translation.
This means that when the mutated gene is transcribed, a codon in the messenger RNA will be different. Instead of the normal codon GAG, the messenger RNA will contain the codon GUG. This in turn will result in a mistake during translation. In a healthy individual the codon GAG on the messenger RNA matches with the anticodon CUC on the transfer RNA carrying the amino acid glutamic acid. However, if the mutated gene is present then GUG on the messenger RNA matches with the anticodon CAC on the transfer RNA which carries the amino acid valine. So the base substitution mutation has caused glutamic acid to be replaced by valine on the sixth position on the polypeptide. This results in haemoglobin S being present in red blood cells instead of the normal haemoglobin A. This has an effect on the phenotype as instead of normal donut shaped red blood cells being produced some of the red blood cells will be sickle shaped. As a result these sickle shaped red blood cells cannot carry oxygen as efficiently as normal red blood cells would. However, there is an advantage to sickle cell anemia. The sickle cell red blood cells give resistance to malaria and so the allele Hbs on the Hb gene which causes sickle cell anemia is quite common in parts of the world where malaria is found as it provides an advantage over the disease
Outline the differences between the behaviour of the chromosomes in mitosis and meiosis.
Two divisions in meiosis, only one in mitosis. - Meiosis results in haploid cells, mitosis in diploid cells. - Crossing over only occurs in Meiosis. - No S phase precedes meiosis 2. - Chromosome behavior in meiosis 1 and mitosis is different. - Chiasmata only form during meiosis. - Homologous chromosomes move to the equator in pairs only in meiosis.
Red-green colour blindness and hemophilia as examples of sex-linked inheritance.
X-linked inheritance means that the gene causing the trait or the disorder is located on the X chromosome. Females have two X chromosomes; males have one X and one Y. Genes on the X chromosome can be recessive or dominant. Their expression in females and males is not the same. Genes on the Y chromosome do not exactly pair up with the genes on the X chromosome. X-linked recessive genes are expressed in females only if there are two copies of the gene (one on each X chromosome). However, for males, there needs to be only one copy of an X-linked recessive gene in order for the trait or disorder to be expressed. For example, a woman can carry a recessive gene on one of the X chromosomes unknowingly, and pass it on to a son, who will express the trait:
Cause of SIckle Cell
is a disorder of the blood caused by an inherited abnormal hemoglobin (the oxygen-carrying protein within the red blood cells). The abnormal hemoglobin causes distorted (sickled) red blood cells
Karyotype
is the number and appearance of chromosomes in the nucleus of a eukaryotic cell. The term is also used for the complete set of chromosomes in a species, or an individual organism.
