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Biology > 6.2 Patterns of Inheritance and Variation > Flashcards

6.2 Patterns of Inheritance and Variation Flashcards

1
Q

What is chlorosis ?

A

When leaves look pale or yellow because cells are not producing the normal amount of chlorophyll.

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2
Q

What causes chlorosis ?

A

Lack of light
Mineral deficiencies
Virus infections

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3
Q

What is a genotype ?

A

Alleles expressed on the gene.

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4
Q

What is a phenotype ?

A

Alleles that are expressed as a characteristic.

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5
Q

What is a dominant allele ?

A

Version of gene that is always expressed if present.

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6
Q

What is a recessive allele ?

A

Only expressed if it is homozygous recessive.

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7
Q

What is homozygous alleles ?

A

2 identical alleles for a characteristic.

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8
Q

What is heterozygous alleles ?

A

2 different alleles for a characteristic.

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9
Q

What is continuous variation ?

A

Characteristic that has a value within a range Eg., height, weight

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10
Q

What is discontinuous variation ?

A

Characteristic that only appears in specific values.

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11
Q

What is monogenic inheritance ?

A

Inheritance of a single gene is shown.

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12
Q

What is codominance ?

A

when 2 different alleles occur for a gene.

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13
Q

What are sex linked genes ?

A

Characteristics are determined by genes on the sex chromosomes.

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14
Q

What is dihybrid inheritance ?

A

Used to show the inheritance of 2 genes and this is known as dihybrid inheritance.

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15
Q

What is the ratio for dihybrid crosses ?

A

9:3:3:1

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16
Q

Why do ratios differ significantly from those expected ?

A

Due to linkage meaning genes are located on the same chromosome.

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17
Q

What is autosomal linkage ?

A

When genes that are linked are found on one of the other pairs of chromosomes.

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18
Q

How are linked genes inherited ?

A

Inherited as one unit, there is no independent assortment during meiosis unless alleles are separated by chiasmata.

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19
Q

What are recombinant offspring ?

A

Offspring that have different combination of alleles than either parent.

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20
Q

What is the recombination frequency ?

A

Measure of the amount of crossing over that has happened in meiosis.

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21
Q

How to work out recombinant frequency ?

A

Number of recombinant offspring / total number of offspring.

22
Q

What does recombinant frequency of 50% state ?

A

Indicates that there is no linkage and the genes are on separate chromosomes. Less than 50% indicates there is gene linkage and independent assortment is hindered.

23
Q

What is Chi squared ?

A

Statistical test that measures the size of difference between results you observe and those expected.

24
Q

Does observed value have to be greater than or less than to be significant ?

A

Equal to or greater than to be significant so small probability it is down to chance.

25
How to work out degrees of freedom ?
n-1 (n= number of catagories)
26
What is dominant epistasis ?
Occurs if a dominant allele results in a gene having an effect on another gene.
27
What is epistasis ?
Interaction of genes at different loci. Gene regulation is a form of this, with regulatory genes controlling activity of structural genes.
28
Example of epistasis in Labradors ?
B - black b - brown But this is only case if it has dominant gene for fur, F.
29
What is evolution ?
Change in inherited characteristics of a group of organisms over time. Occurs due to changes in frequency of different alleles within a population.
30
Factors affecting evolution ?
Mutation, sexual selection, gene flow, genetic drift and natural selection.
31
What is population genetics ?
Investigates how allele frequencies within populations change over time.
32
What factors affect size of populations ?
Density-dependent factors such as competition and predation. Density-independent factors such as climate change, natural disasters, seasonal change and human activities.
33
What is the founder effect ?
Extreme example of genetic drift. Establishment of new colonies by a few isolated individuals.
34
What is stabilising selection ?
Norms are selected for and extremes are selected against. Therefore, results in a reduction in frequency of alleles at extremes and increase in frequency of average alleles.
35
What is directional selection ?
Occurs when there is change in the environment and the normal phenotype is no longer the most advantageous.
36
What is disruptive selection ?
Extremes are selected for and the norm is selected against.
37
What is speciation ?
Formation of a new species through process of evolution.
38
What leads to speciation ?
Members of population are isolated, alleles undergo random mutations and accumulation of mutations lead to large changes in phenotype.
39
What is allopatric speciation ?
Happens when some members in a population are separated from rest of group by a physical barrier. Eg, finches on Galapagos islands.
40
What is sympatric speciation ?
Occurs within population that share the same habitat. Less frequent and more common in plants. Occurs when members of different species interbreed and form fertile offspring.
41
What are reproductive barriers ?
Prezygotic barriers prevent fertilisation but postzygotic barriers are produced as a result of hybridisation.
42
What are polymorphic populations ?
They display more than one distinct phenotype for most characteristics.
43
What is artificial selection ?
Same as natural selection but changes in environment leading to survival of fittest due to selective breeding of farmers.
44
Problems caused by inbreeding ?
Limits gene pool, causes genetic disorders and results in offspring more likely to be homozygous recessive.
45
What are gene banks ?
Store biological samples that are usually frozen.
46
What does Hardy-Weinberg principle state ?
In a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next and there will be no evolution.
47
What is Hardy-Weinberg principle expresses as ?
p^2 + 2pq + q^2 = 1 p = frequency of homozygous dominant pq = frequency of heterozygous q = frequency of homozygous recessive
48
What is the founder effect ?
New population from small number of isolated individuals.
49
What is stabilising selection ?
Average is selected for and the extremes are selected against. So causes a reduction in the frequency of alleles.
50
What is directional selection ?
Organisms that are less common and have more extreme phenotypes are positively selected. Allele frequency shifts toward the extreme phenotype.
51
What is disruptive selection ?
Extremes are selected for and the norms selected against.

Biology (23 decks)

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