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WJEC BIO > Inheritance > Flashcards

Inheritance Flashcards

1
Q

What is a gene?

A

A length of DNA on a chromosome that codes for the production of one or more polypeptide chains and functional RNA

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2
Q

Define genotype.

A

The genetic constitution of an organism.

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3
Q

Define phenotype.

A

The expression of an organism’s genetic constitution, combined with its interaction
with the environment.

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4
Q

What is a locus?

A

The fixed position on a DNA molecule occupied by a gene.

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5
Q

What is an allele?

A

Different forms of a particular gene, found at the same locus on a chromosome. A single gene could have many alleles.

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6
Q

Define homozygous

A

Having two identical alleles of a gene e.g. FF or ff

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7
Q

Define heterozygous

A

Having two different alleles of a gene
e.g. Ff

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8
Q

What is a dominant allele?

A

An allele that is always expressed
Represented with a capital letter e.g. F

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9
Q

What is a recessive allele?

A
  • An allele that is only expressed if 2 copies are present
  • Represented with a small letter e.g. f
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10
Q

What is meant by codominant alleles?

A

Two dominant alleles that both contribute
to the phenotype, either by showing a blend of both characteristics, or the characteristics appearing together.

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11
Q

What is an autosome?

A

A chromosome that is not an X or Y
chromosome.

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12
Q

What is a sex chromosome?

A

A chromosome that determines the sex of an organism, e.g. X and Y chromosomes in humans and other mammals.

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13
Q

What is the F 1 generation?

A

The first generation of offspring resulting from the cross of two individuals in the
parental generation.

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14
Q

What is the F 2 generation?

A

The second generation of offspring resulting from the cross of two individuals in the F 1 generation.

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15
Q

Define monohybrid inheritance.

A

Where one phenotypic characteristic is controlled by a single gene.

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16
Q

What is Mendel’s first law of inheritance?

A

Law of segregation
Alleles separate randomly into gametes
Each parent passes one allele to their offspring

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17
Q

What is Mendel’s second law of inheritance?

A

Law of independent assortment
The alleles of genes assort independently of other genes during gamete formation

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18
Q

What is the purpose of a test cross?

A

Used to determine whether an individual
with a dominant trait is heterozygous or homozygous dominant.

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19
Q

Describe how a test cross is carried out.

A

An individual of unknown genotype is bred with a homozygous recessive individual
Offspring phenotypes are observed to determine
the genotype of the unknown individual

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20
Q

Define dihybrid inheritance.

A

The determination of a trait by the inheritance of two genes.

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21
Q

What does Mendelian inheritance assume?

A

It assumes that the genes involved are not linked.

22
Q

What is meant by sex-linkage?

A
  • An allele is located on one of the sex chromosomes
  • Its expression depends on the sex of the individual
23
Q

Give an example of a phenotype which shows sex-linkage.

A
  • Haemophilia
  • Duchenne muscular dystrophy
24
Q

Describe haemophilia.

A
  • X-linked recessive condition
  • Results in excessive bleeding and blood that is slow to clot
25
Q

Describe Duchenne muscular dystrophy.

A
  • X-linked recessive condition
  • Characterised by muscle degeneration and weakness
26
Q

Why are haemophilia and Duchenne muscular dystrophy more common in males?

A

They are X-linked recessive conditions. Males only inherit one X chromosome so are more likely to express the gene in their phenotype.

27
Q

What is linkage?

A
  • Two or more genes positioned on the same autosome
  • Unlikely to be separated by crossing over during meiosis so often inherited together
28
Q

What is the chi-squared test?

A

A statistical test used to determine whether the difference between observed and expected data is due to chance or a real effect. Can be used to compare expected phenotypic ratios with observed ratios.

29
Q

How is a chi-squared test performed?

A

Make a null hypothesis
Used Mendelian ratios to calculate the expected numbers
Calculate chi-squared value using chi-squared equation
Calculate the degrees of freedom
Select an appropriate significant level (normally 0.05)
Find the critical value
Compare the chi-squared value with the critical value
Accept or reject the null hypothesis

30
Q

How are degrees of freedom calculated?

A

The number of categories minus 1.

31
Q

If the chi-squared value is greater than or equal to the critical value, is the null hypothesis accepted or rejected?

A

Rejected.

32
Q

What does it mean if the null hypothesis is rejected?

A

There is a significant difference between the observed and expected results.

33
Q

If the chi-squared value is less than the critical value, is the null hypothesis accepted or rejected?

A

Accepted

34
Q

What does it mean if the null hypothesis is accepted?

A

The difference between the observed and expected results is not significant. The results occured due to chance.

35
Q

What is a mutation?

A
  • An alteration to the volume, arrangement or structure of DNA
  • May affect a single gene or a whole chromosome
36
Q

When do most mutations occur?

A
  • Crossing over in prophase !
  • Non-disjunction in anaphase I and II
37
Q

What is a gene mutation?

A
  • A change to at least one nucleotide base in DNA or the arrangement of bases
  • May occur spontaneously during DNA replication and can be beneficial, damaging, or neutral
38
Q

Give an example of condition caused by a gene mutation.

A

Sickle cell anaemia

39
Q

Describe sickle cell anaemia.

A
  • Recessive genetic disorder caused by a substitution mutation on chromosome 11
  • Results in abnormal haemoglobin which distorts red blood cells
40
Q

What is a chromosome mutation?

A

A change in the structure or number of chromosomes, affecting many genes.

41
Q

Give an example of condition caused by a chromosome mutation.

A

Down’s syndrome

42
Q

Describe Down’s syndrome.

A

Genetic disorder characterised by delayed development and learning disabilities
* Due to non-disjunction, an affected individual possesses three copies of chromosome 21

43
Q

What is chromosome nondisjunction?

A

Failure of homologous chromosomes to separate in meiosis I or sister chromatids to separate in meiosis II. Results in gametes with one extra or less chromosome than normal.

44
Q

What is a mutagen?

A

A chemical, biological or physical agent that increases the rate of gene mutations above normal level.

45
Q

Give some examples of mutagens.

A

lonising radiation (gamma radiation, UV, X-rays)
Chemicals (e.g. polycyclic hydrocarbons)

46
Q

What is a carcinogen?

A

A type of mutagen that causes cancer.

47
Q

What is an oncogene?

A

Mutations of proto-oncogenes that are activated continuously, resulting in uncontrolled cell division.

48
Q

Define epigenetics,

A

The study of changes in gene expression that are not due to alterations in the nucleotide base sequence of DNA

49
Q

How can histone modification affect gene expression?

A
  • Alteration of histones by the addition of methyl, acetyl or phosphate groups
  • Increases or decreases gene expression by causing the histone to coil more tightly or loosely
50
Q

How can DNA methylation affect gene expression?

A
  • Addition of a methyl (CH3) group to cytosine bases
  • Prevents recognition of the bases, reducing gene expression

WJEC BIO (14 decks)

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