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Inheritance Flashcards

1
Q

What is sexual reproduction?

A

● Type of reproduction.
● Involves the production of gametes by meiosis.
● A gamete from each parent fuses 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 (sperm cells and egg cells in
animals, pollen and egg cells in flowering
plants).
● Haploid (half the number of chromosomes).

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3
Q

What is meiosis?

A

● Form of cell division involved in the formation of
gametes (non-identical haploid cells) in reproductive
organs.
● Chromosome number is halved.
● Involves two divisions.

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4
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 cell (the side to which each
chromosome is pulled is random, creating variation).
● Chromosome number is halved.

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5
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 produced.

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6
Q

Why is meiosis important for sexual reproduction?

A

● It increases genetic variation.
● It ensures that the zygote formed at
fertilisation is diploid.

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7
Q

Describe fertilisation and its resulting outcome

A

Gametes join together to restore the normal
number of chromosomes and the new cell then
divides by mitosis (which increases the number
of cells).
As the embryo develops, cells differentiate

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8
Q

What is DNA?

A

A double-stranded polymer of
nucleotides, wound to form a double
helix.
The genetic material of the cell found in
its nucleus.

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9
Q

Define genome

A

The entire genetic material of an organism.

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10
Q

Why is understanding the human genome
important?

A

The whole human genome has been studied and is
important for the development of medicine in the future.
● Searching for genes linked to different types of disease.
● Understanding and treating inherited disorders.
● Tracing human migration patterns from the past.

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11
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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12
Q

How many chromosomes do human body cells
have?

A

46 chromosomes (23 pairs)

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13
Q

Define gene

A

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

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14
Q

What are alleles?

A

Different versions of the same gene.

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15
Q

What is a dominant allele?

A

A version of a gene where only one copy
is needed for it to be expressed.

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16
Q

What is a recessive allele?

A

A version of a gene where two copies
are needed for it to be expressed.

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17
Q

What is meant when an organism is
homozygous?

A

When an organism has two copies of the
same allele (two recessive or two
dominant).

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18
Q

What is meant when an organism is
heterozygous?

A

When an organism has two different
versions of the same gene (one
dominant and one recessive).

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19
Q

What is the genotype?

A

The genes present for a trait

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20
Q

What is the phenotype?

A

The visible characteristic.

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21
Q

What is an inherited disorder?

A

A disorder caused by the inheritance of
certain alleles.

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22
Q

Give 2 examples of inherited disorders

A

● Polydactyly (having extra fingers or toes) -
caused by a dominant allele.
● Cystic fibrosis (a disorder of cell
membranes) - caused by a recessive allele.

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23
Q

How are embryos screened for inherited disorders?

A

During IVF, one cell is removed (from an 8 cell
embryo) and tested for disorder-causing
alleles. If the cell doesn’t have any indicator
alleles, then the originating embryo is
implanted into the uterus.

24
Q

What are the ethical issues concerning embryo
screening?

A

● It could lead to beliefs in society that being disabled or having a
disorder is less human or associated with inferiority.
● The destruction of embryos with inherited disorders is seen by
some as murder as these would go on to become human beings.
● It could be viewed as part of the concept of designer babies as it
may be for the parents convenience or wishes rather than the
child’s wellbeing.

25
What are the economic issues concerning embryo screening?
● Costs of hospital treatment and medication will need to be considered if it is known that a child will have an inherited disorder and financial support explored if necessary.
26
What are the social issues concerning embryo screening?
● Social care for children with inherited disorders may need to be considered if parents are unable to provide care. ● If an embryo is found to have an inherited disorder and is terminated, this can prevent a child and its parents from potential suffering in the future due to the disorder.
27
What is variation?
Differences in the characteristics of individuals in a population is called variation.
28
What are the two causes of variation within a species?
● Genetics ● Environment ● A mixture of both of the above
29
What is genetic variation?
● Variations in the genotypes of organisms of the same species due to the presence of different alleles. ● Creates differences in phenotypes.
30
What is a mutation?
A random change to the base sequence in DNA which results in genetic variants. They occur continuously.
31
What is the consequence of a new phenotype caused by a mutation being suited to an environmental change?
There will be a rapid change in the species.
32
What is evolution?
● A gradual change in the inherited traits within a population over time. ● Occurs due to natural selection which may result in the formation of a new species.
33
Outline the theory of natural selection
All species of living things have evolved from simple life forms that first developed more than 3 billion years ago. 1. Genetic variation exists due to spontaneous mutations. 2. Selection pressures (e.g. competition, disease) exist.
34
How do two populations become different species?
When their phenotypes become different to the extent that they can no longer interbreed to produce fertile offspring.
35
What is selective breeding?
The process by which humans artificially select organisms with desirable characteristics and breed them to produce offspring with similar phenotypes.
36
Outline the main steps involved in selective breeding
1. Identify a desired characteristic e.g. disease resistance. 2. Select parent organisms that show the desired traits and breed them together. 3. Select offspring with the desired traits and breed them together. 4. Process repeated until all offspring have the desired traits.
37
Give examples of characteristics selected for in selective breeding.
● Disease resistance in crops ● Higher milk or meat production in animals ● Gentle nature in domestic dogs ● Large flowers
38
What is the main advantage of selective breeding?
Creates organisms with desirable features: ● Crops produce a higher yield of grain ● Cows produce a greater supply of milk ● Plants produce larger fruit ● Domesticated animals
39
Outline the disadvantages of selective breeding (4)
● Reduction in the gene pool (which becomes especially harmful if sudden environmental change occurs). ● Inbreeding results in genetic disorders. ● Development of other physical problems e.g. respiratory problems in bulldogs. ● Potential to unknowingly select harmful recessive alleles.
40
What is genetic engineering?
● The modification of the genome of an organism by the insertion of a desired gene from another organism - genes from chromosomes of humans and other organisms can be ‘cut out’ and transferred to cells of other organisms. ● Enables the formation of an organism with beneficial characteristics.
41
Describe the benefits of genetic engineering (3)
● Increased crop yields for growing population e.g. herbicide-resistance, disease-resistance. ● Useful in medicine e.g. insulin-producing bacteria, anti-thrombin in goat milk, possibility to overcome some inherited disorders (being explored in medical research). ● GM crops produce scarce resources e.g. GM golden rice produces beta-carotene (source of vitamin A in the body).
42
Describe the risks of genetic engineering (4)
● 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. ● GM seeds are expensive. LEDCs may be unable to afford them or may become dependent on businesses that sell them.
43
Describe the process of genetic engineering
1. DNA is cut at specific base sequences by restriction enzymes to create sticky ends. 2. Vector DNA cut using the same restriction enzymes to create complementary sticky ends. 3. Ligase enzymes join the sticky ends of the DNA and vector DNA forming recombinant DNA. 4. Recombinant DNA mixed with and ‘taken up’ by target cells.
44
State two kinds of evidence used to show evolution.
● Fossils ● Antibiotic resistance in bacteria
45
How are fossils formed?
● Parts of organisms that have not decayed due to conditions needed for decay being absent. ● Parts of organisms that have been replaced by minerals as they decayed eg. bones. ● Traces of organisms are preserved, covered in sediment and becoming rock.
46
How do fossils act as evidence for evolution?
Scientists can identify the ages of the fossils and use them to show how organisms change over time
47
What is extinction?
Where there are no individuals of a species still alive.
48
State the factors that may lead to extinctions.
● New disease ● Predation ● Competition ● Changes to the environment ● Catastrophic events
49
Outline the process of antibiotic resistance bacteria evolving.
● Mutations occur in bacteria producing genetic variation. ● Certain strains are resistant to antibiotics and are not killed when the antibiotic is applied. ● Resistant strains survive and reproduce. ● Over time, the population of the resistant strains increase.
50
Why are resistant strains of bacteria dangerous?
People have no immunity to them and there is no effective treatment.
51
What can be done to reduce the rate of development of antibiotic resistant bacteria?
● Refrain from inappropriately prescribing antibiotics eg. for viral diseases. ● Patients should complete the prescribed course of antibiotics. ● Restrict agricultural uses of antibiotics.
52
Why is it difficult to keep up with emerging resistance strains?
Developing antibiotics have a high cost and take a long time to develop.
53
What are the classes of organisms as determined by Carl Linnaeus?
Kingdom, phylum, class, order, family, genus, species.
54
What is the binomial system of naming organisms?
Genus name followed by species name.
55
Why were new classification models proposed?
● Developments in microscopy allowed better examination of internal structures. ● Improvement in understanding of biochemical processes.
56
State the three domains.
● Archaea ● Eukarya ● Bacteria
57
How are evolutionary trees created?
By examining the DNA of different species and analysing how similar the sequences are.

Biology (8 decks)

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