genetics Flashcards
1
Q
What is a chromosome
A
Structures in the nucleus of a cell that contain DNA
2
Q
What is a gene
A
a gene is a section of DNA which controls part of a cells chemistry
3
Q
How many chromosomes do humans have
A
Humans 23 pairs of chromosomes, giving 46 in total
4
Q
What is a karyotype
A
The complete set of chromosomes of a species
5
Q
Why do organisms need to produce new cells during their lifetimes
A
Growth, repair of damaged tissues or replacement of worn out cells
6
Q
Describe the process of mitosis
A
- The cell copies the chromosomes (DNA replication)
- The chromosomes line up and then split apart to produce a new nucleus
- The cytoplasm divides to produce a second cell with this new nucleus in
- Therefore, mitosis is cell division, producing 2 genetically identical daughter cells
7
Q
Why are most cells produced through mitosis
A
It is essential that the new cells formed contain all the genetic information of the previous cells
8
Q
What is the cell cycle
A
The time between the formation of a cell and when it undergoes cell division, it is not the same as the life cycle of a cell
9
Q
Name the chemical molecule that chromosomes are made of
A
DNA (deoxyribonucleic acid)
10
Q
Name the male and female gamete in animals
A
Sperm and egg
11
Q
Explain ow a fertilised egg has the correct number of chromosomes
A
Gametes have half the number of chromosomes, during sexual reproduction the male and female gametes combine restoring the full number of chromosomes
12
Q
Give 4 ways in which asexual reproduction is different to sexual reproduction
A
- ar does not involve gametes
- ar produces genetically identical offspring
- ar is faster than sr
-Ar only requires one parent
13
Q
Name the cell division used in asexual reproduction
A
mitosis
14
Q
Where in the body does meiosis take place
A
Ovaries (female), and testes (male)
15
Q
What happens to the DNA at the very start of meiosis, before the cell starts to divide
A
The DNA replicates
16
Q
How many cell divisions are there during the process of meiosis
A
2
17
Q
Briefly describe the results of meiosis
A
- meiosis produces 4 daughter cells
-each daughter cell is haploid (contains half the number of chromosomes as the original cell)
-The daughter cells are genetically different from eachother and the parent cell
18
Q
What happens to the cells in the embryo as it develops in order to form the whole organism
A
The cells differentiate to become specialized for different functions
19
Q
An unfavourable environmental change affects a population of organisms
explain why sexual reproduction increases the chance of the population surviving
A
- sexual reproduction creates genetic variation because offspring inherit a combination of genes from both parents
-some individuals may have traits that make them better suited to survive the new environment
-those with beneficial traits are more likely to survive, reproduce and pass on their genes
-over generations, the population can evolve and become more resistant to environmental changes increasing its chances of survival
20
Q
What is homozygous
A
If an individual has 2 copies of the same version of a gene
21
Q
What is heterozygous
A
If an individual has two different versions of the same gene
22
Q
How can you tell whether the allele for a disease is dominant or not
A
If the disease is dominant, there wouldn’t be any carriers since everyone with the allele causing the disease would be infected
23
Q
Even if both parents each carry one copy of the allele that causes cystic fibrosis, there is only a relatively small chance that their offspring will have the disorder. Explain why this is the case
A
-c.f is caused by a recessive allele
- carriers have only one copy of the faulty allele
- if both parents are carriers, there is only a 25% chance that their child will inherit both recessive alleles
24
Q
Suggest three arguments AGAINST embryo screening
A
- destroying embryos with genetic disorders raises moral and ethical questions about the value of life
- it could lead to a society where only ‘desirable’ traits are selected, increasing discrimination against ppl
- screening can be costly and may only be accessible to wealthier ppl leading ot discrimination
25
Suggest three arguments FOR embryo screening
- reduces likelihood of children being born with severe inherited diseases improving their quality of life
- fewer ppl with genetic disorders mean lower long term medical costs for families and healthcare systems
- parents can make educated choices about their pregnancy and prepare for any potential medical needs
26
Scientists didn't realise the importance of Gregor Mendel's work until after his death
Suggest why scientists at the time didn't understand how important Mendel's work was
Because they didn't know about genes or DNA scientific knowledge of inheritance at the time was very limited
27
Briefly outline the discoveries made after Mendel's work that built on hi discovery of 'hereditary units'. Include how these led to our current understanding of genes
-scientists identified chromosomes, which carry genetic information
-it was proposed that genes are located on the chromosomes linking Mendel's work to inheritance
-the discovery of DNA's structure revealed how genetic information is stored and passed on
-scientists decoded the genetic code, explaining how genes control protein production
- genes are now known to be segments of DNA that determine traits and are inherited through Mendelian principles
28
What is genetic engineering
The process of manipulating an organism's DNA to alter the organisms's traits or characteristics
29
The process of genetic engineering has several steps
the useful gene is first isolated from an organism's DNA
Explain how this is done
By using enzymes to cut the DNA to separate the useful gene from the rest of the genetic material
30
The gene is then inserted into the target organisms genome
Explain how this is achieved so that the organism develops with the desired characteristics
- the gene is inserted into a vector, which is used to carry the gene into the target organisms cells
- the vector is introduced to the target organism
- once inside the cell, the gene integrates into the organism's genome, allowing it to be expressed and passed onto future generations
31
Give two examples of how genetic engineering has been used to treat human diseases, or how it could potentially be used
-Insulin production
- genetic engineering could be used to treat genetic disorders by replacing or repairing defective genes in a patients cells
32
What does gm stand for when referring to crops that have been genetically engineered
Genetically modified
33
Suggest three ways in which a crop plant's genes can be altered to increase its yeild
Larger fruit, pest resistance and drought tolerance
34
Give one concern people may have with GM crops
Reduced biodiversity as widespread growing of gm crops may displace natural plant species and limit genetic variation within ecosystems
35
What is a dominant allele
An allele expressed if one or more copies are inherited
36
What is a recessive allele
An allele only expressed if two copies are inherited
37
Name the process in which an egg and sperm join together
Fertilisation
38
Describe the process of meiosis
-the cell copies the chromosomes (DNA replication)
- the homologous chromosome pairs line up, swap sections, and then separate with one from each pair moving into each of two new cells
-the chromosomes line up again and then are pulled apart, the cytoplasm divides forming 4 haploid cells
39
Explain how meiosis and sexual reproduction give rise to variation
-During meiosis chromosomes are randomly distributed into gametes leading to different combinations of alleles in the offspring
- homologous chromosomes exchange sections of DNA resulting in new allele combinations
40
What is meant by mutation
a change in the DNA sequence of a gene which can result in a new trait or characteristic
41
Are all mutations harmful? Explain the reason for your answer
No not all mutations harmful some can be neutral, having no effect on an organism and some can be beneficial, leading to traits that improve survival and reproduction rates
42
It is very difficult to get red flowering peo plants that breed true. Explain why you cannot guarantee to breed by self pollination, pea plants that only have red flowers
- red flowers are dominant so a pe plant with red flowers could be a carrier of the white flower gene
- when self pollinated a heterozygous red flowering plant could produce some white flowering offspring
43
Suggest in terms of natural selection why the recessive allele for green flies b was able to spread through the population
-if green flies were less visible to predators than black flies, they would survive and reproduce more successfully
- overtime, the recessive Alle b would increase in frequency in the population as BB flies would have higher survival and reproduction rates passing this alleles onto future generations
44
One of Mendel's crosses produced numbers that do not match the expected ratio suggest why
Random chance in inheritance causing variation from the expected ratio
45
Explain why each chromosome must become two strands before the cell divides
- each chromosome must replicate to ensure both new cells receive a full set of DNA
- this keeps genetic information identical in daughter cells after division
46
What evidence may support the claim that 2 flowers came from a common ancestor
-Similar flower structure
- similar chromosome shape and patterns
47
Two plants have different numbers of chromosomes suggest why it cannot reproduce sexually
The offspring has an uneven number of chromosomes which cannot pair properly during meiosis this prevents the formation of gametes, meaning the plants cannot reproduce sexually
48
Compare the issues involved in the sue of embryo screening for cystic fibrosis and polydactyly
- CF is a life threatening condition whereas p is only causing extra digits
- CF is caused by a recessive allele meaning both parents need to be carriers for a child to inherit the disease while p is caused by a dominant allele meaning only one affected parent is needed
- CF reduces life expectancy while p does not
- embryo screening for p is unethical as embryos may be discarded for a cosmetic issue whereas CF is more justifiable due to severe impact on quality of life
- expensive and should only be used for severe conditions like CF not p
-p can be corrected by surgery after birth unlike CF
49
Why do scientists use stem cells to develop a treatment for CADASIL
Because they have the ability to differentiate into various types of cells allowing them to replace damaged cells in the brain and potentially repair damage caused by CADASIL
50
Suggest one advantage of using stem cells from adult skin cells
Avoids ethical concerns associated with using embryonic stem cells as no embryos are harmed or destroyed in the process
51
When a foal grows up explain why it will look similar to its parents
a foal inherits genes from birth parents which determine its characteristics, so it will look similar to them
52
Explain why it will not be identical to either of its parents
the foal receives a unique combination of genetic material from both parents through sexual reproduction, due to genetic variation from the combination of alleles the foal will have a different mix of genes makin git genetically different from both parents
53
Suggest one advantage to a farmer of growing herbicide resistant crops
They can use herbicides more effectively to control weeds without damaging the crops leating to higher crop yield and reduced crop loss
54
Apart from having the herbicide resistant gene the herbicide resistant plants are identical to the herbicide susceptible plants
- the HR plants have the same genetic background as the hs plants only the hr gene is inserted
-The rest of the plants traits and characteristics remain the same
55
Why is is an advantage to make crop plants resistant to glyphosate (a herbicide)
-glyphosate resistant crops allow farmers to use glyphosate to kill weeds without harming the crops
- as weeds are controlled more efficiently there are fewer competition for resources increasing yield
- farmers can now use glyphosate alone reducing no of different herbicides needed lowering costs
56
Plant cells are put on agar plate containing glyphosate explain why the scientists add glyphosate to the agar
-the glyphosate kills the plant cells and bacteria that fo ot have the hr gene
- only the cells with the inserted resistance gene will survive allowing scientists to identify which cells have been successfully modified
57
a journalist used this data to claim 'scientists shows that GM crops cause kidney disease in humans
Use figure 2 to evaluate evidence for this claim
- correlation does not mean causation - the graph only shows a link but does not prove glyphosate / GM crops cause kidney disease
- no direct evidenced the data lacks scientific proof / a biological explanation
- other factors - kidney disease can be caused by lifestyle, genetics or other environmental factors
- limited data - only shows USA trends; no comparison with other countries
