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NSFC AQA A level Biology Year 2 > 3.7.1 Inheritance (Unit 7 Inheritance and Populations) > Flashcards

3.7.1 Inheritance (Unit 7 Inheritance and Populations) Flashcards

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1
Q

What is a genotype?

A

The genetic make up on an organism. It describes ALL the alleles that an organism has.

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2
Q

What is an allele?

A

A different version of the same gene

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3
Q

What is a gene?

A

Short section of DNA made up of nucleotide bases, which codes for a specific order of amino acids which makes a polypeptide.

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4
Q

What is a phenotype?

A

Observable characteristics due to environment and genetic makeup

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5
Q

What is a homologous pair?

A

A pair of chromosomes - maternal and paternal. Also known as a bivalent

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6
Q

What is a recessive allele?

A

An allele whereby you need 2 copies of it (homozygous) to express that characteristic. Its not expressed if the dominant allele is present.

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7
Q

What is a dominant allele?

A

An allele that is always expressed

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8
Q

Homozygous dominant means?

A

Two dominant alleles present (in the genotype)

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9
Q

Homozygous recessive means?

A

Two recessive alleles present (in the genotype)

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10
Q

Heterozygous means?

A

One recessive and one dominant allele present (in the genotype)

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11
Q

A codominant allele is?

A

Where both alleles contribute/expressed in the phenotype

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12
Q

What are multiple alleles?

A

Where you have more than two alleles for a particular gene

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13
Q

In a diploid organism (human) how many chromosome pairs are there?

A

23

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14
Q

In meiosis what happens to the diploid number?

A

It becomes haploid - halves

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15
Q

Characteristics are determined by your allele combinations, how many alleles for each characteristics end up in the gamete?

A

1

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16
Q

Pure breeding plants are said to be

A

Homozygous

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17
Q

If there are 30 boys and 15 girls what is the ratio?

A

2:1

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18
Q

Why are actual ratios not exactly the same as theoretical ratios in genetics?

A

Because fertilisation of gametes occurs by chance - each time a gamete is fertilised, it is an independent event of what has gone before it.

Small sample size

Lethal phenotypes
Epistasis
Linkage

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19
Q

How can you try and get theoretical ratios to match observed/actual ratios?

A

Increase sample size so its more representative

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20
Q

If you were to perform a statistical test on Mendelian genetics and you where looking at observed and expected ratios - what test would you do and why?

A

Chi Squared - because you are comparing observed and expected values and determining if there is a statistical difference

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21
Q

Suppose you obtained a chi squared value of 5 and the critical value was 5.99 (2dof) - what can you conclude?

A

Because the chi squared value is SMALLER than the critical value - you accept the null hypothesis and there is greater than a 0.05 probability that the difference in the results are due to chance. There is no significant difference.

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22
Q

Suppose you obtained a chi squared value of 8 and the critical value was 5.99 (2dof) - what can you conclude?

A

Because the chi squared value is LARGER than the critical value - you reject the null hypothesis and there is less than a 0.05 probability that the difference in the results are due to chance. There is a significant difference.

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23
Q

What is the difference between monohybrid inheritance and dihybrid inheritance?

A

Monohybrid is the inheritance of a SINGLE gene, dihybrid is the inheritance of TWO genes (that are located on different chromosomes)

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24
Q

Give an examples of a characteristic that involves multiple alleles

A

Blood groups - IA, IB and IO

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25
Q

Identify the chromosomes that determine sex

A

Sex Chromosomes - X and Y

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26
Q

Female sex chromosomes are

A

XX

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27
Q

Male Sex Chromosomes are

A

XY

28
Q

Which sex determines the sex of the child?

A

Males - as females always pass on a X in their gametes.

29
Q

What are the criteria must be met to perform a chi squared test?

A

sample size is large (20+), data falls into catergories (green, yellow), compare experimental observations with theoretical ones (expected)

30
Q

When performing a statistical test what must you always state before you carry the test out?

A

Null hypothesis - this states that there is ‘no significant difference’….

31
Q

What is are autosomes?

A

The 22 pairs of chromosomes (not the sex chromosomes)

32
Q

What is meant by autosomal linkage?

A

This is the situation where two (or more) genes are carried on the SAME chromosome

33
Q

For autosomal linkage genetic crosses, what do we have to assume?

A

That there is no crossing over, therefore all the genes remain together during meiosis

34
Q

What is epistasis?

A

This is when the allele of one genes affects or masks the expression of another allele in the phenotype.

35
Q

If the ratio of 9:3:3:1 is not achieved when the individuals of the F1 generation are crossed what does this suggest about inheritance?

A

It is NOT your typical dihybrid cross and there is some other explanation - e.g. epistasis, linkage

36
Q

locus is

A

position on a chromsome

37
Q

a carrier is

A

a person carrying an allele not expressed in the phenotype

38
Q

what does diploid mean?

A

having 2 sets of chromosomes (pairs)

39
Q

what does haploid mean?

A

having 1 set of each chromosome

40
Q

dominant alleles are represented by using…

A

a capital letter

41
Q

recessive alleles are represented by using …

A

lower case letter

42
Q

monohybrid inheritance looks at..

A

the inheritance of a characteristic controlled by a single gene

43
Q

In blood groups which allele is recessive?

A

O

44
Q

In blood groups which alleles are codominant?

A

A and B

45
Q

A person with an A and a B allele for blood group would have what blood type?

A

AB

46
Q

A person who inherits a B allele off one parent and an O allele off another would have what blood type?

A

B

47
Q

dihybrid inheritance looks at

A

the inheritance of 2 genes located on separate chromosomes

48
Q

In a monohybrid cross what phenotypic ratios do you get in the F2 generation?

A

3:1

49
Q

In a dihybrid cross what phenotypic ratios do you get in the F2 generation?

A

9:3:3:1

50
Q

In a codominant cross what phenotypic ratios do you get in the F2 generation?

A

1:2:1

51
Q

Sometimes you do not get expected phenotypic ratios because of …

A

sex linkage, autosomal linkage, epistasis, small sample size

52
Q

Name a sex linked condition

A

haemophilia, colour blindness

53
Q

A characteristic is said to be sex linked when..

A

its carried on the sex chromosome

54
Q

How can you tell from looking at the family tree if a condition is sex linked?

A

males will only be affected

55
Q

Why are males more likely to express recessive traits of sex linked conditions

A

only have 1 copy of X - so a recessive trait would be expressed

56
Q

How are the X and Y chromosomes different?

A 
X bigger (more genes), Y smaller (fewer genes)
no homologous portion on the Y
57
Q

During autosomal linkage what happens?

A

genes are inherited together

58
Q

When might genes that are on the same chromosome NOT be inherited together?

A

if crossing over during meiosis 1 has occurred

59
Q

The closer together 2 genes are the more closely linked they are - why?

A

because cross over is less likely to split them up

60
Q

what does the null hypothesis always start with?

A

there is no significant difference….

61
Q

If 2 genes are said to be linked what does this mean?

A

they are on the same chromosome

62
Q

a gene pool is

A

ll the alleles (of all of the genes) in a population

63
Q

what is meant by the genome

A

all the DNA in a cell/organism

64
Q

Why might you see VARIATION in the phenotypes of offspring?

A

Mutation
Crossing over between homologous chromosomes
Random fusion of gametes
Independent Segregation between homologous chromosomes
(likely insignificant differences)

65
Q

How do you calculate the degrees of freedom in chi2

A

n-1

66
Q

How do you explain autosomal linkage?

A

Say the expected ratio
State which gametes you are you seeing more often in the actual outcomes. Say these are linked.
State the gametes you are seeing less often. Say they are formed less often due to crossing over.

NSFC AQA A level Biology Year 2 (27 decks)

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