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A Level Biology > 6.1.2 Patterns of Inheritance > Flashcards

6.1.2 Patterns of Inheritance Flashcards

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1
Q

What influences the phenotype?

A
  • its genotype
  • its environment
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2
Q

What are some mutagens that can increase the rate of mutation?

A
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3
Q

What characteristics do mutations that occur during gamete formation have?

A
  • persistent: they can be transmitted through many generations without change
  • random: they are not directed by a need on the part of the organism in which they occur
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4
Q

What are some types of chromosome mutations during meiosis?

A
  • deletion: part of a chromosome, containing genes and regulatory sequences, is lost
  • inversion: a section of a chromosome mat break off, turn through 180 degrees and join again
  • genes may still be present, but too far away from their regulatory nucleotide to be properly expressed
  • translocation: a piece of one chromosome breaks off and then becomes attached to another
  • duplication: a piece of a chromosome may be duplicated
  • non-disjunction: one pair of chromosomes or chromatids fail to separate, leaving one gamete with an extra chromosome e.g. Down syndrome
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5
Q

What is aneuploidy?

A
  • the chromosome number is not an exact multiple of the haploid number for the organisms
  • sometimes chromosomes or chromatids fail to separate during meiosis
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6
Q

What is polyploidy?

A
  • if a diploid gamete is fertilised by a haploid gamete, the resulting zygote will be triploid (has three sets of chromosomes)
  • the fusion of two diploid gametes can make a tetraploid zygote
  • many cultivated plants are polyploid
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7
Q

What may genetic variation result from?

A
  • meiosis producing genetically different gametes due to:
  • allele shuffling during crossing over in prophase 1
  • independent assortment of chromosomes during metaphase/anaphase 1
  • independent assortment of chromatids during metaphase/anaphase 2
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8
Q

What does haploid mean?

A
  • contain only one of each pair of homologous chromosomes
  • contain one allele for every gene
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9
Q

How does random fusion of gametes create more genetic diversity?

A
  • any male gamete can potentially combine with any female gamete from an organism of the same species
  • the random fertilisation of gametes, that are already genetically unique, produces extensive genetic diversity among the resulting offspring
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10
Q

What is some phenotypic variation caused solely by the environment?

A
  • dialect
  • losing a digit or limb
  • scars
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11
Q

What is an example of variation caused by the environment interacting with genes?

A
  • if plants are kept in dim light after germination, or if the soil contains insufficient magnesium, then leaves do not develop enough chlorophyll and are yellow
  • this plant is chlorotic, suffering from chlorosis
  • it cannot photosynthesise
  • they have the genotype for making chlorophyll, but environmental factors are preventing the expression of these genes
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12
Q

What does heterozygous mean?

A
  • not true breeding
  • having different alleles at a particular gene locus on a pair of homologous chromosomes
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13
Q

What does homozygous mean?

A
  • true breeding
  • having identical alleles at a particular gene locus on a pair of homologous chromosomes
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14
Q

What does monogenic mean?

A
  • determined by a single gene
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15
Q

How can we ascertain the genotypes of phenotypically similar individuals?

A
  • using the test cross
  • the organisms exhibiting the dominant phenotypes but of unknown genotype is crossed with one showing the recessive phenotype
  • if any of the offspring have the recessive phenotype, the dominant is heterozygous
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16
Q

Show an example of a dihybrid cross

A
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17
Q

What is the ratio of phenotypes for dihybrid inheritance?

A
  • 9:3:3:1
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18
Q

How can a gene have multiple alleles?

A
  • when three or more alleles at a specific gene locus are known, the gene has multiple alleles
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19
Q

What is codominance?

A
  • where both alleles present in the genotype of a heterozygous individual contribute to the individual’s phenotype
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20
Q

What is an example of multiple alleles?

A
  • human ABO blood groups
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21
Q

What determines the four blood groups on humans?

A
  • determined by three alleles of a single gene on chromosome 9
  • the gene encodes an isoagglutinogen, I, on the surface of erythrocytes
  • IA and IB are codominant
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22
Q

What are the coat colours in rabbits?

A
  • agouti: wild type, each hair has a grey base, a yellow band and a black tip
  • albino
  • chinchilla: silvery grey, lack of yellow band
  • himalayan: white but with black feet, ears, nose, tail
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23
Q

What are the rabbit coat colours determined by and what is the dominance hierarchy?

A
  • they are determined by one gene that has four alleles
  • Agouti, C, is dominant to all other alleles
  • Chinchilla, Cch , is dominant to Himalayan Ch
  • Albino, c, is recessive to all other alleles
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24
Q

What are the autosomes?

A
  • the other 22 pairs of chromosomes that are not the sex chromosomes
  • they are fully homologous (match for length and contain same genes at same loci)
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25
Q

How can XX and XY sex chromosomes pair up during meiosis if they are not fully homologous?

A
  • a small part of one matches a small part of the other
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26
Q

Briefly describe the human X chromosome

A
  • contains over 1000 genes that are involved in determining many characteristics
  • not concerned with sex determination
  • most of them have no partner alleles on the Y chromosome
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27
Q

What happens if a female has one abnormal allele on one of her X chromosomes?

A
  • she will probably have a functioning allele of the same gene on her other X chromosome
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28
Q

Why do males inherit diseases on X-linked genes?

A
  • if he inherits an X chromosome with an abnormal allele for a particular gene, he will suffer from a genetic disease
  • he will not have a functioning allele for that gene
  • males are functionally haploid, or hemizygous for X-linked genes
  • they cannot be heterozygous or homozygous for X-linked genes
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29
Q

Describe how haemophilia A is a sex-linked genetic disease

A
  • one of the genes on the non-homologous region of the X chromosome codes for a blood-clotting protein called factor 8
  • a mutated form of the allele codes for non-functioning factor 8
  • a female with one abnormal and one functional allele produces enough factor 8 to allow her blood to clot normally, so she is a carrier for the disease
  • if she passes the fault X chromosome to her son, he will suffer from haemophilia A
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30
Q

How is colour blindness a sex-linked disease?

A
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31
Q

Describe sex linkage in cats

A
  • one of the genes, C, for coat colour is sex-linked
  • it is on the non-homologous region of the X chromosome
  • the allele CO produces ginger/orange fur
  • the allele CB produces black fur
  • these alleles are codominant, as cats with XCO XCB are tortoiseshell
  • both orange and black alleles contribute to the phenotype, but the orange allele is only expressed in cells where the X chromosome bearing the black coat colour inactivated
  • male cats cannot be tortoiseshell
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32
Q

Why do females not express twice the number of X-linked genes if they have two X chromosomes?

A
  • a mechanism prevents this
  • in every female cell nucleus, one X chromosome is inactivated
  • this is random and happens during early embryonic development
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33
Q

What does codominant mean?

A
  • where both alleles present in the genotype of a heterozygous individual contribute to the individual’s phenotype
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34
Q

Describe an example of codominance in animals

A
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35
Q

Describe codominance in the MN blood groups in humans

A
  • the MN blood group system is controlled by a single gene with two alleles, GM and GN
  • it codes for a particular protein on the surface of erythrocytes
  • these alleles are codominant
36
Q

Describe the codominance in sickle cell anaemia

A
  • it is caused by a mutation in the gene that codes for the beta-globin chain of haemoglobin
  • HbS is the mutant allele
  • HbN is the normal allele
  • in heterozygous people, at least half the haemoglobin in red blood cells in normal, and half is abnormal, but they do not suffer from sickle cell anaemia
  • if the type of haemoglobin is the phenotype, then alleles are codominant
  • but if sickle cell anaemia is the phenotype, then this disorder has a recessive inheritance pattern
37
Q

Give some examples of codominance in plants

A
  • some types of camellia have red flowers
  • some have white flowers
  • if they are crossed, the offspring will have red and white spotted flowers
38
Q

What is autosomal linkage?

A
  • gene loci present on the same autosome that are often inherited together
39
Q

How are some linked genes always inherited as one unit?

A
  • if linked genes are not affected by crossing over of non-sister chromatids during prophase 1 of meiosis, they are always inherited as one unit
40
Q

Give an example of inheritance of autosomally linked genes with no crossing over

A
41
Q

Show how autosomally linked genes may cross over

A
42
Q

Give an example of autosomally linked genes with crossing over

A
43
Q

What is epistasis?

A
  • interaction of non-linked gene loci where one masks or suppresses the expression of the other
  • the genes may work together antagonistically or in a complementary fashion
  • they assort independently during gamete formation because the gene loci are not linked
  • epistasis reduces the number of phenotypes produced in the F2 generation of dihybrid crosses and therefore it reduces genetic variation
44
Q

In what two types of epistasis do genes work antagonistically?

A
  • recessive epistasis
  • dominant epistasis
45
Q

Describe recessive epistasis

A
  • the homozygous presence of a recessive allele at the first locus prevents the expression of another allele at the second locus
  • the alleles at the first locus are epistatic to those at the second locus, which are hypostatic to those at the first
46
Q

Give an example of recessive epistasis

A
  • recessive epistasis in the inheritance of flower colour in Salvia
47
Q

Describe dominant epistasis using feather colour in chickens

A
  • there is an interaction between two gene loci, I/i and C/c
  • the hypostatic gene, I/i, prevents the formation of colour, even if one C allele is present
  • individuals carrying at least one dominant allele, I, have white feather, even if they also have one dominant allele for coloured feathers
  • birds that are homozygous for the recessive allele, c, are also white, as this mutated allele does not causer pigment to be made
48
Q

How can genes work in a complementary fashion?

A
  • epistasis is more often explained in terms of the genes working to code for two enzymes that work in succession, catalysing sequential steps of a metabolic pathway
49
Q

Using the information, draw the reaction pathway of coat colour in mice

A
50
Q

Describe how flower colour uses complementary epistasis

A
51
Q

Describe how combs of domestic chickens uses complementary epistasis

A
52
Q

When can you use the chi-squared test?

A
  • the data are in categories and are not continuous
  • we have a strong biological theory to use to predict expected values
  • sample size is large
  • the data are only raw counts
  • there are no zero scores in the raw count data
53
Q

How do you write the null hypothesis for chi-squared tests?

A
  • there is no statistically significant difference between the observed and expected data
  • any difference is due to chance
54
Q

How do you apply the chi-squared test?

A
55
Q

What is discontinuous variation?

A
  • genetic variation producing discrete phenotypes
  • two or more non-overlapping categories
  • e.g. male or female, earlobes, ABO blood groups
56
Q

Why are characteristics that exhibit discontinuous variation usually monogenic?

A
  • they are usually determined by the alleles of a single gene locus
  • however, sometimes the alleles of two genes interact to govern a single characteristic
57
Q

How much of an extent do alleles and gene loci affect characteristics in discontinuous variation?

A
  • different alleles at a single gene locus have large effects on the phenotype
  • different gene loci have quite different effects on the characteristic
58
Q

What is continuous variation and give examples of it

A
  • variation that produces phenotypic variation where the quantative traits vcary by small amounts between one geoup and the next
  • foot size, finger length, height, skin colour, heart rate in humans
  • cob length in maize plants
  • leaf length in many plants
  • tail length in mice
  • red kernel colour in wheat
59
Q

Why are characteristics with continuous variation polygenic?

A
  • many genes are involved in determining such characteristics
  • the alleles of each gene may contribute a small amount to the phenotype
  • therefore alleles have an additive effect on the phenotype
  • as a result, the phenotypic categories vary in a quantitative way
  • the greater the number of gene loci contributing to the determination of the characteristic, the more continuous the variation
60
Q

Does the environment affect the expression of monogenic or polygenic characteristics more greatly?

A
  • the environment affects the expressions of polygenes/polygenic characteristics more greatly
61
Q

Describe what natural selection is

A
  • mutations and migration introduce new alleles inito populations
  • some individuals within a population will be better adapted than others to the environment, due to different in their genotypes and phenotypes
  • these individuals are more likely to survive and reproduce, passing on the advantageous alleles
  • over time, allele frequencies within the population will change
  • this is natural selection
  • natural selection may also maintain constancy of a species, as well as leading to new species
62
Q

What are the three main types of natural selection?

A
  • stabilisinig selection
  • directional selection
  • disruptive selection
63
Q

What is stabilising selection?

A
  • this normally occurs when the organisms’ environment remains unchanged
  • it favours intermediate phenotypes
  • e.g. in humans, babies of birth mass 3.5kg are more likely to survive
  • their offspring inherit alleles from them, leading to this mean birth mass
64
Q

What is directional selection?

A
  • if the environement changes, such as by becoming colder, there may now be an advantage to being larger
  • so a new larger mass becomes the ideal and will be selected for
  • if more larger iindviduals survive and reproduce, they will more likely to pass genes and alleles for larger size to their offspring
  • over several generations, there is a gradual shift in the optimum value for the trait
65
Q

How is directional selection used by breeders?

A
  • plant and animal breeders use directional selection to produce desirable traits
66
Q

When does directional selection occur in nature?

A
  • within a population, period of directional selection may alternate with period of stabilising selection
67
Q

What is disruptive selection?

A
68
Q

What is genetic drift?

A
  • if a population descends from a small number of parents, the gene pool will lack genetic variation
  • some alleles resulting from mutation confer neither an advantage not disadvantage on the individual so there will be no selection pressure acting upon them
  • chance events may drastically alter the allele frequency
  • imagine if you have a small population descended from one set of heterozygous parents
  • the alleles are A and a
  • if a catastrophic event occurs, leading to the death of many of an already small population, one of the alleles may disappear from this population
  • when the population recovers and increases, it will have less genetic diversity than before and may lack particular alleles
  • the alleles in question did not disappear due to selection pressure, but due to genetic drift
69
Q

What two occurrences may lead to genetic drift?

A
  • after a genetic bottleneck
  • as the result of the founder effect
70
Q

Describe a genetic bottleneck

A
  • when a population size shrinks and increases again, it is said to have gone through a genetic bottleneck
  • after this, the genetic diversity within the population is reduced
  • there may be a loss of some advantageous alleles or a disproportionate frequency of deleterious alleles
  • this may put the population’s chance of long-term survival at risk
  • sometimes, a population shrink to such a small size that fertility is affected, leading to species endangerment and then extinction
  • however, if the ones that survive have a particular advantage, then a bottleneck could improve the gene pool whilst also shrinking genetic diversity
71
Q

Describe the Founder effect

A
  • if a new population is established by a very small number of individuals who originate from a larger, parent population, the new population is likely to exhibit a loss of genetic variation
  • some groups of migrating humans, have resulted in a small gene pool
  • e.g. Iceland, Easter Island, Amish in North America
72
Q

What is a population?

A
  • members of a species, living in the same place and at the same time, that can interbreed
73
Q

What does population genetics study?

A
  • it studies the variation in the alleles and genotypes within the gene pool and how their frequencies vary over time
74
Q

What factors affect allele frequencies within populations?

A
  • population size
  • mutation rate
  • migration
  • the types of natural selection
  • changes to the environment e.g. bottleneck
  • isolation of a population from other populations of the same species (founder effect)
  • non-random mating
  • genetic drift
  • gene flow
75
Q

What is the Hardy-Weinberg principle and what does it assume?

A
  • the population is large enough to make sampling error negligible
  • mating within the population occurs at random
  • there is no selective advantage for any genotype and hence no selection
  • there is no mutation, migration or genetic drift
76
Q

Describe the process of speciation

A
  • for a species to evolve into two species, it must be split into two isolated populations
  • if this happens, then any mutations that occur in one population are not transmitted by interbreeding to the other population
  • in each location, there will be different selection pressure and each population will accumulate different allele frequencies
  • hence each population can evolve along its own lines
  • at times during the evolutionary process, the two populations will be different but still be able to interbreed
  • this is called sub-species
  • when there have been sufficient genetic, behavioural and physiological changes in the two populations so that they can no longer interbreed, they are then separate species
77
Q

What are the two types of isolating mechanisms that lead to speciation?

A
  • geographical isolation
  • reproductive isolation
78
Q

Describe geographical isolation

A
  • if populations are separated and isolated from each other by geographical features such as lakes, rivers, oceans and mountains, these also act as barriers to gene flow between populations
  • the isolated populations are subject to different selection pressures in two different environments, so undergo independent changes to the allele frequencies and/or chromosome arrangement within their gene pools
  • these genetic changes may be the result of mutation, selection and genetic drift
  • as a result of natural selection, each population becomes adapted to its environment
  • this type of speciation is called allopatric speciation (in different countries)
79
Q

Describe reproductive isolation

A

Biological and Behavioural:

  • biological and behavioural changes within a species may lead to reproductive isolation of one population from another
  • if a mutation leads to some organisms in a population changing their foraging behaviour and becoming at a different time of day, it enables them to exploit a new niche
  • so, the members of the diurnal populations will be unlikely to mate with crepuscular or nocturnal populations

Genetic:

  • a change in chromosome number may:
  • prevent gamete fusion
  • make zygotes less viable so that they will fail to develop
  • lead to infertile hybrid offspring with an odd number of chromosomes, so that chromosome pairing during meiosis cannot occur

Mating:

  • courtship behaviour e.g. time of year for mating or courtship rituals
  • animal genitalia or plant flower structure

Speciation resulting from reproductive isolation is called sympatric (same country) speciation

80
Q

What is artificial selection?

A
  • selective breeding of organisms
  • involves humans choosing the desired phenotypes and interbreeding those phenotypes individually
  • therefore, selecting the genotypes that contribute to the gene pool of the next generation of these organisms
81
Q

What kind of organisms are bred for artificial selection?

A
82
Q

What is inbreeding depression?

A
  • at each stage of selective breeding, individuals with the desirable characteristics and no or few undesirable characteristics are selected
  • this leads to genetic diversity reduction in the gene pool
  • if related individuals are crossed, inbreeding depression can result
  • the chances of an individual inheriting two copies of a recessive harmful allele are increased
83
Q

What is hybrid vigour?

A
84
Q

Why does climate change mean a new type of wheat may have to be developed?

A
85
Q

What are some examples of gene banks?

A
86
Q

What are some ethical consideration of artificial selection?

A
87
Q

Describe some health conditions certain dog breeds may be susceptible to

A

A Level Biology (25 decks)

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