B3 Flashcards
What is sexual reproduction?
Involves the production of gametes by meiosis and a gamete from each parent to fuse and become a zygote
What are gametes?
Sex cells
What is meiosis important for sexual reproduction?
It increases genetic variation
What are the advantages of sexual reproduction?
It increases genetic variation
Increase the likelihood of a species adapting to the environment
What are the disadvantages of sexual reproduction?
Two parents are required so finding a partner may take longer
More energy is required so fewer offspring
What is asexual reproduction?
Involves mitosis
Produces 2 genetically identical cells
What are the advantages of asexual reproduction?
Only one parent required
Requiring less energy
What are the disadvantages of asexual reproduction ?
No genetic variation
Species can become extinct more easily
What is DNA?
a double stranded polymer in a double helix structure
What are the monomer of DNA?
Nucleotides
What are nucleotides made of ?
Sugar,phosphate and bases (a,t,c,g)
What are the 4 bases ?
Adenine, thymine, cytosines and guanine
What does the sugar and phosphate do?
Join to create a sugar phosphate backbone in each dna strand
What is a genome ?
Th entire genetic material of an organism
What is a chromosome?
A long coil of molecules of DNA that carries genetic information
Define gene
A section of DNA that codes for a specific sequence of amino acids
What are the steps to extract DNA from a fruit ?
- Crush the fruit and add a detergent and salt mix into it
2.filter the mister and collect the liquid
Pour chilled ethanol into the filtrate
3.Wait for the precipitate to form a white solid and collect the precipitate with a glass rod
What do you add detergent to extract the fruit dna ?
It disrupts the cell membrane d releasing DNA into a solution
What do you add chilled ethanol into the filtrate?
DNA is insoluble in ethanol wich encourages the precipitation
What is protein synthesis?
The formation of a protein from a gene
What are the 2 stages of protein synthesis?
Transcription and translation
What is transcription?
The formation of mRNA from a DNA template
Explain the steps transcription?
DNA double helix unwinds an RNA polymerase binds to the bases then the mRNA detaches and leaves the nucleus
What does translation involve?
A ribosome joins an amino acid dictated by the mRNA to form a protein
What are alleles ?
Different versions of the same gene
Define homozygous?
Having 2 identical alleles
eg FF or ff
Define heterozygous?
Having 2 different alleles of a gene
eg Ff
What is the chromosome for a male
XY
What are the female chromosomes ?
XX
Name the 4 different blood groups ?
A, B, AB and O
What are 2 causes of variation in species?
Genetic and environmental
Describe how nucleotides interact to form a molecule of DNA?
• Sugar and phosphate molecules join to form a sugar-phosphate backbone in each DNA strand
• Base connected to each sugar
• Complementary base pairs (A pairs with T, C pairs with G) joined by weak hydrogen bonds
Describe the difference between mRNA and DNA?
• mRNA is single stranded whereas
DNA is double stranded
• mRNA uses U whereas DNA uses T
Why is mRNA used in translation rather than DNA?
DNA is too large to leave the nucleus so cannot reach the ribosome.
Outline translation?
- mRNA attaches to a ribosome
- Ribosome reads the mRNA bases in triplets. Each triplet codes for one amino acid which is brought to the ribosome by a tRNA molecule
- A polypeptide chain is formed from the sequence of amino acids which join together
How is a tRNA molecule adapted to its function?
Each tRNA molecule has an anticodon which is specific to the codon of the amino acid that it carries.
What is a mutation?
A random change in the base sequence of DNA which results in genetic variants
Describe the effect of a gene mutation in coding DNA?
• If a mutation changes the amino acid sequence, protein structure and function may change
• If a mutation does not change amino acid sequence, there is no effect on protein structure or function
What is non-coding DNA?
DNA which does not code for a protein but instead controls gene expression
Describe the effect of a gene mutation in non-coding DNA?
• A mutation may affect the ability of RNA polymerase to bind to non-coding DNA
• This may affect protein production and the resulting phenotype of the organism
Outline how the work of Mendel helped scientists to develop their understanding of genetics?
• Mendel studied the inheritance of different phenotypes of pea plants
• He established a correlation between parent and offspring phenotypes
• He noted that inheritance was determined by ‘units’ passed on to descendants
Why was Mendel’s work initially overlooked?
Scientist’s didn’t understand Mendel’s work as there was no knowledge of genes or DNA at the time.
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
What creates genetic variation in a species?
• Spontaneous mutations
• Sexual reproduction
What is a mutation?
A random change to the base sequence in DNA which results in genetic variants
State the three types of gene mutation?
• Insertion
• Deletion
• Substitution
How may a gene mutation affect an organism’s phenotype?
• Neutral mutation does not change the sequence of amino acids.Protein structure and function same. No effect on phenotype.
• Mutation may cause a minor change in an organism’s phenotype e.g. change in eye colour.
• Mutation may completely change the sequence of amino acids. This may result in a non-functional protein. Severe changes to phenotype.
What is environmental variation?
• Variations in phenotype that are acquired during the lifespan of an organism
• Due to environmental factors e.g. diet, lifestyle, climate, exposure to light etc.
What is the Human Genome Project?
• Scientific research project involving thousands of scientists across the globe which successfully mapped the entire human genome
• Scientists now aim to identify the function of every gene in the human genome
How can the results of the Human Genome Project be applied to medicine?
• Enables scientists to understand how lifestyle factors interact with genes - identifying predisposition to disease and possible preventions
• Disease-causing alleles identified more rapidly and the appropriate treatments prescribed earlier on
• Scientists can predict an individual’s response to certain drugs. New drugs can be developed which are tailored to a specific allele.
What are drawbacks associated with the discoveries of the Human Genome Project?
• Knowledge of predisposition to a disease can be stressful
• Societal pressure influencing the decision to have children
• Discrimination by employers, insurance firms etc.
Define genotype?
An organism’s genetic composition, describes all alleles
Define phenotype?
An organism’s observable characteristics due to interactions of the genotype and environment (which can modify the phenotype)
What is a dominant allele?
Describes an allele that is always expressed.
Represented with a capital letter e.g. F
What is a recessive allele?
An allele that is only expressed in the absence of a dominant allele.
Represented with a small letter e.g. f
What is monohybrid inheritance?
The inheritance of a single gene
What is the problem with single gene crosses?
Most characteristics are controlled by multiple alleles rather than just one
What are sex chromosomes?
A pair of chromosomes that determine sex:
• Males have an X and a Y chromosome
• Females have two X chromosomes
Why does the inheritance of a Y chromosome mean that an embryo develops into a male?
Testes development in an embryo is stimulated by a gene present on the Y chromosome
Other than using a punnett square, how else can monohybrid inheritance be represented?
Using a family pedigree
What is a sex-linked characteristic?
A characteristic that is coded for by an allele found on a sex chromosome.
Why are the majority of genes found on the X chromosome rather than the Y chromosome?
The X chromosome is bigger than the Y chromosome so more genes are carried on it.
Why are men more likely to show the phenotype for a recessive sex-linked trait than women?
• Many genes are found on the X chromosome that have no counterpart on the Y chromosome
Give an example of a characteristic that is determined by more than one allele?
Blood group is determined by three alleles
Name the four different blood groups?
A, B, AB, O
What are codominant alleles?
Alleles that equally contribute to an organism’s phenotype. They are expressed to an equal extent.
