Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Biology A-level OCR Yr13 > INHERITANCE AND VARIATION > Flashcards

INHERITANCE AND VARIATION Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

Describe chlorosis

A

chlorosis is when the cells are not producing the normal amount of chlorophyll, reducing photosynthesis. Most plants with chlorosis have the normal genes coding for chlorophyll production. The change in their phenotype is a result of their environment.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What are the environmental factors causing chlorosis?

A

-lack of light: plants will turn off their chlorophyll production to conserve resources.
-mineral deficiencies (e.g lack of iron or magnesium): iron is needed as a cofactor by some enzymes that make chlorophyll and magnesium is found in chlorophyll molecule
-virus infections: viruses can interfere with metabolism of cells at the point they can no longer support the synthesis of chlorophyll.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

Genetic variation is due to?

A

sexual reproduction involving meiosis (the formation of gametes) and the random fusion of gametes at fertilisation.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

what is a genotype?

A

the genetic constitution of that organism (the alleles it has for a gene)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a phenotype?

A

the expression of the genes and its interaction with the environment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is a dominant allele?

A

version of the gene that will always be expressed if present in an organism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a recessive allele?

A

version of gene that will only be expressed if two copies of this allele are present in an organism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

what is homozygous?

A

a pair of homologous chromosomes carrying the same alleles for a single gene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

what is heterozygous?

A

a pair of homologous chromosomes carrying two different alleles for a single gene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Describe continuous variation?

A

-a characteristic that can take any value within a range
-genetic and environmental causes
-polygenes (controlled by multiple genes)
-e.g animal mass, skin colour

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

Describe discontinuous variation?

A

-a characteristic that can only appear in specific (discrete) values
-mostly genetic causes
-one or two genes involved
-e.g blood group, albinism

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

How do you perform a genetic cross?

A

-state phenotype for both parents
-state genotype for both parents
-state gametes for each parent
-punnett square
-state proportion of each genotype which are produced in the offspring (ratio)
-state the corresponding phenotype for each possible genotype

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is codominance?

A

occurs when two equally dominant alleles occur for a gene. As a result both alleles for a gene are expressed in the phenotype of the organism if present.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Describe how blood group is determined by a gene with multiple alleles?

A

the immunoglobulin gene codes for the production of antigens on the surface of red blood cells. There are three alleles for this gene.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What is the male and female chromosome pair?

A

male- X Y
female- X X

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

Describe the X and Y chromosomes?

A

X chromosome is large and contains many genes not involved in sexual development. Y chromosome is very small, containing almost no genetic variation but it does carry the gene that causes the embryo to develop as a male

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is a sex-linked gene?

A

characteristics determined by genes carried on the sex chromosomes. As X chromosomes are much bigger than Y chromosomes, any characteristic caused by a recessive allele on the section of the X chromosome, which is missing on the Y chromosome, occurs more frequently in males

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is haemophilia?

A

sex-linked disorder in which blood clots extremely slowly due to the absence of a protein blood-clotting factor. This can lead to prolonged bleeding and if untreated can be fatal

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

How is haemophilia sex-linked?

A

if a male inherits the recessive allele that codes for haemophilia (on their X chromosome) they cannot have a corresponding dominant allele on their Y chromosome and so develop the condition. Most haemophilia sufferers are male

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

What is a dihybrid cross?

A

show the inheritance of two different characteristics, caused by two genes, which may be located on different pairs of homologous chromosomes. Each of these genes can have two or more alleles.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

what is the expected ratio in a dihybrid cross between two heterozygous individuals?

A

9:3:3:1

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

why might the ratio not meet the expected ratio of 9:3:3:1?

A

-random fertilisation of gametes
-crossing over may have occurred disrupting the linked genes (genes on the same chromosome)

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

what is an autosome?

A

chromosome not concerned with sex determination

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

what is linkage?

A

genes are located on the same chromosome. Linked genes are inherited as one unit- there is no independent assortment during meiosis unless the alleles are separated by chiasmata.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

What is autosomal linkage?

A

when the genes that are linked are found on one of the other pairs of chromosome

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

what are recombinant offspring?

A

have a different combination of alleles than either parent. The closer the genes are on a chromosome, the less likely they are to be separated during crossing over and fewer recombinant offspring produced.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

what is recombination frequency?

A

a measure of the amount of crossing over that has happened in meiosis.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

recombination frequency equation?

A

number of recombinant offspring/ total number of offspring

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

A recombination frequency of 50 percent indicates?

A

indicates that there is no linkage and the genes are on separate chromosomes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

A recombination frequency of less than 50 percent indicates?

A

indicates that there is gene linkage and the random process of independent assortment has been hindered.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

the degree of crossing over is determined by what?

A

how close the genes are on a chromosome

32
Q

Describe the chi squared test?

A

statistical test that measures the size of the difference between the observed and expected results, helps to determine significance.

33
Q

How do you calculate degrees of freedom in chi squared test?

A

n(number of categories)-1

34
Q

in a chi squared test, what is the null hypothesis?

A

there is no significant difference between the observed and expected results

35
Q

If the chi squared value id less than the critical value found in the table at 5 percent significance (p=0.05)?

A

we do not have sufficiently strong evidence to reject null hypothesis therefore we accept null.

36
Q

If the chi squared value is higher than the critical value found in the table at 5 percent significance (p=0.05)?

A

reject the null- some other factor is likely to be causing a significant difference between the expected and observed results.

37
Q

what is epistasis?

A

interaction of genes at different loci

38
Q

what is an epistatic gene?

A

gene that effects the expression of another gene

39
Q

what is a hypostatic gene?

A

gene that is affected by another gene

40
Q

what is recessive epistasis?

A

if the presence of two recessive alleles at a gene locus led to the lack of an enzyme

41
Q

what is dominant epistasis?

A

the expression of the dominant allele of the epistatic gene prevents the expression of the hypostatic gene. This means that any genotypic combination with either one or two of the dominant alleles for the epistatic gene will suppress the expression of the hypostatic gene

42
Q

what is the gene pool?

A

the sum of all the genes in a population at any given time

43
Q

what is the allele frequency?

A

the relative frequency of a particular allele in a population

44
Q

how do you calculate allele frequency?

A

p + q = 1
p- dominant genotype
q- recessive genotype

45
Q

what does the Hardy-Weinburg 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.

46
Q

The Hardy-Weinberg principle equation?

A

p(squared) + 2pq + q(squared) = 1
p(squared)- frequency of homozygous dominant genotype
2pq- frequency of heterozygous genotype
q(squared)- frequency of homozygous recessive genotype

47
Q

Assumptions from the Hardy-Weinberg principle?

A

population of diploid organisms is:
-large
-isolated
-random mating
-no mutations
-no mutations (no evolution)

48
Q

factors which lead to the changes in frequency of alleles within a population and so they therefore affect the rate of evolution?

A

-mutation
-sexual selection (improves mating success)
-gene flow (movement of alleles between populations, immigration and emigration)
-genetic drift (random mutation, appearance of a new allele which will have a greater impact on a smaller population).
-natural selection

49
Q

what are density-dependent factors?

A

affect is dependent on population size and include competition, predation and disease

50
Q

what are density-independent factors?

A

affect populations of all sizes in the same way including climate change, natural disasters, seasonal change and human activity (e.g deforestation)

51
Q

what is a population bottle neck?

A

large reductions in population size which lasts for at least one generation. The gene pool and genetic diversity is greatly reduced.

52
Q

what is a positive aspect of genetic bottleneck?

A

a beneficial mutation will have a greater impact and lead to the quicker development of a new species

53
Q

what is genetic drift?

A

describes change in allele frequencies in the gene pool of a population (evolution) due purely to chance events and not selection pressures. It has a greater influence on smaller populations.

54
Q

what is the founder effect?

A

When a new population is established by a small number of individuals, the founding population will have low genetic diversity and be heavily influenced by genetic drift.

55
Q

what is stabilising selection?

A

in a normal distribution curve, the average is selected for (positive selection) and the extremes are selected against (negative selection). Therefore results in a reduction in the frequency of alleles at the extremes and an increase in the frequency if the average alleles

56
Q

what is directional selection?

A

occurs when there is a change in the environment and the normal (most common) phenotype is no longer advantageous . The extreme phenotype is positively selected. The allele frequency then shifts towards the extreme phenotypes and evolution occurs

57
Q

what is disruptive selection?

A

the extremes are selected for and the norm is selected against. This is the opposite of stabilising selection.

58
Q

what is a species?

A

group of organisms in which two individuals can mate to produce fertile offspring

59
Q

what is speciation?

A

formation of new species through the process of evolution

60
Q

what events occur leading to speciation?

A

-members of a population become isolated and no longer interbreed with the rest of the population (no gene flow)
-alleles within the group undergo random mutations. The environment of each group may be different or change (resulting in different selection pressures) so different characteristics will be selected for and against.
-the accumulation of mutations and changes in allele frequencies over many generations. Members of different population become so different, they cannot interbreed. Reproductively isolated.

61
Q

Describe allopatric speciation

A

-more common form of speciation
-speciation when a population is separated by a physical barrier (e.g river or sea)- geographical isolation. The environments are different meaning different selection pressures resulting in different physical adaptations. This will lead to founder effect leading to genetic drift.

62
Q

Describe sympatric speciation

A

-occurs within populations that share the same habitat
-happens less frequently than allopatric speciation
-more common in plants than animals
-members of two different species interbreed and form fertile offspring. Hybrid formed is a new species which will have a different number of chromosomes to either parent and may no longer be able to interbreed with members of either parent population. This stops gene flow and reproductively isolates the hybrid organisms.

63
Q

Describe prezygotic reproductive barriers?

A

prevent fertilisation and the formation of a zygote

64
Q

Describe postzygotic reproductive barriers?

A

often produced as a result of hybridisation, reduce the viability or reproductive potential of offspring

65
Q

what is a polymorphic population?

A

display more than one distinct phenotype for most characteristics

66
Q

what is the wild type allele?

A

the allele coding for the most common characteristic is called the wild type allele.

67
Q

what are mutant alleles?

A

other forms of allele, apart from wild type allele, resulting from mutations.

68
Q

what is artificial selection (or selective breeding)?

A

selection of breeding plants or animals with desirable characteristics determined by humans (farmers or breeders)

69
Q

what are the problems caused by inbreeding?

A

limited gene pool decreases genetic diversity and reduces chances of a population of inbred organisms evolving and adapting to changes in their environment.

70
Q

how does inbreeding caused genetic disorders?

A

breeding of closely related organisms results in offspring with a greater chance of being homozygous for these recessive traits. They are less biologically fit and less likely to survive and reproduce.

71
Q

describe seed banks?

A

keep sample of seeds from both wild type and domesticated varieties

72
Q

Describe gene banks?

A

store biological samples which are usually frozen (e.g sperm and egg)

73
Q

Describe outbreeding?

A

-e.g alleles from gene banks can be used to increase genetic diversity, owing to the problems caused by inbreeding
-e.g breeding unrelated or distantly related varieties
This reduces occurrence of homozygous recessives

74
Q

what is sex linkage?

A

a gene whose locus is on the X chromosome

75
Q

what is epistasis?

A

when one gene modifies or masks the expression of a different gene at a different locus

76
Q

what is monohybrid?

A

genetic inheritance cross of a characteristic determined by one gene

77
Q

what is dihybrid?

A

genetic inheritance cross for a characteristic determined by two genes

Biology A-level OCR Yr13 (15 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions