topic 7 - genetics, population, evolution and ecosystems

Question 1

define dominant allele

Answer 1

only a single allele is required for the characteristic to be expressed in the phenotype

Question 2

define recessive allele

Answer 2

two copies of the allele are required for the characteristic to be expressed in the phenotype
this means it is only expressed in a homozygous individual

Question 3

define homozygous and heterozygous

Answer 3

homozygous is an individual that carries two copies of the same allele

heterozygous is an individual that carries two different alleles

Question 4

define phenotype

Answer 4

the observable characteristics of an organism expressed as a result of the genotype and its interaction with the environment

Question 5

what is monohybrid inheritance?

Answer 5

the inheritance of a characteristic controlled by a single gene
the phenotypic ratio of the F2 generation is 3:1

Question 6

what is a dihybrid cross?

Answer 6

it considers the inheritance of two different genes at the same time
the phenotypic ratio of the F2 generation is 9:3:3:1

Question 7

what is codominance?

Answer 7

both alleles are expressed in the phenotype
neither allele is dominant or recessive

Question 8

what are the rules of codominance?

Answer 8

when writing the genotype for codominance the gene is symbolised as a capital letter and the alleles are written as superscript letters e.g. Cᴿ

Question 9

define sex linked

Answer 9

a gene whose locus is on the X chromosome

Question 10

why are males more likely to develop as sex linked disorder

Answer 10

-there x chromosome is longer than y
-no homologous Y area for most of X
-hence males only require 1 copy of a recessive allele for expression on the phenotype

Question 11

define autosomal linkage

Answer 11

two or more genes that are located on the same chromosome which is not a sex chromosome
this means they are less likely to be seperated during crossing over so are inherited together

Question 12

define epistasis

Answer 12

when one gene modifies or masks the expression of a different gene at a different locus

Question 13

what is the hardy weinberg principle

Answer 13

it is a mathematical model which can be used to predict the allele frequencies within a population

Question 14

what are the five assumption for the hardy weinberg equation

Answer 14

-no migration to introduce or remove alleles from the population
-no mutations to create new alleles
-no selection which would favour particular alleles
-the mating is random
-the population is large

Question 15

define gene pool

Answer 15

all the alleles of all genes within a population at one time

Question 16

define allele frequency

Answer 16

the proportion of alleles within a gene pool

Question 17

what is the equation for the hardy weinberg principle

Answer 17

p^2 + 2PQ + Q^2 = 1
the equation is simultaneously used with the equation P + Q = 1
either p or q must be identifies before using the first equation
p is the frequency of the dominant allele
q is the frequency of the recessive allele
p2 is the frequency of the homozygous dominant genotype
2pq i the frequency of the heterozygous genotype
q2 is the frequency of the homozygous recessive genotype

Question 18

how is variation introduced

Answer 18

-the primary source of genetic variation is mutation
-meiosis and random fertilisation of gametes
-predation, disease and competition for the meals of survival and reproduction in natural selection

Question 19

explain allopatric speciation

Answer 19

-geographical isolation
-separation of gene pools so no interbreeding
-variation arise due to mutation
-different selection pressures cause differential reproductive success
-this leads to a change in the allele frequency
-the two populations cannot interbreed and produce fertile offpsring so they are considered two different species

Question 20

explain sympatric speciation

Answer 20

-occurs in the same habitat
-mutation causes variation
-populations become reproductively isolated due to difference in their behaviour such as performing a different courtship ritual
-due to this the two populations will not reproduce and different alleles are passed on to their offspring
-the two populations cannot interbreed and produced fertile offspring so two different species produced

Question 21

describe genetic drift

Answer 21

-random change in allele frequency in a gene pool
-the effect is much more drastic in small populations
-it is driven by chance not selection

Question 22

define community

Answer 22

all of the populations of different species in the same area at the same tim e

Question 23

define ecosystem

Answer 23

a community of biotic and abiotic factors of an area and their interactions

Question 24

why is an ecosystem described as dynamic

Answer 24

-populations constantly fall and rise
-any small change can have a large effect
-the biotic and abiotic factors may alter the conditions of an ecosystem

Question 25

define niche

Answer 25

an organisms role within an ecosystem including their psotion in the food web and habitat

Question 26

define carrying capacity

Answer 26

the maximum population size an ecosystem can support

Question 27

give examples of abiotic factors

Answer 27

-the non living features of an ecosystem

Question 28

give examples of biotic factors

Answer 28

-the living features of an ecosystem
-such as predation, diease and food supply

Question 29

what is interspecific competition

Answer 29

-when members of different species are in competition for the same resources that is in limited supply

Question 30

what is intraspecific competition

Answer 30

when members of the same species are in competition for the same resources and a mate

Question 31

outline the method for random sampling

Answer 31

-two numbered axis are laid out over sample area
-random number generator provides coordinates for the area of study
-quadrat is placed and dates is collected
-repeat at least 30 times to get a mean
-this method removes bias, allows use of statistical tests and the data is representative

Question 32

outline the process of mark capture release method

Answer 32

-capture a known sample and mark them without causing harm and must be weather resistant
-release back into the community
-allow time for reintegration
-the community is revisited and a given number of individuals are caught again
-the number of marked individuals is counted
-population size is estimated using equation
estimated population = number of organisms initially caught x number of marked organisms recaptured

Question 33

describe the steps in primary succession

Answer 33

-colonisation occurs by a pioneer species
-the pioneer specie cause a change in the environment
-this enables other species to colonise once there is a change
-this increase species diversity
-the stability increases the environment is less hostile
-climax community is reached