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Separate Biology Edexcel GCSE > Topic 3 - Genetics > Flashcards

Topic 3 - Genetics Flashcards

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1
Q

What is sexual reproduction?

A
  • type of reproduction
  • involves the production of gametes by meiosis
  • a gamete from each parent sues to form a zygote
  • genetic information from each gamete is mixed so the resulting zygote is unique
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2
Q

What are gametes?

A

Sex cells
Haploid

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3
Q

What is meiosis ?

A

Form of cell division involved in the formation of gametes

Chromosome number is havked

Involves two divisions

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4
Q

What must occur prior to meiosis ?

A

Interphase

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5
Q

What happens during the first stage of meiosis ?

A

Chromosome pairs line up along the cell equator

The pair of chromosomes are separated and move to opposite poles of the cells

Chromosome number is halved

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6
Q

What happens during the second stage of meiosis ?

A

Chromosomes line up along the cell equator
The chromatids are separated and move to opposite poles of the cell
Four unique haploid gametes are produces

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7
Q

Why is meiosis important for sexual reproduction?

A

It increases variation
In ensures that the resultant zygote is diploid

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8
Q

What is the advantage of sexual reproduction?

A

It creates genetic variation , increasing the probability of a species adapting to and surging environmental changes

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9
Q

Describe the disadvantages of sexual reproduction

A

Two parents are requires. This makes reproduction diffuse in endangered populations or in species which exhibit solitary lifestyles

More time and energy is required so fewer offspring are produces

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10
Q

What is asexual reproduction?

A
  • type of reproduction
  • involves mitosis
  • produces genetically identical offspring known as daughter cells
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11
Q

Describe the advantages of asexual reproduction

A
  • Only one parent required
  • Lots of offspring can be produced in a short period of time enabling the rapid colonisation of an area and reducing competition from other species
  • requires less energy
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12
Q

What is the disadvantage of asexual reproduction

A

No genetic variation reducing the probability of a species being able to adapt to environmental change

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13
Q

What is DNA?

A

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

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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 pairs ( A and T or C and G) joined by weak hydrogen bonds
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17
Q

Define genome

A

The entire genetic material of an organism

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18
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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19
Q

Define gene

A

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

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20
Q

Describe the method used to extract DNA from fruit

A
  1. Place a piece of fruit in a beaker and crush it
  2. Add detergent and salt and mix
  3. Filter the mixture and collect the liquid in a test tube
  4. Pour chilled ethanol into the test tube
  5. DNA precipates forming a fibrous white solid
  6. Use a glass rod to collect the DNA sample
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21
Q

Why is detergent added to the crushed fruit?

A

It disrupts the cell membranes releasing DNA into the solution

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22
Q

Why is salt added to the crushed fruit ?

A

Salt encourages the precipitation of DNA

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23
Q

Why is chilled ethanol added rather than water?

A

DNA is insoluble in ethanol , encouraging its precipitation

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24
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 the order of amino determines the structure and function of protein formed

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25
Q

Why is the folding of amino acids important in proteins such as enzymes?

A

Determines the shape of the active site which must be highly specific to the shape of the substrate

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26
Q

What is protein synthesis?

A

The formation of a protein from a gene

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27
Q

What are the two stages of protein synthesis ?

A
  1. Transcription
  2. Translation
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28
Q

What does transcription involve?

A

The formation from mRNA from a DNA template

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29
Q

Outline transcription?

A
  1. DNA double helix unwinds
  2. RNA polymerase binds to a specific base sequence of non coding DNA in front of a gene and moves along the DNA strand
  3. RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand
  4. mRNA formation complete . mRNA detaches and leaves the nucleus
30
Q

What is the difference between mRNA and DNA?

A

mRNA is single stranded whereas DNA is DNA is a double stranded

mRNA uses U whereas DNA uses T

31
Q

Why is mRNA used in translation rather than DNA?

A

DNA is too large to leave the nucleus so cannot reach the ribosomes

32
Q

What does translation involve?

A

A ribosome joins amino acids in a specific order dictated by mRNA to form a protein

33
Q

Outline Translation

A
  1. mRNA attaches to a ribosome
  2. Ribosome read the mRNA bases in triplets. Each triplet codes for one amino acid which is brought to the ribosomes by a tRNA molecule
  3. A polypeptide chain is formed from the sequence of amino acids which join together
34
Q

How is a tRNA molecule adapted to its function?

A

Each tRNZ molecules has an anticodon which is specific to the codon of the amino acid that it carries

35
Q

What is a mutation?

A

A random change in the base sequence of DNA which results in genetic variants

36
Q

Describe the effect of a gene mutation in coding DNA

A

If a mutation changes the amino acid sequence, protein structure and function may change

If a mutation does not change amino acid sequence there is no effect on protein structure or function

37
Q

What is non coding DNA?

A

DNA which does not code for a protein but instead controls gene expression

38
Q

Describe the effect of a gene mutation in non coding DNA

A

A mutation may affect the ability of RNA polymerase to bind to non coding DNA

This may affect protein production and the resulting phenotype of the organism

39
Q

Outline how the work of Mendel helped scientists 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

40
Q

Why was Mendel’s work initially overlooked ?

A

Scientists didn’t understand Mendel’s work as there was no knowledge of genes or DNA at the time

41
Q

What is a chromosome?

A

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

42
Q

Define gene

A

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

43
Q

What are alleles?

A

Different versions of the same gene

44
Q

Define genotype

A

An organism’s genetic composition

45
Q

Define phenotype

A

An organisms observable characteristics due to interact is of the genotype and environment

46
Q

Define homozygous

A

Having two identical alleles of a gene - FF or ff

47
Q

Define heterozygous

A

Having two different alleles of a gene - Ff

48
Q

What is a dominant allele ?

A

Describes an allele that is always expressed
Represented with a capital letter

49
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

50
Q

What is the problem with single gene crosses?

A

Most characteristics are controlled by multiple allele rather than just one

51
Q

What are sex chromosomes?

A

A pair of chromosomes that determine sex

Males have and X and a Y chromosome

Females have two X chromosomes

52
Q

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

A

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

53
Q

What is a sex linked characteristic?

A

A characteristic that is coded for by an allele found on a sex chromosome

54
Q

Why are the majority of genes found on the X chromosome rather than the Y chromosome?

A

The X chromosome is bigger than the Y chromosome so more genes are carried on it

55
Q

Why are men more likely to show the phenotype for a recessive sex linked trait than women ?

A

Many genes are found on the X chromosome that have no counterpart on the Y chromosomes

Women have two alleles for each sex linked gene whereas men often only have one allele

Only one recessive allele is requires to produce the recessive phenotype in males

56
Q

Give an example of a characteristic that is determined by more than one allele?

A

Blood group is determined by 3 alleles

57
Q

Name the four different blood groups

A

A B AB O

58
Q

What are codominant alleles?

A

Alleles that equally contribute to an organisms phenotype . They are expressed to an equal extent

59
Q

Describe codominance in blood groups

A

IA and IB are codominant
Gives the blood group AB

60
Q

Why does IA IO give blood group A?

A

IO is recessive to IA
IA is dominant and is expressed giving blood group A

61
Q

What are the possible genotypes for blood group B?

A

IB IO
IB IB

62
Q

What is the genotype for blood group O ?

A

IO IO

63
Q

What are the two causes of variation within a species?

A

Genetics
Environment

64
Q

What is genetic variation?

A

Variations in the genotype of organisms of the same species due to the presence of different alleles

Creates differences in phenotypes

65
Q

What creates genetic variation in a species ?

A

Spontaneous mutations
Sexual reproduction

66
Q

What is a mutation ?

A

A random change to the base sequence in DNA which results in genetic variants

67
Q

State the three types of gene mutation

A

Insertion
Deletion
Substitution

68
Q

How may a gene mutation affect an organisms phenotype ?

A
  • neutral mutation does not change the sequence of amino acids. Protein structures and function same. No effect on phenotype
  • mutation may causes a minor change in organism phenotype like eye colour
  • mutation may completely change the sequence of amino acids . This may result in a non functional protein. Severe changes to phenotype
69
Q

What is environmental variation?

A

Variations in phenotype that are acquired during the lifespan of an organism

Due to environmental factors - diet , lifestyle, exposure to light

70
Q

What is the Human Genome Project?

A
  • scientific research project involving thousands of scientists across the globe which successfully mapped the entire human genome.
  • scientists now aim to identify the function of every gene in the human genome
71
Q

How can the results of the Human Genome Project be applied to medicine?

A

Enables scientists to understand how lifestyle factors interact with genes

Disease causing alleles identifies more rapidly and the appropriate treatments prescribed earlier on

Scientists can predict an individual’s response to certain drugs. New drugs can be developed which are tailored to a specific allele

72
Q

What are drawbacks associated with the discoveries of the Human Genome Project

A

Knowledge of predisposition to a disease can be stressful

Societal pressure influencing the decision to have children

Discrimination by employers

Separate Biology Edexcel GCSE (5 decks)

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