Genetics and Evolution
Genetics and Evolution:
Inheritance of acquired characteristics: States that characteristics developed during an organism’s life can be passed to offspring which is wrong.
Artificial selection: Selecting which animals were allowed to reproduce to change its traits.
Darwin’s theory of evolution by natural selection states that living things with beneficial traits produce more offspring than others do. This produces changes in the traits of living things over time.
During his voyage on the Beagle, Darwin made many observations that helped him develop his theory of evolution. His most important observations were made on the Galápagos Islands.
Darwin was influenced by other early thinkers, including Lamarck, Lyell, and Malthus. He was also influenced by his knowledge of artificial selection.
Wallace’s paper on evolution confirmed Darwin’s ideas. It also pushed him to publish his book, On the Origin of Species. The book clearly spells out his theory. It also provides evidence and logic to support it.
Paleontologist: Scientists who find and study fossils.
Comparative anatomy: The study of similarities and differences in the structures of different species.
Homologous structures: Structures similar in related organisms, inherited from a common ancestor.
Analogous structures: Similar structures in unrelated species.
Comparative embryology: The study of similarities and differences in the embryos of different species.
Vestigial Structures:It is a tiny remnant of a once larger organ. Evolution reduced its size because it became useless.
Biogeography: Is the study of how and why plants and animals live where they do. It also provides evidence for evolution. On island chains, such as the Galápagos, one species may evolve into many new species to fill available niches. This is called adaptive radiation.
Adaptive radiation: The process by which a single species evolves into many new species to fill available niches.
Fossils provide a window into the past. They are evidence for evolution. Scientists who find and study fossils are called paleontologists.
Scientists compare the anatomy, embryos, and DNA of living things to understand how they evolved. Evidence for evolution is provided by homologous structures. These are structures shared by related organisms that were inherited from a common ancestor. Other evidence is provided by analogous structures. These are structures that unrelated organisms share because they evolved to do the same job.
Microevolution: Occurs over a relatively short period of time within a population of species.
Macroevolution: Occurs over a geological time above the level of species.
Population genetics: Science that focuses on evolution within population.
Gene pool: Consists of all the genes of all the members of the population.
Allele frequency: How often an allele occurs in a gene pool relative to the other alleles for that gene.
The population in the table has 100 members. In a sexually reproducing species, each member of the population has two copies of each gene. Therefore, the total number of copies of each gene in the gene pool is 200. The gene in the example exists in the gene pool in two forms, alleles A and a. Knowing the genotypes of each population member, we can count the number of alleles of each type in the gene pool. The table shows how this is done.
Genotype | Number of Individuals in the Population with that Genotype | Number of Allele A Con- tributed to the Gene Pool by that Genotype | Number of Allele a Con- tributed to the Gene Pool by that Genotype |
AA | 50 | 50 x 2 = 100 | 50 x 0 = 0 |
Aa | 40 | 40 x 1 = 40 | 40 x 1 = 40 |
aa | 10 | 10 x 0 = 0 | 10 x 2 = 20 |
Total | 100 | 140 | 60 |
Let the letter p stand for the frequency of allele A. Let the letter q stand for the frequency of allele a. We can calculate p and q as follows:
• p = number of A alleles/total number of alleles = 140/200 = 0.7
• q = number of alleles/total number of alleles = 60/200 = 0.3
• Notice that p + q = 1.
Hardy-Weinberg equilibrium: Allele frequencies do not change if certain conditions are met:
-No new mutations. -No migration.-Mating is random.-No natural selection.
Genotype | Genotype Frequency |
AA | p² |
Aa | 2pq |
aa | q² |
Hardy and Weinberg used mathematics to describe an equilibrium population (p = frequency of A, q = frequency of a
a): p² + 2pq + q² = 1. In Table 10.2, if p = 0.4, what is the frequency of the AA genotype?
Mutation: Creates new genetic variation in a gene pool.
Gene flow: Occurs when individuals move in or out of a population.
Genetic drift: Random change in allele frequencies that occurs in a small population.
Stabilizing selection occurs when phenotypes at both extremes of the phenotypic distribution are selected against. This narrows the range of variation. An example is human birth weight. Babies that are very large or very small at birth are less likely to survive. This keeps birth weight within a relatively narrow range.
Directional selection occurs when one of two extreme phenotypes is selected for. This shifts the distribution toward that extreme. This is the type of natural selection that the Grants observed in the beak size of Galápagos finches.
Disruptive selection occurs when phenotypes in the middle of the range are selected against. This results in two overlapping phenotypes, one at each end of the distribution. An example is sexual dimorphism. This refers to differences between the phenotypes of males and females of the same species. In humans, for example, males and females have different heights and body shapes.
Speciation: The process by which a new species evolves.
Allopatric speciation: Members of a species get separated geographically and evolves into a different species that prevent them from interbreeding for the original species.
Sympatric speciation: A new factor is introduced into a population and members of the species change their lifestyle to use it and start to adapt and evolve towards it and rarely interbreed with the original species thus becoming unable to do so thus becoming a new species.
Evolution: Occurs response to a change in the environment.
Gradualism: A type of model of the timing of evolution when geologic and climate conditions are stable, and evolution may occur gradually.
Punctuated equilibrium: When geologic and climatic conditions are changing, evolution may occur quicker. Thus, long periods of little change may be interrupted by bursts of rapid change.
Genetic Disorders:
Genetic disorders: Caused by mutations in one or a few genes or by having an abnormal number of chromosomes.
Genetic disorders caused by mutations:
Genetic Disorder | Direct Effect of Mutation | Signs and Symptoms of the Disorder | Mode of Inheritance |
Marfan syndrome | defective protein in connective tissue | heart and bone defects and unusually long, slender limbs and fingers | autosomal dominant |
Sickle cell anemia | sickle-shaped red bloodcells that clog tiny blood vessels, causing pain and damaging organs and joints | autosomal recessive | |
Vitamin D-resistant rickets | soft bones that easily become deformed, leading to bowed legs and other skeletal deformities | X-linked dominant | |
Hemophilia A | internal and external bleeding that occurs easily and is difficult to control | X-linked recessive |
Genetic disorders caused by having an abnormal number of chromosomes:.
Genetic Disorder | Genotype | Phenotypic Effects |
Down syndrome | extra copy (complete or partial) of chromosome 21 (see Figurebelow) | developmental delays, distinctive facial appearance, and other abnormalities (see Figurebelow) |
Turner’s syndrome | one X chromosome but no other sex chromosome (XO) | female with short height and infertility (inability to reproduce) |
Triple X syndrome | three X chromosomes (XXX) | female with mild developmental delays and menstrual irregularities |
Klinefelter’s syndrome | one Y chromosome and two or more X chromosomes (XXY, XXXY) | male with problems in sexual development and reduced levels of the male hormone testosterone |
Nondisjunction: The results of mistakes that may happen during meiosis. It si is the failure of replicated chromosomes to separate during meiosis.
Genetic counselors: Professionals that can help to understand the risk of the child being affected.
Prenatal: A test to see if the fetus has any genetic disorder.
Amniocentesis: Fetal cells are extracted from the fluid surrounding the fetus, and the fetal chromosomes are examined.
Gene therapy: inserting normal genes into cells with mutant genes.
Most chromosomal disorders involve the X chromosome. The X and Y chromosomes are very different in size, so nondisjunction of the sex chromosomes occurs relatively often. The x chromosome is bigger.
Biotechnology:
Biotechnology: Is the use of technology to change the genetic makeup of living things for human purposes.
Gene cloning: The process of isolating and making copies of a gene.
In isolation, an enzyme (called a restriction enzyme) is used to break DNA at a specific base sequence. This is done to isolate a gene.
During ligation, the enzymeDNA ligase combines the isolated gene with plasmid DNA from bacteria. (A plasmid is circular DNA that is not part of a chromosome and can replicate independently.) The DNA that results is called recombinant DNA.
In transformation, the recombinant DNA is inserted into a living cell, usually a bacterial cell. Changing an organism in this way is also called genetic engineering.
Selection involves growing transformed bacteria to make sure they have the recombinant DNA. This is a necessary step because transformation is not always successful. Only bacteria that contain the recombinant DNA are selected for further use.
Recombinant DNA: The DNA that results from combining isolated gene and plasmid DNA from bacteria by the enzyme DNA ligase.
Genetic engineering: Inserting the recombinant DNA into a living cell, usually a bacteria cell.
Polymerase chain reaction: Makes many copies of a gene or other DNA segmentThis might be done in order to make large quantities of a gene for genetic testing.
Denaturing involves heating DNA to break the bonds holding together the two DNA strands. This yields two single strands of DNA.
Annealing involves cooling the single strands of DNA and mixing them with short DNA segments called primers. Primers have base sequences that are complementary to segments of the single DNA strands. As a result, bonds form between the DNA strands and primers.
Extension occurs when an enzyme (Taq polymerase or Taq DNA polymerase) adds nucleotides to the primers. This produces new DNA molecules, each incorporating one of the original DNA strands.
Biotechnology can be used to transform bacteria so they are able to make human proteins, such as insulin.
It can also be used to create transgenic crops, such as crops that yield more food or resist insect pests.
Transgenic crops: Genetically modified crops with genes that code for traits useful to humans.
