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A LEVEL BIOLOGY > 6.1.2 Patterns of inheritance > Flashcards

6.1.2 Patterns of inheritance Flashcards

1
Q

Types of variation

A
  • continuous= phenotype in population varies within a range i.e height (polygenic and influenced by environment)
  • discontinuous= when there are 2 or more distinct categories the phenotype can fall into (monogenic and not influenced by environment)
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2
Q

Environmental factors on phenotype variation

A

-able to influence gene expression through controlling characteristics i.e chlorosis + animal body mass
-caused by differences in environment

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3
Q

Chlorosis

A

-when plants don’t produce enough chlorophyll + leaves turn yellow/pale
-most plants do show normal genes coding for chlorophyll production but environmental factors affect their phenotype and stop production of proteins i.e
- lack of light(plant stops production to conserve resources)
- mineral deficiencies i.e lack of iron + magnesium means a plant cannot produce chlorophyll
- viral infections(affect metabolism of cells)

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4
Q

Animal body mass

A

-determined by a combination of environmental + genetic factors
-amount + quality of food, quantity of exercise, presence of disease= environmental
-genetic mutations could change the pattern of fat deposition in the body + cause obesity

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5
Q

Genetic variation affecting phenotype variation

A

-created through the individual mix of alleles inherited from both parents–} combination determined by meiosis(crossing over + independent assortment), random fusion of gametes + any mutations in DNA replication
-i.e human blood group

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6
Q

Genotypes and phenotypes

A
  • genotype= combination of allele an organism inherits for a characteristic
    -for most genes there are 2 alleles inherited, one from each parent
  • phenotype= observable characteristics of an organism
    -any changes the environment makes to an organism’s phenotype are not inherited, they are modifications not mutations(changes to DNA)
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7
Q

Definition of gene and allele

A

-a gene is a sequence of DNA that codes for a protein(resulting in a characteristic)
-alleles are different versions of the same gene –} order of bases in each is slightly different

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8
Q

Definition of recessive and dominant alleles

A

-dominant= the version of the gene that will always be expressed if present in an organism
-recessive= will only be expressed if 2 copies of this allele are present in an organism

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9
Q

Definition of homozygous and heterozygous

A

-homozygous= 2 identical alleles for a characteristic –} could be dominant(2 alleles for dominant phenotype) or recessive(2 alleles for recessive phenotype)
-heterozygous= 2 different alleles for a characteristic
–} dominant allele will be expressed

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10
Q

What are genetic cross diagrams?

A

-show the possible genotypes of an offspring so can be used to predict the genotypes + phenotypes of offspring produced when two parents are bred

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11
Q

What is monogenic inheritance?

A

-inheritance of a characteristic controlled by a single gene
-show the likelihood of different alleles of that gene being inherited by offspring

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12
Q

Steps to performing a a genetic cross

A

-state the phenotype of both parents i.e Green
-state the genotype of both parents i.e GG
-state the gametes of each parent(contain only one allele for each gene)
-use a Punnett square to find potential alleles for offspring
-state the proportion of each genotype + state corresponding phenotype

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13
Q

3 rules for monogenic inheritance

A

-true bred cross (homozygous) will always produce heterozygous offspring
-F1 cross is a cross of offspring from a true bred
-F1 crosses for monogenic always produce a 3:1 phenotypic ratio

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14
Q

What is codominance?

A

-when 2 different alleles occur for a gene and both are equally dominant
-as a result, both alleles of the gene are expressed in the phenotype of the organism if present

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15
Q

Snapdragon example of codominance

A

-snapdragons’ petal colour is controlled by the C gene and its allele can either be red or white:
- Cr Cr (red flowers, homozygous)
- Cw Cw (white flowers, homozygous)
- Cr Cw (pink flowers, heterozygous)

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16
Q

What is the expected F1 ratio for codominance?

A

1:2:1
homozygous: heterozygous: homozygous

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17
Q

What are multiple allele crosses?

A

-some genes have more than 2 versions or multiple alleles–} however as an organism only carries 2 versions of the gene, only 2 alleles will be present in the individual

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18
Q

How are human blood groups determined?

A

-determined by 3 alleles(a, o, b) on gene I
-the gene encodes a specific antigen that will be present on the surface of the RBC
-Ia and Ib are codominant and when both are present, they will both be expressed in the phenotype

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19
Q

What is the expected phenotypic ratio for the different blood groups?

A

-because any offspring could have any one of the 4 blood groups, the ratio would be 1:1:1:1
(A:B:O:AB)

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20
Q

What is a dihybrid cross?

A

-the inheritance of 2 different characteristics, caused by 2 genes that may be located on different pairs of homologous chromosomes
-each of the 2 genes can have two or more alleles
-the crosses can be used to show the likelihood of offspring inheriting certain combinations of the 2 characteristics

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21
Q

How many alleles in a genotype and in a gamete?

A

-4 alleles in a genotype(2 for each characteristic)
-2 alleles per gamete

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22
Q

What is the rule for a true bred cross in dihybrid crosses?

A

-all the offspring produced in the F1 generation will have a heterozygous genotype i.e YyRr

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23
Q

What is the expected phenotypic ratio for an F2 dihybrid generation?

A

9:3:3:1
both dominant: dominant first recessive second: recessive first, dominant second: both recessive

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24
Q

What factors can affect the phenotypic ratio?

A

-crossing over
-random fertilisation of gametes

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25
Q

What is sex linkage?

A

-when the gene coding for a certain characteristic is located on a sex chromosome
-the Y chromosome is smaller than the X chromosome and carries less genes–} males only have 1 X chromosome so often only have 1 allele for sex-linked genes
-therefore they are more likely to express that characteristic in their phenotype even if it is recessive
-if there us a faulty gene on the X chromosome of females, they are more likely to become carriers for the disease + only display it if the faulty gene is on both x chromosomes

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26
Q

Haemophilia

A

-recessive blood disorder carried on the X chromosome
-if a male inherits the recessive allele that codes for haemophilia, they develop the condition
-females who are heterozygous for the haemophilia gene are carriers
-the alleles for the condition are shown alongside the chromosome they are found on i.e Xh

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27
Q

What is autosomal linkage?

A

-occurs on any chromosome that is not a sex chromosome
-genes that are linked when they are on the same chromosome–} they will stay together during independent assortment in meiosis 1 and their alleles will be passed on to the offspring together unless crossing over changes the combination of genes on the chromosome
-linked genes will be inherited together

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28
Q

How does crossing over affect autosomal linkage?

A

-the closer together two genes are on the chromosome, the less likely that crossing over will split them up and vice versa
-offspring affected by crossing over are known as recombinant offspring

29
Q

What is recombination frequency and how is it calculated?

A

-a measure of the amount of crossing over that has happened in meiosis
- recombinant frequency: no. of recombinant offspring/total no. of offspring
-recombination of 50%= no linkage and genes are on separate chromosomes
-recombination of less than 50%= gene linkage and the random process of independent assortment is hindered

30
Q

What is the expected phenotypic ratio for F1 offspring?

A

1:1:1:1

31
Q

What is epistasis?

A

-when the allele of one gene masks the expression of the alleles of another gene
-many genes control the same characteristic + they interact to form the phenotype

32
Q

Examples of epistasis

A

-widow’s peak is controlled by 1 gene and baldness is controlled by another–} the bald gene would mask the widow’s peak gene
-flower pigment is controlled by 2 genes: yellow pigment + a gene that codes for an enzyme that turns the pigment orange–} yellow pigment is epistatic to colour changing gene(doesn’t matter if you have gene 2 when you do not have the yellow pigment gene)

33
Q

What is the expected phenotypic ratio for recessive epistatic gene in the F2 generation?

A

-crossing a homozygous recessive parent with homozygous dominant parent results in 9:3:4
-dominant epistatic: recessive other: recessive epistatic

34
Q

What is the expected phenotypic ratio for dominant epistatic gene in the F2 generation?

A

-crossing a homozygous recessive parent with a homozygous dominant parent would produce a 12:3:1 phenotypic ratio

35
Q

How many alleles in each genotype and gamete for epistasis?

A

-4 alleles per genotype and 2 alleles per gamete

36
Q

What is chi-squared and why is it used?

A

-stat test that measures the size of the difference between observed and expected results and whether expected results fit the observed pattern
-determines whether differences in the expected and observed results are statistically significant or due to chance (accept/reject null hypothesis)

37
Q

what is the chi-squared formula?

A

X^{2}=total of (observed value-expected value)^{2}/expected value

38
Q

steps to using chi-squared?

A

-start with an experimental theory that is used to make a prediction of the results-expected results
-experiment is carried out and the actual results are recorded-observed result
-state the null hypothesis (no statistically significant different between the observed and expected result)
-calculate chi-squared and compare to the critical value
-the outcome will either accept the null hypothesis(due to chance) or reject it

39
Q

comparing chi-squared to critical value

A

-if the calculated value is greater than/equal to the critical value, there is a significant difference, less than 5% probability that the results are due to chance
-if the calculated value is less than the critical value, there is no significant difference, more than 5% probability that the results are due to chance

40
Q

What is a gene pool?

A

-the range of alleles present in a population

41
Q

what is allele frequency?

A

-the relative frequency of an allele in a population

42
Q

what affects allele frequency and how does this link to evolution?

A

-allele frequency changes over time dependent on environmental influence
-evolution is a long term change in the allele frequency of a population over time

43
Q

Factors affecting evolution: mutation

A

-new alleles are usually generated by mutations in genes–} leads to genetic variation

44
Q

Factors affecting evolution: sexual selection

A

-leads to an increase in frequency of alleles which code for characteristics that improve mating successes

45
Q

Factors affecting evolution: gene flow

A

-the movement of alleles between populations i.e emigration results in changes of allele frequency within a population

46
Q

Factors affecting evolution: natural selection

A

-evolution in larger populations is predominantly driven by natural selection(any changes by chance in allele frequency tend to even out in a larger population)
-leads to an increase in the no. of individuals with beneficial characteristics
-more likely to reproduce and pass on alleles–} high frequency of beneficial alleles

47
Q

Factors affecting evolution: genetic drift

A

-usually has a bigger impact on evolution in small populations*
-change in allele frequency due to the random nature of mutations
*less alleles in the gene pool of a smaller population

48
Q

How does genetic drift work?

A

-individuals within a population show variation in their genotypes i.e A and B
-by chance, the allele for genotype B is passed on to the offspring more often than others–} no. of individuals with that allele increases
-if this continues, it leads to evolution as the allele becomes more common in a population

49
Q

How does population size affect evolution?

A

-genetic drift and natural selection work alongside each other to drive evolution but the one with the greatest impact is determined by population size
-small populations with limited genetic diversity cannot adapt to change as easily and are more likely to become extinct than large populations with a larger gene pool(easy to adapt to change over time)

50
Q

Genetic bottlenecks

A

-an event that causes a big reduction in population size i.e natural disasters/diseases/habitat disruptions from humans
-the resulting population would have a small gene pool(may lead to the extinction of a particular allele) and limited genetic diversity

51
Q

What is a positive aspect of genetic bottleneck?

A

-a beneficial mutation will have a much greater impact and lead to the quicker development pf a new species

52
Q

Founder effect

A

-when a new population is created with a few individuals from a larger population due to migration and geographical isolation or through cultural choice
-these small populations have much smaller gene pools and less genetic variation
-alleles that were rare in the original population will be much higher and have bigger impact on natural selection in the new population if carried

53
Q

What does the stability an ecosystem affect?

A

-which characteristics are selected for by natural selection

54
Q

Describe stabilising selection

A

-the environment of the organism remains mostly unchanged
-the phenotype of the organism favours the average and not the extremes

55
Q

Describe directional selection

A

-occurs when there is a selection pressure against one of the phenotypic extremes
-distribution of the phenotypes move more towards the extreme

56
Q

Describe disruptive selection

A

-favours the extreme of the phenotype + the intermediate phenotype is selected against

57
Q

What is the Hardy-Weinberg principle and what are its assumptions?

A

-can be used to predict allele frequencies
-predicts that the frequencies of alleles in a stable population will remain constant from one generation to the next and there will be no evolution
-assumes that:
- the population is large enough to make a sampling error negligible
- there is no selective advantage for any genotype–} no selection
- there is no mutation, migration or genetic drift
- random mating(all possible genotypes can breed with another)
(conditions virtually never occur in a natural environment)

58
Q

Hardy-Weinberg equation for allele frequency

A

p + q = 1
-p= frequency of dominant allele
-q= frequency of recessive allele
(total frequency always equals 1)

59
Q

Hardy-Weinberg equation for genotype frequency

A

p² + 2pq + q² = 1
-p²= frequency of homozygous dominant genotype
-2pq= frequency of heterozygous genotype
-q²= frequency of homozygous recessive genotype

60
Q

What is speciation?

A

-the formation of a new species through evolution
-the organisms belonging to the new species will no longer be able to interbreed to produce fertile offspring with the original species

61
Q

What are the events leading up to speciation?

A

-members of the population become isolated and no longer interbreed with the rest of the population–} in no gene flow between the groups
-alleles in both groups undergo random mutations + environment of each group may change/be different–} different selected characteristics
-accumulation of mutations + changes in allele frequencies over generations lead to large changes in the phenotype–} reproductively isolated and become a new species

62
Q

Describe allopatric speciation

A

-formation of 2 different species from 1 due to geographical isolation–} physical barrier i.e sea
-populations adapt to different conditions in their environment–} different characteristics will be more common via natural selection(different selection pressures)
-mutations change allele frequencies different and lead to different changes in their phenotype

63
Q

Describe sympatric speciation

A

-formation of 2 different species from 1 due to reproductive isolation within the same habitat
-random mutations could occur within a population, preventing member of that population breeding with members of the same species
-hybrid fertile offspring(formed from 2 different species interbreeding) may not be able to interbreed with the members of either parent population–} stops gene flow

64
Q

What act as reproductive barriers?

A

-seasonal changes
-mechanical changes
-behavioural changes

65
Q

What is artificial selection?

A

-artificial change in the environment leading to survival of the fittest–} selection for breeding of plants/animals with desirable characteristics by farmers
-populations are usually polymorphic for most characteristics
-alleles coding for the most common characteristic is called the wild type allele and other forms are called the mutant

66
Q

Examples of artificial selection

A

-dairy cows: farmer breeds female with high milk yield and male whose mother had a high milk yield together, select the best offspring and breed them together, continued over many gens
(milk should be high quality + cows should have a long lactation period, large udders, be resistant to diseases, a calm temperament
-bread wheat: wheat plants with a high wheat yield are bred together, offspring with best yield are bred together, continued over many gens
(wheat should have a high tolerance of cold, short stalks(don’t collapse), uniform stalk height(easier harvesting)

67
Q

What is inbreeding and what is the problem with it?

A

-the breeding of closely related individuals
-leads to a limited gene pool–} decreases genetic diversity and limits chances of a population of inbred organisms evolving
-being too genetically similar increases chances of having the same recessive alleles which reduces ability to survive and reproduce(more susceptible to genetic disorders)

68
Q

What are gene/seed banks and how are they useful?

A

-seed banks keep samples of seeds from both wild + domesticated varieties
-gene banks store biological samples i.e eggs
-alleles from banks can be used to increase genetic diversity via outbreeding(breeding unrelated/distantly related varieties)–} reduces occurrence of homozygous recessives + increases potential to adapt to environmental changes

A LEVEL BIOLOGY (22 decks)

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