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GCSE Biology OCR 21st Century (Triple) (9-1) > B1 - You and your genes > Flashcards

B1 - You and your genes Flashcards

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1
Q

State the two types of cell

A

Eukaryotic (animals and plants)
&
prokaryotic

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2
Q

What is the difference between a

eukaryotic and prokaryotic cell?

A

A eukaryotic cell contains a nucleus and
membrane-bound organelles. A
prokaryotic cell does not.

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3
Q

How can the structure of eukaryotic cells

be observed?

A

Using a light microscope

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4
Q

How is genetic information stored in a

eukaryotic cell?

A

Within the nucleus, arranged in

chromosomes

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5
Q

How is genetic information stored in a

prokaryotic cell?

A

Found free within the cytoplasm as:

● Single large loop of circular DNA
● Plasmids

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6
Q

What are plasmids?

A

● Small, circular loops of DNA found free in the
cytoplasm and separate from the main DNA

● Carry genes that provide genetic advantages
e.g. antibiotic resistance

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7
Q

Define genome

A

The entire genetic material of an

organism

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8
Q

What is a chromosome?

A

A long, coiled molecule of DNA that
carries genetic information in the form of
genes

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9
Q

What is DNA?

A

A double-stranded polymer of
nucleotides, wound to form a double
helix

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10
Q

Define gene

A

A section of DNA that codes for a
specific sequence of amino acids which
undergo polymerisation to form a protein

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11
Q

What are alleles?

A

Different versions of the same gene

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12
Q

Define genotype

A

An organism’s genetic composition,

describes all alleles

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13
Q

Define phenotype

A

An organism’s observable characteristics
due to interactions of the genotype and
environment (which can modify the
phenotype)

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14
Q

What are the monomers of DNA?

A

Nucleotides

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15
Q

What are DNA nucleotides made up of?

A

● Common sugar
● Phosphate group
● One of four bases: A, T, C or G

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16
Q

Describe how nucleotides interact to

form a molecule of DNA

A

● Sugar and phosphate molecules join to form a
sugar-phosphate backbone in each DNA strand

● Base connected to each sugar

● Complementary base pairing: A pairs with T, C pairs with G

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17
Q

Explain how a gene codes for a protein

A

● A sequence of three bases in a gene forms a triplet

● Each triplet codes for an amino acid

● The order of amino acids determines the structure
and function of protein formed

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18
Q

Describe the differences between mRNA

and DNA

A

mRNA is single stranded whereas
DNA is double stranded

● mRNA uses U whereas DNA uses T

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19
Q

What is protein synthesis?

A

The formation of a protein from a gene

20
Q

Outline protein synthesis

A

In the nucleus, DNA is used as a template to form mRNA

  1. mRNA exits the nucleus, moving into the cytoplasm where
    it attaches to a ribosome
  2. The ribosome joins amino acids in a specific order,
    dictated by mRNA to form a protein.
21
Q

Why does mRNA rather than DNA join to

a ribosome in the cytoplasm

A

DNA is too large to leave the nucleus so

cannot reach the ribosome

22
Q

What is a mutation?

A

A random change to the base sequence

of DNA which results in genetic variants

23
Q

State the three types of gene mutation

A

● Insertion
● Deletion
● Substitution

24
Q

Describe the effect of a gene mutation in

coding DNA

A

● If a mutation changes the sequence of amino acids,
protein structure and function may change

● If a mutation does not change the sequence of amino
acids, there is no effect on protein structure or
function

25
Q

What is non-coding DNA?

A

DNA which does not code for a protein

but instead controls gene expression

26
Q

Describe the effect of a gene mutation in

non-coding DNA

A

Gene expression may be altered,
affecting protein production and the
resulting phenotype

27
Q

What are gametes?

A

Reproductive cells (e.g. egg and sperm
cells) that contain a single copy of each
chromosome

28
Q

Describe sexual reproduction in terms of

chromosome number

A

● Two gametes with a single copy of each
chromosome fuse

● Resulting embryo has two chromosomes for
each gene and two copies of each allele

29
Q

Define homozygous

A

Having two identical alleles of a gene

e.g. FF or ff

30
Q

Define heterozygous

A

Having two different alleles of a gene

e.g. Ff

31
Q

What is a dominant allele?

A

Describes an allele that is always expressed

Represented with a capital letter e.g. F

32
Q

What is a recessive allele?

A

An allele that is only expressed in the
absence of a dominant allele

Represented with a small letter e.g. f

33
Q

What is the problem with single gene

crosses?

A

Most characteristics are controlled by

multiple alleles rather than just one

34
Q

What are sex chromosomes?

A

A pair of chromosomes that determines sex:

● Males have an X and a Y chromosome
● Females have two X chromosomes

35
Q

Why does the inheritance of a Y
chromosome mean that an embryo
develops into a male?

A

Testes development in an embryo is
stimulated by a gene present on the Y
chromosome

36
Q

Other than using a punnett square, how
else can single gene inheritance be
represented?

A

Using a family tree

37
Q

Outline how the work of Mendel helped
scientists to develop their understanding
of genetics

A

● Mendel studied the inheritance of different phenotypes of pea plants
● He established a correlation between parent and offspring phenotypes
● He noted that inheritance was determined by ‘units’ passed on to
descendants
● Using gene crosses, he devised the terms ‘dominant’ and ‘recessive’

38
Q

What is genome sequencing?

A

Finding out the order of nucleotides in
the DNA of an organism, enabling the
function and interaction of genes to be
assessed

39
Q

Why is genome sequencing important?

A

● Allows the comparison of genomes of healthy
individuals with patients who have a disease
● Potential disease-causing alleles are identified
● Individuals can then undergo genetic testing for these
alleles

40
Q

Outline how genetic testing can be used

to improve healthcare (3)

A

● Enables awareness of potential risks and the introduction
of lifestyle changes to reduce these associated risks
● Enables early treatment plans to begin
● Prediction of a patient’s reaction to certain drugs -
‘personalised medicine’

41
Q

Outline the drawbacks of using genetic

testing in healthcare

A

● Discrimination by employers, insurance firms
etc. if a person is likely to develop a disease

● Person may develop anxiety, depression etc.

42
Q

Outline how genetic testing can be used

in family planning

A

● Parental carrier testing - parents tested for the presence of recessive disease-causing alleles
● Prenatal testing - egg fertilised In vitro, embryo tested for
genetic disorders
● Fetus tested for genetic disorders via amniocentesis or
chorionic villus sampling (CVS)

43
Q

Outline the drawbacks of using genetic

testing in family planning

A

● False-positive/false-negatives

● Ethical considerations - involves the destruction of
embryos and potential terminations

● Amniocentesis and CVS carry a slight risk of miscarriage

● Could lead to ‘designer babies’

44
Q

What is genetic engineering?

A

● The changing of the genome of an organism by the
insertion of a desired gene from another organism

● Enables the formation of an organism with beneficial
characteristics

45
Q

Describe the process of genetic

engineering

A
  1. Desired gene isolated using enzymes
  2. Gene replicated
  3. Gene placed into vector (e.g. plasmid, virus)
  4. Vector mixed with and ‘taken up’ by target cells
  5. Modified cells identified, selected and cultured
46
Q

Describe the benefits of genetic

engineering

A

● Increased crop yields for growing population e.g.
herbicide-resistance, disease-resistance

● Useful in medicine e.g. insulin-producing bacteria, antithrombin in goat milk

● GM crops produce scarce resources e.g. GM golden rice
produces beta-carotene (source of vitamin A in the body)

47
Q

Describe the risks of genetic engineering

A

● Long-term effects of consumption of GM crops unknown

● Negative environmental impacts e.g. reduction in
biodiversity, impact on food chain, contamination of
non-GM crops forming ‘superweeds’

● Late-onset health problems in GM animals

GCSE Biology OCR 21st Century (Triple) (9-1) (6 decks)

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