Biology Unit 4.4 - Variation and Evolution

Question 1

Explain variation and evolution…

Answer 1

If a species is to survive in a constantly changing environment sources of variation are essential

Question 2

How does sexual reproduction cause variation?

Answer 2

Produces genetic variation amongst individuals in a population:
* Crossing over during chiasmata produces new combinations and seperation of linked genes
* Chromosomes arrange themselves randomly on the spindle and seperate independently, so daughter cells contain different combinations
* Random distribution of chromatids at metaphase II
* Chromosome making up a homologous pair carries different genetic material

Question 3

What is continuous variation?

Answer 3

Characteristics controlled by the number of genes, where differences are not clear cut e.g.,:
* Height
* Weight
* Hand span
* Length of feet
* Milk yield

Question 4

What is discontinuous variation?

Answer 4

Characteristics that are clear cut and easy to tell apart, which are controlled by a single gene

Question 5

What is non-heritable variation?

Answer 5

Phenotypic variation caused by environmental factors

Question 6

What are the methods of creating variety?

Answer 6

• Prophase I - crossing over at chiasmata during synapsis where genetic material can be exchanged
• Metaphase I - random independent assortment of chromosomes along the equator
• Metaphase II - random independent assortment of chromatids along the equator

Question 7

What is continuous data?

Answer 7

Data containing a ranger, where a T-test is used to compare means

Question 8

What is discontinuous data?

Answer 8

Data consisting of disctint categories, where a Chi-squared test is used to compare expected and observed results

Question 9

What environmental factors control population?

Answer 9

Biotic:
* Predation
* Parasitism
* Disease
* Competition

Abiotic:
* Natrual disaster
* Temperature
* pH
* Light intensity

Question 10

What is intraspecific competition?

Answer 10

Compeition for resources between members of the same population or species

Question 11

What is intraspecific competiton?

Answer 11

Competition for resources between members of different species within the same community

Question 12

What is selection pressure?

Answer 12

Factor whis has a direct effect on the numbers of individuals in a population e.g., food supply, nesting sites and climate

Question 13

What are the effect of mutations on adaptation?

Answer 13

New genes can appear in a species by mutation which may lead to fantastic adaptations to the environment

Question 14

What is a gene pool?

Answer 14

Sum of all the different genes in a population, where the frequency of any given allele is known as the allele or gene frequency

Question 15

What factors change allele frequency?

Answer 15

Environmental changes:
* Allele specific mortality or emigration
* Allele specific reproduction or immigration
* Chance

May cause some phenotypes to be selected for while others are selected against, leading to some alleles becoming more or less frequenct while others are totally lost

Question 16

What is the Hardy-Weinberg principle?

Answer 16

The frequencies of dominant and recessive alleles and genotypes will remains contant from one generation to the next if:
* Population is large
* No selection for or against a particular phenotype
* Random mating
* No mutations
* Population is isolated

Question 17

How can the Hardy-Weinberg principle be applied?

Answer 17

Demonstartes that a large proportion of recessive allels exist in the heterozygotes, meaning they are a reservoir for genetic variability

Question 18

What is the Hardy-Weinberg equation?

Answer 18

p2 + 2pq + q2 = 1

p +q = 1

Question 19

What is genetic drift?

Answer 19

Chance increases or decreases in allele frequencies over time, which has the greatest effect within small or isolated populations

Question 20

Why is the frequency of the sickle-cell anemia allele still high?

Answer 20

Heterozygous advantage, as heterozygous individuals are less susceptible to malaria, but homozygous individuals are very susceptible to malaria

Question 21

What is the origin of species?

Answer 21

Species are groups of closely related organisms that can interbreeding and produce fertile offspring, which often have morphological similarity

Question 22

How is speciation caused by isolation?

Answer 22

Population is split into ateast two isolated populations with no gene exchange between the two, leading to mutation and natural selection occuring independently allowing for evolution into new species

Question 23

What is allotropic isolation?

Answer 23

Isolation where a physical barrier prevents two population form mating and interbreeding

Question 24

What is sympatric isolation?

Answer 24

Isolation where organisms inhabitating an area are seperated/becom reproductively isolated into two groups due to non-georgaphical reasons

Question 25

What is hybdrid sterility?

Answer 25

Different species, which are related, can reproduce, but this leads to the production on infertile offspring

Question 26

What is the cause of hybrid sterility?

Answer 26

The parent species have different chromosome numbers of, so they can’t produce viable gametes as chromosomes are not homologous and cannot form bivalent during prophase I of meiosis

Question 27

Describe Charles Darwin’s theory of evolution?

Answer 27

• Reproduction leads to overproduction of offspring
• Not all offspring survive, so population number remains fairly constant
• Selection pressures are harsh but help maintain a constant population number
• Variation due to sexual reproduction, mutations and meiosis confer selective advantages and disadvantages to the offsrping, where high genetic variation is key to a species’ surivial
• Better adapted offsping have a selective advantage and are more likley to survive, while those less well adapted are more likley to die
• Offspring inherit beneficial characteristics from their parents, which is repeated every generation, causing organisms to become highly adapted to their environment
• Gradual changes overtime, may lead to the formation of a new species