Genetics

Question 1

causes of sickle cell anaemia?

Answer 1

Mutation in the gene that codes for one of the
polypeotides in haemoglobin
▪ Base substitution mutation in the 6th codon of
the gene
▪ GAG (glutamic acid) become GTG (valine)

Question 2

what does the human genome consist of?

Answer 2

46 chromosomes in the nucleus +
DNA in the mitochondria

Question 3

what does the plant genome consist of?

Answer 3

DNA molecules in the chromosomes
+ DNA in mitochondria and chloroplasts

Question 4

what does the prokaryote genome consist of?

Answer 4

DNA in the circular
chromosome + any plasmids present

Question 5

describe how genomes are sequenced and how technology has advanced this?

Answer 5

Genome broken up into small lengths
▪ Single stranded copies are made using DNA polymerase
▪ Non standard nucleotides for each base are added
separately (i.e. 4 samples obtained
▪ This stops replication and gives varying lengths of DNA
▪ Separated by size using gel electrophoresis
▪ For each number of nucleotides there is a band in 1 of
the 4 tracks from which the sequence can be deduced
▪ Speeded up using fluorescent markers used to identify
different bases
▪ Samples all mixed together in gel electrophoresis and a
laser used to make the fluorescent markers fluoresce
▪ Optical detector detects the different colours and a
computer deduces the base sequence

Question 6

what is the human genome and its aims?

Answer 6

Aim: To find the base sequence of the entire human
genome
Allowed a better estimate of gene numbers
Promoted improvements in sequencing techniques
It sequenced a single genome and work now continues to
explore the variations between individuals

Question 7

Chromosomes in a prokaryote?

Answer 7

-contain 1 chromosome
-are: ▪ Circular
▪ Not associated with proteins – naked
▪ Not compartmentalised in a nucleus

Question 8

what are plasmids?

Answer 8

Extra circular, naked DNA molecules in prokaryotes

Question 9

name some features of a plasmid?

Answer 9

▪ Not required for basic life processes
▪ Contain genes that may be useful (e.g. resistance)
▪ Not always replicated at the same time or rate
▪ Can be multiple copies
▪ Unevenly distributed in cell division

Question 10

chromosomes in eukaryote?

Answer 10

-linear and associated with histone proteins

Question 11

What are the differences between chromosomes in a
given organism?

Answer 11

Length; Position of centromere; Different genes or
alleles

Question 12

what are homologous chromosomes?

Answer 12

-have the Same sequence of genes but can be different
alleles

Question 13

what is the difference between a haploid and diploid nuclei?

Answer 13

haploid- has 1 chromosome of each type
diploid-has 2 chromosomes of each type (pairs of homologous chromosomes)

Question 14

what is a karyogram?

Answer 14

Visible stains showing the chromosomes of an
organism in homologous pairs of decreasing length

Question 15

Describe Cairns’s technique for measuring DNA length using autoradiography

Answer 15

▪ Cells grown on a medium of tritiated thymine – contains
radioactive isotope of hydrogen
▪ Cell walls digested with lysozyme releasing DNA onto a dialysis membrane
▪ Photographic emulsion applied to surface and put in
dark
▪ Atoms of tritium decay & emit high energy electrons
that react with the film
▪ Film developed after 2 months
▪ Dark grains appear where tritium decays giving an
outline of the DNA – shows length and shape

Question 16

Why is DNA replicated before meiosis?

Answer 16

so that each chromosome now consists of 2 sister chromatids

Question 17

How does meiosis promote genetic variation?

Answer 17

-Random orientation generates variation between genes on different chromosomes. There are 2n
combinations of possible chromosomes
-Crossing over allows linked genes (on same chromosome) to be reshuffled and to produce new allele combinations.
-fusion of gametes is completely random, depends on which sperm meets egg

Question 18

What is a monohybrid cross?

Answer 18

Cross to predict the
inheritance of one characteristic

Question 19

difference between homozygous and heterozygous?

Answer 19

-homo- have 2 identical copies of allele
hete- have 2 different copies of allele

Question 20

What is gel electrophoresis?

Answer 20

Process used to separate proteins or
fragments of DNA according to size

Question 21

how is gel electrophoresis done?

Answer 21

▪ DNA must be broken into small fragments
▪ Samples placed in wells in a gel immersed
in a conducting fluid.
▪ Electric field is applied.
▪ Charged molecules move through the gel
▪ DNA is negatively charged
▪ Smaller fragments move faster & further

Question 22

What is PCR and what is it used for?

Answer 22

-polyermease chain reaction
-used to amplify small amounts of DNA

Question 23

describe PCR?

Answer 23

▪ DNA heated to 95oC – separates the strands
▪ Cooled to 54oC but prevented from
annealing by an excess of single stranded
primers
▪ Enzyme Taq DNA polymerase then adds
complementary nucleotides to these
primers to copy the DNA

Question 24

What is genetic modification/ gene transfer

Answer 24

the transfer of genes from one species to another

Question 25

describe the process of genetic modification

Answer 25

▪ mRNA extracted from human pancreas cell.
▪ Complementary DNA created using reverse
transcriptase
▪ Plasmid removed from a bacteria cell
▪ Cut with a restriction endonuclease (same one used to cut the human gene out)
▪ Generates ‘sticky ends’
▪ Plasmid and cDNA fused using DNA ligase
▪ Recombinant plasmid introduced into host cells
▪ Bacteria multiply in a fermenter
▪ Produce the product of that gene (e.g. Insulin)
▪ Product can be separated and purified

Question 26

benefits of genetic modification

Answer 26

-produce drought, pest and disease resistant crops
-produce varieties that lack allergens or toxins
-increase vitamin content of foods
-produce edible vaccines

Question 27

risks of genetic modification

Answer 27

-could spread into pathogenic bacteria
-non target organisms could be affected
-reduced biodiversity
-spread of resistance to non crop plants

Question 28

what are clones?

Answer 28

Production of genetically identical organisms

Question 29

give examples of natural cloning

Answer 29

-Strawberry plants grow horizontal stems with plantlets at the end. When they reach the soil they grow roots and photosynthesise using their leaves – becoming independent of the parent plant
- Jellyfish can clone themselves by budding

Question 30

How can animal embryos be cloned?

Answer 30

▪ Separating individual cells in the early embryo creates clones
▪ Early embryonic cells are pluripotent and can develop into all tissue types

Question 31

Describe how animals can be cloned using differentiated cells (e.g. Dolly the Sheep)

Answer 31

▪ Adult cells are taken from a desirable individual
▪ Unfertilised egg cell taken from a different individual and the nucleus removed and discarded
▪ This enucleated cell is fused with the desired adult cell using an electric pulse
▪ Resulting embryo is transferred to uterus of a third
individual acting as a surrogate mother
▪ Surrogate gives birth to a clone of the first individual
that cells were taken from