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Alevel Biology OCR > 6.1.2 - Patterns of Inheritance > Flashcards

6.1.2 - Patterns of Inheritance Flashcards

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1
Q

What is continuous variation?

A

a characteristic that can take any value in a range

  • polygenic (under the control of multiple genes)
  • affected by genetics and environment
    eg. skin colour, leaf surface area
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2
Q

What is discontinuous variation?

A

a character that can only appear in discrete categories

  • under the control of one gene
  • affected by genes
    eg. blood group, pea shape
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3
Q

What is chlorosis?

A

a plant condition when plant cells don’t produce the normal amount of chlorophyll, causing the leaves to become pale/yellow
-caused by lack of light, mineral deficiencies and viral infections

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4
Q

What is a gene?

A

a section of DNA found at a locus that controls a particular characteristic
-codes for a protein

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5
Q

What is an allele?

A

a form of a particular gene

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6
Q

What is monogenic inheritance?

A

the inheritance of a characteristic on a single gene

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7
Q

What is multiple alleles?

A

more than two forms of a gene

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8
Q

What is dihybrid inheritance?

A

the inheritance of two different characteristics caused by two different genes simultaneously

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9
Q

How can you tell if an individual bred is homozygous or heterozygous?

A

by breeding with a homozygous recessive individual

-if their offspring is homozygous recessive, the individual is heterozygous

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10
Q

What is codominance?

A

when two alleles are equally expressed in the phenotype

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11
Q

What is sickle cell anaemia?

A
  • an example of codominance
  • mutation where β chains of haemoglobin are affected
  • amino acid in position 6 is changed from (soluble) glutamic acid to (insoluble) valine
  • when oxygenated, the β chain becomes more soluble and crystalline, making the red blood cell less flexible and sickle shapes
  • red blood cells therefore get stuck in capillaries
  • is caused by codominant alleles
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12
Q

What chromosomes do male humans have?

A

XY

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13
Q

What chromosomes do female humans have?

A

XX

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14
Q

What is sex linkage?

A

genes carried on the sex chromosomes which control a specific characteristic
-only alleles on X chromosome expressed

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15
Q

What is haemophilia?

A

A sex-linked genetic disorder where blood clots very slowly due to the absence of a protein blood-clotting factor
-males have it (females can be carriers when heterozygous -is very rare for them to be homozygous haemophilic)

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16
Q

Why are males not heterozygous for sex-linked characteristics?

A

they only have 1 allele but you need to have 2 alleles to be heterozygous

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17
Q

What is (autosomal) linkage?

A

genes found close to eachother on the same chromosome which are not separated during crossing over in prophase 1
-causes unusual ratio like 5:1:1:5 when a ratio of 1:1:1:1 is expected

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18
Q

What causes a ratio of 5:1:1:5 in the offspring to be produced?

A

autosomal linkage

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19
Q

What are recombinant offspring?

A

offspring with different combinations of alleles to either parent (due to autosomal linkage)

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20
Q

recombination frequency =

A

no. recombinant offspring
_____________________
total no. of offspring

>50% = no linkage (genes on separate chromosomes)
<50% = linkage
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21
Q

What is epistasis?

A

the interactions between different genes at different loci

eg. gene regulation (like LAC operon)

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22
Q

What is a locus?

A

a position of a gene on a chromosome

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23
Q

What are the types of epistasis?

A
  • antagonistic epistasis (recessive and dominant epistasis)

- complementary epistasis

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24
Q

What is antagonistic epistasis?

A

epistasis where genes work against eachother

-dominant or recessive

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25
Q

What is an epistatic allele?

A

allele on first locus which causes the affect

26
Q

What is a hypostatic allele?

A

allele at second locus which is affected (by epistatic allele) that stops the protein synthesis of the allele

27
Q

How can the hypostatic allele stop protein synthesis of the allele?

A

produces a…

  • repressor protein which binds to allele and stops transcription
  • enzyme breaks down mRNA
  • protein binds to mRNA and prevents it binding to the ribosome
  • protein binds to ribosome so that mRNA can’t
28
Q

What is the ratio of offspring produced by recessive epistasis?

A

9:4:3

29
Q

What causes a ratio of 9:4:3 in the offspring to be produced?

A

recessive epistasis

30
Q

What is the ratio of offspring produced by dominant epistasis?

A

12:3:1

31
Q

What causes a ratio of 12:3:1 in the offspring to be produced?

A

dominant epistasis

32
Q

What is complementary epistasis?

A

epistasis where genes work together

33
Q

What is the ratio of offspring produced by complementary epistasis?

A

9:7

34
Q

What causes a ratio of 9:7 in the offspring to be produced?

A

complementary epistasis

35
Q

What is the chi-squared test used for?

A

to determine (the significance of) the difference between observed and expected results

36
Q

What must you have in order to use the chi-squared test?

A
  • 20+ individuals in sample
  • discrete categories
  • raw data (aka not percentage values)
37
Q

What factors can affect the evolution of a species?

A
  • stabilising selection
  • directional selection
  • genetic drift
  • genetic bottleneck
  • founder effect
38
Q

What is stabilising selection?

A

natural selection favouring average phenotypes

-extreme phenotypes are selected against

39
Q

What is directional selection?

A

natural selection which favours one extreme phenotype

40
Q

What is genetic drift?

A

random change of allele frequency

-particularly in small populations

41
Q

What is genetic bottleneck?

A

when large numbers of a population die, leading to a reduced gene pool and therefore a lower genetic biodiversity in the population
-particularly in small populations

42
Q

What is the founder effect?

A

when a few individuals of a species colonise a new area, leading to a reduced genetic variation in the offspring
-rare alleles can become more common

43
Q

What does the Hardy-Weinberg principle state?

A

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.

44
Q

What assumptions are made when using the Hardy-Weinberg principle’s equations?

A
  • population is large
  • mating is random
  • no selection occurs (no selection pressures)
  • no mutations, migration or genetic drift occurs
45
Q

What does p stand for in p+q = 1 (in Hardy-Weinberg’s principle’s equations)?

A

dominant allele frequency

46
Q

What does q stand for in p+q = 1 (in Hardy-Weinberg’s principle’s equations)?

A

recessive allele frequency

47
Q

What does p^2 stand for in p^2 +2pq +q^2 (in Hardy-Weinberg’s principle’s equations)?

A

homozygous dominant genotype frequency

48
Q

What does q^2 stand for in p^2 +2pq +q^2 (in Hardy-Weinberg’s principle’s equations)?

A

homozygous recessive genotype frequency

49
Q

What does 2pq stand for in p^2 +2pq +q^2 (in Hardy-Weinberg’s principle’s equations)?

A

heterozygous dominant genotype frequency

50
Q

What is a species according to the biological species concept?

A

a group of organisms that can interbreed to produce fertile offspring
eg. all dogs

51
Q

What is speciation?

A

the formation of a new species

52
Q

Why does speciation occur?

A
  • populations become isolated from eachother (no gene flow)
  • random mutations (produces different alleles may be selected for)
  • changes in allele frequencies over many generations (populations change so much they no longer breed)
53
Q

What are the two types of speciation?

A
  • allopatric speciation

- sympatric speciation

54
Q

What is allopatric speciation?

A

speciation that occurs as a result of geographical isolation

  • most common form
  • diff environments in diff locations select for diff alleles
    eg. galapagos finches
55
Q

Name an example of allopatric speciation

A

Galapagos finches

56
Q

What is sympatric speciation?

A

speciation that occurs as a result of reproductive isolation

  • two organisms of diff species interbreed to produce fertile offspring
  • organisms continue to share same habitat
  • common in plants, rare in animals
57
Q

What is artificial selection?

A

selective breeding of organisms involving humans selecting desired characteristics (aka phenotypes) and interbreeding them to produce desired offspring

58
Q

Name some examples of selective breeding in plants

A
  • disease resistant plants in food crops
  • increased crop yield
  • plants with drought resistance
  • plants that produce better tasting/larger fruits
  • plants with larger flowers
59
Q

Name some examples of selective breeding in animals

A
  • cows, sheep, etc bred for higher yield of milk or meat (large udders, muscular, fertile, etc)
  • chickens bred to lay large eggs
  • domestic dogs bred to have a gentle nature or desirable appearance
  • horses bred to have desirable appearance and/or fast pace
60
Q

Why is it important to maintain a resource of genetic material for use in selective breeding?

A

ensures gene pool doesn’t become too small (which would reduce variation and make species more vulnerable to disease or climate change)

61
Q

What ethical considerations are there surrounding the use of artificial selection?

A
  • inbreeding reduces gene pool so increases chance of harmful genetic defects being inherited and organisms being vulnerable to disease
  • intensive artificial processes have resulted in damaging conditions/diseases like breathing difficulties in pugs

Alevel Biology OCR (26 decks)

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