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IB Biology > 10.2 Inheritance > Flashcards

10.2 Inheritance Flashcards

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1
Q

What does the law of independent assortment say about alleles?

A

Pairs of alleles are inherited independently of one another if their gene loci are on separate chromosomes

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2
Q

If gene loci are on separate chromosomes called?

A

Unlinked genes

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3
Q

What causes unlinked genes?

A

The random orientation of homologous pairs during metaphase I of meiosis

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4
Q

What does the independent segregation of unlinked genes cause a greater number of?

A

Of potential gamete combinations and a greater variety of possible phenotypes

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5
Q

What does a greater variety of possible phenotypes cause?

A

More complex inheritance patterns

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5
Q

What does a dihybrid cross determine?

A

The genotypic and phenotypic combinations of offspring for two particular genes that are unlinked

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6
Q

Why can there be up to four different gamete combinations?

A

Because there are two genes each with two alleles

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7
Q

What is the best way to work out potential gamete combinations in a dihybrid cross?

A

The FOIL method

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8
Q

What are the five steps to complete a dihybrid cross?

A
  1. designate characters to represent the alleles
  2. Write down the genotype and phenotype of the parents
  3. Write down all potential gamete combinations for both parents
  4. Use a Punnett square to work out potential genotypes of offspring
  5. Write out the phenotype ratios of potential offspring
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9
Q

What does a capital letter represent?

A

A dominant allele

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10
Q

What does a lower case letter represent?

A

A recessive allele

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11
Q

What should go first when writing down the genotype/phenotype?

A

The capitals first (AaBb not ABab)

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12
Q

When writing genotypes/ phenotypes what should you pair?

A

Alleles from the same gene

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13
Q

When using a Punnett square what should you only include?

A

The different gamete combinations for each parent

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14
Q

What do phenotypic ratios reflect?

A

The mathematical probabilities only and may not necessarily reflect actual offspring ratios

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15
Q

What is a linkage group?

A

A group of genes whose loci are on the same chromosome and don’t independently assort

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16
Q

How will linked genes be inherited?

A

Together

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17
Q

What do linked genes fail to follow?

A

Normal mendelian inheritance for a dihybrid cross

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18
Q

What will linked genes be more closely aligned to and why?

A

A monohybrid cross as the two genes are inherited as a single unit

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19
Q

How may linked genes become separated?

A

Via recombination

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20
Q

How are linked genes represented?

A

As vertical pairs

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21
Q

What did Thomas Hunt Morgan do?

A

Provided a key contribution to our current understanding of gene linkage by discovering non-mendelian ratios in fruit flies

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22
Q

What did Morgans breeding experiment with fruit flies show?

A

That linked genes were not independently assorted

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23
Q

When Morgan worked with red eyed wild types and white eyed mutants what did he discover?

A

A clear sex bias in phenotypic distribution

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24
Q

How did Morgan describe this distribution and explain why it happened:
All female offspring of a red-eyed male were red-eyed, whereas all male offspring of a white-eyed female were also white-eyed?

A

As sex limited inheritance and it was caused by the gene for eye colour was found on the sex chromosome

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25
Q

What did Morgan observe that the amount of crossing over between linked genes differed dependent on?

A

The combination of traits

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26
Q

What is crossover frequency a product of?

A

The distance between two genes on a chromosome

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27
Q

Describe the distance between genes with a higher crossover frequency?

A

Further apart

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28
Q

Describe the distance between genes with a lower crossover frequency?

A

Closer together

29
Q

What are recombinants of linked genes?

A

Those combinations of genes not found in the parents

30
Q

What causes recombinants to happen?

A

Crossing over of genetic material during prophase I of meiosis

31
Q

What happens if linked genes become separated by chiasma?

A

There will be an exchange of alleles between the non sister chromatids

32
Q

What do recombinants create?

A

New allele combinations that are different to those of the parent

33
Q

Why is the frequency of recombinant phenotypes within a population is typically be lower than that of non-recombinant phenotypes?

A

Because crossing over is a random process

34
Q

Do chiasmata form at the different locations in each meiotic division?

A

Yes

35
Q

What is the relative frequency of recombinant phenotypes dependent on?

A

The distance between linked genes

36
Q

Why will the recombination frequency between two linked genes be greater when the genes are further apart on the chromosome?

A

Because there are more possible locations where a chiasma could form between the genes

37
Q

How can recombinant phenotypes be identified?

A

By performing a test cross

38
Q

What can you tell by looking at the frequency of potential phenotypes?

A

Whether two genes are linked or unlinked

39
Q

What possibility do offspring with unlinked genes have of inheriting any potential phenotypic combination?

A

Equal

40
Q

When will offspring with linked genes express the phenotypic combinations present in either parent?

A

If crossing over occurs

41
Q

Do unlinked recombinant phenotypes occur more or less frequently than linked parental phenotypes?

A

Less frequently

42
Q

What are chi squared tests?

A

A statistical measure that are used to determine whether the difference between an observed and expected frequency distribution is statistically significant

43
Q

If observed frequencies do not conform to those expected for an unlinked dihybrid cross, what does it suggest?

A

Genes are linked and not independently assorted
or
The inheritance of the traits are not random but are maybe affected by natural selection

44
Q

What are the five steps of performing a chi squared test?

A

Identify hypothesis (null vs alternative)
Construct a table of frequencies (observed versus expected)
Apply the chi squared formula
Determine the degree of freedom
Identify the p value

45
Q

What is a null hypothesis?

A

There is no significant difference between observed and expected frequencies

46
Q

What is an alternative hypothesis?

A

There is a significant difference between observed and expected frequencies

47
Q

How do you calculate expected frequencies?

A

By determining the expected ratios and then multiplying against the observed total

48
Q

How do you calculate degrees of freedom?

A

df = (m – 1) (n – 1)

Where: m = number of rows ; n = number of columns

49
Q

What is the chi squared formula?

A

x2 = ∑ (O-E)2 / E

50
Q

What are the two types of variation in phenotypes?

A

Discrete or continuous

51
Q

What are monogenic traits?

A

Characteristics controlled by a single gene loci

52
Q

What are polygenic traits?

A

Characteristics controlled by more than one gene loci

53
Q

What type of variation do monogenic traits exhibit?

A

Discrete variation

54
Q

What type of variation do polygenic traits exhibit?

A

Continuous variation

55
Q

What will an individuals phenotype be in a monogenic trait?

A

One of a number of distinct phenotypes

56
Q

What will an individuals phenotype be in a polygenic trait?

A

Somewhere in a continuous spectrum of potential phenotypes

57
Q

What does increasing the number of loci responsible for a particular trait do?

A

Increases the number of possible phenotypes

58
Q

What does the distribution shape of a phenotype follow?

A

A bell shaped normal distribution curve

59
Q

What is an example of a polygenic trait?

A

Maize grain colour

60
Q

What is maize colour controlled by?

A

Three gene loci

61
Q

What is the colour range of maize?

A

White to dark red

62
Q

What does each maize allele have and what does it code for?

A

Two alleles which either code for red or white pigment

63
Q

What is the most frequent combination of allele types in maize?

A

An equal number of both allele types

64
Q

What does the overall patter of maize colour inheritance show?

A

Continuous variation

65
Q

What are the two things that influence phenotypes?

A

Genotype and environmental factors

66
Q

What is the added effect of environmental pressures functions?

A

Increases the variation seen for a particular trait

67
Q

What are examples of a polygenic trait which is influenced by environmental factors?

A

Human height and skin colour

68
Q

What controls human height?

A

Multiple genes resulting in a bell shaped spectrum of potential phenotypes

69
Q

What environmental factors can influence an individual humans height?

A

Diet and health

70
Q

What controls skin colour?

A

Multiple melanin producing genes

71
Q

What environmental factors affect skin colour?

A

Sun exposure

IB Biology (57 decks)

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