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Biology > Genetics, Populations, Evolution and Ecosystems > Flashcards

Genetics, Populations, Evolution and Ecosystems Flashcards

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AP® Biology flashcards Biology 101 flashcards
1
Q

What is a gene?

A

a length of DNA/ sequence of nucleotide bases that codes for a particular polypeptide

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2
Q

What is a locus?

A

The position of a gene on a particular DNA molecule

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3
Q

What are alleles?

A

different forms of the same gene

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4
Q

What is the genotype?

A

The genetic make-up of an organism

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5
Q

What is a phenotype?

A

observable characteristics of an organism resulting from the expression of its genes and its interactions with the environment.

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6
Q

State (and describe) what is meant by an enzymatic mechanism

A

A mechanism that brings about a characteristic.
(All genes code for polypeptides which may be an enzyme that is involved in a biochemical pathway, which leads to a characteristic)

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7
Q

How many chromosomes do human cells contain? Which cells are the 2 exceptions and how many chromosomes do they contain?

A

46 chromosomes
GAMETES: 23 chromosomes
RED BLOOD CELLS: 0 chromosomes (no nucleus)

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8
Q

What is meant by the term Homozygous?

A

The alleles on each of the chromosomes are the same

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9
Q

What is meant by the term Heterozyous?

A

The alleles on each of the chromosomes are different

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10
Q

What is meant by the term Dominant?

A

The allele of the heterozygote that expresses itself in the phenotype (e.g. BB is homozygous DOMINANT)

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11
Q

What is meant by the term Recessive?

A

The allele of the heterozygote that is not experssed in the phenotype (e.g.
If B- is a dominant allele for black fur in bears
& b- is a recessive allele for brown fur in bears
a heterozygote Bb will not express the recessive b
SO it appears black.)

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12
Q

What is meant by the term modification?

A

Changes made to the phenotype of an organism, that is not usually inherited by future generations

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13
Q

What is a mutation?

A

a random change in the base sequence of a gene

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14
Q

What is meant by Monohybrid inheritance?

A

The inheritance of a single gene, where crosses involve only a single pair of alleles

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15
Q

What are homologous chromosomes ?

A

Chromosomes that contain DNA which code for the same genes.

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16
Q

Why does only 1 allele from each pair pass into a single gamete?

A

Due to meiosis-

Separation of homologous chromosomes during the first division of meiosis separates the allele pairs.

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17
Q

What is the “first filial”?

A

The first generation (F1)

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18
Q

Describe what is meant by pure breeding?

A

Repeatedly breeding the dominant phenotype with other organisms of the dominant phenotype
Leads to a homozygous dominant organism

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19
Q

How could you find out whether an organism with a dominant phenotype was homozygous dominant (e.g. TT) or Heterozygous? (Tt)

A
  • Cross organism with a homozygous recessive (e.g. tt) and look at the offspring
  • If all the offspring express the dominant phenotype, the organism was homozygous dominant (TT)
  • If at least one of the offspring express the recessive phenotype, the organism was heterozygous (Tt)
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20
Q

What is meant by the term Dihybrid Inheritance?

A

Where 2 characters, determined by 2 different genes located on different chromosomes are inherited.

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21
Q

What does it mean for offspring to be “recombinants”?

A

Offspring that have a combination of the characteristics from both the original parents.

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22
Q

Why are 4 types of gametes formed after Dihybrid Inheritance?

A

An allele from one pair of chromosomes can enter the gamete with either allele from the other pair because of independent assortment.

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23
Q

When does Co-dominance occur?

A

When 2 inherited alleles are both equally dominant (therefore both alleles are experessed in the phenotype)

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24
Q

What is meant by the term “multiple alleles”?

A

When there are several different alleles of a gene

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25
Q

What is meant by the term “Dominance Hierarchy”?

A

When there are more than 3 alleles for a particular gene the hierarchy involves alleles that are dominant to those below it

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26
Q

what are autosomes?

A

Any chromosome that is not a sex chromosome

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27
Q

What is meant the term “sex- linked”?

A

Any gene that is carried on the X or Y chromosomes (sex chromosomes)

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28
Q

Why is it that most sex-linked diseases are more common in males than females?

A
  • Characteristics controlled by recessive alleles on the X chromosome will appear more commonly in males
  • The X chromosome is much longer than the Y
  • Therefore, these characteristics do not have a homologous portion that could have a dominant allele to save them from it
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29
Q

What sex chromosomes do males have? what do females have?

A

Males- XY

females- XX

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30
Q

What is “Autosomal Linkage”?

A

If 2 genes (A and B) occur on the same non-sex chromosomes (autosomes), they are linked

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31
Q

What is Epistasis?

A

when an allele of 1 gene affects or masks the expression of another in the phenotype (This can happen where genes act in sequence by determining the enzymes in a biochemical pathway)

32
Q

What are chi-squared tests used for? When do you use chi-squared?

A

Asses whether deviations from expected results are significant or simply due to chance
-Used when categorical data is given

33
Q

Why might the observed results differ from the expected results in a chi-squared test?

A
  • Fertilisation of gametes is random
  • Independent assortment in meiosis is random
  • Crossing over is random
34
Q

What is the formula for chi-squared?

A

Σ(observed value-expected value)squared/(expected value)

35
Q

What is the criteria needed to carry out a chi-squared test?

A
  • Sample must be relatively large (above 20)
  • Data should be discrete categories (no overlapping values)
  • Used in scenarios where obtained data is compared to expected data
  • Raw values must be used (no percentages)
36
Q

What is the general Null Hypothesis for a chi-squared test?

A

There is no significant difference between the expected number of… and the observed number of …

37
Q

How do you work out the degrees of freedom in a chi-squared test?

A

DOF = no. Of classes - 1

38
Q

What value is always used in a chi-squared test for the probability that deviation is due to chance alone

A

0.05 or 5%

39
Q

What are the conditions for a null hypothesis to be rejected or accepted in a chi-squared test?

A

Probability > critical value
ACCEPT null hypothesis

Probability < critical value
REJECT null hypothesis

40
Q

What is the Hardy- Weinberg principle? And what is it used for?

A

An equation to work out the frequencies of the alleles of a particular gene in a population

41
Q

What 6 things must be true, before you can use the Hardy- Weinberg Principle ?

A
  • Organisms must be diploid
  • Only sexual reproduction occurs
  • Mating is random
  • Population size is large
  • Allele frequencies are equal in the sexes
  • There is no migration, mutation or selection
42
Q

How many alleles does a person have for each of their genes? What value does the sum of the frequencies equal?

A

Every person has 2 alleles of a gene

Frequencies of the 2 alleles must add up to 1

43
Q

Why do we need to use the Hardy- Weinberg Principle, and not just the fact that the 2 alleles add up to 1?

E.g if it is TT the frequency of T is
1

If it is Tt the frequency of T is 0.5

A

Realistically you see a mixture of genotypes in a population

44
Q

What is a heterozygote?

A

An individual having 2 different alleles for a particular gene

45
Q

What is meant by the term “gene pool”?

A

all the alleles of all the genes in a population

46
Q

What is meant by the term “Allelic Frequency”?

A

The number of times an allele occurs within a gene pool

47
Q

What is the equation for the Hardy-Weinberg Principle? What do the letters represent? What other equation can you use these letters in?

A

p^2 + 2pq+ q^2=1
p= frequency of the dominant allele
q= frequency of the recessive allele
so, p+q=1

48
Q

In which scenarios do you use the 2 different Hardy-Weinberg equations?

A

use (p^2+2pq+q^2=1)
when information about the phenotypes/ genotypes is given
Use (p+q=1)
when information about the allele frequency is given

49
Q

Describe the structure of a chromosome

A

A DNA molecule associated with proteins called histones

50
Q

State the difference between intraspecific and interspecific competition

A

INTRAspecific:
-Same species competing for resources
-The larger the availability of resources, the larger the population
-Availability of resources will determine population size
INTERspecific:
-Different species competing for resources
-Individuals of different species occupying the same niche will have a competitive advantage over one another (Competitive Exclusion Principle)
-One population size will grow, as the other will shrink

51
Q

State and explain what is meant by the Competitive Exclusion Principle?

A

CEP:”where populations of 2 species initially occupy the same niche, one normally has a competitive advantage”

  • The population of 1 species will gradually grow, whilst the other diminishes
  • conditions remain the same
  • leads to the complete removal of 1 of the species
52
Q

Why is it difficult to conclude that it was due to competition that a population size changed?

A
  • Many abiotic/biotic factors have an affect on population size
  • Hard to establish a casual link for an observed correlation
  • Data on natural population sizes are hard to obtain and are not always reliable
53
Q

What is Predation?

A

When 1 organism is consumed by another

54
Q

During lab observations of Predation, the prey is usually eventually exterminated. Why does this not happen in nature?

A
  • Labs have confined spaces, making it easier for the prey to be hunted and consumed
  • Whereas in nature, the population can travel a greater area and the variety of areas for the prey to use as refuge is much more diverse.
55
Q

State some problems with studying in the wild

A
  • Difficult to count all of the individuals in a population
  • Can be dangerous for the organisms being studied (e.g. if factors such as tranquilizers must be used)
  • Dangerous for the researcher
  • Only estimates using sampling techniques can be made
  • Need to ensure it’s not mating season (drastic changes in population sizes are difficult to monitor)
56
Q

State the effect of predator-prey relationships on population size

A

-Predators eat prey- population of prey is reduced
-Predators now in greater competition between each other for remaining prey
-Predator population falls
-Fewer predators; fewer preys being eaten
-Prey population increases
-Predators have more food- predator population increases
CYCLE CONTINUES

57
Q

What are the 2 conditions needed for Natural Selection to occur?

A
  • Intense competition

- Predation

58
Q

What is meant by the term “Selection pressures”? Give examples

A

“Environmental factors that limit the population of a species”

E.g, Predation, competition and disease

59
Q

What is meant by the term “Population”?

A

All the members of 1 species in a particular space at a particular time, potentially capable of interbreeding

60
Q

What is a community?

A

All the populations in a given area at a given time

61
Q

What is an ecosystem?

A

The community and all the non-living components in the environment

62
Q

What is a habitat?

A

The place where an organism lives

63
Q

What is a niche?

A

The place where an organism is found & what is does there
“The organisms role in the ecosystem”

64
Q

What is meant by a populations “Carrying capacity”

A

The certain/ maximum size the population can reach within the ecosystem

65
Q

What is meant by the term “species”?

A

Organisms that have similar features that are able to interbreed to produce fertile offspring

66
Q

How does allele frequency lead to reproductive success?

A
  • Organisms in a population produce offspring, with a variety of alleles
  • There is competition between the offspring to survive
  • Some members have certain alleles that make them better suited to survive
  • These members live longer (successful individuals), produce more offspring and pass on their advantageous alleles
  • Over many generations, the frequency of the advantageous allele will increase
67
Q

Describe Directional selection, when does it occur? Give an example

A
  • Occurs when there is a change in the environment
  • A phenotype at one extreme of the range is selected for, and the other extreme is selected against

E.g, Allele for high speed in cheetahs increased over time

68
Q

State the effects of Directional selection on a distribution graph

A
  • The mean value for the phenotype shifts

- Range stays the same

69
Q

Describe Stabilising selection, when does it occur? Give an example

A
  • More likely to occur when the environment is NOT changing
  • Favors average individuals
  • Eliminates extremes of a certain phenotype

E.g, Mammalian fur length

70
Q

State the effects of Stablilisng selection on a distribution graph

A
  • Mode is in the same position
  • Mode value increases
  • Range decreases (reduced variation)
71
Q

Describe Disruptive selection and give an example

A

(OPPOSITE OF STABILISING)
-Favors extreme phenotypes at the expense of the intermediate phenotypes
-Least common
-2 sub populations can form over time
E.g, Both pale colored and dark colored snails could camouflage in a particular environment.

72
Q

Define Speciation

A

Evolution of new species from existing ones

73
Q

What are polyploid offspring?

A

Offspring that have an additional set of chromosomes

74
Q

Describe what is meant by Allopatric speciation

A

Speciation that occurs due to geographical isolation/ separation

75
Q

Explain how species evolve through Allopatric speciation

A
  • Geographical isolation
  • Separate gene pools/ no interbreeding between the populations
  • Varation due to mutations
  • Different selection pressures/ enviornments
  • Different reproductive success
  • Leads to a change (an increase) in allele frequency
76
Q

Describe what is meant by Sympatric speciation

A

Speciation that occurs within a population in the same area, leading to them reproducing separately

77
Q

Explain how species evolve through Sympatric specitation

A
  • Variation due to
  • Mutation
  • Some individuals have the allele to survive
  • Differential reproductive success
  • Increase in allele frequency
  • No interbreeding

Biology (7 decks)

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