Topic 3: Genetics Flashcards
What is chromosomes?
A long, coiled molecule of DNA that carries genetic information in the form of genes
What is a gene?
A section of DNA that codes for a specific sequence of amino acids which undergo polymerisation to form a protein
What are alleles?
Different versions of the same genes
What is a genotype?
An organisms genetic composition, describes all alleles
What is a phenotype?
An organisms observable characteristic due to interaction of the genotype and environment
What is homozygous?
Having two identical alleles of a gene
What is heterozygous?
Having two different alleles of a gene
What is a dominant allele?
Describes an allele that is always expressed, represented with a capital letter
What is recessive allele?
An allele that is only expressed in the absence of a dominant allele, represented with a small letter
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
Why does the inheritance of a Y chromosome mean that an embryo develops into a male?
Tested development in an embryo is stimulated by a gene present on the Y chromosome
How can monohybrid inheritance be represented?
Punnet square and using a family pedigree
What is a sex-linked characteristic?
A characteristic that is coded for by an allele founded 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 woman?
Many genes are found on the X chromosome that have no counterpart on the Y chromosome and woman have two alleles for each sex-linked gene whereas men often only have one allele only one recessive allele is required to produce the recessive phenotype in males
What are the four different blood groups?
A, B, AB and O
What are codominant alleles?
Alleles that equally contribute to an organism’s phenotype, they’re expressed to an equal extent
What does AO give blood group A?
O is recessive to A, A is dominant and is expressed giving blood group A
What is the genotype for blood group O?
OO
What is sexual reproduction?
Type of reproduction, involves the production of gametes by meiosis, a gamete from each parent fuses to form a zygote and genetic information from each gamete is mixed so the resulting zygote is unique
What are gametes?
Sex and haploid cells
What is meiosis?
Form of cell division involved in the formation of gametes, chromosome number is halved and involves two division
What must occur prior to meiosis?
Interphase
What happens during the first stage of meiosis?
Chromosome pairs line up along the cell equator, the pair of chromosomes are separated and move to opposite poles of the cell (chromosome is pulled is random, creating variation) and chromosome number is halved
What happens during the second stage of meiosis?
Chromosomes line up along the cell equator, the chromatids are separated and move to opposite poles of the cell and four unique haploid gametes are produced
Why is meiosis important for sexual production?
Increases genetic variation and ensures that the resultant zygote is diploid
What is the advantage of sexual reproduction?
It create genetic variation, increasing the probability of species adapting to and surviving environmental changes
What are the disadvantages of sexual reproduction?
Two parents are required, this makes reproduction difficult in endangered populations or in species which exhibit solitary lifestyle and more time and energy is required so fewer offspring are produced
What is asexual reproduction?
Type of reproduction, involves mitosis and produces genetically identical offspring known as daughter cells
What are the advantages of sexual reproduction?
Only one parent is required, lots of offspring can be produced in a short period of time, enabling the rapid colonisation of an area and reducing competition from othrt species and requires less energy
What is the disadvantage of asexual reproduction?
No genetic variation reducing the chance of a species being able to adapt to environmental changes
What is DNA?
a double stranded polymer of nucleotides, wounded to form a double helix
What are the monomers of DNA?
Nucleotide
What are DNA nucleotides made up of?
Common sugar, phosphate group and one of the four bases (A, T, C or G)
How do nucleotide 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 and complementary base pairs joined by weak hydrogen bonds
What is a genome?
The entire genetic material of an organism
What is the method used to extract DNA from fruit?
Place a piece of fruit in a beaker and crush it, add detergent and salt, mix, filter the mixture and collect the liquid in a test tube, pour chilled ethanol into the test tube, DNA precipitates forming a fibrous white solid and use a glass rod to collect the DNA sample
Why is detergent added to the crushed fruit?
It disrupts the cell membrane, releasing DNA into solution
Why is salt added to the crushed fruit?
Salt encourages the precipitation of DNA
Why is chilled ethanol to the crushed fruit rather than water?
DNA is insoluble in ethanol, encouraging its precipitation
How do a gene code for a protein?
A sequence of three bases in a gene forms a trip,et, each triplet codes for an amino acid and the order of amino acids determines the structure and function of the protein formed
Why is the ‘folding’ of amino acids important in proteins such as enzymes?
The folding of amino acids determines the shape of the active site which must be highly specific to the shape of its substrate
What is protein synthesis?
The formation of a protein from a gene
What are the two stages of protein synthesis?
Transcription and Translation
What does transcription involve?
The formation of mRNA from a DNA template
What is the process of transcription?
DNA double helix unwinds, RNA polymerase binds to a specific base sequence of non-coding DNA in front of a gene and moves along the DNA strand, RNA polymerase joins free RNA nucleotides to complementary bases on the coding DNA strand and mRNA formation complete so the mRNA detaches and leaves the nucleus
What are the differences between mRNA and DNA?
mRNA is single stranded whereas DNA is double stranded and mRNA uses U whereas DNA uses T
Why is mRNA used in translation rather than DNA?
DNA is toll large to leave the nucleus so cannot reach the ribosome
What does translation involve?
A ribosome joins amino acids in a specific order dictated by mRNA to form a protein
What is the process of 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 and 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 variation
What the effect of a gene mutation in coding DNA?
If a mutation changes the amino acid sequence, protein structure and function may change and if a mutation doesn’t change amino acid sequence, there is no effect on protein structure or function
What is non-coding DNA?
DNA which doesn’t code for a protein but instead controls gene expression
What is the effect of gene mutation in non-coding DNA?
A mutation may affect the ability of RNA polymerase to bind to non-coding DNA and this may affect protein production and the resulting phenotype of the organism
How did the work of Mendel help 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 y ‘units’ passed on to descendants and using gene crosses, devised the terms ‘dominant’ and ‘recessive’
Why was Mendel’s work initially overlooked?
Scientists didn’t understand Mendel’s work as there was no knowledge of genes or DNA at that time
What are the two cause of variation within a species?
Genetics and Environment
What is genetic variation?
Variations in the genotypes of organisms of the same species due to the presence of different allleles and creates differences in phenotypes
What creates genetic variation in species?
Spontaneous mutations and sexual reproduction
What is a mutation?
A random change to the base sequence in DNA which results in genetic variats
What are the three types of gene mutation?
Insertion, deletion and substitution
How many a gene mutation affect an organisms phenotype?
Neutral mutation doesn’t change the sequence of amino acids, protein structure and function same, no effect on phenotype. Mutation may cause a minor change in an organisms phenotype. 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 and due to environmental factors
What is the human genome project?
Scientific research project involving thousands of scientists across the globe which successfully mapped the entire human genome and 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 presdisposition to disease and possible prevention, disease-causing alleles identified more rapidly and the appropriate treatments prescribed earlier on and scientists can predict an individuals response to certain drugs and new drugs can be developed which are tailored to a specific allele
What drawbacks associated with the discoveries of the human genome project?
Knowledge of predisposition to a disease can be stressful, societal pressure influenced by the division to have children and discrimination against employees
