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BIOLOGY A LEVEL > CHAPTER 20 - PATTERNS OF INHERITANCE AND VARIATION > Flashcards

CHAPTER 20 - PATTERNS OF INHERITANCE AND VARIATION Flashcards

1
Q

How can plants develop chlorosis

A

Lack of light
Mineral deficiencies
Virus infections

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2
Q

What is an organisms genotype

A

The combination of alleles an organism inherits for a characteristic

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3
Q

What is an organisms phenotype

A

Observable characteristics an organism has

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4
Q

What are the terms for an organisms genotype

A

Homozygous and heterozygous

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5
Q

What is continuous variation

A

A characteristic that can take any value within a range

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6
Q

What is discontinuous variation

A

A characteristic that can only appear in specific discrete values

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7
Q

What are the causes of continuous variation

A

Genetic and environmental

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8
Q

What are the causes of discontinuous variation

A

Mostly genetic

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9
Q

What is continuous variation controlled by

A

Polygenes - controlled by a number of genes

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10
Q

What is discontinuous variation controlled by

A

One or two genes

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11
Q

Examples of continuous variation

A

Leaf surface area
Animal mass
Skin colour

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12
Q

Examples of discontinuous variation

A

Blood group
Albinism
Round and wrinkled pea shape

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13
Q

State the difference between a homozygous and heterozygous genotype

A

Homozygous – contains identical alleles of a gene.
Heterozygous – contains different alleles of a gene

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14
Q

Explain the difference between the phenotype and genotype of an oak tree

A

Phenotype – the displayed characteristics of the oak tree e.g., how tall it grows (1);

Genotype – the
alleles present for each characteristic

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15
Q

Using named examples, state and explain the difference between continuous and discontinuous variation

A

Continuous – a characteristic which can take any value within a range

Discontinuous – a
characteristic which can take only specific values

continuous – affected by environmental and
genetic factors

discontinuous – affected by only genetic factors example of continuous
variation with explanation e.g., height, as genes affect potential height but diet can limit this
potential

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16
Q

How do you perform a genetic cross

A

State phenotype of both parents

State genotype of both parents

State gametes of each parents and circle letters

Use punnet square

State proportion of each genotype

State the corresponding phenotype

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17
Q

What is codominance

A

When two different alleles occur for a gene, but both of which are equally dominant

eg. AB blood group

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18
Q

How is sex determined

A

23rd pair depends, if sperm cell contains X chromosome, then it is a female, if it contains Y chromosome, it is a male

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19
Q

What are sex linked genes

A

Genes that are carried on the sex chromosomes

Y is smaller than X so there is only one copy of a gene, so diseases can be more frequent on sex linked alleles

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20
Q

What is haemophillia

A

A sex-linked genetic disorder, where blood clots extremely slowly due to the absence of a protein blood-clotting

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21
Q

What is special about the phenotypes formed as a result of a gene which has codominant alleles

A

Codominant alleles are equally dominant

a heterozygous individual would display a phenotype
caused by the expression of both alleles

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22
Q

State the difference between monogenic inheritance and dihybrid inheritance

A

Monogenetic inheritance is the study of the inheritance of one gene,

whereas dihybrid inheritance is
the study of the inheritance of two genes

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23
Q

State and explain why the offspring produced form a particular genetic cross may differ from the expected ratio

A

For example, genes are linked –
cannot be inherited independently

sample size is too small

unlikely to produce exact ratio
from small sample size, due to random nature of each individual outcome, crossing over of
chromosomes

new allele combinations created

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24
Q

What is autosomal linkage

A

Found on one of the pairs of chromosomes, and there is no independent assortment so they are inherited as one, unless they are separated by chiasmata

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25
What are recombinant offspring
A different combination of alleles than either parent (pg 531)
26
How is recombination frequency calculated
RF = Number of recombinant offspring/total number of offspring Less than 50% indicates a linkage over 50 means there is no linkage
27
What does the Chi squared test measure
Size of the difference between the results you got vs the results you expected to get
28
What is epistasis
Interaction of genes on different loci, when one gene affects the expression of another (pg 535 and 536)
29
Horse coat colour is an example of epistasis. Two genes are involved. The different colours and the genotypes responsible are summarised here G_ _ _ produces a grey horse ggE_ produces a black horse ggee produces a chestnut horse Explain, giving your reasons, which form of epistasis this represents
Dominant epistasis black allele / E, is dominant to, chestnut allele / e grey allele / G, is dominant to g G (allele) is epistatic to E (allele) E (allele) is hypostatic to G (allele)
30
A biologist test crosses a plant that is heterozygous for the alleles Xx and Yy in order to see how far apart the gene loci are on a chromosome. The offspring of this cross contains 5.2% recombinant individuals. State the difference between these alleles Describe how the biologist could determine where a third gene with the alleles Zz is on the chromosome relative to Xx and Yy Suggest why this sort of investigation is best carried out with genes that are relatively close to each other
A) 5.2 genetic map units B) Cross Z,z with X,x and Z,z with Y,y (1); idea that if Z locus closer to Y than X then order is X, Y, Z or X, Z, Y idea that if Z is more than 5.2 GMU from Y then order is X, Y, Z idea that if Z is less than 5.2 GMU from X then order is X, Z, Y C) Genes further apart more likely to cross more than once (this will) cancel previous cross so incorrect recombination frequency
31
What is the gene pool
The sum total of all the genes in a population at any given time
32
What is allele frequency
The relative frequency of a particular allele
33
What is Hardy-Weinberg principle states
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
34
How do you calculate allele frequency
p+q=1
35
How is the hardy weinberg principle expressed
p^2 + 2pq + q^2 = 1
36
What are the factors affecting evolution
Mutation is necessary for the existence of different alleles Sexual selection Gene flow Genetic drift Natural selection
37
What are the limiting factors which limit or decrease population size
Density-dependent factors eg. competition, predation, parasitism, communicable disease Density-independent factors eg. climate change, natural disasters, human activities
38
What is a genetic bottleneck
A natural disaster or epidemic (or change in environment) that can drastically reduce a population, reducing gene pool (pg 541)
39
What is the founder effect
the reduction in genomic variability that occurs when a small group of individuals becomes separated from a larger population
40
What is stabilising selection
The average is selected for (positive selection) and the extremes are selected against, increasing frequency of average alleles eg. baby weight
41
What is directional selection
When there is a change in the environment and the most occurring phenotype is no longer advantageous leading to organisms with less common alleles are positively selected eg. peppered moth colour
42
What is disruptive selection
Extremes are selected for and the norm is selected against, opposite to stabilising selection eg. Darwins finches (pg 543/544)
43
Explain why Evolution does not occur within single organisms but groups of organisms
Evolution is change in allele frequency alleles do not change within organism single organisms do not adapt
44
Around the world, humans choose their partners from right of reasons. Explain why this might affect any conclusions about human evolution drawn, using the hardy Weinberg principle.
The Hardy–Weinberg principle assumes a stable, isolated breeding population of diploid organisms with random mating, no mutations, and no selection pressure Because people choose their partners or have them chosen for them by their parents, mating is not random Any conclusions based on Hardy–Weinberg principles will not, therefore, be valid, because the equilibrium only holds in ideal conditions individuals do not reproduce with visibly similar organisms
45
Eukaryotic organisms have large quantities of non-coding DNA, whereas most prokaryotic organisms have very little. Suggest with reference to the different forms of reproduction in eukaryotes and prokaryotes why eukaryotes may have evolved to have more non-coding DNA
Sexual reproduction in eukaryotes and asexual reproduction in prokaryotes (involves) meiosis crossing over idea that non-coding regions of DNA reduce disruption of genes (during crossing over)
46
What are the events that lead to speciation
Members of a population became isolated and no longer interbreed Allele within the groups continue to undergo random mutations Accumulations of mutations and changes in allele frequencies over many generations eventually lead to a change of phenotype
47
What is allopatric speciation
When some members of a population are separated from the rest of the group by a physical barrier such as a river or sea (pg 546)
48
What is adaptive radiation
Rapid organism diversification takes place
49
What is sympatric speciation
Speciation that occurs within populations that share the same habitat It can occur when members of two different species into breed and form a fertile offspring, which forms a hybrid, but will have a different number of chromosomes to the parent and may no longer be able to interbreed, so it is reproductively isolated and stops gene flow (pg 547)
50
What are prezygotic reproductive barriers
Prevent fertilisation and formation of a zygote
51
What are postzygotic reproductive barriers
Reduces the viability or reproductive potential of offspring eg. by hybridisation
52
What is polymorphic
When there are more than one distinct phenotype in a population
53
What is artificial selection/selective breeding
Natural selection except for the nature of the pressure applied farmers/breeders breed animals with desirable characteristics
54
What is inbreeding
The breeding of closely related individuals
55
What are some problems with inbreeding
Limiting gene pool - reducing genetic diversity and chances of adapting to environment Genetic disorders caused by recessive alleles are more prevalent - breeding partners likely to have same recessive alleles
56
What are gene banks used for
Storing biological samples Used to increase genetic diversity by outbreeding
57
Describe with examples, the difference between pre-zygotic and post-zygotic reproductive barriers
Pre-zygotic reproductive isolation before fertilisation stage e.g., geographical, behavioural, seasonal, anatomical post-zygotic reproductive isolation after fertilisation e.g., zygote not viable, offspring infertile
58
A small population of adders in Sweden underwent inbreeding depression and farming activities, isolated them from other other populations. The numbers of stillborn and formed offspring increased as compared to the original population. Research is introduce atoms from other population, and the isolated population recovered and produce a high proportion of viable offspring. Name, the type of breeding carried out by the researches Explain how this type of breathing reduces the problems caused by inbreeding
Outbreeding Introduces new alleles, which can be beneficial, Increasing (genetic) variation (population) more able to cope with changes in environment / new selection pressures number of homozygous recessive loci reduced (over time)
59
Discuss what variation within a species has to be present for speciation to occur
(Isolated) organisms exposed to different environments (so) different selection pressures variation means that a wide range of alleles is present (in different environments) different alleles selected for different changes in allele frequency leads to formation of different species
60
Allopatric speciation is considered by most biologist to be the most common way in which new species, evolve Outline the differences between sympatric, speciation, and allopatric speciation, and suggest why some biologist thinks sympatric speciation is a rare event
Sympatric speciation occurs within same habitat selection pressures the same for all allopatric speciation occurs within isolated groups isolated groups (may have) different selection pressures (some) gene flow in sympatric speciation and no gene flow in allopatric speciation organisms not isolated in sympatric speciation so gene flow is still possible

BIOLOGY A LEVEL (24 decks)

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