Topic 7 Last

Question 1

Geneotype vs Phenotype

Answer 1

• Genotype is the genetic constitution of an organism
• Phenotype is the expression of this genetic constitution and its interaction with the environment.

Question 2

What are alleles?

Answer 2

• Different forms of the same gene

Question 3

Dominant, recessive, co-dominant

Answer 3

• Dominant allele needs one allele present to be expressed in the phenotype
• Recessive alleles need 2 copies present to appear in the phenotype
• Co-dominant alleles are alleles that are both expressed in the phenotype.

Question 4

What is monohybrid inheritance

Answer 4

• Inheritance of one single character, controlled by a single gene.

Question 5

What is dihybrid inheritance?

Answer 5

• Inheritance of 2 characteristics, controlled by 2 genes
• Involves 2 genes on 2 different chromosomes

Question 6

What is codominance

Answer 6

• Both alleles will be expressed in the phenotype

Question 7

What are the 3 possible phenotypes in codominance

Answer 7

1) Heterozygous of both alleles
2) Homozygous of one allele
3) Homozygous of another allele

Question 8

What are multiple alleles?

Answer 8

• Where some genes have more than 2 alleles, for example bloody type, where type a and b are codominant over allele iO.

Question 9

What is sex-linkage and what impact do Male’s XY have?

Answer 9

• A gene that is found on a sex chromosome is said to be ‘sex-linked’
• Most genes on sex chromosomes are carried by the X chromosome so males are much more likely to show recessive phenotypes for sex linked genes as they only have one X chromsome .

Question 10

Why are females said to be carriers of recessive genes?

Answer 10

• Their dominant allele on their X chromsome may cancel out the recessive allele on the Y chromosome.

Question 11

What is autosomal linkage?

Answer 11

• Autosomal Genes that aren’t found on sex chromosomes.
• Genes found on the same autosome are said to be ‘linked’
• They will stay on the same chromosome during independent segregation in meiosis 1 and offspring will inherit these alleles together.
• The more closely two genes are together on the same chromosome, the less liekly they’ll be split by crossing over.

Question 12

Why is there a 3:1 ratio during autosomal linkage?

Answer 12

• Because the 2 linked alleles are inherited together.

Question 13

What is epistasis?

Answer 13

• The effect of one gene upon another.
• 2 genes interact, so that one may be masked (prevented from being expressed) by another.

Question 14

Why does epistasis make it difficult for genetic investigations?

Answer 14

• If the effect of one locus is altered by the effect at another locus, power to detect the first locus is reduced.

Question 15

What is chi-squared used for?

Answer 15

• Used to compare the goodness of fit of observed phenotypic ratios with expected ratios
• Can use to see if there is a dihybrid cross with linkage or no linkage

Question 16

Why is it rare to get exactly the expected phenotypic ratios?

Answer 16

• Random fertilisation of gametes
• Epistasis
• Small sample size

Question 17

What is a population?

Answer 17

• A group of organisms of the same species occupying a particular space at a particular time that can interbreed.

Question 18

What is the gene pool?

Answer 18

• The complete range of alleles present in a population.

Question 19

What is the allele frequency?

Answer 19

• How often an allele occurs in a population.

Question 20

What is the prediction of Hardy Weinberg?

Answer 20

• Mathematical model which predicts that allele frequencies will not change from generation to generation.

Question 21

Equations of Hardy Weinberg?

Answer 21

P+Q=1 (allele frequencies)
p^2+2pq+q^2=1 (frequency of individuals)
P - frequency of dominant alleles
Q - frequency of recessive alleles
2pq - Homozygous

Question 22

What is Hardy Weinberg used for?

Answer 22

• To see whether the frequency of alleles is changing (if there is a selection pressure)
• We know this as we can measure the frequency of individuals in a population

Question 23

Assumptions by the Hardy Weinberg

Answer 23

1) No natural selection meaning equal chance of survival and reproduction
2) Assumes there is no gene flow, introducing new genes or altering existing genes.
3) Assumes the population is large and isn’t affected by genetic drift
4) Assumes that there are no mutations as allele frequencies don’t get altered.

Question 24

What is disruptive selection?

Answer 24

• When two extreme genotypes at both ends of the range are the most common and likely to survive and reproduce.

Question 25

What is evolution?

Answer 25

- The change in allele frequencies in a population

Question 26

What is speciation

Answer 26

- When new species develop from a common ancestor

Question 27

Process of speciation

Answer 27

1) Geographic isolation by a natural barrier so reproductively isolated 2) Each population finds itself in a different environment, so experiences different selection pressures 3) Natural selection occurs and different alleles are of an advantage in the different populations. 4) Allele frequencies change in the two gene pools 5) Two populations are so genetically different that they no longer interbreed to produce fertile offspring.

Question 28

Allopatric speciation vs Sympatric speciation

Answer 28

Allopatric - physical reproductive isolation via a river or moutanin range Sympatric - Populations don't become physically separated but there are other reasons for reproductive isolation. (change in genetics, behavioural changes)

Question 29

Genetic drift

Answer 29

- When allele frequencies change due to chance - Not every individual will become a parent - Not the same offsprint when they do have kids. (as a result, chance rather than selection pressures dictates the likelihood of reproduction)

Question 30

Why does genetic drift have more of an impact in smaller populations?

Answer 30

- Because more individuals make up a larger proportion of the population.

Question 31

Relationship between natural selection and genetic drift?

Answer 31

- Work alongside each other in evolution but ultimately one may drive evolution more, depending on the size of the population. - Unlike natural selection, genetic drift doesn't cause better adaptation to the environment.

Question 32

Community

Answer 32

- Populations of different species in a habitat

Question 33

Ecosystem def

Answer 33

- Community and the non-living components of its environment

Question 34

What is a niche?

Answer 34

- A species' role within an ecosystem

Question 35

What happens when 2 species try to compete for the same niche?

Answer 35

- They will compete with each other.

Question 36

What is the carrying capacity?

Answer 36

- The maximum stable population size of a species that an ecosystem can support.

Question 37

Factors which affect the carrying capacity...

Answer 37

- The effect of abiotic factors such as light intensity, water availability, food availability, soil pH and temperature - Interactions between organisms such as inter and intraspecific competition - Predation

Question 38

Interspecific vs intraspecific competition

Answer 38

- Interspecific competition is when organisms of different species compete for resources. - Interspecific competition results in decreasing food availability for both species - So population size decreases as survival and reproduction is less likely. Intraspecific competition is when organisms of the same species compete with each other for resources

Question 39

How does predation affect carrying capacity

Answer 39

- Happens when one organism eats another. - As population size increase, predator population increases but as predators eat prey, their population will also decrease when food becomes scarce.

Question 40

How do we estimate population sizes using radnomly placed quadrats and on what type of organism?

Answer 40

Measure on slow moving organisms 1) Randomly place quadrats, being random to avoid bias. 2) Plot coordinates and use a radnom number generator to generate coordinates. 3) Place a 1mx1m quadrat and count the number of individuals, repeating many times. 4) Calculate the mean 5) Multiple mean x area.

Question 41

Why do we use quadrats?

Answer 41

- To measure gradual changes in population size across an area. - By taking samples at regular intervals along a transect. - More samples means more reliability.

Question 42

How do you estimate population sizes for mobile organisms.

Answer 42

- Mark-release-recapture 1) Capture a sample of individuals from the population by using E.g pitfall traps for insects. 2) Count the number of individuals and mark them in a harmless way 3) Return them to mix with the population 4) Capture second sample and count the number of individuals caught and number of those marked. 5) S1 x S2 divided by the number marked in S2

Question 43

Assumptions from mark-capture-release

Answer 43

- Marking doesn't affect survival by making them more visible to predators. - We also assume that marked individuals mix randomly and evenly with the population. - We assume no change in population size

Question 44

Outline primary succession

Answer 44

- Takes place on land that is newly formed or has been exposed 1) Pioneer species are those that live in extreme abiotic conditions that are hostile with little nutrients or water. 2) Adaptations allow them to live in these conditions such as asexual reproduction. Or the ability to fix nitrogen and tolerant to salt. 3) Pioneer species change the environemnt to make abiotic conditions less hostile such as eroding the rock and releasing minerals or adding more humus. 4) New species makes the environment more hostile for the previous species. 5) Over time conditions become less hostile and organisms becoming better adapted and outcompete older species. 6) Climax community is formed meaning the same species is stable and has been present over a long period of time.

Question 45

Outline secondary succession

Answer 45

1) Climax community is cleared in some way 2) Succession occurs quicker due to soil that contains seeds and nutrients to start a new community. 3) Pioneer species are larger plants therefore climax community reaches much quicker due to the lack of hostile conditions.

Question 46

Why would we prevent succession from continuing through conservation?

Answer 46

- We prevent succession from continuing to preserve an ecosystem in its current stage of succession. - If another species arrived and dominated, existing species would be outcompeted and die out.

Question 47

Methods of conservation

Answer 47

- Grazing and mowing to remove growing tips so no climax community is reached. - Managed fires so all species are wiped out and secondary succession will occur. Small species are pioneer species and grow more quickly than larger trees and shrubs.