Section 7: Genetics, populations, evoloution, and ecosystems Flashcards
(93 cards)
1
Q
Define genotype and phenotype
A
Genotype: The genetic constitution of an organism (the alleles it has for a gene)
Phenotype: The expression of the genes and its interaction with the environment
2
Q
What is homozygous and heterozygous?
A
Homozygous: A pair of homologous chromosomes carrying the same alleles for a single gene
Heterozygous: A pair of homologous chromosomes carrying two different alleles for a single gene
3
Q
What is it called when both alleles are equally dominant and expressed in the phenotype?
A
Codominant
4
Q
What is monohybrid inheritance
A
the inheritance of a single gene with one trait
5
Q
What is the difference between monohybrid and dihybrid inheritance
A
- Monohybrid inheritance:
• Involves the inheritance of one trait controlled by a single gene with two alleles (e.g., flower color).
• Example: Crossing a pea plant with purple flowers (Pp) with one having white flowers (pp).- Dihybrid inheritance:
• Involves the inheritance of two traits controlled by two different genes, each with two alleles (e.g., seed color and seed shape).
• Example: Crossing a plant with yellow round seeds (YyRr) with one having green wrinkled seeds (yyrr).
- Dihybrid inheritance:
6
Q
What is Mendels law of independent assortment
A
Each member of the a pair of alleles may combine randomly with either of another pair of
the alleles of two (or more) different genes get sorted into gametes independently of one another. In other words, the allele a gamete receives for one gene does not influence the allele received for another gene.
7
Q
What are the sex chromosomes of females and males in humans
A
Females XX chromosomes
Males XY chromosomes
8
Q
What are non-sex-linked chromosomes called
A
autosomes
9
Q
What is autosomal linkage and what does it presume?
A
When two or more genes are carried on the same autosome
assuming there is no crossing over and don’t segregate.
10
Q
What is it called when an allele of one gene affects or masks the expression of another in the phenotype
A
Epistasis
11
Q
What is epistasis
A
when an allele of one gene affects or masks the expression of another in the phenotype
12
Q
If my critical value at p=0.05 is greater than my calculated value of chi-squared is the data significant?
A
This means there is no significant difference between the observed and expected data. In this case, you accept the null hypothesis and conclude that any differences are likely due to chance.
13
Q
How do you calculate degrees of freedom
A
Number of classes minus 1
14
Q
What are the conditions for the hardy-weinberg principles
A
no mutations arise
population is isolated
no selection
population is large
mating is random
15
Q
What are the equations of the hardy weinberg principles
A
p + q = 1
p2 + q2 + 2pq = 1
Let the probability of allele A = p
and the probability of allele a = q
16
Q
Define the term allelic frequency
A
Number of times an allele occurs in a gene pool
17
Q
State what the hardy-weinberg principle predicts
A
The proportion of dominant and recessive alleles in a gene pool remains the same from one generation to the next
18
Q
Genetic variation arises as a result of:
A
Mutations
Meiosis
Random fertilisation of gametes
19
Q
State how genetic variation is increases in asexually reproducing organisms
A
mutation only
20
Q
State four factors that lead to differential survival and reproduction
A
predation
competition
disease
natural disasters
21
Q
What are the three types of selection
A
stabilising selection - eliminate extremes
directional selection - one extreme favoured
disruptive selection - extremes favoured
22
Q
What is speciation
A
the evolution of new species from existing ones
23
Q
Distinguish allopatric and sympatric speciation
A
• Allopatric speciation: Occurs when populations are geographically isolated, preventing gene flow and leading to the formation of new species.
• Sympatric speciation: Happens within the same geographic area, often due to reproductive barriers like behavioral differences, polyploidy, or ecological niche specialization.
24
Q
Explain how isolation can lead to the formation of new species ( 5 marks )
A
- Populations become isolated (e.g., geographically or reproductively).
- No gene flow occurs between the isolated populations.
- Each population experiences different selection pressures.
- Beneficial mutations arise, and natural selection increases the frequency of advantageous alleles.
- Over time, genetic differences accumulate, and the populations can no longer interbreed to produce fertile offspring, forming new species.
25
Define the term “ecosystem”. (2 marks)
1. An ecosystem is a community of living organisms (biotic) and their interactions with the non-living (abiotic) environment.
2. It involves the flow of energy and cycling of nutrients.
26
Explain the difference between biotic and abiotic factors in an ecosystem. (2 marks)
1. Biotic factors are the living components, such as predators or competition.
2. Abiotic factors are the non-living components, such as temperature, light, and pH
27
What is meant by the term “carrying capacity”? (2 marks)
1. The maximum stable population size that an environment can support.
2. It is determined by factors like food availability, space, and abiotic conditions.
28
Describe how a population size is regulated by negative feedback. (3 marks)
1. If population size exceeds carrying capacity, resources become limited, leading to competition and increased death rates.
2. If population size falls below carrying capacity, resources become more abundant, increasing reproduction rates.
3. This maintains population size around the carrying capacity.
29
Explain the role of pioneer species in primary succession. (3 marks)
1. Pioneer species colonize bare or inhospitable environments.
2. They change abiotic factors, such as improving soil quality by adding organic matter.
3. This makes conditions suitable for other species, leading to ecological succession.
30
How does interspecific competition differ from intraspecific competition? (2 marks)
1. Interspecific competition occurs between individuals of different species competing for the same resources.
2. Intraspecific competition occurs between individuals of the same species competing for resources.
31
Explain how mark-release-recapture is used to estimate population size. (4 marks)
1. Capture a sample of the population, mark them, and release them back.
2. Allow time for the marked individuals to mix with the population.
3. Recapture a second sample and count how many are marked.
4. Use the formula: (Number marked in 1st sample × Total in 2nd sample) ÷ Number marked in 2nd sample.
32
What is conservation, and why is it important? (3 marks)
1. Conservation is the management of ecosystems to maintain biodiversity.
2. It ensures the survival of species and their genetic diversity.
3. It provides ecosystem services, like air and water purification, and resources for humans.
33
Describe the difference between primary and secondary succession. (3 marks)
1. Primary succession begins on newly formed or bare land with no soil (e.g., volcanic rock).
2. Secondary succession occurs on land where soil is present but vegetation has been removed (e.g., after a fire).
3. Secondary succession is faster because soil and seeds are already present.
34
What is a dihybrid cross? (2 marks)
1. A genetic cross involving two traits controlled by two different genes.
2. Example: Crossing pea plants for seed color (yellow/green) and seed shape (round/wrinkled).
35
What is the difference between dominant and recessive alleles? (2 marks)
1. A dominant allele is expressed in the phenotype even if only one copy is present.
2. A recessive allele is only expressed in the phenotype if both alleles are recessive.
36
Explain why males are more likely than females to show recessive sex-linked traits. (3 marks)
1. Males have one X and one Y chromosome.
2. Recessive alleles on the X chromosome are expressed as there is no equivalent allele on the Y chromosome.
3. Females have two X chromosomes, so a dominant allele on one X can mask the recessive allele on the other.
37
Describe the purpose of a test cross and how it is carried out. (3 marks)
1. Used to determine the genotype of an individual showing a dominant phenotype.
2. Cross the individual with one that is homozygous recessive.
3. Analyze the offspring phenotypes: a 1:1 ratio indicates heterozygosity.
38
Explain how codominance affects the phenotypes of offspring. (3 marks)
1. In codominance, both alleles are expressed in the phenotype.
2. Heterozygotes show a combination of both alleles.
3. Example: In blood groups, IAIB results in the AB phenotype.
39
What is epistasis, and how does it affect phenotypic ratios? (4 marks)
1. Epistasis is when one gene affects the expression of another gene.
2. It can modify Mendelian ratios.
3. For example, in dihybrid inheritance, the ratio may change from 9:3:3:1 to 9:4:3 due to epistasis.
4. One gene may mask or suppress the other gene.
40
State the Hardy-Weinberg equation and explain what each term represents. (3 marks)
1. Equation: p^2 + 2pq + q^2 = 1 .
2. p^2 : Frequency of homozygous dominant individuals.
3. 2pq : Frequency of heterozygous individuals.
4. q^2 : Frequency of homozygous recessive individuals.
41
What is genetic drift, and in which populations does it have a greater effect? (3 marks)
1. Genetic drift is the random change in allele frequencies in a population over time.
2. It has a greater effect in small populations.
3. Alleles can be lost or fixed by chance more easily in smaller populations.
42
Explain how natural selection leads to evolution. (5 marks)
1. Variation exists in a population due to mutations.
2. Some individuals have advantageous alleles.
3. These individuals are more likely to survive and reproduce.
4. They pass on their advantageous alleles to their offspring.
5. Over generations, the frequency of the advantageous allele increases in the population.
43
Describe how you could estimate the number of plants in a field
Place two tape measures at 90 degrees to each other to create grids
Obtain random coordinates
count number of plants in each coordinate
Large sample (10+) and calculate a mean
Area of the field multiplied by mean number of plants in each quadrant
44
If i multiply Xmm by 1000 what unit have i converted the value X to
Um
cant find symbol
45
How would i convert Xcm into um
multiply by 10,000
46
km -> m -> mm -> um -> nm
what would i multiply each one by to convert the units
x 1000
47
Suggest factors that result in phenotypic diversity
Habitat differences
Gene mutations
48
Define Sex-linkage?
A gene whose locus is on the X chromosome
49
Define Epistasis
When one gene modifies or masks the expression of a finger et gene at a different locus
50
What is the locus?
The position of a gene on a particular DNA molecule
51
In genetic crosses, the observed phenotypic ratios obtained in the offspring are often not the same as the expected ratios. Suggest two reasons why.
Small sample size
Fusion/fertilisation of gametes is random
Linked genes
Epistasis
Lethal genotypes
52
What is pure-breeding?
When an organisms are bred repeatedly to consistently give rise to a specific charateristic
53
What is the name for when a single character is passed on from one generation to the next?
Mono hybrid inheritance
54
What is dihybrid inheritance?
how two characters, determined by two different genes located on different chromosomes, are inherited
55
In dihybrid inheritance, what are the two characteristics determined by and where are they located?
Determined by two different genes located on different chromosomes
56
What is the law of independent assortment?
Each member of a pair of alleles may romaine randomly with either of another pair
57
What is codominance?
When both alleles are expressed in the phenotype
For example a red and white allele expresses as pink
58
Why can only two alleles be present in an individual at one time?
Because there are only two homolougous chromosomes and therefore only two gene loci
59
What is meant by multiple alleles?
Where there are more than two alleles, of which only two may be present at the loci of an individual’s homologous chromosomes
60
What are the sex chromosomes for male and female in humans?
Females XX
Males XY
61
What qualifies two genes to be called linked?
Any two genes that occur on the same chromosomes are said to be linked
62
What are the chromosomes that are not the sex chromosomes called?
Autonomies
63
What is an autosome?
The non sex chromosomes
64
Define autosomal linkage.
Two or more genes are carried on the same autosome
65
What is the properties of inheritance two genes carried on the same autosome (autosomal linkage)
Assuming there is no crossing over, all the linked genes remain together during meiosis and so pass into gametes
They do not segregate in accordance with Mendelssohn Law of Independent Assortment
66
Distinguish between sex-linkage and autosomal linkage.
In sex-linkage the linked genes are on the same sex chromosome (usually the X chromosome ) whereas in autosomal linkage they are on any chromosome other than the sex chromosomes
67
What is epistasis?
When the allele of one generation affects or masks the expression of another in the phenotype what is
68
Genetic variation arises as a result of:
1. Mutations
2. Meiosis
3. Random Fertilisation of gametes
69
State how genetic variation is increasing in asexually reproducing organisms.
Mutation only
70
Define gene pool.
The total number of all the alleles of all the genes of all the individuals within a particular population at a given time
71
What is intraspecific competition?
Competition amoungst individuals within the same species for limited resources
72
State four factors that lead to differential survival and reproduction
predation
Competition for (food/water/space)
disease
natural disasters
73
What are the three main types of selection and describe them?
Stabilising - average phenotype (stays around the mean)
Directional - favours phenotype that vary in one direction from the mean
Disruptive - favours individuals with extreme phenotypes
74
What is the allelic frequency?
The number of times an allele occurs within the gene pool
75
Name and differentiate the two forms of speciation
Allopathic speciation - two populations become geographically seperated
Sympathetic speciation - same area but different factor leading to them becoming reproductively seperated
76
What is adaptive radiation?
Adaptive radiation is when one species evolves into several different species, each adapted to a different environment or way of life.
77
What is genetic drift?
Genetic drift is a random change in the frequency of alleles in a population, especially in small populations.
For example in rabbits if the brown rabbits randomly cannot mate then the allele for brown fur will decrease
78
Explain the meaning of the term speciation.
evolution a species from an existing species
79
Describe the process of geographical separation
When a physical barrier such as mountains or oceans prevents two populations from breeding with one another
80
Distinguish between abiotic and biotic factors.
Abiotic - non-living (temperature, rainfall)
Biotic - living (completion, predation)
81
Define population
A group of individuals of one species that occupy the same habitat at the same time
82
83
Define carrying capacity.
An ecosystem supports a certain size of population
84
Define community.
all the populations of differnt species living and interacting in a particular place at the same time.
85
Define habitat.
place where an organism normally lives and is characterised by physical conditions and the other types of organisms present. (within ecosystems there are many habitats)
86
Define niche
how an organism fits into the environment
where an organism lives and what it does there
87
What is interspecific competition?
when individuals of different species compete for resources such as food, light, water
88
What are the two sampling techniques used in the study of habitats?
1. Random Sampling using frame quadrants or point quadrants
2. Systematic sampling along a belt transect
89
What different ways would i measure/record results of a sample for a species that does’nt move?
Frequency - likely hood of a particular species occurring in a quadrat
Percentage cover - estimate of the area within a quadrat that species covers
90
What assumptions does mark-release-recapture rely on?
The proportion of marked to unmarked individuals in the second sample reflects the same proportion in population
The marked individuals from the first sample distribute themselves evenly
The population has a definite boundary so that there is no immigration or emigration out of the population
There are few, if any, deaths and births within the population
The method of marking does not affect the individuals survival chance
The mark or label is not rubbed off
91
State the general name given to the first organism to colonise bare land
pioneer species
92
Describe how changes in the environment lead to increased biodiversity during succession
Primary colonisers (pioneer species) photosynthesise and fix nitrogen —> these die and form a soil with nutrients —> further colonisers can survive in this soil —> enviroment is a little less hostile —> more habitats and food sources available —> other species are able to survive in this—> increased biodiversity
93
State the name that is given to the stable, final stage of any succession.
climax community
