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Biology > Genetics, Populations, Evolution and Ecosystems > Flashcards

Genetics, Populations, Evolution and Ecosystems Flashcards

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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
What is meant by the term "Dominance Hierarchy"?
When there are more than 3 alleles for a particular gene the hierarchy involves alleles that are dominant to those below it
26
what are autosomes?
Any chromosome that is not a sex chromosome
27
What is meant the term "sex- linked"?
Any gene that is carried on the X or Y chromosomes (sex chromosomes)
28
Why is it that most sex-linked diseases are more common in males than females?
- 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
29
What sex chromosomes do males have? what do females have?
Males- XY | females- XX
30
What is "Autosomal Linkage"?
If 2 genes (A and B) occur on the same non-sex chromosomes (autosomes), they are linked
31
What is Epistasis?
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
What are chi-squared tests used for? When do you use chi-squared?
Asses whether deviations from expected results are significant or simply due to chance -Used when categorical data is given
33
Why might the observed results differ from the expected results in a chi-squared test?
- Fertilisation of gametes is random - Independent assortment in meiosis is random - Crossing over is random
34
What is the formula for chi-squared?
Σ(observed value-expected value)squared/(expected value)
35
What is the criteria needed to carry out a chi-squared test?
- 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
What is the general Null Hypothesis for a chi-squared test?
There is no significant difference between the expected number of... and the observed number of ...
37
How do you work out the degrees of freedom in a chi-squared test?
DOF = no. Of classes - 1
38
What value is always used in a chi-squared test for the probability that deviation is due to chance alone
0.05 or 5%
39
What are the conditions for a null hypothesis to be rejected or accepted in a chi-squared test?
Probability > critical value ACCEPT null hypothesis Probability < critical value REJECT null hypothesis
40
What is the Hardy- Weinberg principle? And what is it used for?
An equation to work out the frequencies of the alleles of a particular gene in a population
41
What 6 things must be true, before you can use the Hardy- Weinberg Principle ?
- 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
How many alleles does a person have for each of their genes? What value does the sum of the frequencies equal?
Every person has 2 alleles of a gene | Frequencies of the 2 alleles must add up to 1
43
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
Realistically you see a mixture of genotypes in a population
44
What is a heterozygote?
An individual having 2 different alleles for a particular gene
45
What is meant by the term "gene pool"?
all the alleles of all the genes in a population
46
What is meant by the term "Allelic Frequency"?
The number of times an allele occurs within a gene pool
47
What is the equation for the Hardy-Weinberg Principle? What do the letters represent? What other equation can you use these letters in?
p^2 + 2pq+ q^2=1 p= frequency of the dominant allele q= frequency of the recessive allele so, p+q=1
48
In which scenarios do you use the 2 different Hardy-Weinberg equations?
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
Describe the structure of a chromosome
A DNA molecule associated with proteins called histones
50
State the difference between intraspecific and interspecific competition
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
State and explain what is meant by the Competitive Exclusion Principle?
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
Why is it difficult to conclude that it was due to competition that a population size changed?
- 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
What is Predation?
When 1 organism is consumed by another
54
During lab observations of Predation, the prey is usually eventually exterminated. Why does this not happen in nature?
- 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
State some problems with studying in the wild
- 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
State the effect of predator-prey relationships on population size
-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
What are the 2 conditions needed for Natural Selection to occur?
- Intense competition | - Predation
58
What is meant by the term "Selection pressures"? Give examples
"Environmental factors that limit the population of a species" E.g, Predation, competition and disease
59
What is meant by the term "Population"?
All the members of 1 species in a particular space at a particular time, potentially capable of interbreeding
60
What is a community?
All the populations in a given area at a given time
61
What is an ecosystem?
The community and all the non-living components in the environment
62
What is a habitat?
The place where an organism lives
63
What is a niche?
The place where an organism is found & what is does there "The organisms role in the ecosystem"
64
What is meant by a populations "Carrying capacity"
The certain/ maximum size the population can reach within the ecosystem
65
What is meant by the term "species"?
Organisms that have similar features that are able to interbreed to produce fertile offspring
66
How does allele frequency lead to reproductive success?
- 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
Describe Directional selection, when does it occur? Give an example
- 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
State the effects of Directional selection on a distribution graph
- The mean value for the phenotype shifts | - Range stays the same
69
Describe Stabilising selection, when does it occur? Give an example
- 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
State the effects of Stablilisng selection on a distribution graph
- Mode is in the same position - Mode value increases - Range decreases (reduced variation)
71
Describe Disruptive selection and give an example
(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
Define Speciation
Evolution of new species from existing ones
73
What are polyploid offspring?
Offspring that have an additional set of chromosomes
74
Describe what is meant by Allopatric speciation
Speciation that occurs due to geographical isolation/ separation
75
Explain how species evolve through Allopatric speciation
- 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
Describe what is meant by Sympatric speciation
Speciation that occurs within a population in the same area, leading to them reproducing separately
77
Explain how species evolve through Sympatric specitation
- 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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