B13 Reproduction Flashcards
1
Q
How many chromosomes would you find in a human skin cell?
A
46
2
Q
What does mitosis result in the formation of?
A
2 genetically identical daughter cells
3
Q
What is the difference between a gene and a chromosome?
A
Chromosomes contain many genes. A gene is a small section of DNA that codes for a specific protein/characteristic
4
Q
What is the main difference between prokaryotic and eukaryotic cells?
A
Eukaryotic cells have a nucleus, prokaryotic cells do not
5
Q
By which process to bacterial cells divide?
A
Binary fission
6
Q
What is asexual reproduction?
A
Involves only one individual and the offspring is identical to the parent. There is no fusion of gametes or mixing of genetic information
7
Q
What is sexual reproduction?
A
Involves the fusion (joining) of male and female gametes producing genetic variation in the offspring
8
Q
what is meiosis?
A
2 stage process of cell division that reduces the number of chromosomes of daughter cells. Involved in making gametes for sexual reproduction
9
Q
describe the process of sexual reproduction
A
- Genes from two parents
- Inherit mixture of features from both parents, so variation occurs
- Females produce sex cells (gametes) called eggs and male gametes are called sperm
- Gametes are formed by meiosis
- A sperm and egg fuse together to make the offspring = fertilisation
- When gametes fuse a zygote forms
10
Q
Process of asexual reproduction
A
- Genes from only one parent
- All are clones (genetically identical) to the parent
- Only mitosis is involved in asexual reproduction
- No gametes (sex cells) involved
11
Q
Advantages of asexual reproduction
A
- Only one parent needed
- Many identical offspring can be reproduced when conditions are favourable
- Faster than sexual reproduction
- More time and energy efficient as do not need to find a mate
12
Q
Disadvantages of asexual reproduction
A
- No variation
- Susceptible to environmental change
13
Q
Advantages of sexual reproduction
A
- Produces variation in the offspring
- If the environment changes variation gives a survival advantage by natural selection
- Natural selection can be sped up by humans in selective breeding to increase food production
14
Q
Disadvantages of sexual reproduction
A
- Two parents are required, makes reproduction difficult for endangered species
- More time and energy is required so fewer offspring are produced
- Slower than asexual reproduction
15
Q
What is fertilisation?
A
- When gametes fuse to form a zygote
- Gametes join at fertilisation to restore the normal number of chromosomes
- The zygote then starts dividing through mitosis
16
Q
What happens after fertilisation?
A
- The zygote then starts dividing through mitosis
- The number of cells increases
- As the embryo develops cells differentiate
17
Q
compare the processes of mitosis and meiosis
A
Mitosis
- cell divides once
- 2 cells are produced
- 46 chromosomes, the same number as the original cell
- used to make new body cells
- occurs in all parts of the body
Meiosis
- cell divides twice
- 4 cells are produced
- 23 chromosomes, half the number of chromosomes as the original cell
- how gametes are made
- happens only in testes and ovaries
18
Q
what are the gametes in plants and animals?
A
flowering plants: pollen and egg cells
animals: sperm and egg cells
19
Q
what are gametes?
A
Sex cells produced in meiosis
20
Q
Explain why mutations in sex cells may be more serious than mutations in body cells
A
Mutations in sex cells will also affect the offspring, while mutations in body cells will only affect one individual
21
Q
By which cell division type does asexual reproduction rely on?
A
Mitosis
22
Q
How are gametes formed?
A
Meiosis
23
Q
How is a gamete different from a normal body cell?
A
A gamete only contains half of the genetic information
24
Q
Name the structure formed by fertilisation
A
Zygote
25
How many divisions do a cell undergo in meiosis?
2
26
describe the structure of fungi
- Made up of a mass of thin threads called hyphae
- The mass of the hyphae form the structure of fungi
27
Reproduction in fungi
- Asexual most common
- Toadstools etc are asexual fruiting bodies full of spores
- In asexual reproduction the fungal spores are produced by mitosis and they are genetically identical to the parent
- Some fungi also reproduce sexually in unfavourable conditions.
- Two hyphae form different fungi join and the nuclei fuse
- The new hypha has 2 sets of chromosomes
- It then undergoes meiosis to make haploid spores, which are different from the original hyphae
- Some of the spores may produce fungi better adapted to survive the adverse conditions
28
Are fungi haploid or diploid most of the time?
Haploid
29
When do two hyphae join together?
When the environmental conditions are unfavourable
30
Is mushroom asexual or sexual?
Asexual
31
When do fungi undertake meiosis?
After two hyphae have joined together
32
Which type of pathogen is malaria?
Protist
33
Which two types of cells are targeted by malaria in humans?
Liver cells and red blood cells
34
Malaria lifecycle - Where does fertilisation take place?
In the stomach of the mosquito
35
Malaria lifecycle - Where does asexual reproduction take place?
In the human host
36
What are the effects of malaria on humans?
Fever, loss of blood, brain damage, coma, death
37
Reproduction in malaria parasites
- The malaria parasites has both sexual and asexual reproduction as part of its normal life cycle
- The parasites in the human host are haploid and reproduce asexually by mitosis
- When a female mosquito drinks blood containing these, the temperature drop makes them produce the sexual form, which burst out of the blood cells and fuse to form a diploid zygote
- This undergoes meiosis, which introduces variation. Instead of forming gametes they form the asexual version of the parasite, which eventually get passed on to another human host
38
Reproduction in plants
- Flowers are the sexual reproductive organs of plants
- They make haploid gametes (pollen and egg cells) by meiosis that fuse to form diploid seeds that are genetically different to their parents
- Many plants can also reproduce asexually, for example, strawberry plant runners or daffodil bulbs dividing
- This involves only mitosis so the offspring are genetically identical to the parent
- This is an advantage when flowers are destroyed or unfertilised or need to colonise areas quickly when conditions are good
39
What does the term haploid mean?
Each nucleus contains one set of chromosomes
40
What does the term diploid mean?
Each nucleus contains two sets of chromosomes
41
How many sets of chromosomes are there in each nucleus of normal fungal hyphae?
One
42
What does DNA stand for?
Deoxyribonucleic acid
43
What is DNA?
The genetic material of the cell found in its nucleus
44
Structure of DNA
Spiral shape called a double helix
45
DNA nucleotides
- The backbone of the long stand of DNA is made of alternating sugar and phosphate molecules. Attached to each sugar is one of four bases
- The combination of a sugar, phosphate and a base is a nucleotide
- The DNA polymer is made of repeating nucleotide units
46
What is a gene?
- A small section of DNA on a chromosome
- Each gene codes for a particular sequence of amino acids, to make a specific protein
47
What are the four bases of DNA?
A, T, C, G
48
DNA Base pairs
A and T
C and G
- Base pairs hold the two strands of the DNA helix together
- It is the sequence of these bases along a DNA molecule that forms the genetic code
49
Which two molecules make up the backbone of the DNA?
Sugar and phosphate
50
What is a nucleotide?
The combination of phosphate, sugar and a base which, when in a repeating unit makes the DNA polymer
51
What is a genome?
- All the genetic material of an organism
- It includes all of the chromosomes, and the genetic material found in the mitochondria as well
- The human genome has the ability to make many different proteins from the same gene by suing it in different ways, or switching part of a gene on or off
52
Which is larger, a gene or a chromosome?
Chromosome
53
Where in the cell is DNA used to produce mRNA?
Nucleus
54
Allele
A gene or a combination of genes that we receive from our parents
55
Genotype
Combination of alleles
56
Phenotype
An organism's observable characteristics due to interactions of the genotype
57
Dominant allele
Expressed in the phenotype
58
Recessive allele
Not expressed in the phenotype, unless the combination includes double recessive alleles
59
Homozygote
An individual with two identical alleles for a characteristic
For example, BB, bb
60
Heterozygote
An individual with different alleles for a characteristic
For example, Bb
61
Definition of genome
All the genetic material of an organism
62
Definition of chromosome
A large molecule of DNA containing many genes
63
Definition of gene
A small section of DNA on a chromosome
64
Definition of DNA
A polymer with a double helix structure, formed of many nucleotides
65
Definition of nucleotide
A molecule made up of a sugar, a phosphate group, and one of four different bases
66
Definition of ribosome
Where protein synthesis takes place
67
Definition of base
Nitrogenous compounds that make up part of the structure of DNA and RNA. They are represented by the letters A, T, C, and G
68
Definition of protein
Large molecules made up of many amino acids bonded together
69
Where in the cells are proteins made?
Ribosomes
70
Explain the process of protein synthesis
- Genes in the DNA produce a template for the protein
- The template reflects the sequence of bases but it is small enough to fit through the nuclear pore
- The template binds to the ribosome surface
- Carrier molecules, each attached to a specific amino acid attach themselves to the template in the order given by the DNA
- The amino acids are joined together to form a specific protein
- Carrier molecules keep bringing specific amino acids to add to the growing protein chain in the correct order until the template is completed
- The protein detaches from the carrier molecules and the carrier molecules detach from the template and return to the cytoplasm to pick up more amino acids
- The protein chain then folds up in to the unique shape of the protein
71
How many base codes for an amino acid?
3
72
What brings amino acids to the ribosomes?
Carrier molecule (tRNA)
73
Name three uses of proteins in the body
- Enzymes
- Antibodies
- Hormones
74
Why can't DNA move into the cytoplasm?
It is too large to move through the nuclear pores
75
What is transcription?
The process of making mRNA from DNA
76
What is the function of the non-coding regions of DNA?
- Non-coding regions are the parts of DNA in between the genes
- Non-coding parts switch genes on or off, so variations in these areas of DNA can affect how genes are expressed
- When the gene is switched on they make the protein, when it is turned off the gene stops making the protein
77
Effects of a mutation
- No change in amino acids or a slight change which doesn't effect the protein structure
- Altered protein, so the protein may not work e.g. active site of enzyme may no longer fit substrate
- Mutation within non-coding region nearby to a gene may effect the expression (production) of a protein
78
Mutations - mitosis vs meiosis
Mitosis
- affects localised cells
Meiosis
- affects the whole organism
79
Explain how a change in one amino acid in an enzyme molecule could stop the enzyme working
If there is a mutation in an amino acid in an enzyme molecule, the enzyme's structure could be altered and a different protein would be formed. The active site of the enzyme may be changed and no longer fit the substrate.
80
Explain how DNA controls the synthesis of proteins in a cell
- Template (mRNA) is produced that reflects sequence of bases in DNA of a single gene
- Template is small enough to leave the nucleus through the nuclear pores, and binds to the surface of the ribosome in the cytoplasm
- Carrier molecules (tRNA) in the cytoplasm, each attached to a specific amino acid, attach themselves to template in order given by DNA until template completed
- Amino acids join together to form specific protein
- Protein detaches from carrier molecules, which detach from template and return to cytoplasm to pick up more amino acids
- Once protein chain is complete, the molecule folds up to form a unique shape that will enable it to carry out its function in the cell
81
What is the difference between genotype and phenotype?
Genotype is the genetic makeup/alleles present whereas phenotype is the resulting characteristic
82
Name the three parts of a DNA molecule
Sugar, phosphate, base
83
Where in the cell are proteins synthesised?
Ribosomes
84
Is cystic fibrosis caused by a dominant or recessive allele?
Recessive
85
What is a change in a DNA sequence called?
Mutation
86
What is cystic fibrosis caused by?
Caused by a single recessive allele, which means that only homozygous individuals will develop the disease
87
What is cystic fibrosis a disorder of?
- Affects the respiratory and digestive systems by producing abnormally thick mucus
- Affects the cell membranes in the lungs and intestines
88
What are the symptoms of cystic fibrosis?
Symptoms often develop during early childhood
Thick mucus clogs the airways leading to:
- breathlessness and coughs
- repeated chest infections, bacteria trapped and thrive in the thick mucus
Mucus can block pancreatic duct and block enzyme secretion which can lead to low weight gain
89
What is polydactyly caused by?
Caused by a dominant allele, so can be passed on by just one parent
90
What are the symptoms of polydactyly?
Abnormal number of fingers and toes
91
Why would a blocked pancreatic duct lead to low weight gain in sufferers of cystic fibrosis?
Mucus blocks enzyme secretion so food cannot be digested. If the food is not digested the body cannot store it as anything including weight.
92
What is polydactyly a disorder of?
Disorder in the regulation of genetic sequencing (that forms limbs)
93
Embryo screening
All methods take cells from the embryos so that their DNA can be analysed for genetic disorders
94
What are the three methods of embryo screening?
- Chorionic villus sampling
- Amniocentesis
- Pre-implantation genetic screening (in IVF only)
95
Chorionic villus sampling
- Sample of placental tissue taken through wall of abdomen or vagina
- 10-12 weeks
- 1-2% miscarriage risk
96
Amniocentesis
- Needle inserted into amniotic fluid to collect cells from placenta and foetus
- 15-16 weeks
- 0.5-1% miscarriage risk
97
Pre-implantation genetic screening
- For use in IVF before the embryo is implanted
- Embryos are analysed for genetic disorders or defects
98
IVF Process
- Egg donor is given fertility drugs
- Multiple eggs are produced and collected from the ovaries
- Eggs are fertilised to produce embryos
- Embryos analysed for genetic defects
- Only healthy embryos are injected into uterus
- Mother gives birth to genetically healthy baby
99
Where are cells taken from in chorionic villus sampling?
Placenta
100
Which method has the highest chance of miscarriage?
Chorionic villus sampling
101
Which method is only possible using IVF?
Pre-implantation genetic screening
102
What is the purpose of screening for genetic disorders?
To identify the possibility of the child having a genetic disorder, so the parents can decide whether to terminate the pregnancy or in order to prepare for having a child with a genetic disorder
103
Advantages of embryonic screening
- Can prepare and reduce high societal cost of health care and support for raising a child with a genetic disorder
- Could avoid children being born into pain or suffering caused by genetic disorders
104
Disadvantages of embryonic screening
- Religious issues: everything should have the potential of life
- Collecting cells from foetus increases the risk of miscarriage
- Screening necessitates decisions about termination
- Could give rise to 'designer babies' a baby whose genetic makeup has been selected or altered
- Screening is expensive
- No current cures for genetic disorders identified in screening
- Screening is not entirely reliable, can give false positive or negative results
105
Describe what happens when a cell divides to form gametes
- Copies of the genetic information are made
- The cell divides twice to form four gametes, each with a single set of chromosomes
- All gametes are genetically different from each other
106
Describe examples of organisms that reproduce both by asexual and sexual reproduction
- Malarial parasites reproduce asexually in the human host, but sexually in the mosquito
- Many fungi reproduce asexually by spores but also reproduce sexually to give variation
- Many plants produce seeds sexually, but also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils
107
Why is meiosis important for sexual reproduction?
- It increases genetic variation
- It ensures that the zygote formed at fertilisation is diploid
108
What are DNA nucleotides made of?
- A sugar
- A phosphate
- One of the four bases: A, T, C, G
109
Explain how a gene codes for a protein
- 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
110
What are the two stages of protein synthesis?
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