SB3 Genetics Flashcards
SB3a
1) What is sexual reproduction?
2) What is asexual reproduction?
3) What is the name of the cell formed from two gametes at fertilisation?
1) Sexual reproduction involves the joining of two sex cells, or gametes during fertilisation. The offspring have 2 parents, and are genetically unique to the parent cells.
2) Asexual reproduction is when an organism reproduces without fertilisation. It only involves one parent, and so produces a clone (offspring that are genetically identical to the parent).
3) A zygote
SB3a
1) What are the advantages and disadvantages of asexual reproduction?
2) Would you expect a species that only reproduces asexually to have a more or less variation than one that produces sexually, and explain why?
3) Explain why it may be more beneficial for organisms to reproduce sexually.
1) Asexual reproduction advantages include:
- You can inherit genetic strengths
- It is more time and energy efficient as you don’t need a mate
Asexual reproduction disadvantages include:
- No variation and a lack of adaptation
- If there is an environmental change, then it is very unlikely that the species will have the characteristics to survive.
- Disease may affect all the individuals in a population
2) A species that only reproduces asexually should have less genetic variation because sexual reproduction increases genetic variation in a species. Without sexual reproduction, no new combinations of alleles would be produced in the offspring.
3) Reproducing sexually creates genetic variation in the population. This means that if there’s an environmental change, it’s more likely that some individuals will have the characteristics to survive the change. This would allow organism to evolve and become better adapted to their new environment.
SB3a
What are the advantages and disadvantages of sexual reproduction?
The advantages of sexual reproduction:
- It produces variation in the offspring
- If there is an environmental change, then it is likely that some individuals will have the characteristics to survive the change, so they can evolve and adapt to the new environment
- Disease is less likely to affect all the individuals in a population
The disadvantages of sexual reproduction:
- Time and energy are needed to find a mate
- It is not possible for an isolated individual
SB3b
1) What is meiosis?
2) Why are haploid gametes needed for sexual reproduction?
3) What is the function of genes?
4) What happens to a cell’s chromosomes before meiosis, and how will they look after meiosis?
1) Meiosis is a type of cell division that produces four haploid daughter cells, which are gametes. These cells are genetically unique.
2) Haploid gametes are needed so that when the two gametes fuse at fertilisation, the resulting cell/ zygote ends up with the full/ diploid number of chromosomes.
3) A gene is a small section of DNA on a chromosome, that codes for a particular sequence of amino acids, which makes a specific protein.
4) A cell duplicates its DNA before meiosis, so one X-shaped chromosome pair would become 2 pairs. After meiosis, there will be straight strands of chromosomes in each daughter cell, as one pair of chromosomes doubles to become 2, then divides into 4 strands, one in each daughter cell.
SB5b
1) What is an organism’s genome?
2) Where are gametes found?
3) What is a genetic code?
4) What does a chain of amino acids form?
1) The genome of an organism is the entire genetic material of that organism.
2) In animals it is found in the sperm and egg, in plants it is found in the pollen and ovum.
3) A genetic code is a sequence of bases.
4) A chain of amino acids forms a protein.
SB3c
1) Describe how DNA is stored in the nucleus of eukaryotic cells.
2) Name the bases in DNA.
3) Recall the pairing of bases in DNA, and what it is called.
4) What is complementary base pairing?
1) It is stored as chromosomes, which are long, coiled up molecules of DNA.
2) The four bases are: adenine, thymine, cytosine and guanine. Thymine is replaced with uracil during mRNA transcription.
3) A always pairs with T, and C always pairs with G. The matching bases are called complementary base pairs.
4) Complementary base pairing is the process that ensures the mRNA produced is a complementary copy of the gene. It pairs bases with its complementary base.
SB3c
1) How are DNA strands held together?
2) What is the overall structure of DNA, and what are the monomers in DNA called and made of?
3) How do the DNA monomers look on a diagram, and how are they joined up?
4) What are the double helix sides called and made of?
1) DNA strands are held together by weak intermolecular hydrogen bonds between pairs of bases.
2) DNA is made from two strands wrapped around each other, joined by bases to form a double helix. DNA is a polymer, made up of monomers called nucleotides. The nucleotides consist of the phosphate, deoxyribose sugar, and a base that is joined to the deoxyribose sugar.
3) On a diagram, the phosphate is a circle, joined to a deoxyribose sugar which is drawn as a pentagon. The pentagon is joined to a base drawn as a rectangle.
4) The double helix sides is called the sugar phosphate backbone, which is made up with phosphate and deoxyribose sugar.
SB3d
1) Where are proteins made?
2) How can the shape of a protein be determined?
3) What determines the order of amino acids in a protein?
1) Proteins are made in the cytoplasm.
2) The folding of amino acids determines the shape of the active site which must be highly specific to the shape of its substrate.
3) The DNA determines the order of the amino acids.
SB3d
1) What is transcription?
2) Why does transcription happen?
3) What are the steps of transcription during protein synthesis?
1) Transcription is the process that occurs in the nucleus where the genetic code (sequence of base) in one strand of DNA is used to make mRNA.
2) Transcription happens because the DNA cannot move out of the nucleus, as it is too big to fit through the nuclear pores.
3) Steps of transcription:
1. In the nucleus, an enzyme called RNA polymerase attaches to the DNA in a non-coding region. (The non-coding region does not code for protein). The function of RNA polymerase is to join together RNA nucleotides (to make mRNA).
2. The RNA polymerase unzips (separates) the two DNA strands.
3. The enzyme then moves along one of the DNA strands (the template strand), and uses base pairing to add complementary RNA nucleotides. This uses the same bases and base pairing as DNA, except that uracil (U) is used instead of thymine (T).
4. The nucleotides link to form a strand of messenger RNA (mRNA)
5. The mRNA strand travels out of the nucleus through the nuclear pores into the cytoplasm.
SB3d
1) What is translation?
2) What are the steps of translation during protein synthesis?
3) What is the function of mRNA?
1) Translation is the process in the cytoplasm where the genetic code (the sequence of bases) in a molecule of mRNA is used to make a polypeptide (a chain of amino acids).
2) Steps of translation:
1. In the cytoplasm, a ribosome attaches to the mRNA strand.
2. At each mRNA codon (triplet base), a molecule of transfer RNA (tRNA) with complementary bases lines up. Each tRNA molecule carries a specific amino amino acid.
3. A ribosome moves along and joins the amino acids from the tRNA molecules together. This forms a polypeptide.
4. The polypeptide chain then folds up to form a protein (such as an enzyme) with a specific shape.
3) mRNA’s function is to carry the triplet code from DNA in the nucleus to the ribosomes in the cytoplasm (where protein synthesis takes place).
SB3e
1) What is mutation?
2) What are some ways in which mutation occurs?
3) What are possible effects of mutations on amino acid sequences?
4) Explain how a genetic variant will be different to the normal version of a gene
1) A mutation (or genetic variant) is a change in the bases of a gene.
2) It can be caused when DNA is not copied properly during cell division, or due to environmental factors.
3) Mutation can change the codon so that a different amino acid is produced. This may result in the shape of the protein changing so that it cannot carry out its function. It can also cause a protein to be too short or too long.
4) It will have a different sequence of bases due to a mutation
SB3e
1) How is gene transcription regulated?
2) What are the effects of mutations on protein synthesis?
3) How can mutations influence RNA polymerase binding and so alter protein production?
1) Gene expression (or gene regulation) is the process by which specific genes are activated to produce a required protein. The gene expression process is made up of the transcription and translation of DNA sequences.
2) The change in codons will create a different amino acid, which will create a different protein, as the amino acids will fold into a different shape.
3) If mutations occur in the non-coding section of DNA that the RNA polymerase attaches to, it can make it easier or more difficult for the RNA polymerase to bind to the coding region. If it is more difficult, then less mRNA will be transcribed, and less protein will be produced. This can affect the phenotype.
SB3f
1) Who discovered the basics of genetics?
2) How was breeding pea plants was used to work out the basis of genetics?
3) Why was is difficult to understand inheritance before the idea of genes?
1) Gregor Mendel was a monk from the 19th century who discovered the basics of genetics.
2) Mendel bred pea plants with different characteristics and observed the offspring, comparing the characteristics of the offspring with the characteristics of the parent plants. He concluded that there must be dominant and recessive ‘hereditary units’ (now known as genes), that the offspring receive from the parents.
3) It was difficult to understand inheritance because scientists could not understand how ‘hereditary units’ could explain characteristics with multiple variations such as human eye colour, and how evolution would work if the ‘hereditary units’ could not change.
SB3g
1) What is the difference between a gene and an allele?
2) What are the effects of alleles on inherited characteristics (explain the 2 different types)?
3) What is the relationship between a genotype and a phenotype?
1) A gene contains instructions to create a specific protein. An allele is a different form of the same gene.
2) There is a dominant and recessive allele. Every organism has two. The dominant allele will always be expressed, while the recessive allele will only be expressed if there are two of them.
3) A genotype is the alleles in an organism. The visible characteristics that are caused by the genotype is called the phenotype.
SB3h
1) How do you use Punnett squares to work out possible combinations of alleles in the offspring of parents?
2) How is a family pedigree chart used?
1) To use a Punnett square:
- Determine the parental genotypes. You can use any letter you like but select one that has a clearly different lower case, for example: Aa, Bb, Dd.
- Split the alleles for each parent and add them into your Punnett square around the edges. It is good practice to put male on the top and female on the side
- Work out the new possible genetic combinations inside the Punnett square.
2) Family pedigree charts: Doctors can use a pedigree analysis chart to show how genetic disorders are inherited in a family. They can use this to work out the probability that someone in a family will inherit a condition.
