BIO 101 Lecture Notes: Ecology and Biology - PDF

VERITAS UNIVERSITY, ABUJA FACULTY OF NATURAL AND APPLIED SCIENCES LECTURE NOTE ON GENERAL BIOLOGY I CODE: BIO 101 DEPARTMENT OF BIOTECHNOLOGY AND ENVIRONMENTAL BIOLOGY COURSE LECTURER Dr. Emmanuela Onyinye Ibeh Ogar Ecology The term ecology is derived from the Greek word “oikos meaning home and logos meaning the study of”. Ecology therefore means the study of an organism in its natural home. The study of the relationships between living organisms and their environment IS TERMED ECOLOGY. It is important for humanity to understand its environment because we have the ability to modify the environment through the use of technology. CLASSIFICATION OF ECOLOGY Based on study area Autecology : It deals with the study of an individual species of organisms and it’s relation with the environment. It is also called the Species ecology. Synecology : It deals with the study of communities, their composition, their behaviour and relation with the environment. It is also called as Ecology of communities. CLASSIFICATION OF ECOLOGY Based on study Environment or habitat Aquatic ecology : The study of interaction of organisms in the water Marine water ecology - Ocean, Deep Sea, Estuary Freshwater Ecology - Lotic (Running water) – River, Stream, Spring Lentic (Standing Water) –Pond, Lake. Terrestrial Ecology : The study of interaction of organisms on CLASSIFICATION OF ECOLOGY Based on Advancement in the ﬁeld of ecology Population ecology Community ecology Ecosystem ecology Microbial ecology Pollution ecology Levels of ECOLOGICAL Organization This is the organization of the biosphere from the smallest to the broadest level: They are; Organism/Species Population Community Ecosystem Biome Biosphere Organism and population Species: A group of living organism consisting of similar individuals, capable of interbreeding. Population: a group of individuals of the same species living in the same area at the same time, that can interbreed and produce fertile offspring. Organisms that aren't in the same population can't have fertile offspring. A local population could occupy a very small habitat, such as a puddle Example: Every member of a species of monkey that occupies a large island. Community Organisms do not live randomly scattered through the earth. They live in communities. Community = are collections of different species living in the same area at the same time. Such as a group of Zebra and a group of elephants that live in the same area of Africa. At the community level, interactions between organisms can be observed such as; Predator/prey Consumer/producer Competition and cooperation Ecosystem Ecosystem: A community of organisms together with its physical environment is known as an Ecosystem. An Ecosystem is just the community plus the abiotic factors in that environment. Example of an Ecosystem Zebras and elephants, including all the water, sunlight, soil, and temperature in that environment, would be called an "ecosystem". Biome Biome is an area of planet that can classiﬁed according to the plants and animals that live in it. The major types of biomes are; Tundra (coldest), Forest (rain forest, Temperate and Taiga), Grassland (savannah) and Desert (driest)camel. \ AIt is deﬁned as a community of various plants and animals that inhabit a particular type of geographic region of Earth. Biomes are often deﬁned by their climate, rainfall/water characteristics, elevation, and plant characteristics (leaf type, spacing, etc). Biosphere Biosphere = The biosphere is deﬁned as the region on, above, and below the Earth’s surface where organisms live. It includes all of Earth’s ecosystems. The biosphere includes the lithosphere, hydrosphere, and atmosphere The hydrosphere is the combined mass of water found on, under, and above the surface of the earth. The Atmosphere is a protective layer of gases that shelters all life on Earth, keeping temperatures within a relatively small range and blocking out harmful rays of sunlight.” The lithosphere is the solid outer layer of Earth, comprised of the crust and the upper mantle. Habitat and Niches Habitat—is the place where particular plants or animals live. Within the habitat, organisms occupy different niches. Niche: A niche is the functional role of a species in a community. Types of habitats: The biosphere has three major types of habitats. 1.Terrestrial Habitat (Land) Organisms that live and move on land are called terrestrial organisms. The terrestrial habitat is marked by rapid f luctuations in temperature, moisture and climate. Life on land is sustained by air, soil temperature, and rainfall. Some common terrestrial organisms are trees, ferns, elephant, camel, man, HABITAT 2. Aquatic Habitats Organisms which live in water are known as aquatic organisms. They are classif ied as freshwater organisms, if they inhabit a river, pond, lake, stream, etc. Marine organisms are those which live in sea water [marines, Sea]. The well-known aquatic organisms are algae, small animals and ﬁshes. 3 Aerial or Arboreal Habitats A number of animals are tree dwelling (arboreal) like monkeys and squirrels Relationships and Interactions in an Ecosystem The distribution and abundance of organisms is shaped by both biotic and abiotic factors. - The Abiotic components are nonliving chemical and physical factors which affect the ability of organisms to survive and reproduce such as temperature, light, water, and nutrients. - The Biotic components are living factors such as other organisms that directly or indirectly affect the environment. Thus, the organisms, their presence, parts, interaction, and wastes are all biotic factors. Autotrophs and Heterotrophs The biotic component of an ecosystem is made up of all the living organisms in it. These organisms are divided into two main groups according to the way they feed: Autotrophs and Heterotrophs. Autotrophs: These are organisms that are able to use sunlight or chemical energy to manufacture their own food. Since autotrophs are the only organisms that can produce food in an ecosystem, they are known as primary food producers. Autotrophs include all green plants, some bacteria (Cyanobacteria) and photosynthetic protists (Brown and Red Algae, Euglena). Autotrophs and Heterotrophs Heterotrophs: These organisms cannot manufacture food. They feed on ready-made food which comes from the tissues of organisms in their environment. In an ecosystem, heterotrophs may be consumers or decomposers. They include all animals, carnivorous plants, fungi and most protists and bacteria. Energy Flow in Ecosystems The sun is the ultimate source of energy for almost all ecosystem. Because green plants makes their own food from inorganic substances, they are called the producers of all the food in the ecosystem. P l ants e v e ntual l y d i e. T he i r re m ai ns are usual l y b ro ke n d o w n b y decomposers (organisms that acquire their food molecules from dead organic materials). In the process of extracting energy and nutrients from this material, decomposers release some of the nutrients back into the ecosystem, where they are again available to producers. Energy Flow in Ecosystems Energy, by contrast, is not cycled but is continuously lost from an ecosystem. As energy is not recycled, energy must consistently be captured by producers. This energy is then passed on to the organisms that eat the producers. Most ecosystem also contain consumers (animals and other organisms that eat plants or each other). These may die and pass directly to the decomposers, or they may be eaten by carnivores, also called secondary consumers. Food Relationship All liv ing org anism s m ust ob tain energ y and nutrients f rom their environment in order to remain alive. This is seen through their feeding pathway/food relationship. The feeding pathway in nature follows a certain pattern; It begins with a primary producer The primary producer is eaten by a primary consumer The primary consumer is eaten by a secondary consumer The secondary consumer is consumed by the tertiary consumer The decomposers convert the remains of dead producers and consumers Trophic level In an ecosystem, energy and nutrients are transferred step by step among organisms along a feeding pathway. For example, in a grassland ecosystem, a lion eats a zebra, that ate grass, that manufactured its own food by converting sunlight into chemical energy. Each step along a feeding pathway is known as trophic level. The feeding positions in a food chain or web are called trophic levels. Many consumers feed at more than one trophic level. Humans, for example, are primary consumers when they eat plants such as vegetables. They are secondary consumers when they eat cows. They are tertiary consumers when they eat snake. Trophic level Energy is passed from organisms at one trophic level or energy level to organisms in the next trophic level. Energy is passed up a food chain or web from lower to higher trophic levels. Most of the energy at a trophic level – about 90% – is used at that trophic level. Organisms need it for locomotion, heating themselves, and reproduction. So, animals at the second trophic level have only about 10% as much energy available to them as do organisms at the ﬁrst trophic level. Animals at the third level have only 1% as much available to them as those at the second level. Trophic Level Where It Gets Food Example 1st Trophic Level: Producer Makes its own food Plants make food 2nd Trophic Level: Primary Consumes producers Mice eat plant Consumer seeds 3rd Trophic Level: Secondary Consumes primary Snakes eat mice Consumer consumers 4th Trophic Level: Tertiary Consumes secondary Hawks eat snakes Consumer consumers Food Chains and Food Webs Food chains and food webs are diagrams that represent the feeding relationships from producers to consumers to decomposers. They show who eats whom. In this way, they model how energy and matter move through ecosystems. Food Chains A food chain represents a single pathway through which energy f lo w through an ecosystem. It shows the transfer of energy and nutrients from organisms to organisms in a pathway. Producers use energy from the sun to make food and therefore start the chain The arrows represent the direction of energy f low, pointing from the organism being consumed to the organism receiving the energy Decomposers may feed on organisms at any stage of the food chain. Decomposers recycle nutrients back into the ecosystem. At each level of a food chain, a lot of energy is lost. Only about ten percent of the energy passes to the next level. Where does that energy go? Some energy is given off as heat. Some energy goes into animal wastes. A food web represents multiple pathways through which energy and matter ﬂow through an ecosystem. It includes many intersecting food chains. It demonstrates that most organisms eat, and are eaten, by more than one species. Energy Pyramid Energy Pyramid is a diagram that shows the relative amounts of energy located within each trophic level Most of the energy in an energy pyramid is used or lost as heat energy as it moves up the pyramid, therefore each level in an energy pyramid has less energy available to it than the level below (only about 10% of the energy produced at each level is available to the one above it) Producers are the foundation of all pyramids ENERGY PYRAMID Symbiosis Symbiosis is the interaction between individuals of different biological species. One of the organisms receive a beneﬁt from the interaction, the other can either receive a beneﬁt, be harmed, or not be affected in any way. Three main kinds of symbiotic relationships: commensalism, mutualism, and parasitism SYMBIOSIS In mutualism, both the involved organisms beneﬁt from each other. Example – Coral reefs are nothing but a mutualistic association between coral organisms and various types of algae residing inside them. In commensalism, only one organism beneﬁts, while the other is neither beneﬁted nor harmed. Example – Hermit crabs use gastropod shells to protect their bodies. In parasitism, one organism is beneﬁted while the other organism is harmed. Example – Liver ﬂuke attaches itself to the liver and makes its way to the tissue and bile. SYMBIOSIS CHART INTERACTION SPECIES A SPECIES B Commensalism Receives beneﬁts Not Affected Mutualism Receives beneﬁts Receives beneﬁts Parasitism Receives beneﬁts Harmed Amensalism No beneﬁt Harmed Other Relationships Amensalism: this is a type of biological interaction where one species causes harm to another organism without any beneﬁt to itself. Example: When cattle trample on grass, the grass is crushed. However, the cattle do not beneﬁt from this action nor is harmed in the process. Modes of Amensalism: There are two modes of amensalism; Competition:two organisms compete for the same resources such as food, water, shelter, space, mate. A larger organism deprives a smaller, weaker organism of food or space. Example: When a goat feeds on the same type of shrub as a beetle. The goat is unharmed when it consumes the shrub, however, the beetle loses signiﬁcant quantities of food and may accidentally be eaten by the goat. This mode of amensalism is called competition. Some higher plants secrete substances that inhibit the growth of—or kill—nearby competing plants. Other Relationships Antibiosis: An organism is either damaged or killed by a chemical secretion of another organism. Example: An example of antibiosis is the interaction between Penicillium and bacteria. The mould Penicillium creates the secretion known as penicillin, which is extremely toxic to bacteria. This ﬁnding formed the basis for antibiotic called penicillin. Predator/Prey: predator hunts, kills, and eats prey Cooperation: an interaction where organisms work together, ex. wolf packs Population Ecology (The study of population) Each group of organisms of the same species living in the same area forms a population. Population ecology is the branch of ecology that studies the structures of populations and how they change. In population studies of a habitat, we investigate the following; i. The types of organisms that are present; ii. The dominant species and iii. The characteristic features of each population Types of organisms This is a qualitative study which lists all the various types of populations that are found in the habitat. Dominant species In any community, one or a few species are dominant over the others in numbers or size or both. These dominant species often exert a great inﬂuence on the habitat. Population characteristics These include population size, frequency, density, percentage cover and distribution. Size: population size is important as it affects the survival of a given species in a habitat. A small population may easily be wiped away by events such as f ir es, diseases, e.t.c. A large population stands a better chance of surviving dangers. Density: this is the average number of individuals of a species per unit area of the habitat. It is used to estimate the total number of individuals in a population. Density = population size/area of habitat Frequency: the frequency of any species is simply how often the species occurs at different sites in its habitat. Percentage cover: this is the area of ground covered or occupied by a given species in its habitat. Distribution: this is the way in which individuals of a particular population are arranged in a given habitat. Generally, the individuals may be clumped, evenly spaced or randomly spaced. Conducting population studies Population of a place is always changing be it that of plants and animals. It is therefore very dif ficult to count the number or estimate the population of organisms in a given habitat by counting them one by one. In order to eliminate this dif ficulty, a method known as SAMPLING is used. In the case of very small organisms, slow movers, plants or other non-mobile organisms, scientists use what is called a quadrat Quadrat is a rectangular or square frame made from thick wire. The quadrat is thrown at random several times into a measured plot of land and at each landing, the area covered by it is noted. The plants and animals enclosed at each throw is noted and their numbers recorded, the average number of times each species appeared is calculated and the most frequent or dominant species is then determined. To determine the density of a particular species in a habitat, the following steps are taken: a. Frequency of an organism: this is the total number of times an organism occurs in all the quadrat’s throws (say for instance 100 times) b. Number of tosses/throws, say 20 times Therefore, average number of organisms per quadrat toss = frequency/number of tosses i.e 100/20= 5 How Population Size and Density Are Calculated Population density = average frequency/area of habitat = 5/1= 5perm2 Transect method In this method, a measuring tape which has been marked at convenient intervals is stretched across the area. The plants encountered at the interval marks are recorded. This is repeated a few times. A fairly accurate estimate of the number and types of plants in the area can be made using this method. Capture and recapture: Obviously a quadrat would not work for animals that move a round a great deal. So to determine the population size of more mobile organisms, the mark and recapture method is used. Here, individual animals are captured and then marked with a paint or something similar. The animal is released back into its environment. Then at a later date, another set of animals is captured, and that set may include those already marked, as well as unmarked animals. Capture and recapture: Animals of the same species in an area are caught, counted (A1), marked and released. The next day the same number of animals are caught (A2) and recorded. At the same time the number of marked animals (A3) from the previous day, that were found in this sample are also counted and recorded. The population of animals present in the area is found by the formula: Population=A1* A2/A3 Assuming 200 Tilapia ﬁsh (A1) are captured in a pond The next day 200 Tilapia f ish (A2) were also caught. This 200 f ishes included 40 that were marked on the ﬁrst day, i.e A3=40 The total number of Tilapia ﬁsh population is 200x200/40= 1000 Some instruments used in investigating animal life Butterf ly/sweep net: This is made of mosquito net and used to skim the surface of the water for collecting surface specimens. Flying insects such as butterﬂy can also be captured with this net. Traps: Commercial traps are used in capturing many animals including small mammals and nocturnal animals. Attractive baits are included when setting such traps. Tullgren funnel: This is f it ted with wire gauze for collecting soil organisms from soil samples. The soil sample is placed on the gauze and heated by lighted bulb. As the animals move away from the heat, they drop into the container of alcohol below the funnel and are collected. Plankton net: This is made of ﬁne cloth/net with ﬁne mesh for collecting tiny organisms/planktons from aquatic habitats e.g pool, pond, lakes, streams, seas etc. The net is slowly trailed in water. Plankton accumulates at its tip as the water is ﬁltered. Fish trap: Has two large opening which tappers towards the center. Fishes that get in, swim towards the center and are trapped. Pooter: Is used to collect small insects, spider and other invertebrates from leaf litter, tree trunks and crevices of rocks and wall surfaces. This can be used by pointing the collecting tube towards tree trunks/rock. Then suck through the mouth piece. CARRYING CAPACITY Because the real world does not offer unlimited resources, the number of individuals in a growing population eventually will reach a point when resources become scarcer. Then the growth rate will slow and level off. Once a population reaches this leveling-off point, it is considered the greatest population the environment can sustain. The term for this phenomenon is carrying capacity. The letter K represents carrying capacity. What is carrying capacity? The carrying capacity of a biological species refers to the maximum number of individuals (of that species) that the environment can carry and sustain. FACTORS THAT AFFECTS POPULATION SIZE FACTORS THAT AFFECTS POPULATION SIZE FACTORS THAT AFFECTS POPULATION SIZE FACTORS THAT AFFECTS POPULATION SIZE What is a Biogeochemical Cycle? Biogeochemical cycles refers to the movement and transformation of chemical elements and compounds between living organisms and non living parts of an ecosystem, the atmosphere and the earth’s crust. The term biogeochemical is derived from “bio” meaning biosphere, “geo” meaning the geological components and “chemical” meaning the elements that move through a cycle. The earth obtains energy from the sun which is radiated back as heat, rest all other elements are present in a closed system. The major elements include: Carbon, Hydrogen, Nitrogen, Oxygen, Phosphorus, Sulphur, water Biogeochemical Cycle Water Cycle: The water from the different water bodies evaporates, cools, condenses and falls back to the earth as rain. This biogeochemical cycle is responsible for maintaining weather conditions. The water in its various forms interacts with the surroundings and changes the temperature and pressure of the atmosphere. Carbon Cycle: It is one of the biogeochemical cycles in which carbon is exchanged. All green plants use carbon dioxide and sunlight for photosynthesis. Carbon is thus stored in the plant. The green plants, when dead, are buried into the soil that gets converted into fossil fuels made from carbon. These fossil fuels when burnt, release carbon dioxide into the atmosphere. Also, the animals that consume plants, obtain the carbon stored in the plants. This carbon is returned to the atmosphere when these animals decompose after death. The carbon also returns to the environment through cellular respiration by animals. Biogeochemical Cycle Huge carbon content in the form of carbon dioxide is produced that is stored in the form of fossil fuel (coal & oil) and can be extracted for various commercial and non-commercial purposes. When factories use these fuels, the carbon is again released back in the atmosphere during combustion. Nitrogen Cycle: Here, nitrogen is converted into several forms and it gets circulated through the atmosphere and various ecosystems. The nitrogen in the atmosphere is ﬁxed by the nitrogen-ﬁxing bacteria present in the root nodules of the leguminous plants and made available to the soil and plants. The bacteria present in the roots of the plants convert this nitrogen gas into a usable compound called ammonia. Ammonia is also supplied to plants in the form of fertilizers. This ammonia is converted into nitrites and nitrates. The denitrifying bacteria reduce the nitrates into nitrogen and return it into the atmosphere. Natural Environmental Impacts Volcanoes: release of greenhouse gases can increase global temperature. Fire: ﬁres can be beneﬁcial through clearing out areas for new plants to grow, or they can be harmful to animals through decreasing food sources and increasing erosion Plants: plants has multiple beneﬁts to the Earth, including preventing erosion and improving air/soil quality Human Environmental Impacts Human activities can change the balance in Earth's processes; careless human activity can also alter or destroy habitats and damage ecosystems Humans hurt the Earth through pollution, resource use, and introduction of invasive species Humans can also help the Earth through conservation and preservation HEREDITY In the simplest of words, heredity refers to the passing of traits or characteristics through genes from one generation (parent) to the other generation (offspring). Basic terms in Heredity A few key genetics terms are particularly useful when talking about inheritance: ✓ Genes: Def ined as factors that control traits. GENES ARE SECTIONS OF DNA WHICH CODES FOR A SPECIFIC TRAITS (e.g eye colour, height, e.t.c). ✓ Alleles: Different forms of the same gene are called alleles; more like different f lavor or varieties. The gene that controls pea plant height has two variations, or alleles — one for tallness and one for shortness. For example, if coca-cola is the gene, the varieties will be diet coke, classic coke, e.t.c. HEREDITY Genes speciﬁes which traits, alleles specify what form gene takes Homozygous – Each organism has two alleles for every gene (Each chromosome has one each). In homozygous, both the alleles are same. For Example, “TT” is the homozygous expression for tallness trait. Heterozygous – If the two alleles are different from each other, then they are heterozygous in nature. For Example, “Tt” is the heterozygous expression for tallness trait. Chromosomes – These are thread-like structures made up of nucleic acids (DNA) and proteins. They are mostly found in the nucleus of the cells. They carry the hereditary or genetic information in the form of genes. HEREDITY ✓ Loci: These are the locations on a chromosome where genes are found. Each gene is located at a speciﬁc place, or locus, on its chromosome. ✓ Genotype: The combination of alleles that an organism has is its genotype. An organism genetic information. BB or Bb or bb ✓ Phenotype: The appearance of an organism’s traits is its phenotype. The physical expression of gene. Gregor Mendel- The Father of Genetics Gregor Mendel, also known as the Father of Genetics, conducted immense research and studies on this inheritance of traits. HEREDITY He researched on plant breeding and conducted his experiments on pea plants to show the inheritance of traits in living organisms. He observed the pattern of inheritance from one generation to the other in these plants. And thus he came up with Mendel’s Laws of Inheritance, which can be summarized under the following headings:  Law of Dominance: hybrid offspring will only inherit the dominant trait in the phenotype.  Law of Segregation: states that every individual possesses two alleles and only one allele is passes on to the offspring.  Principle of Independent Assortment: states that the inheritance of one pair of genes is independent of inheritance of another pair. Monohybrid Cross It is the cross between two organisms that have one pair of contrasting characters, for example, a cross between a tall pea plant (TT) and a short (dwarf) plant (tt). Observations & Conclusion  In the ﬁrst generation (F1), the progeny were tall. There was no medium height plant.  In the second generation (F2), 1/4th of the offspring were short and 3⁄4were tall.  The Phenotypic ratio in F2 – 3: 1 (3 tall: 1 short)  The Genotypic ratio in F2 – 1: 2: 1 – (TT: Tt: tt)  For a plant to be tall, a single copy of “T” is enough. But if a plant has to be short, both the copies should be “t”  In Tt, ‘T’ is expressed and ‘t’ is suppressed. Hence, the characters ‘T’ is the dominant trait and ‘t’ is the Dihybrid Cross I t is the c ross between two pairs of c ontrasting c harac ters. This takes into consideration alternative traits of two different characters. For example, a cross between one pea plant with round and green seeds and the other pea plant having wrinkled and yellow seeds. Consider this cross A pea plant that is heterozygous for round, yellow seeds is self-fertilized, what are the phenotypic ratios of the resulting offspring? St e p 1: D e t e rmi ne t he pare nt al ge no t ype s fro m t he t e x t abo v e , t he wo rd " heterozygous" is the most important clue, and you would also need to understand that self-fertilized means you just cross it with itself. RrYy x RrYy Dihybrid Cross Step 2: Determine the gametes. Combine the R's and Ys of each parent to represent sperm and egg. Do this for both parents Gametes after "FOIL" RY, Ry, rY, ry (parent 1) and RY, Ry, rY, ry (parent 2) DIHYBRID CROSS Step 3: Set up a large 4x4 Punnet square, place one gamete set from the parent on the top, and the other on the side Step 4: Write the genotypes of the offspring in each box and determine how many of each phenotype you have. In this case, you will have 9 round, yellow; 3 round, green; 3 wrinkled, yellow; and 1 wrinkled green. VARIATION Variation occurs due to some errors in DNA copying. Variation is important because it contributes to the evolution and forms the basis of heredity. How Sexual Reproduction Creates Genetic Variation Sexual reproduction increases genetic variation in offspring, which in turn increases the genetic variability in species. You can see the effects of this genetic variability if you look at the children in a large family and note how each person is unique. Mutations Exposure of cells to mutagens (environmental agents, such as X-rays and certain chemicals, that cause changes in DNA) can increase the number of mutations that occur in cells. When changes occur in a cell that produces gametes, future generations are affected. VARIATION Crossing-over When homologous chromosomes come together during prophase I of meiosis, they exchange bits of DNA with each other. This crossing-over results in new gene combinations and new chances for variety. Crossing-over is one way of explaining how a person can have red hair from his mother’s father and a prominent chin from his mother’s mother. Independent assortment Independent assortment occurs when homologous chromosomes separate during anaphase I of meiosis. When the homologous pairs of chromosome line up in metaphase I, each pair lines up independently from the other pairs. So, the way the pairs are oriented during meiosis in one cell is different from the way they’re oriented in another cell. VARIATION Fertilization Fertilization presents yet another opportunity for genetic variability. Imagine millions of genetically different sperm swimming toward an egg. Fertilization is random, so the sperm that wins the race in one fertilization event is going to be different than the sperm that wins the next race. And, of course, each egg is genetically different too. So, fertilization produces random combinations of genetically diverse sperm and eggs, creating unlimited possibilities for variation. Non-disjunction Mistakes may occur during meiosis that results in non-disjunction. This is the failure of replicated chromosomes to separate during meiosis. Some of the resulting gametes will be missing a chromosome, while others will have an extra copy of the chromosome. If such gametes are fertilized and form zygotes, they usually do not survive. If they do survive, the individuals are likely to have serious genetic disorders.

BIO 101 Lecture Notes: Ecology and Biology - PDF

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