Populations Flashcards
3 to 1 ratio
AKA Mendelian ratio. Expressed in the F2 generation. 3 dominant to 1 recessive-displaying offspring.
Gene vs. allele
A gene is a stretch of DNA that can mutate into variations (eg, eye color). An allele is the variation (eg, blue eyes).
Phenotype
Expression of a trait. The phenotype is expressed through the action of enzymes and other structural proteins (which are encoded by genes).
Genotype
Individual’s genetic makeup
Complete dominance
Exhibited by the flowers in Mendel’s experiment. For any one trait, a diploid individual will have 2 chromosomes each containing a separate gene that codes for that specific trait.
These 2 chromosomes are homologous by definition.
Their corresponding genes are located at the same locus or position on respective chromosomes.
Each gene contributes an allele to the genotype. However- only one allele (the dominant allele)- is expressed.
If both alleles are dominant, then the dominant phenotype is expressed. If both alleles are recessive, then the recessive phenotype is expressed.
Heterozygous
AKA hybrid. An individual with a genotype having one dominant and one recessive allele is said to be heterozygous for the trait.
Law of Segregation
Mendel’s first law of heredity. Alleles segregate independently of each other when forming gametes. Any gamete is equally likely to possess any allele.
The phenotypic expression of the alleles is not a blend of the two, but an expression of the dominant allele (the principle of complete dominance).
Incomplete dominance
AKA partial dominance.
When a heterozygous individual exhibits a phenotype that is intermediate between its homozygous counterparts, the alleles are referred to as partial (incomplete) dominants.
Alleles showing partial dominance are represented with the same capital letter, and distinguished with a prime or superscript.
For instance, a cross between red flowered sweet peas and white flowered sweet peas may produce pink flowers. The genotype for the pink flowered individual would be expressed as either CC’ or CrCw.
Punnett square
For predicting genotypic ratios of offspring. Each offspring genotype is also equally likely.
Law of Independent Assortment
Mendel’s second law of heredity. States that genes located on different chromosomes assort independently of each other. In other words, genes that code for different traits (such as pea shape or pea color), when located on different chromosomes, do not affect each other during gamete formation. The closer they are on the chromosome, the more likely they will remain together.
Dihybrid cross
Make the assumption that genes for different traits are on separate chromosomes, and will assort independent of each other. The phenotypic ratio of a dihybrid cross is 9: 3: 3: 1.
Codominance
If the heterozygote exhibits both phenotypes, the alleles are codominant. Human blood type alleles are codominant because a heterozygote exhibits A and B antigens on the blood cell membrane.
Sex chromosomes
In humans, the 23rd pair of chromosomes establishes the sex of the individual, and each partner is called a sex-chromosome. Males are XY, females are XX.
Karyotype
Map of the chromosomes
Sex-linked
When a gene is found on the sex chromosome it is called sex linked.
Generally, in humans, the Y allele does not carry the allele for the sex-linked trait; thus the allele that is carried by the X chromosome in the male is expressed whether it is dominant or recessive. The female- who has 2 X chromosomes- ‘s genotype is found through the normal rules.
Barr body
In most somatic cells, one of the X chromosomes of the female will condense, and most of it’s genes will become inactive. The tiny dark object form is called the Barr body. These are formed at random, so the active allele is split about evenly among the cells. Nevertheless, in most cases, the recessive phenotype is only displayed in homozygous recessive individuals.
Carrier
A female may carry a recessive trait on her 23rd pair of chromosomes without expressing it. Such a recessive trait has a strong chance of being expressed in her male offspring regardless of the genotype of her mate, because the Y chromosome doesn’t contribute. See the Punnett square for hemophilia for more clarification.
Gene pool
The total of all the alleles in a population. Even if the ratio of individuals temporarily changes, as long as the gene pool remains the same breakdown, the population has not evolved.
Evolution
A change in the gene pool
Classification system for animals
Kingdom, phylum, class, order, family, genus, species. Note that plants and fungi use divisions instead of phyla.
Since organisms within the same group have similar genetic structures, they probably share similar phylogenies, or evolutionary histories.
Domains
Be aware of the new super kingdoms called domains. There are three domains: Bacteria, Archaea, and Eukarya, this basically puts the kingdoms of Protista, Fungi, Plantae, and Animalia into the domain Eukarya. It makes the kingdom Monera obsolete dividing into the domains of Bacteria and Archaea. The two domains of Bacteria and Archaea are divided into several kingdoms each. Archaea is more closely related to Eukarya then it is Bacteria.
Naming an organism
The genus and species name are given an order. Typically, they are both written in italics, and the genus is capitalized while the species is not.
Ontogeny recapitulates phylogeny
The course of development of an organism from embryo to adult reflects its evolutionary history. For instance, the human fetus has pharyngeal pouches reflecting a gilled ancestor.
Species
All organisms that can reproduce fertile offspring with each other. If two organisms can reproduce fertile offspring, they might be the same species. If their gametes are incompatible, they are definitely not the same species.
Organisms of different species may be prevented by reproducing by such things as: geographic isolation, habitat isolation, seasonal isolation, mechanical isolation, gametic isolation, developmental isolation, hybrid inviability, hybrid sterility, selective hybrid elimination, and behavior isolation.
Niche
In order to survive, the members of the same species will exploit their environment in a unique manner not shared by any other species. The way in which a species exploits its environment is called it’s niche. No two species can occupy the same niche indefinitely.
Survival of the fittest
Predicts that one species will exploit the environment more efficiently, eventually leading to the extinction of the other with the same niche. The definition of the fittest organisms in this theory is the organism which can best survive to reproduce offspring which will, in turn, we produce offspring and so on generation after generation. This definition may include living beyond reproduction in order to provide a better chance for offspring to reproduce.
Two opposing reproduction strategy
R selection and K selection.
R-strategists
Involves producing large numbers of offspring that mature rapidly with little or no parental care. Generally have a high mortality rate. Their population growth curves are exponential. Generally found in unpredictable, rapidly changing environments affected by density independent factors such as floods or drastic temperature change.
K-strategists
The other side of the spectrum, which involves small brood size with slow maturing offspring and strong parental care. Sigmoidal growth curve which levels off at the carrying capacity. The carrying capacity is the maximum number of organisms that environment can maintain. Carrying capacity is a density dependent factor.
Speciation
The process by which new species are formed. When gene flow ceases between two sections of the population, speciation begins. Factors which bring about speciation include geographic, seasonal, and behavior isolation.
Adaptive radiation
Occurs when several separate species arise from a single ancestral species, such as the 14 species of Galapagos finches that all evolved from one ancestor.
Evolutionary bottleneck
A species may face a crisis so severe as to cause a shift in the allelic frequencies of the survivors of the crisis.
Divergent evolution
Exists when two or more species evolving from the same group maintain a similar structure from the common ancestor, called a homologous structure. An example is the eye.
Convergent evolution
Two species may independently evolve similar structures. Such similar structures are said to be analogous or homoplastic. An example is the wings evolved by bats and birds, the two do not share a common ancestor from which they received their wings.
Polymorphism
Some phenotypic forms vary gradually within a species, such as height. Other forms are distinct, like flower color, either red or white, or chicken plumage. The occurrence of distinct forms is called polymorphism.
Symbiosis
A relationship between two species, which can be beneficial for both, called mutualism, beneficial for one and not the other, called commensalism, or beneficial for one and detrimental to the other, called parasitism.
Assumptions of Hardy-Weinberg equilibrium
- Large population
- No mutation
- No immigration or emigration
- Random mating
- No natural selection
If any of these things are occurring, they must not change the gene pool.
Genetic drift
Small populations are subject to genetic drift, where one allele may be permanently lost due to the death of all members having that allele. Genetic drift is not caused by selective pressure, so it’s results are random in evolutionary terms.
Binomial theorem
p squared plus two p q plus q squared
Predicts the genotype frequency of a gene with only two alleles in a population in Hardy-Weinberg equilibrium. If there are only two alleles, p + q = 1, where p is the dominant allele and q is the recessive allele.
Urey- Miller experiment
An experiment attempting to re-create the atmosphere of early Earth, which resulted in the auto synthesis of molecules such as urea, amino acids, and even adenine. Early Earth probably had an atmosphere made mainly from nitrogen and hydrogen gas, and very little oxygen.
Coacervates
The first cells are thought to have evolved from these lipid or protein bilayer bubbles. They spontaneously form and grow from fat molecules suspended in water.
The oldest fossils
Are 3.6 billion years old
Photosynthetic bacteria
Around two .3 billion years ago, the ancestors of cyanobacteria involved. They were able to sunlight and water to reduce carbon dioxide. These are the first oxygen producing, photosynthetic bacteria. The atmosphere began to fill with oxygen. Eukaryotes did not evolve until about 1.5 billion years ago, did not develop into multicellular organisms until several million years later.
Chordata
The phylum containing humans. All chordates have bilateral symmetry. They are deuterostomes. They have a coelom.
At some stage of their development, they possess a notochord, pharyngeal slits, a dorsal, hollow nerve cord, and detail.
Vertebrata
Members from this subphylum have their notochord replaced by a segmented cartilage or bone structure. They have a distinct brain enclosed in a skull. Most chordates are vertebrates.
Jawless fish arose first and separately from the rest about 470 million years ago. Amphibians arose from bony fish. Reptiles arose from amphibians about 300 million years ago. Birds and mammals arose from reptiles. Mammals arose from reptiles about 220 million years ago.
Deuterostomes
When your anus develops from or near the blastopore, like members of the phylum Chordata. Compare to protostomes, where the mouth develops from or near the blastopore.
Coelom
A body cavity within mesodermal tissue
Notochord
An embryonic axial support, not the backbone.
Taxonomy of humans
Animalia, Chordata, mammalian, primata, homididae, Homo sapiens.
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