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Genetics: 1
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). |
| Inheritance of characters by a single gene may deviate from simple Mendelian patterns in what situations? | When alleles are not completely dominant or recessive, when a gene has more than two alleles and when a gene produces multiple phenotypes. |
| Degrees of Dominance | Complete dominance, incomplete dominance and in co-dominance, two dominant alleles affect the phenotype in separate, distinguishable ways. |
| Complete dominance | When phenotypes of the heterozygote and dominant homozygote are identical. |
| Incomplete dominance | When the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties. |
| Co-dominance | When two dominant alleles affect the phenotype in separate, distinguishable ways. |
| Pleiotropy | Where most genes have multiple phenotypic effects. |
| Examples of the multiple symptoms of hereditary diseases caused by pleiotropic alleles. | Cystic fibrosis and sickle-cell disease. |
| Cystic fibrosis | A hereditary disorder affecting the exocrine glands. It causes the production of abnormally thick mucus, leading to the blockage of the pancreatic ducts, intestines, and bronchi and often resulting in respiratory infection. |
| Sickle-cell disease | A severe hereditary form of anaemia in which a mutated form of haemoglobin distorts the red blood cells into a crescent shape at low oxygen levels. It is commonest among those of African descent. |
| Epistasis | The phenomenon of the effect of one gene being dependent on the presence of one or more 'modifier genes', the genetic background. Thus, epistatic mutations have different effects in combination than individually. |
| Polygenic inheritance | Occurs when one characteristic is controlled by two or more genes. Often the genes are large in quantity but small in effect. Usually indicated in quantitative variation. |
| Quantitative variation | Characters that vary in the population along a continuum. Example is a bell-curve of a population's skin color or height. |
| Another exception from Mendelian genetics? | Phenotypes that arise from external/environmental factors. |
| Pedigree | A family tree that describes the interrelationships of parents and children across generations. |
| Carriers of recessive genetic disorders | Heterozygous individuals who carry the recessive allele but are phenotypically normal. |
| Consanguineous matings | Increase the chance of mating between two carriers of the same rare allele. |
| Achondroplasia | A form of dwarfism caused by a rare dominant allele |
| Huntington’s disease | A progressive brain disorder that causes uncontrolled movements, emotional problems, and loss of thinking ability (cognition). Adult-onset Huntington disease, the most common form of this disorder, usually appears in a person's thirties or forties. |
| The “blending” hypothesis | The idea that genetic material from the two parents blends together (like blue and yellow paint blend to make green) |
| The “particulate” hypothesis | The idea that parents pass on discrete heritable units (genes). |
| Hybridization | Mating two contrasting true-breeding varieties to produce an offspring. |
| P generation | Parent generation |
| F1 generation | Hybrid offspring of P generation |
| F2 generation | Hybrid offspring of F1 generation |
| Alleles | Each of two or more alternative forms of a gene that arise by mutation and are found at the same place on a chromosome. |
| Monohybrid cross | Individuals that are heterozygous for one character. |
| Dihybrid cross | Individuals with different varietiesthat differ in two observed traits. |
| Genetics | The scientific study of heredity and variation. |
| Heredity | The transmission of traits from one generation to the next. |
| Variation | The differences in appearance that offspring show from parents. |
| Genes | The units of heredity, and are made up of segments of DNA. Each gene has a specific location called a locus on a certain chromosome. |
| Gametes | Genes are passed to the next generation through reproductive cells. |
| Asexual reproduction | One parent produces genetically identical offspring. |
| Clone | A group of genetically identical individuals from the same parent |
| Sexual reproduction | Two parents give rise to offspring that have unique combinations of genes inherited from the two parents |
| Somatic cells | Any cell other than a gamete. |
| Karyotype | An ordered display of the pairs of chromosomes from a cell |
| Homologous chromosomes | Two chromosomes in each pair |
| Sex chromosomes | X and Y chromosomes |
| Autosomes | Pairs of chromosomes that do not determine sex. There are 22 autosomes in human, |
| Diploid cell (2n) | Two sets of chromosomes. For humans, the diploid number is 46 (2n = 46) |
| Haploid (n) | A gamete (sperm or egg) contains a single set of chromosomes. For humans, the haploid number is 23 (n = 23) |
| Fertilization | The union of gametes (the sperm and the egg) |
| Zygote | The fertilized egg which has one set of chromosomes from each parent |
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