Biolgy Unit 2

  • Created by: danielle
  • Created on: 15-04-19 15:08
**What is Evolution?
is the change over time in the proportion of individuals in a population differing in one or more inherited traits.
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What are the 2 processes that evolution can occur through?
Random; Genetic Drift & Non-random; Natural & Sexual Selection
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What is the definition of Geneetic Drift?
The random change in frequency of alleles in a population.
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Why is Genetic Drift more important in small populations?
Alleles are more likely to be lost from the gene pool.
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What is the definitonof Natual and Sexual Selection?
Natural; non-random increase in frequency of DNA sequences that increase survival & Sexual; non-random selection for traits that increase reproductive success
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What is variaiton a result of?
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What is the likelihood of cells undergoing harmful/neutral/beneficial mutation?
Most mutations are neutral/harmful. In rare cases, they can be beneficial to the fitness of the individual.
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What is Absolute Fitness?
Is the ratio of frequencies of a particular genotype in one generation compared to the previous generation. 1 is the absolute fitness; less than 1= frequencyof the genotype is less stable VICE VERSA
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What is Relative Fitness?
Compares the absolute fitness of genotype wit the absolute fitness of the most successful genotype. The most successful= 1 & the rest are relative to 1 (<1)
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Through inheritance, what is most likely to become more frequent in subsequent generations?
Favoured Traits
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What are selection pressures?
are factors that affect the ability of an organismto survive and reproduce
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Rate of evolution can be rapid when selection pressures are high or low?
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What factors increase the rate of evolution?
Shorter generation times; Warmer Environments; Sharing of beneficial DNA Sequences between lineages through sexual repoduction & Horizontal Gene Transfer
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What is coevolution?
Coevolution is seen in pairs of species that interact frequently or closely.
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Give 4 examples where coevolution is involved.
Herbivores & Plants; Predatory & Prey; Pollinator & Plants; Parasites & Hosts
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Describe coevolution and Selection pressures
In coevolution, a change in one species acts as a selectio pressure to the other.
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What Hypothesis explains the idea of coevolution between a parasite and host?
The Red Queen Hypothesis. ''keep running to stay still''; coevolution
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Describe the relationship between a host and parasite.
Hosts are better able to tolerate & resist parasites due to havin a greater fitness. Parasites are better able to feed, reproduce and find new hosts have greater fitness.
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**When compared to asexual reproduction, sexual reproduction appears to have two disadvantages. What are they?
1;Half of the population (males) are unable to reproduce & 2; each parent are only able to pass 50% of their genetic material
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Why do the benefits outweigh the disadvantages of sexual reproduction?
Due to sexual reproduction providing an increase in genetic variaiton in the population
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What does genetic variation provide?
Provides a raw material required to continue adapting in the Red Queen's arm race between parasites and their hosts.
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Where can asexual reproduction be a successful reproductive strategy?
In very narrow, stable niches or when recolonising distured habitats
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Give 2 examples of reproduction strategies in eukaryotes.
Vegetative cloning in plants & Parthenogenic animals that lack fertilisation
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Describe Vegetative cloning and Parthogenesis.
Vegatative Cloning; e.g. reproductionvia bulbs (onions) and runners (spider plants) & Parthogenic animals embryo's result from unfertilised eggs & therefore offspring will be haploid e.g. Komodo dragons that reproduce in the absense of males
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Where is Parthogenesis more common?
In cooler climates that are disadvantageous to parasites or low regions of parasite density/diversity
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Describe the mechanisms of organisms that reproduce asexually.
They often have mechanisms for horizontal gene transfer between individuals, such as the plasmids of bacteria and yeast
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What is Meosis?
It is the process where gametes are produced. Where 1 Diploid Gamete Mother Cell divides into 4 Haploid Cells.
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Explain what the term ''homologous chromosomes''
a pair of chromosomes of the same size, same centromere position and the same genes at the same loci.
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What is disimilar about the homologous chromosomes?
The Alleles of the genes in the H.M. may be disimilar because of the inheritance of different parents
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How is variation increased in meosis?
It is increased throught the production of haploid gametes by meosis in gamete mother cells.
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Describe what happens during Meosis 1.
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Describe what happens during Meosis 2.
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In most organisms, gametes are formed directly from the cells produced by meosis. What may happen in other groups?
Mitosis may occur AFTER meosis to form a haploid organism; gametes form later by differentiation/
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What are Simultaneous Hermaphrodites?
are organisms with both female and male reproductive organs.
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What are Sequential Hermaphrodites?
are born as one sex and may change to the other sex.
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Why does sex usually change in sequential hermaphrodites?
This is when reproductive success is likely to be greater by becoming the other sex
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What environmental factors effect the determination of sex or sex ratio?
Size, Competition or Parasitic Infection
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Give an example of an insect in which sex is determined through a set of specific chromosomes- the Sex Chromosomes (X & Y)
In Drosophila
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What does the gene on the Y chromosome determine?
Development of maleness
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What does the heterogamtic (XY) male lacks?
They lack homologous alleles on the smaller (Y) chromosome.
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Why are males at a disadvantage in comparison to females?
Males have a greater chance of being affected by certain recessive condition e.g. colour blindness, this is because females would need 2 copies of the recessive allele to be affected and males only need one.
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Describe X-chromosome inactivation.
In females, the portions of the X-chromosome that are lacking on the Y chromosome are randomly inactivated in one of the homologous X chromosomes in each cell. This prevents a double dose of gene product, which could be harmful to cells.
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Is the X-chromosome inactivation process random?
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Compare sperm and egg production in relation to number and energy store.
Eggs; Eggs are much larger and fewer in number due to a high energy store & Sperm; are always more numerous and have a lower energy store
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What are sessile organisms?
They are organisms that are fixed to a surface & therefore cannot move.
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What are some problems with sessile organisms?
Finding a mate is difficult & The meeting of the gametes
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What are some solutions for sessile organisms?
Being self-fertile (such as plants that can self-pollinate), Synchronised Spawning (such as in coral, the gametes are released into the environment at the same time to increase chances of fertilisation)
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Describe the costs and benefits of eternal & internal fertilisation.
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Describe Parental Investment
It is costly but increases the probability of production and survival of young.
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The level of Parental car can be classified into two groups, what are they?
R-Selected populations & K-selected populations (Humans)
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Explain both populations in relation to Environment, Maturation Time, Lifespan, Death Rate, No. of offsrping produced per reproductive episode, No. of reproductions in lifetime, Timing of 1st reproduction, Size of offspring or eggs & Parental care
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Variour Repdroduction strategies have evolved; Describe The 4 basic mating systems.
SEE YELLOW SHEET (Monogomy; Polygyny; Polyandry & Polygnandry
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Sexual Dimorphism is a product of sexual selection. What is Sexual Dimorphism?
It is a phenotypic differentiation between males & females of the same species. Typically in terms of seze and coloration.
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What three ways can sexual selection be realised?
Male to Male Rivalry, Female Choice & Lekking Species
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Describe Male to Male Rivalry.
Where males compete aggressively amongst themselves. Larger size/weaponary increases access to females. Alternatively, some males are successful by acting as sneakers.
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What are sneakers?
Are smaller, weaker & more inferior males that adapt a set of behaviours that will allow them to gain a few matings.
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Describe Female Choice
Females have a higher parental investment and therefore face more pressure to make a good mate decision. It involves females assessing honest signals of the fitness of the males. Fitness can be in terms of good genes & low parasite burden.
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In a lekking species, alternative successful strategies of dominant and satelite males..What is a lek?
A lek is an aggregation of males that gather to engage in competitive displays tha may entic visiting females into mating. There is a strong female choice & group male displays. The satelite males cluster aroung the attractive males; relying on him t
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What is a lek? p2
to attract females to increase their chance of mating.
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In Birds and Fish, successful courtship behavious is a result of what?
A species-specific sighn stimuli and Fixed action pattern responces
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Desribe species-specific sighn stimuli and Fixed action pattern responces
FAP is a sequence of coordinated movements that are oerformed together & triggered by a unique stimulus known a sign stimulus. They are highly specif signals that are encountered at an appropriate time.
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What is Imprinting?
An irreversible developmental processes that occur during a critical period in young birds which may influence mate choice later in life
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Describe what a parasite is and what it does.
A parasite is a symbiont that gains benefit in terms of nutrients at the expense of the host.
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What is the parasite's reproductive potential in comparison to the host?
Unlike in a predator-prey relationship, the reproductive potential of the parasite is greater than the host.
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What is an ecological niche?
A multidimentional summary of tolerances and requirements of a species.
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What does a parasite's niche tend to be?
Parasites tend to have a narrow niche that is very host-specific
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Many Parasites are degenerate, why is this?
Because they lack in structures & organs found in other organisms and therefore the host provides so many of the parasite's needs
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What are the 2 types of Parasites?
Ectoparasite; lives on the suurface of the host & Endoparasite; lives within the host.
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What is the Definitive host?
The organism where the parasite reaches sexual maturity
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What is the Intermediate Host?
May also be required for the parasite to compete its life cycle (secondary host)
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What plays an active role in the transmission of the parasite and may also be the host?
A Vector
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In ecology, 2 niches exist. What are they?
The Fundamental Niche; a niche in the absence of any interspecific competing influences & The Realised Niche;is the nich that the organism occupies in the presence of intersecific competition
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What is a result of interspecific competition?
Competitive Exclusion; This is where the niche of 2 species are so similar that one declines to local extinction
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What is a result of the absence of interspecific competition?
Resource Partioning; When the Realised Niches are sufficiently different, potential competition can co-exist by Resource Partioning.
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What is the definition of Transmission and Virulence?
Transmission; is the spread of a parasite to host & Virulence; The harm caused to a host species by a parasite.
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Describe the relationship between Transmission and Virulence.
The higher the transmission rate, the Greater the virulence
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What are 2 factors that increase the rate of transmission
1. Overcrowding of hosts at a high density 2. A means of transmission; such as a presence of vectors (e.g. mosquitos) & waterborne disposal stages (e.g. cholera)
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Host behaviours can become part of an extended phenotype of the parasite; give 5 examples of ways in which host behaviour can be altered.
Foraging, Sexual Behaviour, Movement, Habitat Choice & Antipredator Behaviour
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What is foraging?
It is searching for wild food resources.
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Describe the effect parasites have on the host's immune system, size, lifespan and reproductive rate.
Parasites supress the host immune system & modify the host size, lifespan and reproductive rate in ways that benefit the parasite growth, reproduction or transmission.
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What phases allow rapid evolution & rapid build up of parasite population?
Sexual and Asexual Phases. (The distribution of parasites is NOT UNIFORM)
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What are the 5 Non-specific defences of mammals?
Physical barriers (skin); Chemical secretions (stomach acid, mucus); Inflammatory Responce; Phagocytes & Natural Killer cells (lymphocytes)
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What are Phagocytes?
Phagocytes are white blood cells with a non-specific role in defence.
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Describe the process of Phagocytosis.
1.Phagocy. move to site of injury; 2. Plasma membrane of the phagocy. engulfs the parasite; 3. Parasite is brought into the phagocyte in a vacuole; 4. Lysomes moves towards the vacuole; 5. Lysomes fuse with the vacuole releasing & parasite is digest
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What do natural killer cells do?
they are lymphocytes (white blood cells) responsible for destroying abnormal cells.
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What is your inflammatory responce?
When the skin is damaged, the external barrier to parasites is broken. The inflammatory responce is triggers redness, swelling, heat and pain.
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Lymphocytes are a type of specific respone, what 2 types of lymphocytes are mammals armed with?
B Lymphocytes; B cells & T Lymphocytes; T cells
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What do B cells produce?
They produce proteins called antibodies that are specific in shape to an antigen
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How do T cells work?
T cells work by destroying specific infected or damaged cells by bringing about Apoptosis (programmed cell death)
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Both B & T Lymphocytes carry out clonal selection. What is clonal selection?
The process by which lymphocytes become amplified undergoing the process of mitosis.
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What do long term survival of some members of t & B lymphocyte clones act as?
Immunological memory cells
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What is epidemiology?
It is the study of the outbreak and spread of infectious disease
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What is the herd immunity threshold?
It is the density of resistant hosts in the population required to prevent an epidemic.
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What do endoparasites do to reduce they chances of destruction?
They mimic host antigens to evade detection by the immune system and modify host-mmune responce.
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Some parasites show huge Antigenic variation. What is this?
Antigenic variation promotes rapid evolution rate. This is faster than the host immune system to respond to new antigens.
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Common Parasites include:
Protists (single-celled; amoebas); Platyhelminths (flatworms); Nematodes (roundworms); Athropods (ticks); Bacteria & Viruses
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What does the parasite Plasmodium spp. cause?
Plasmodium causes the disease malaria
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What does the platyhelmith, Schistosoma spp. cause?
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How do ectoparasites such as ticks and lice usually transmit from host to host?
via direct contact
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How are endoparasites transmit?
Through secondary hosts (Vectors)
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Give examples of parasites that complete their life cycle in one host.
Endoparasitic amoebas and Ectoparasitic arthropods, bacteria & Viruses
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What is Turbuculosis caused by?
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What is both Ifluenza and HIV caused by?
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What are viruses and where do they replicate?
Viruses are infectious agents that can only replicate inside a host cell.
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What do viruses contain and what are they packaged in?
Viruses contain genetic material in the form of DNA or RNA, packaged in a protective protein coat.
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What does the outer surface of a virus contain?
Antigens that a host cell may or may not be able to detect as foreign
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What enzyme do RNA Retroviruses use to form DNA?
Reverse Transcriptase
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What happens to this DNA?
It gets inserted into the genome of the host cell.
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What does the virus gene form when transcribed?
New viral particles.
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Describe 3 challenges to overcome in the successful treatment and control of parasites.
Some Parasites are difficult to CULTURE in the lab; RAPID ANTIGEN CHANGE has to be regulated in the design of vaccines & the similarities between the host and parasite metabolism makes it difficult to find drug compounds that only target the parasite
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Why is designing vaccines for some paraistes almost impossible and very expensive?
Due to the rapid antigen change of parasites.
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What has helped improve sanitation?
Civil engeneering projects and Coordinated vector control have been practical control strategies
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Challenges arise where parasites spread most rapidly. What is this a result of?
Overcrowding & Tropical climates
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What do improvements in Parasite control cause?
Reduces Child Mortality & results in Population-wide Improvements in Child Development & Intelligence as individuals have more resources for Growth & Development.
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Card 2


What are the 2 processes that evolution can occur through?


Random; Genetic Drift & Non-random; Natural & Sexual Selection

Card 3


What is the definition of Geneetic Drift?


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Card 4


Why is Genetic Drift more important in small populations?


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Card 5


What is the definitonof Natual and Sexual Selection?


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