Paper 2: Topic 6 Inheritance, variation & evolution - Reproduction (includes DNA & genetics) (LV) Flashcards
Name the genetic material found in the nucleus
DNA
What does DNA stand for?
Deoxyribonucleic acid
How is the DNA arranged in the nucleus of a eukaryotic cell?
As chromosomes
How is the DNA arranged in a prokaryotic cell?
- Free in the cytoplasm as a nucleoid
- And additional pieces of DNA are also found in bacteria in small loops called plasmids
How do chromosomes normally exist in cells?
In pairs
Where do the chromosomes in the nucleus originate (come) from?
One from each pair comes from the maternal ovum and one from each pair comes from the paternal sperm
What type of molecule is DNA?
Polymer
DNA is a polymer. What are the monomers that are linked other to form DNA called?
Nucleotides
Describe the general shape of a DNA molecule
A double helix
Define the term gene
A small section of DNA that codes for the sequence of amino acids that makes a specific protein
How many amino acids exist naturally?
20
Define the term genome
The entire set of genetic material that exists in a single organism
Why has the study of the Human genome been useful for scientists?
Hint: give 4 reasons
- They have Identified genes linked to specific diseases
- Gained an understanding of how some diseases are inherited
- Used this understanding of inheritance to develop effective treatments
- Used the genome to determine historical migration patterns of certain groups of people
State the 3 main components of a nucleotide
- Phosphate group
- Sugar (called deoxyribose)
- Base
How many different types of base are found within DNA?
4
What are the 4 different types of base found in DNA nucleotides?
A, T, C and G
How do the bases pair up in DNA?
- A always pairs with T
- C always pairs up with G
How do the nucleotide bases code for the production of proteins?
- 3 bases codes for one amino acid
- So the sequence of bases codes for the sequence of amino acids that are linked together to make a protein
Some parts of the DNA do not code for specific proteins. What is the role/function of these parts of the chromosome?
- To control if the genes are expressed
- Which determines if the proteins are actually produced
Which organelle is responsible for producing proteins?
Ribosomes
How are proteins made? Hint: 5 steps
- The instructions in the gene are copied into a messenger molecule called mRNA
- The mRNA leaves the nucleus and travels to the cytoplasm
- Ribosomes attach to the mRNA
- Carrier molecules carry amino acids to the ribosome
- The ribosome joins the amino acids together in the sequence that is determined by the mRNA
After the amino acids are joined together in a long chain, what must happen before the protein can carry out it’s function?
- When the protein chain is complete it folds up to form a unique shape.
- This unique shape enables the proteins to do their function
Give 5 different functions of proteins
Hint: think STEAM H
Structural role e.g. collagen (found in blood vessel walls), keratin (found in hair and nails)
Transport role e.g. haemoglobin (carries oxygen around the body)
Enzymes e.g. proteases
Antibodies
Mechanical role e.g. myosin (found in muscle cells to allow muscle cells to contract)
Hormones e.g. insulin
Define the term mutation
- A change to the sequence of DNA bases
- This changes the genetic code
Describe how often mutations occur
Continuously, spontaneously and randomly
State the 3 effects of mutations
- Neutral
- Harmful
- Beneficial
State 3 factors that increase the risk of a mutation occurring
- Exposure to UV light
- Exposure to X-rays
- Exposure to certain chemicals e.g. benzene
How does a change in DNA bases cause a change in the protein structure and function?
- A change in one or more DNA bases will change the triplet sequence of the DNA
- This will change the sequence of triplets on the mRNA
- This will change the carrier molecule that brings the amino acids to the ribosome
- The sequence of amino acids will then change
- This changes the structure of the protein
- Which then changes the function of the protein
Suggest how mutations may cause a change in enzyme activity
- The mutation will cause the amino acids sequence to change
- This could change the shape of the active site
- This could prevent the substrate from fitting into the active site
- This then prevents the formation of enzyme-substrate complexes
- So the rate of reaction will decrease
Suggest how mutations may cause a change in structural proteins
- The amino acid sequence in the protein will be changed
- This changes the shape of the protein
- This reduces the strength of the structural protein
Describe the function of the non-coding parts of the DNA
- Non-coding parts of DNA can switch genes on and off
- Mutations in these areas of DNA may affect how genes are expressed
Explain why a mutation may not alter gene expression
The mutation may occur in part of the DNA that does not code for a protein
State the 3 different types of mutation
- Insertion
- Deletion
- Substitution
Describe an insertion mutation
- An new additional nucleotide base is inserted into the DNA
- This will alter how the triplets of DNA bases are ‘read’
- Each triplet will change at the point after the insertion
- This is described as a frameshift mutation
Describe a deletion mutation
- A nucleotide base is deleted from the DNA
- This will alter how the triplets of DNA bases are ‘read’
- Each triplet will change at the point after the deletion
- This is described as a frameshift mutation
Describe a substitution
- A nucleotide base in the DNA sequence is changed to a different nucleotide base
- This may alter which amino acid is inserted into the sequence
Name the two types of reproduction
- Asexual reproduction
- Sexual reproduction
Define asexual reproduction
- Asexual reproduction involves only one parent and no fusion of gametes
- There is no mixing of genetic information
- This leads to genetically identical offspring (clones)
- Only mitosis is involved
Define sexual reproduction
- Reproduction that involves two parents
- It involves the mixing of genetic information
- This leads to variety in the offspring
- The formation of gametes involves meiosis
- It involves the fusing of gametes
State the 2 types of gametes that are involved in sexual reproduction in animals
- sperm
- ova (egg cells)
State the 2 types of gametes that are involved in sexual reproduction in flowering plants
- pollen
- ova (egg cells)
Give 3 advantages of sexual reproduction
- 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
Give 4 advantages of asexual reproduction
- Only one parent needed
- More time and energy efficient as do not need to find a mate
- Faster than sexual reproduction
- Many identical offspring can be produced when conditions are favourable
Name 3 organisms that reproduce by both asexual and sexual reproduction depending on the circumstances
- Malarial parasites
- Fungi
- Plants e.g. strawberry plants
State how malarial parasites demonstrate both sexual and asexual reproduction
Malarial parasites reproduce asexually in the human host, but sexually in the mosquito
State how fungi demonstrate both sexual and asexual reproduction
- Many fungi reproduce asexually by spores
- They also reproduce sexually by spores to give variation
Remember: fungal spores can be produced asexually and sexually
Explain why it is an advantage for fungi to be able to produce spores asexually and sexually
- When conditions are favourable the fungi can produce spores asexually to make many identical spores in a short period of time
- When conditions are unfavourable fungi can produce spores sexually to make genetically different spores to increase the chances of surviving the environmental conditions
State how some plants demonstrate both sexual and asexual reproduction
- Flowering plants produce seeds sexually
- They also reproduce asexually by runners such as strawberry plants, or bulb division such as daffodils
State the type of cell division involved in asexual reproduction
Mitosis
State the type of cell division involved in sexual reproduction
Meiosis
Which type of reproduction involves the production of haploid gametes
Meiosis
State the term that describes the fusing of two gametes to form a zygote
Fertilisation
How many chromosomes are found in a gamete?
- Half the full number i.e. haploid (n)
- For human cells this is 23
How many chromosomes are found in a somatic (body) cell?
- A full set of chromosomes i.e. diploid (2n)
- For human cells this is 46
Explain why sexual reproduction causes greater genetic variation in the offspring
- Sexual reproduction involves the fusing of two gametes
- Each gamete contains genetic material from each parent
- The zygote will have half the DNA from the mother and half from the father
- This mixture of genetic information produces variation
State the 4 advantages of sexual reproduction
- It increases genetic variation
- Genetic variation increases the chances of survival of the species if there is a change in the environment
- Genetic variation will mean some individuals will be better adapted to the environment and therefore more likely to survive and breed and pass the successful alleles on to the next generation (called natural selection)
- Scientists can use selective breeding to speed up natural selection
State the 5 advantages of asexual reproduction
- Only one parent is required (so there is no need to find a mate)
- This means asexual reproduction uses less energy (no energy used in finding a mate, producing gametes)
- It is also faster (as no time is used in finding a mate)
- Many genetically identical offspring can be produced when conditions are favourable
- It maintains genetic stability by producing genetically identical cells
Explain the importance of producing haploid gametes
- Gametes must contain half the chromosomes number so that when 2 gametes fuse during fertilisation the chromosome number is restored
- If the gametes had a full set of chromosomes (2n) then the chromosome number would double at each generation
How many daughter cells are produced in mitosis?
2
How many daughter cells are produced in meiosis?
4
State the 3 main stages of mitosis
- Copies of the genetic information are made
- The cell divides once to form two daughter cells, each with a full set of chromosomes (2n)
- All somatic cells are genetically identical to each other.
State the 3 main stages of meiosis
- 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
State where meiosis occurs
In the reproductive organs
- testes
- ovaries
State the type of cell division that occurs in an embryo to form a fetus
Mitosis
How does the cell number change as the embryo forms a fetus?
The number of cells increases The number of cells doubles after each division
As the embryo develops the cells become specialised. Name this process.
Differentiation
Put these structures in order of increasing complexity: Gamete Organism Fetus Embryo Zygote
Gamete → zygote → embryo → fetus → organism
Give an example of asexual reproduction in plants
- Runners e.g. strawberry plants
- Bulbs e.g. daffodils
How many pairs of chromosomes are found in a somatic (body) cell?
23
Please note the questions asked you for the number of PAIRS
What is the name for the pair of chromosomes that determines the gender of the individual?
Sex chromosomes
What 2 sex chromosomes are found in all somatic (body) cells of a female human?
XX
What 2 sex chromosomes are found in all somatic (body) cells of a male human?
XY
What percentage of female ova will carry an X chromosome?
100%
What percentage of male sperm will carry an X chromosome?
50%
What percentage of male sperm will carry a Y chromosome?
50%
State the gamete will determine the sex of a human at fertilisation. Explain your answer.
- Male
- If the ovum is fertilised by a sperm carrying an X chromosome the individual will be female.
- If the ovum is fertilised by a sperm carrying a Y chromosome the individual will be male.
Define the term heterozygous
The individual has a genotype that has 2 alleles that are different (one dominant and one recessive)
Define the term homozygous
The individual has a genotype that has 2 alleles that are same
What are the two possible genotypes for a homozygous individual?
- Homozygous dominant (2 dominant alleles are present)
- Homozygous recessive (2 recessive alleles are present)
State the genotype of a human male
XY
State the genotype of a human female
XX
State what controls the characteristics an individual develops
The genes the individual inherits from its parents AND the environment
Define the term gene
A sequence of DNA bases that codes for the production of a specific protein
Define the term allele
A variety of a gene
Remember: A gene is the characteristic determined by the protein e.g. hair colour The allele is the actual variety of hair colour e.g. red, blond, brown, black
State the 2 different forms of alleles that can exist for a gene
- Dominant
- Recessive
How do alleles determine an individual’s phenotype
- The alleles present operate at a molecular level to develop characteristics that can be expressed
- They determine which protein(s) are or are not made
Define a dominant allele
An allele that is expressed in an individual irrespective if there is another dominant allele OR a recessive allele present
Define a recessive allele
An allele that is only expressed in the absence of a dominant allele and the presence of a second recessive allele
Define the term phenotype
- The physical characteristic expressed by an individual due to the genotype they have
- Most characteristics are a result of multiple genes interacting, rather than a single gene
Name a disease caused by a recessive allele
Cystic fibrosis
Describe 2 symptoms of cystic fibrosis
- It results in the production of excess mucus
- The mucus is also very sticky
State which part of the cell is affected by cystic fibrosis
It is a disorder of the cell membranes
Name a disease caused by a dominant allele
Polydactyly
Describe 2 symptoms of polydactyly
- Extra fingers
- Extra toes
With recessive genetic disorders some individuals can either have the disorder, not have the condition or be a carrier. Define the term carrier
- The individual is heterozygous
- They have one dominant (normal) allele
- And they have one recessive (affected) allele
What is the chance of 2 parents who are both carriers for cystic fibrosis having a child with CF?
25% (Must be homozygous recessive)
What is the chance of 2 parents who are both carriers for cystic fibrosis having a child who is also a carrier?
50% (Must be heterozygous)
What is the chance of 2 parents who are both carriers for cystic fibrosis having a child who has not chance of passing the CF allele on to their own children?
25% (Must be homozygous dominant)
How can genetic disorders be detected in individuals?
Embryo screening
State 2 situations when embryo screening can take place
- During IVF – prior to implanting the embryo in the female’s uterus
- After the female has conceived: cell can be removed from the developing embryo and analysed in the lab
Give 3 reasons why some people are in favour of carrying out embryo screening
- It will reduce the number of individuals being born with certain genetic diseases reducing suffering
- It will decrease the cost of treating disorders (if less people are born with the disorder)
- There are very tight laws in place that will and do prevent the technology from going too far e.g. selecting an embryo on the basis of sex
Remember: it is possible to legally select an embryo on the basis of sex but there have to be medical reasons for this e.g. to prevent certain disorders which are only found in men
Give 3 ethical concerns some people may have about embryo screening
- It implies people with disorders are of less value and can be ‘disposed of.
- It is possible in the future the technique could be used to permit designer babies being selected
- The cost of screening is high
Using a punnett grid show the chance of a couple having a daughter is 50%
Show using a Punnett grid why both parents must have the recessive allele for their child to have cystic fibrosis
Show using a Punnett grid why only one of the parents needs to have the dominant allele for their child to have polydactyly
