Topic 4 - Genetics Flashcards
What are eukaryotic chromosomes made of?
DNA and proteins
What is a gene?
A heritable factor that controls a specific characteristic
What is an allele?
One specific form of a gene, differing from other alleles by one or a few bases only and occupying the same gene locus as other alleles of the gene
What is a genome?
The whole of the genetic information of an organism
What is gene mutation?
A change to the base sequence of a gene
What is the consequence of a base substitution mutation in relation to the processes of transcription and translation? Use sickle-cell anemia as an example
- The base sequence that codes for a polypeptide forming part of haemoglobin is altered due to mutation, CTC → CAC
- CAC is transcripted into GUG instead of GAG
- GAG is translated to the corresponding amino acid valine instead of glutamic acid
- Blood cells become sickle shaped and carry oxygen less efficiently but give resistance to malaria
What is meiosis?
A reduction division of a diploid nucleus to form haploid nuclei
What are homologous chromosomes?
Homologous chromosomes have the same genes as each other, in the same sequence, but not necessarily the same alleles of those genes
What are the stages of meiosis?
Two divisions:
- Prophase I
- Metaphase I
- Anaphase I
- Telophase I
- Prophase II
- Metaphase II
- Anaphase II
- Telophase II
What happens in meiotic prophase I?
- Chromosomes become visible
- Homologous chromosomes pair up
- Crossing over occurs
- Spindle microtubules grow from each pole
What happens in meiotic metaphase I?
- Bivalents line up at the equator
- Nuclear membrane disintegrates
- Spindle microtubules attach to different chromosomes in each pair
What happens in meiotic anaphase I?
- Homologous chromosomes are pulled to opposite poles → chromosome number halves
(Each chromosome still consists of two chromatids)
What happens in meiotic telophase I?
- Meiotic spindles and microtubules disintegrate
- Chromosomes uncoil and new nuclear membranes form
- At the end, cytokinesis occurs
At this stage cells are haploid but each chromosome ahs its sister chromatid
What happens in meiotic prophase II?
- DNA condenses and new meiotic spindle appears
- New spindle microtubules start to grow to the equator
What happens in meiotic metaphase II?
- Nuclear membranes disintegrate
- Random orientation of chromosomes at the equator
- Microtubules attract each sister chromatid at centromeres
What happens in meiotic anaphase II?
- Centromeres split and each chromatid becomes a chromosome
- Microtubules pull chromosomes to opposite poles
- Due to random orientation, chromosomes can be pulled to either side
What happens in meiotic telophase II?
- Chromosomes unwind
- Nuclear membranes form
- Cytokinesis occurs → four haploid cells are formed
- Each nucleus has half as many chromosomes as the nucleus of the parent cell
What can lead to changes in chromosome number?
Non-disjunction (non-separation of chromosomes)
What is done in karyotyping?
Chromosomes are arranged in pairs according to their size and structure
How can chromosomes be collected from cells for karyotyping?
- Amniocentesis
- A sample of amniotic fluid is removed from the amniotic sac around the fetus - Chorionic villus sampling
- Cells are removed from fetal tissues in the placenta called chorionic villi
- Collected cells are incubated with chemicals that stimulate them to divide by mitosis
- Another chemical is used to stop mitosis in metaphase (chromosomes are most easily visible in metaphase)
- Cells are burst and chromosomes spread out
- A photograph is taken of all chromosomes
- Chromosomes are arranged into pairs according to their size and structure
What is a genotype?
The alleles of an organism
What is a phenotype?
The characteristics of an organism
What is a dominant allele?
An allele that has the same effect on the phenotype whether it is present in the homozygous or heterozygous state
What is a recessive allele?
An allele that only has an effect on the phenotype when present in the homozygous state
What are codominant alleles?
Pairs of alleles that both affect the phenotype when present in a heterozygote
What is locus?
The particular position on homologous chrosomes of a gene
What does homozygous mean?
Having two identical alleles of a gene
What does heterozygous mean?
Having two different alleles of a gene
What is a carrier?
An individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele
What is a test cross?
A way to test a suspected heterozygote by crossing it with a known homozygous recessive
Do some genes have more than two alleles?
Yes
How is blood type determined?
- There are three alleles, IA, IB, i
- IA + IA = Group A
- IB + IB = Group B
- IA + IB = Group AB
- i + i = Group O
How is the sex of an individual determined?
- XX → female
- XY → male
lol
Why are some genes present on the X chromosome and absent from the Y chromosome?
Because the X chromosome is larger and there is more space for more genes than on the Y chromosome
What is sex linkage?
The association of a characteristic with gender, because the gene controlling the characteristic is located on a sex chromosome.
How is colour blindness and hemophilia inherited?
- Produced by recessive a sex-linked allele on the X chromosome
- The Y chromosome does not carry either allele of the gene
- If a male inherits the recessive X chromosome, he shows the disease
- If a female inherits one recessive X chromosome, she is not affected
Females can be homozygous or heterozygous with respect to sex-linked genes
What is the genotype of a female carrier?
Heterozygous recessive
How is polymerase chain reaction (PCR) used to copy and amplify small quantities of DNA?
- DNA is copied again and again to produce many copies of the original molecules
- Useful when very small quantities of DNA are found in a sample and larger amounts are needed for analysis
- DNA from very small samples of semen, blood, or other tissue can be amplified
- PCR is carried out at high temperatures using a DNA polymerase enzyme from a bacterium
What happens to fragments of DNA in electrophoresis?
Fragments move in an electric field and are separated according to their size
What is gel electrophoresis used for?
DNA profiling
Outline the function of gel electrophoresis?
- A method of separating mixtures of proteins
- Mixture is placed on a thin sheet of gel
- An electric field is applied
- Depending on the charge of the particle, they move towards one of the electrodes
- The rate of movement depends on the size and charge of the molecules
- Small and highly charged molecules move faster than larger or less charged ones
How is DNA profiling used to determine paternity and in other investigations?
- Length of satellite DNA varies greatly between individuals
- By gel electrophoresis these fragments are separated according to their charge and size
- A pattern of bands forms on the gel
- The patterns are very unique
- Highly similar patterns show paternity and stuff
What are three outcomes of the sequencing of the complete human genome?
- Easier to study how genes influence human development
- Easier identification of genetic diseases
- Allows the production of new drugs based on DNA base sequences
(gives new insights into the origins, evolution, and migrations of humans)
What happens to the amino acid sequence of polypeptides when genes are transferred between species?
It remains unchanged because the genetic code is universal
Outline the stages of genetic modification (use the production of insulin)
- mRNA coding for insulin is extracted from human pancreas cells
- DNA copies of the mRNA are made using reverse transcriptase
- Sticky ends are added to both ends of the strands by adding extra G nucleotides
- Plasmids are cut open at specific base sequences using restriction enzymes
- Sticky ends are made by adding extra C nucleotides
- The insulin gene and the plasmid are mixed. They link by complementary base pairing between the sticky ends
- DNA ligase seals up the nicks in the DNA by making sugar-phosphate bonds
- The plasmid with the human insulin gene is called a recombinant plasmid
- A host cell is chosen to receive the cell, in this case E. coli
- The recombinant plasmids are mixed with the host cells. The host cells absorb them
- The genetically modified E. coli are cultured in a fermenter
- The bacteria start to produce human insulin, which is extracted, purified, and used
What are two examples of genetically modified crops?
- Salt tolerance in tomato plants
- Tomatoes were made more tolerant to higher levels of salt in the soil, which made it easier to grow in certain regions of high salinity - Beta carotene in rice
- The body uses beta carotene to form vitamin A
- Rice was made to produce beta carotene. Aim was that the people who eat this rice won’t have deficiencies in vitamin A
What are the potential benefits and harmful effects of genetic modification of Bt maize?
Bt maize is modified to toxicate corn borer insects
Benefits
- Less pest damage and therefore higher crop yields
- Less land needed for crops
- Less use of insecticide sprays, which are expensive and harmful
Harmful effects
- Humans or farm animals that eat the genetically modified maize might be harmed by the bacterial DNA or the toxin
- Insects that are not pests could be killed
- Populations of wild plants might be changed (survival of the fittest)
What is a clone?
A group of genetically identical organisms or a group of genetically identical cells derived from a single parent cell
Outline a technique for cloning using differentiated animal cells
- Udder cells are taken from a a donor sheep
- Unfertilised egg cells are taken from another sheep
- The nucleus is removed from each egg cell
- The nucleiless egg cells are fused with the donor cells using a pulse of electricity
- The fused cells develop like zygotes and become embryos
- The embryos are implanted into another sheep who becomes the surrogate mother
- da baby come out
What are the arguments for and against therapeutic cloning in humans
For:
- It can save lives and reduce suffering
- Cells can be removed from embryos that would have died anyway
- Cells are removed at a stage when embryos have no nerve cells and cannot feel pain
Against:
- Every human embryo is a potential human being
- More embryos may be produced than are needed and the extra ones are killed
- There is a danger of embryonic stem cells developing into tumour cells
