Genetics Flashcards
What is a gene?
heritable factor that consists of a sequence of DNA and influences a specific trait.
What is the position of gene in the chromosome called?
locus
What are alleles?
Alternate forms of a gene that codes for different variations of a specific trait
State the definition of genome
The totality of the genetic information in an organism. It includes all genes and non-coding sequences.
- human cells have 46 chromosomes
What is a gene mutation?
Change in the base sequence of a section of DNA coding for particular characteristic.
What are the two types of gene mutations?
- somatic
- germline
What are the two types of point mutations?
- substitutions (silent, missense or nonsense)
- frameshifts (insertions and deletions)
Somatic mutation
Occurs in the body cell and affects a tissues
Germline
Occurs in a gamete and affects offspring
Silent mutations
Does not affect the amino acid sequence.
Missense mutations
Affects the sequences and changes the code. It produces a different amino acid at a certain position.
Nonsense mutations
Changes in the sequence that results in giving a rise to a stop codon -> uncompleted protein.
What is the sickle cell anemia?
Sickness that affects the shape of red blood cells, which carry oxygen to all parts of the body (autosomal codominant).
Cause of the sickle cell anemia
- base substitution GAG -> GUG (hemoglobin beta)
- amino acid change Glutamic Acid -> Valine
Consequences of sickle cell anemia
- alters hemoglobin structure
- cannot transport oxygen efficiently
- sickle cells are destroyed at higher rate
What is the heterozygous advantage of sickle cell anemia?
It is a codominant trait and heterozygous individuals demonstrate an increased resistance to malaria.
What are the point mutations?
- substitution of a base (ATG-ACG)
- insertion of a base (ATG- ATCG)
- deletion of a base (ATG-AG)
Gene mutations can be…
- beneficial
- detrimental
- neutral
What is the beneficial gene mutation?
Change in the sequence to create new variations of the trait
What is the detrimental gene mutation?
It cuts of the piece of gene sequence and disrupts the normal function of the trait.
What is the neutral gene mutation?
has no effects on functioning of the specific elements
What are the two ways in which fetal cells can be obtained?
- amniocentesis
- chorionic villus sampling
Explain chorionic villus sampling
cells are sampled from the placenta, specifically the chorion. It can be done earlier than the amniocentesis and the sampling tool enter through the vagina.
- conduced to 11 weeks with a higher risk of miscarriage
Explain the amniocentesis
Involves passing a needle through the mothers abdominal wall. The needle is used to withdraw a sample of amniotic fluid of a developing fetus. Later those cells are used to prepare a karyotype.
- conducted to 16 weeks with a slight risk of miscarriage
What was John Cairn technique?
He pioneered a technique for measuring the length of DNA molecules while uncoiled.
What are diploid cells ?
Sexually reproducing organisms receive genetic material from both parents. They contain 2 sets of chromosomes.
What are haploid cells?
These organisms pass only half of their genetic material. They are haploid and have only one set of chromosomes.
What are homologus chromosomes?
Paired chromosomes that have the same genes at identical loci positions.
What are autosomes?
An autosome is any chromosome that is not a sex chromosome. 22 pairs are homologous autosomes
- each pair has identical genes and loci
- alleles may differ
What are sex chromosomes?
Chromosome concerned in determining the sex of an organism. 23rd pair are the sex chromosomes
- females have two X chromosomes
- males have X and Y chromosome
What is Y chromosome responsible for?
Development of the male characteristics
What are karyotypes?
They identify the number and types of chromosomes in a cell.
Purpose of karyotyping
Identifying sex of the offspring and diagnosing potential abnormalities.
What is the karyogram?
Shows the chromosomes of a cell in homologous pairs of decreasing length.
What are two laws of Mendelian genetics?
- segregation
- independent assortment
Explain the law of Segregation
Separation of alleles. There is a 50% chance that we are going to get either of those genes.
Explain the Independent Assortment
It means that traits do not affect each other because they are not in the same chromosome.
What is cystic fibrosis?
Disorder that damages lungs, digestive tract and other organs. It is inherited from generations (autosomal recessive).
- gene called CFTR on chromosome 7, produces mucus
- people with this disorder produce abnormal number of it because they inherited two copies of CFTR
What is the Huntington disease?
Inherited disorder that results in break down and death of nerve cells. This disease is an autosomal dominant disorder
- mutation in HIT gene that codes for huntingtin
Color blindness
Parents pass down the genes for red-green color vision deficiency through the X chromosome.
- X linked recessive inheritance
Chromosomal mutation
Involves long segments of DNA.
- deletions, insertions, inversions or translations of segments of DNA
Examples of the chromosomal mutations
- down syndrome (translocation)
- Turner syndrome (deletion)
Down syndrome
Genetic disorder caused by abnormal cell division that results in extra copy of the 21 chromosome.
Hemophilia
Inherited bleeding disorder in which blood does not clot properly, because it does not have enough blood clotting proteins.
- located on X chromosome
What is the Turner Syndrome?
Condition that affects only females. Results when X chromosome is missing. The error happens during the formation of egg or sperm. It contributes to short height and heart diseases.
Polygene
group of genes that produce a specific phenotype or a trait.
Locus
position on homologous chromosomes of a gene
What is meiosis?
Reduction division of a diploid cell to produce four haploid cells (gametes).
What are the two divisions of meiosis?
- meiosis I that separates homologous chromosomes
- meiosis II that separates sister chromatids
What is the crossing over?
The exchange of genes between homologous chromosomes, resulting in a mixture of parental characteristics in offspring.
- occurs via synapsis in prophase I
Chiasmata
represent the points where genetic information has been exchanged between the homologous pair
State the definition of recombinants
non-sister chromatids that have exchanged DNA
Explain the random assortment
- the homologus pairs orient randomly in the metaphase I
- there is equal chance of resuting gamete containing either the maternal or parental chromosome
Non-disjunction
Chromosomes failing to separate which results in gametes with extra or missing chromosomes.
- failure to separate may involve the homologous pairs in Anaphase I or Anaphase II
Stages of Meiosis I
Prophase I: The nuclear envelope dissolves, the spindle fibers begin to form, and the chromosomes condense.
Metaphase I: the chromosomes line up in the middle of the cell. Spindle fibers attach to the homologous chromosomes at the centromere and allow sister chromatids to stay together.
Anaphase I: The spindle fibers attach to the homologous chromosomes at the kinetochore. Sister chromatids remain intact. Spindle fibers not attached to the chromosomes help push the centrosomes and cell poles away from each other.
Telophase I: The nuclear membrane begins to reform. It is followed by cytokinesis, which results in two haploid daughter cells with a copy of each chromosome.
Stages of Meiosis II
Prophase II: The nuclear envelopes condense again. The centrosomes move way from each other towards the opossite poles and new spindle fibers are formed.
Metaphase II: The sister chromatids are maximally condensed and aligned at the equator of the cell.
Anaphase II: The sister chromatids are pulled apart by the kinetochore microtubules and move toward opposite poles.
Telophase II: The chromosomes arrive at opposite poles and begin to decondense. Nuclear envelopes form around the chromosomes. Cytokinesis separates the two cells into four unique haploid cells. At this point, the newly formed nuclei are both haploid.
What did Gregor Mendel established?
He established the principles of inheritance via experimentation
- cross large numbers of pea plants
What were Gregor Mendel’s findings?
- organisms have genes
- parents contribute equally to inheritance
- gametes contain only one allele on each gene
What is the genotype?
Allele combination for a specific trait
What are the 3 types of allele combinations?
- homozygous - both alleles are the same
- heterozygous - alleles are different
- hemizygous - only one allele
What is the phenotype?
Physical expression of a specific trait
- it is determined by genotype and environmental factors
Modes of inheritance
- complete dominance
- codominance
What is the complete dominance?
one allele is expressed over another
- dominant allele is expressed in heterozygote
- recessive allele is masked in heterozygote
What is the codominance?
both alleles are equally expressed in the phenotype
- example is the ABO blood system
How radiation exposure affects genetic diseases?
It increases mutation rates and can cause genetic diseases
Two types of radiation exposure
- nuclear bombing in Hiroshima
- meltdown in Chernobyl
What are the consequences of radiation exposure?
- increased risk of cancer
- reduced immunity
- disruption of functioning of certain organs
What are monohybrid crosses?
It determines the allele combinations for potential offspring for one gene only.
- they can be represented via Punnett grids.
How monohybrid crosses are calculated?
- made up letters to represent alleles
- identify genotype/phenotype of parents
- determine genotypes of alleles
- work out gamete combination
- identify ratios of offspring (F1 generation)
What is the sex linkage?
Refers to when a gene is on sex chromosome.
- Y chromosome is short
- X chromosome is large
What are sex linked traits?
- males have a higher rate of X linked recessive conditions as they cannot mask the recessive allele -> they are hemizygous
- females can be carriers for X-lined recessive conditions but not express it
What is a pedigree chart?
Chart of genetic history over several generations
- males are represented as squares, while females as circles
- shaded regions denote individual has a specific condition
- horizontal line between male and female represents mating
What is the autosomal dominance in pedigree chart?
If both parents are affected by a trait and any offspring is not, the trait must be dominant (parents are heterozygous)
What is the autosomal recessive in pedigree chart?
If neither parents is affected by a trait but any offspring is, the trait must be recessive (parents are heterozygous)
What is the gel electrophoresis?
a technique that separates proteins or fragments of DNA according to size
What is the process of gel electrophoresis?
- samples placed in a block of gel and current is applied
- smaller samples move faster through the gel (smaller resistance)
- samples will move towards the positive terminus
- DNA is negatively charged
- Proteins are treated with detergent in order to add a uniform negative charge on all molecules
What is the DNA profiling?
technique by which individuals can be indentified and compared by their genetic sequences
How the DNA profiling works?
- individuals have different lengths of particular DNA segments called short tandem repeats (STR)
- these segments are amplified by PCR and then separated by gel electrophoresis for comparison
- unique profiles appear when multiple loci are compared
What is DNA profiling commonly used for?
- investigations to match the suspect to the crime scene
- paternity tests
How the Gene Transfer occurs?
- DNA extraction- gene of interest is isolated from the organism
- Gene is amplified using the PCR
- Digestion and Ligation - plasmid and gene are cut with specific restriction enzyme. Gene is spliced into plasmid vector by DNA ligase
- Transformation and expression- recombinant plasmid is inserted into a host cell. Antibiotic selection may be used to select for successful transgenic cell. Transgenic cells express new protein.
What are the benefits of Genetically Modified Crops (GM Crops)?
- improves nutritional standards
- can grow in many environments
- reduces farming costs
- reduces spoilage
What are the risks of GM Crops?
- risks to health such as allergies
- competes with native plants
What is the example of GM crop?
- Bt corn is a transgenic crop that produces insecticide
- it may be impacting the survival of monarch butterflies
What are clones?
Groups of genetically identical organisms, derived from single original parent cell.
How the human cloning looks like?
Humans produce clones via natural mechanisms. Identical twins are created when fertilized eggs split in two, forming two identical embryos
What are the 4 types of animal cloning?
- binary fission
- budding
- fragmentation
- parthenogenesis
How binary fission contributes to cloning of animals?
Parental organism divides into two clones. occurs in flatworms.
How budding contributes to cloning of animals?
Cells split off from parent, generating smaller clones. Occurs in Hydra.
How fragmentation contributes to cloning of animals?
New organisms grow from separated fragment of parent. Common to starfish.
How parthenogenesis contributes to cloning of animals?
Embryos formed from an unfertilised ova. Occurs in fish, insect, reptile
What is the one technique of plant cloning?
Stem cutting is a separated portion of a plant stem that is used to regrow a new clone via vegetative propagation.
- small pieces of plant can be induced to grow independently
What are two types of artificial cloning?
- embryo cloning
- adult cloning
Embryo cloning
- animals can be cloned from an embryo by separating the embryonic cells into groups
- as embryonic stem cells are pluripotent, each can potentially form a cloned offspring
Adult Cloning
- adults can be cloned via the process of somatic cell nuclear transfer
- the nucleus is removed from an adult body cell and fused with egg cell
- electric shock stimulates division of the egg cell and the growing embryo is implanted into surrogate
What the genetic engineering?
A process in which genes from one organism are transferred to the set of gene of unrelated organism.
Steps of genetic engineering
- identify the gene that codes for the protein of interest for example insulin
- remove gene from a donor
- insert gene into a host
- grow an altered bacteria on a large scale to make the protein product
- isolate protein
Restriction enzymes
They protect against the activity of viruses by cutting up the viral DNA that enters the bacterium. Viral DNA might otherwise take over the host cell.
What is the polymerase chain reaction (PCR)?
Technique that can be used to amplify small quantities of DNA. This makes it possible to study DNA further without the risk of using up the limited sample. Uses primase to make new strands of DNA.
What are the two types of vectors?
- plasmids
- bacteriophages
The function of ligase in genetic engineering
Ligase will repair DNA damaged in replication. Ligase joined sugar phosphate backbones.
Reverse transcriptase
Produces a protein from a particular gene, introns must be removed. DNA can be incorporated into bacterial DNA for protein production.
The use of reverse transcriptase in genetic engineering
- Reverse transcriptase is added to a test tube
- It makes the first DNA strand using the mRNA as a template
- mRNA is degraded by another enzyme
- DNA polymerase synthesizes the second DNA strand
- TH result is cDNA which carries the conding sequence without introns
What is the cDNA?
Complementary DNA that is made from mRNA and it lacks introns. It can be used for protein expression in bacteria.
What is the familial hypercholesterolemia (FH)?
genetic disease in which lipoproteins accumulate in the blood which leads to the coronary heart disease.
Incomplete dominance
Cross where neither of two alleles are completely dominant over each other.
What constitutes a linkage group?
Genes carried on the same chromosome
How sexual reproduction promotes genetic variation?
When a parent forms gamete, only one chromosome from each homologous pair is included at random. An offspring might inherit different combination of chromosomes.
Difference between the behavior of chromosomes in mitosis and meiosis
mitosis:
- one division
- diploid cells
- no crossing over
-homologous chromosomes move to the equator
- no chiasmata
meiosis:
- two divisions
- haploid cells
- crossing over
- homologous chromosomes move to the equator in pairs
- chiasmata
Differences between gene and alleles
Genes are DNA sections that code for specific proteins or functional RNA. Alleles are variations of these genes, leading to diverse traits such as eye color.
One example of inheritance involving multiple alleles
Human blood type- it exists as four possible phenotypes: A, B, AB, O. They are determined by the presence or absense of certain antigenes.
What are unlinked genes?
genes located on different chromosomes or genes located far apart from each other on the same chromosome.
Linkage group
describes a group of genes where loci are on the same chromosomes
Linked genes
They are represented as pairs and will function as a single inheritable unit and will not follow the law of independent assortment.
How linked genes can be separated?
though crossing over
What are dehybrid crosses ?
They determine the allele combinations of offspring for unlinked genes.
- it gives 4 potential gamete combinations
- calculated for first, outside, inside, last
Who was Thomas Morgan?
he determined the concept of gene linkage via breeding experiments involving fruit flies.
What were the results of Thomas Morgan experiment?
- linked genes can be uncoupled via recombination
- linked genes are on the same chromosomes
What are the two types of variations?
- discrete (finite patterns)
- continuous (normal distribution)
What are polygenic traits?
- characteristics controlled by more than two gene loci
- they have a normal distribution pattern
- example human height
What are monogenic traits?
- characteristics controlled by a single gene locus
- they have a finite pattern of expression
- human ABO blood types
Monohybrid cross
cross between two organisms with different variations at one genetic locus of interest.
Multiple alleles
- genes that have more than two alleles
- cross of blood types
A chi-squared test
can be applied to phenotypic ratios to determine if there is a statistically significant likehood that two genes are linked or unlinked.
How to perform the chi-squared test?
- null hypothesis (no association), alternative (association)
- identify observed frequencies
- calculate the ratios through the dihybrid cross
- multiply the ratios by the total of the observed frequencies
- formula: (o-e)squared/e for each observed and expected frequency
- add the numbers together
- calculate the degree of freedom (number of rows - 1) x (number of columns - 1 )
- p < 0.05
determine significance
What is the genetic drift?
changes the composition of a gene pool due to random events within the population
- higher drift in small populations (faster change)
- lower drift in larger populations (greater stability)
What are population bottlenecks?
occur when an event reduces the population size by the order of magnitude
- surviving population has less genetic variability which leads to a drift
What is the founder effect?
- founder effect describes the establishment of a new population by a friction of a larger existing population
- less genetic variability
Two categories of reproductive isolation
- pre-zygotic barriers
- post-zygotic barriers
Reproductive isolation
- barriers prevent two populations from interbreeding
- leads to speciation
What is the pre-zygotic barrier?
no offspring is produced
What is the post-zygotic barrier?
offspring are no viable or infertile
