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Genetics: 2
A deck of flashcards for Undergraduate Study of Biology.
| Question | Answer |
|---|---|
| Mendel’s hereditary factors | Genes. How inherited traits are passed between generations comes from principles first proposed by Gregor Mendel in 1866. Mendel's principles apply to traits in plants and animals – they can explain how we inherit certain traits. |
| How do organisms inherit certain traits? | Genes for different traits can segregate independently during the formation of gametes. Some alleles are dominant while others are recessive; an organism with at least one dominant allele will display the effect of the dominant allele. |
| Chromosome theory of inheritance | Also known as the Boveri–Sutton chromosome theory, is states chromosomes as the carriers of genetic material. It correctly explains the mechanism of the laws of Mendelian inheritance. |
| What are Chromosomes according to the Boveri-Sutton chromosome theory? | It also states that chromosomes are linear structures with genes located at specific sites called loci along them. |
| Mendel's laws of inheritance | Law of segregation, Law of independent assortment and Law of dominance. |
| Law of Segregation | The first Mendelian law that states allele pairs separate or segregate during gamete formation, and randomly unite at fertilization. |
| Law of Independent Assortment | The second Mendelian law stating that when two or more characteristics are inherited, individual hereditary factors assort independently during gamete production, giving different traits an equal opportunity of occurring together. |
| Why fruit flies are a convenient organism for genetic studies? | They breed at a high rate where a generation can be bred every two weeks. They have only four pairs of chromosomes and share 75% of the genes that cause disease with humans, so scientists can learn about human genetics by studying fruit fly genetics. |
| Mutant phenotypes | The allele that encodes the phenotype most common in a particular natural population is known as the wild type allele. Any form of that allele other than the wild type is known as a mutant form of that allele. |
| Inheritance of Sex-Linked Genes | Genes that are carried by either sex chromosome are said to be sex linked. Men normally have an X and a Y combination of sex chromosomes, while women have two X's. Since only men inherit Y chromosomes, they are the only ones to inherit Y-linked traits. |
| How may a recessive sex-linked trait be expressed? | A female needs two copies of the allele while a male needs only one copy of the allele. |
| Why are sex-linked recessive disorders are much more common in males? Give examples of such disorders. | A male needs only one copy of the sex-linked recessive allele. Example of disorders are color blindness, Duchenne muscular dystrophy and Hemophilia. |
| Barr body | A Barr body (named after discoverer Murray Barr) is the inactive X chromosome in a female somatic cell, rendered inactive in a process called lyonization. |
| Non-sex linked genes | Genes located on the same chromosome that tend to be inherited together are called linked genes |
| Parental types | Offspring with a phenotype matching one of the parental phenotypes. |
| Recombinant types | Offspring with non-parental phenotypes (new combinations of traits). |
| Origin of Replication | A particular sequence in a genome at which replication is initiated. |
| Helicase | An enzyme that unwinds the double helix of DNA at the replication forks. |
| Single-strand binding protein | A protein that binds and stabilizes single stranded DNA until it can be used as a template. |
| Topoisomerase | An enzyme which corrects the overwinding strain ahead of replication forks by breaking, swiveling and rejoining DNA strands. |
| DNA polymerase III | An enzyme that adds nucleotides to the 3' end of the copied DNA with an initial nucleotide strand made of a short RNA primer. They do NOT initiate synthesis of a polynucleotide. |
| Primase | An enzyme that synthesizes short RNA sequences called primers. These primers serve as a starting point for DNA synthesis. Since primase produces RNA molecules, the enzyme is a type of RNA polymerase. |
| dNTP | A nucleotide added to a growing DNA strand called nucleoside triphosphate which has deoxyribose as its sugar. |
| dATP | Deoxyadenosine triphosphate; Nucleotide that supplies adenine to DNA |
| dGTP | Deoxyguanosine triphosphate; Nucleotide that supplies guanine to DNA. |
| dCTP | Deoxycytidine triphosphate; Nucleotide that supplies cytosine to DNA. |
| dTTP | Nucleoside triphosphate; Nucleotide that supplies thymine to DNA. |
| What happens as each monomer of dNTP joins the DNA strand? | Each monomer will lose two phosphate groups as a molecule of pyrophosphate (the two phosphate groups). |
| Leading strand | Due to primase only able to work in the 5' to 3' direction, the leading strand is continuously replicated, moving towards the replication fork. |
| Lagging strand | The other new strand which requires the DNA polymerase to work in the direction away from the replication fork. |
| Okazaki fragments | A series of segments which synthesizes the lagging strand by DNA ligase. |
| DNA polymerase I | An enzyme which is responsible in removing the RNA nucleotides of primer from 5' end and replaces them with DNA nucleotides at the lagging strand. |
| DNA ligase | Joins 3' end of DNA that replaces primer to rest of leading strand to rest of leading strand an joins Okazaki fragments of lagging strand. |
| Nucleotide excision repair | Nucleotide excision repair (NER) is a particularly important excision mechanism that removes DNA damage induced by ultraviolet light (UV). A nuclease removes and replaces damaged stretches of DNA. |
| Telomeres | The end nucleotide sequences of DNA molecules which postpones the erosion of genes near the ends of DNA molecules. Suggestions that the shortening of telomeres is connected to aging |
| Telomerase | The enzyme in a eukaryote that repairs the telomeres of the chromosomes so that they do not become progressively shorter during successive rounds of chromosome replication. |
| Is there a possible relationship between telomerase activity and cancer? | Yes, the shortening of telomeres might protect cells from cancerous growth by limiting the number of cell division. Evidence shows that increased activities may allow cancer cells to persist. |
| Nucleoid | An irregularly shaped region within the cell of a prokaryote that contains all or most of the genetic material, called genophore. In contrast to the nucleus of a eukaryotic cell, it is not surrounded by a nuclear membrane. |
| Chromatin | A complex of DNA and proteins that forms chromosomes within the nucleus of eukaryotic cells. |
| Histones | A highly alkaline protein found in eukaryotic cell nuclei that package and order the DNA into structural units in chromatin. |
| 10 nm chromatin fiber | Nucleosome "beads" strung together. |
| 30 nm chromatin fiber | Interactions between nucleosomes which cause the thin fiber to coil or fold into this thicker fiber. |
| 300 nm chromatin fiber | The 30 nm fibers forms loops called looped domains that attach to a choromosome scaffold made of proteins. |
| 700 nm chromatin fiber | The width of a chromatid in a chromosome. |
| Nucleosomes | A structural unit of a eukaryotic chromosome, consisting of a length of DNA coiled around a core of histones. |
| Euchromatin | A lightly/loosely packed form of chromatin that is enriched in genes, and is often (but not always) under active transcription. |
| Heterochromatin | Chromosome material of different density from normal (usually greater), in which the activity of the genes is modified or suppressed. During interphase often of regions with chromatin (centromeres and telomeres) that are highly condensed. |
| Transformation | The process by which foreign DNA is introduced into a cell. change in genotype and phenotype due to assimilation of foreign DNA. |
| Non-disjunction (Abnormal Chromosome Number) | Where pairs of homologous chromosomes do not separate normally during meiosis. |
| Aneuploidy | The results from fertilization of gametes in which non-disjunction occurred. Offspring with this condition have an abnormal number of a particular chromosome. |
| Monosomic zygote | A zygote with only one copy of a particular chromosome (2n-1) |
| Trisomic zygote | A zygote with three copies of a particular chromosome (2n + 1) |
| Polyploidy | A condition where an organism has more than two complete sets of choromosomes, either in Triploidy (3n) and Tetraploidy (4n). |
| Triploidy (3n) | Where an organism has three sets of chromosomes. |
| Tetraploidy (4n) | Where an organism has four sets of chromosomes. |
| What types of changes may occur when there are alterations of chromosome structure? | Deletion, Duplication, Inversion and Translocation. |
| Deletion | Removal of a chromosomal segment. |
| Duplication | Repeats a chromosomal segment. |
| Inversion | Reverses a segment within a chromosomes. |
| Translocation | Moves a segment from one chromosome to another. |
| Down syndrome | An aneuploid condition that results from three copies of chromosome 21. |
| Klinefelter syndrome | The result of an extra chromosome in a male producing XXY individuals. |
| Turner syndrome | Monosomy of X, produces X0 females who are sterile. |
| Cri du chat syndrome | "Cry of the cat", results from a specific deletion of chromosome 5, where a child born of this syndrome i mentally retarded and has a catlike cry; individuals usually die in infancy or early childhood. |
| Chronic myleogenous leukemia (CML) | A type of cancer that are caused by translocation of chromosomes. |
| What are the two normal exceptions to Mendelian genetics? | Imprinted genes and extranuclear genes. |
| Imprinted genes | Genes located in the nucleus. |
| Extranuclear genes | Genes located out of the nucleus. |
| Genomic imprinting | Where the variation of phenotype depends on which parent passed along the alleles for those traits. It is also resulted from the addition of CH3 (methylaton) of DNA. |
| DNA | Deoxyribonucleic acid, the substance of inheritance. |
| James Watson and Francis Crick (1953) | Introduced an elegant double helical model. |
| Watson-Crick model | Suggests Purine + Pyrimidine= width consistent with X-ray data. They determined that A paired with only T and G paired with only C. |
| Watson and Crick's semi-conservative model | A model of replication predicts that when a double helix replicates, each daughter molecule will have one old strand and one newly made strand. |
| Conservative model | Both strands of DNA are completely replicated. |
| Semiconservative model | Only one strand of DNA is replicated. |
| Dispersive model | Only partials segments of a DNA strand is replicated. |
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