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Biology - Module 6 > Patterns of inheritance > Flashcards

Patterns of inheritance Flashcards

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1
Q

what is phenotypic variation

A

difference in phenotypes between organisms of the same species

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2
Q

how does phenotypic variation occur

A

genetic + environmental factors

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3
Q

example of genes effecting phenotype

A

blood group

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4
Q

example of environment effecting phenotype

A

clones with different height due to environmental conditions

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5
Q

example of both genes + environment effecting phenotype

A

recessive allele that causes sickle cell anaemia has a high frequency in populations where malaria is prevalent due to heterozygous individuals being resistant to malaria

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6
Q

how can diet effect fruit flies

A

If the larvae of normal grey flies are given a diet of silver salts, they develop the yellow colour regardless of their genotype

flies that should be grey (according to their genes) can become yellow due to an environmental factor (their diet)

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7
Q

what is chlorosis

A

cells not producing normal amount of chlorophyll

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8
Q

how is chlorosis caused

A

normal genes – but environmental pressures

lack of light – plants turn off chlorophyll production – conserve resources

mineral deficiencies – lack of iron / magnesium

(iron – cofactor for enzymes that make chlorophyll)
(magnesium – centre of chlorophyll molecule)

virus infections – interfere with metabolism + cant support synthesis of chlorphyll

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9
Q

how is etiolation caused

A

Plants that are grown in the dark may also develop long stems with small, curled leaves even though, genetically, they should develop normally

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10
Q

when does crossing over occur

A

prophase 1

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11
Q

describe crossing over

A

homologous chromosomes pair up and are in very close proximity to each other

non-sister chromatids can cross over and get entangled

crossing points are called chiasmata

entanglement places stress on the DNA molecules

section of chromatid from one chromosome may break and re-join with the chromatid from the other chromosome

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12
Q

when does independent assortment occur

A

metaphase 1 + 2

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13
Q

what is independant assortment

A

different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle

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14
Q

how does independant assortment occur

A

Each pair can be arranged with either chromosome on top, this is completely random

The orientation of one homologous pair is independent / unaffected by the orientation of any other pair

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15
Q

what are the number of different combinations of cells resulting from independant assortment

A

2 to the power of n

n = number of chromosomes in haploid cell

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16
Q

summarise meoisis

A
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17
Q

draw a monohybrid cross for Gg

A
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18
Q

what is codominance

A

both alleles are dominant

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19
Q

how to represent codominance

A

one normal letter – two different superscripts

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20
Q

alleles for all blood groups

A
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21
Q

when is a dihybrid cross used

A

to show inheritance of 2 different characteristics – caused by 2 different genes

Could be on different pairs of homologous chromosomes

Could have multiple alleles

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22
Q

draw a dihybrid cross

A
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23
Q

draw a cross with sex linkage

A

HAVE TO SHOW ALLELE ON SEX CHROMOSOME ITS FOUND ON

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23
Q

why does sex linkage exist

A

Y chromosome much smaller then X chromosome

Number of genes on the X chromosome + aren’t matched on the same locus on Y

Y chromosome shorter

doesn’t have a homozygous pair

Only have 1 copy

Any characteristic caused by recessive allele on section of x chromosome (missing on the Y) occurs more frequently in males

Females – may also have dominant on other X

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23
Q

recombinant frequency

A
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23
Q

what is autosomal linkage caused by

A

Genes found on same chromosome / autosome

Inherited as one unit + no independent assortment

Recombinant offspring – different combinations of alleles than either parents
crossing over

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23
Q

what is epistasis

A

interaction of genes at different loci

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24
Q

example of epistasis

A

Lac operon

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25
Q

hypostatic vs epistatic

A

A gene affected by another gene – hypostatic

Gene that affects the expression of another gene – epistatic

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26
Q

what is recessive epistasis

A

where the epistatic allele (the allele that masks another gene) is recessive

two copies of epistatic alleles must be present for expression of hypostatic allele to be affected

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27
Q

what is dominant epistasis

A

epistatic allele is dominant

only one copy of the epistatic allele must be present for expression of the hypostatic allele to be affected

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28
Q

gene

A

length of DNA that codes for single polypeptide

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28
Q

alleles

A

genes existing in two or more different forms

28
Q

locus

A

position of genes on a chromosome

28
Q

ratio - dihybrid unlinked

A

9:3:3:1

28
Q

ratio - monohybrid

A

3:1

28
Q

ratio - dominant epistatic

A

12:3:1

28
Q

difference between continuous + discontinuous variation

A
28
Q

ratio - recessive epistatic

A

9:3:4

28
Q

ratio - dihybrid linked

A

3:1

28
Q

what is continuous

A

differences between individuals of a species where the differences are quantitative (measurable)

29
Q

at genetic level - continuous

A

Different alleles at a single locus have a small effect on the phenotype

Different genes can have the same effect on the phenotype and these add together to have an additive effect

If a large number of genes have a combined effect on the phenotype they are known as polygenes

29
Q

what is discontinuous

A

differences between individuals of a species where the differences are qualitative (categoric

29
Q

at genetic level - discontinuous

A

Different genes have different effects on the phenotype

Different alleles at a single gene locus have a large effect on the phenotype

Factor 8 - heamophillia

29
Q

what is a selection pressure

A

environmental factors that effect chances of survival

30
Q

Factors that affect the size of a population

A

Density – dependant factors
= Dependant on population size
= Competition / predation / parasitism / communicable disease

Density-independent factors
= Effect populations of all sizes in same way
= Climate change / seasonal change / human activities – deforestation

30
Q

Factors affecting evolution

A

mutation

gene flow

genetic drift

genetic bottleneck

founder effect

30
Q

mutation

A
  • Necessary for the existence of different alleles
31
Q

gene flow

A

Movement of alleles between populations

Immigration / emigration result in changes in allele frequency

31
Q

genetic drift

A

Chance affects which individuals in population survive / breed + pass on alleles

E.g – when population is small – chance can affect which alleles get passed onto the next generation

Large populations – less likely - any chance variations in allele frequencies usually even out across the whole population

31
Q

genetic bottlenecking

A

Occurs when previously large population suffers a dramatic fall in numbers

Reduces genetic diversity = alleles are lost

surviving individuals end up breeding and reproducing with close relatives

genetic diversity greatly reduced

32
Q

founder effect

A

extreme example of genetic drift

occurs when only a small number of individuals from a large parent population start a new population

made up of only a few individuals from the original population = only some of the total alleles from the parent population will be present

not all gene pool present

which alleles end up in new population = up to chance

33
Q

what is stabilising selection

A

Natural selection that keeps allele frequencies relatively constant over time

Average individuals favoured

Very-low and very-high birth weights are selected against leading to the maintenance of the intermediate birth weights

33
Q

what is directional selection

A

Natural selection that produces a gradual change in allele frequencies over several generations

Individuals favoured in one direction

Caused by change in environment / new allele that has appeared in population = advantageous

33
Q

process of directional selection

A

Selection pressure that favours phenotype

Phenotype is produced by specific alleles

Individuals with favoured phenotype = fitter / more likely to pass on their alleles to offspring

Frequency of advantageous allele increases

34
Q

what is disruptive selection

A

Extremes are selected for

34
Q

graphs - all selection types

A
34
Q

what is the hardy-weinberg principle used for

A

to calculate allele frequencies in populations

34
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

35
Q

conditions for hardy-weinberg principle

A

Organisms are diploid

Organisms reproduce by sexual reproduction only

There is no overlap between generations, i.e. parents do not mate with offspring

Mating is random

The population is large

There is no migration, mutation, or selection

Allele frequencies are equal in both sexes

35
Q

hardy weinberg equations

A
35
Q
A
35
Q

what is speciation

A

formation of new species through process of evolution

36
Q

events leading to speciation

A

Members of population becomes isolated – no longer interbreed – no gene flow between 2 populations

Alleles within groups – random mutations – different selection pressures

Accumulation of mutations + changes in allele frequency – large difference in phenotype over time

37
Q

what is allopatric speciation

A

occurs as a result of geographical isolation

most common type of speciation

38
Q

describe allopatric speciation

A

occurs when populations of a species become separated from each other by geographical barriers

creates two populations of the same species who are reproductively separated from each other

no genetic exchange can occur between them

If there are sufficient selection pressures acting to change the gene pools (and allele frequencies) within both populations then eventually these populations will diverge and form separate species

changes in the alleles/genes of each population will affect the phenotypes present in both populations

39
Q

what is sympatric speciation

A

takes place with no geographical barrier

A group of same species living in the same place but in order for speciation to take place = exists two populations within that group and no gene flow occurs between them

40
Q

how can sympatric speciation occur

A

via:

Ecological separation

Behavioural separation

Polyploidy

41
Q

what is ecological speciation

A

Populations are separated because they live in different environments within the same area

42
Q

example of ecological separation

A

soil pH can differ greatly in different areas.

Soil pH has a major effect on plant growth and flowering, so a population growing in soil with a slightly different pH may flower at a different time from another population

leading to reproductive separation (and eventually genetic isolation) of the two populations

43
Q

what is behavioural isolation

A

separated because they have different behaviours

differences in feeding, communication or social behaviours = courting behaviours to attract a mate

44
Q

examples of behaviours that lead to sympatric speciation

A
45
Q

what is polyploidy

A

Occurs when an organism has more than two sets of homologous chromosomes

46
Q

example of polyploidy

A

When a newly-arisen tetraploid (4n) plant tries to breed with its ancestral species (a backcross), triploid offspring are formed. These are sterile because they cannot form gametes with a balanced assortment of chromosomes. However, the tetraploid plants can breed with each other. So in one generation, a new species has been formed.

47
Q

process of artificial selection / selective breeding

A
  1. The population shows phenotypic variation - there are individuals with different phenotypes
  2. A breeder selects an individual with the desired phenotype
  3. Another individual with the desired phenotype is selected
  4. two selected individuals should not be closely related to each other
  5. The two selected individuals are bred together
  6. The offspring produced reach maturity and are then tested for the desirable trait. Those that display the desired phenotype to the greatest degree are selected for further breeding
  7. continues for many generations until all offspring display the desirable trait
47
Q

example of selective breeding

A

farmers have selected female cows that have the highest milk yield and crossed them with male bulls related to high yield females

economical benefit to farmers

47
Q

what is artificial selection / selective breeding

A
  • process by which humans choose organisms with desirable traits and selectively breed them together to enhance the expression of these desirable traits over time and over many generations
47
Q

importance of maintaining
a resource of genetic material for use in selective
breeding including wild types.

A

important to maintain a resource of genetic material that includes types that are close to the original wild type (of the organism you are selectively breeding)

This is important as it ensures that the gene pool for a particular species doesn’t become too small (which can weaken the population by reducing variation)

47
Q

ethics of selective breeding

A

lead to inbreeding

results in a reduction in the gene pool

an increased chance of:

  1. Organisms inheriting harmful genetic defects
  • as there is a higher chance of harmful recessive alleles combining in an individual and being expressed in the phenotype
  1. Organisms being vulnerable to new diseases
  • as there is less chance of resistant alleles being present in the reduced gene pool
48
Q

examples of selective breeding in plants
and animals

A

Biology - Module 6 (6 decks)

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