B13 Flashcards
Reproduction
What is asexual reproduction and how does it happen ?
- only one parent needed
- parent produces genetic clones of itself via mitosis
- common in microorganisms as well as a select few larger organisms like some plants and animals
What is sexual reproduction and how does it happen ?
- two parents needed
- parents produce gamete cells via meiosis, which then meet and join to form a zygote
- common in larger organisms and some microorganisms like malaria protists
- offspring are NOT clones of the parent or genetically identical
What are the advantages and disadvantages of asexual vs. sexual reproduction ?
asexual
- advantages:
[] no energy expenditure to find mates needed
[] no risk of not having genetic material needed to reproduce
[] more efficient
[] good for organisms that may have trouble finding a mate of the same species
- disadvantages:
[] no variation in the offspring unless mutations occur; means population very easily wiped out if a change in the environment occurs
sexual
- advantages:
[] VARIATION; offspring receives genetic information from both maternal and paternal parents and thus offers useful alleles from both individuals that help to survive; more variation = more stability of a population if the environment changes
- disadvantages:
[] risky, as depends on finding a mate, then the two gametes meeting and fusing
[] takes energy to find a mate
Describe the stages in meiosis
- parent cell doubles its original chromosome count
- parent cell divides into two
- the two divide again
- four unidentical daughter cells are produced, each with one half set of chromosomes
Describe the general structure of a fungus
- protruding body above ground (mushroom)
[] filled with spores - mycelium (the fungus below ground)
- hyphae (mass of thin threads (usually underground))
Describe how fungi reproduce asexually
- produce genetically identical spores via mitosis, which get stored in the mushroom
- spores released by the mushroom
- spores spread then germinate in soil/on tree bark etc.
Describe when and how fungi reproduce sexually
- when conditions change drastically in order to increase chance of survival through introducing genetic variation
[] drier
[] colder
[] hotter - process:
[] hyphae from 2 different fungi meet then join
[] zygote formed when the nuclei in the hyphae fuse (has two sets of chromosomes)
[] zygote goes through meiosis to form spores with 1 set of chromosomes
[] spores are then released and germinate to form a new fungus
What is the name of the protist that causes malaria ?
plasmodium
Describe how protists reproduce
- plasmodium protists in human blood are dormant and reproduce asexually
- mosquito bites human and the blood taken in is stored in the mosquito’s stomach
- blood cools in the stomach
[] this temperature drop triggers sexual reproduction of the protists - protists mature into zygotes and sexually reproduce
- zygotes formed travel to the outside of the mosquito’s stomach and settle as cysts
- cysts burst and the new protists travel to the mosquito’s salivary gland
- protists travel into new human host via the mosquito’s saliva when bitten
- cycle repeats
Describe how strawberry and spider plants reproduce asexually
- produce runners (vines (specialised stems))
- spread far from the parent plant and start growing a new plant in a different place
Describe how daffodils reproduce asexually
Make bulbs that new plant can grow from even if old dies
What is the genome of an organism ?
The entire genetic material of an organism (included mitochondrial DNA, which is only inherited from the mother)
What is DNA ?
- deoxy-ribonucleic acid
- polymer made of nucleotide monomers that form two strands and curl into a double-helix shape
Why is genome sequencing (of humans and other organisms) important ?
other organisms:
- shows relationships between organisms genetically
- new revelations in similarities and differences between the genetic material of organisms informs classification systems
- sequencing viral and bacterial genomes can help with finding cures for diseases as well as pathogen identification in an infected patient, which can then inform treatment
humans:
- further study and understanding of genetic diseases like cystic fibrosis and polydactyly
- understanding genetic risk factors for diseases like diabetes, cancer etc.
[] helps to identify individuals genetically at risk of these diseases earlier on and to prescribe precautions to reduce risk of developing that particular disease
- helps to study and understand human evolution and history, as well as migration patterns over time
What are the base pairs in DNA ?
A + T
G + C
What is a nucleotide made of ?
- phosphate group
- sugar
- base
How are base sequences read from DNA strands ?
horizontally (not via the pairs (not ATGC etc.))
- DNA strands are complementary to one another
What is a protein ?
- long chain of amino acids folded over itself
- polypeptide/polymer
How many amino acids are there in humans ?
20
How is the function of a protein determined ?
- its shape
[] shape of protein controlled by the order of its amino acids
[] order of amino acids in turn controlled by order of bases in DNA
Describe the stages in protein synthesis
transcription
- takes place in the nucleus
- base sequence of a gene in the DNA is copied onto a complementary template molecule
[] called mRNA (messenger ribonucleic acid)
[] mRNA is SINGLE STRANDED, not double like DNA
- mRNA leaves nucleus and passes into cytoplasm
translation
- takes place in the cytoplasm
- mRNA molecule attaches to a ribosome
- amino acids brought to the ribosome on carrier molecules called tRNA/transfer RNA (diffuse into the cell)
- ribosome reads the triplets of bases encoded on the mRNA strand and arranges amino acids accordingly
[] each base triplet codes for one amino acid
- complete protein strand folds into the proper shape to activate it
Name 6 different types of protein
- enzymes
- hormones
- structural proteins (collagen etc.)
- muscle fibres
- haemoglobin
- fibrinogen that helps clotting in the blood
What is a triplet codon ?
- group of 3 bases that code for ONE amino acid
[] code is non-overlapping (bases in the genetic sequence are only read once)
[] some amino acids can be coded for in different ways (eg. lysine may be AAA or AAG, and leucine may be CTT, CTA etc.)
[] coding for amino acids is UNIVERSAL and is the same in every organism
What are the main causes of mutations in DNA ?
- infectious agents like viruses (HPV is a common one)
[] insert their own genetic material into human cell nuclei - ionising radiation
[] displaces or damages base pairs/genes/gene order in the DNA - chemical mutagens like carcinogens
[] displaces or damages base pairs/genes/gene order in the DNA - random mutation during cell division
What is a mutation ?
Random change in the sequence of bases in DNA
- can be inherited or caused
- may be beneficial or have a negative effect on the phenotype of the organism; oftentimes has no effect however
Describe the way that mutations are inherited in both humans and prokaryotes
prokaryotes
- reproduction via binary fission means that all offspring are clones
[] will ALWAYS inherit ALL mutations in the DNA loop of the parent prokaryote
[] genetic mutations in plasmids may sometimes be passed on or shared between prokaryotes
humans
- mutations in gametes have a chance of being passed to offspring (not always)
- mutations in mitotically dividing cell DNA will always be passed on
[] dangerous as body cells may become cancerous in this way
How are cancer cells formed ?
Genes regulating cell cycle mutate, allowing the cells to divide uncontrollably and rapidly
What are the 3 main types of mutations ?
- substitutions
[] one base substituted with another (eg. AGT becomes TGT)
[] sometimes changes which amino acid is coded for, which affects the protein made or how well it functions, but not always happens - deletions
[] a random base from the sequence is deleted
[] all bases shifted up one, meaning that amino acids coded for are different and thus the protein is different or doesn’t function - insertions
[] a random base is inserted into the sequence
[] all bases shifted down one, meaning that amino acids coded for are different and thus the protein is different or doesn’t function
What happens if a mutation occurs in non-coding DNA ?
- non-coding DNA often controls protein or gene expression via switching genes off/on
- mutations can affect how much a protein is expressed (produced by the body)
[] this is an example of how diabetes comes about
In heterozygotes, which allele is expressed ?
dominant allele
How can recessive alleles be expressed ?
when two are paired together as a homozygote
Draw a punnet square for the offspring of a mouse with brown fur (genotype BB) and a mouse with black fur (genotype bb)
All offspring should have the heterozygotic genotype Bb (brown fur, as B is the dominant allele)
Draw a punnet square for the offspring of a mouse with brown fur (genotype Bb) and a mouse with black fur (genotype bb)
- 2 heterozygote offspring (Bb) with brown fur
- 2 homozygote offspring (bb) with black fur
Draw a punnet square for the offspring of a mouse with brown fur (genotype Bb) and another mouse with brown fur (genotype Bb)
- 1 homozygote offspring (BB) with brown fur
- 2 heterozygote offspring (Bb) with brown fur)
- 1 homozygote offspring (bb) with black fur
Why don’t the theoretical ratios of offspring with a certain phenotype get reflected accurately in real life without a very large sample ?
- inheritance is RANDOM
[] probabilities of the different phenotypes in a theoretical ratio are very different irl - eg. the chance of offspring being a dominant-allele-homozygote may be 80%, whilst all other phenotypes are 20% combined
[] genetic information in gametes is unique and randomised during meiosis - too small of a sample
How many X and Y chromosomes are present in human males vs. females ?
male = XY
female = XX
What is polydactyly ?
- genetic disorder that is inherited by a DOMINANT allele
[] even heterozygous people have the disorder expressed - results in people having extra fingers or toes
[] can be removed or kept - doesn’t have that big of an effect on daily life
What is cystic fibrosis and how is it treated ?
- genetic disorder caused by a RECESSIVE allele
[] heterozygous people with an allele for cystic fibrosis don’t express the disorder, but are called carriers as they can pass the disorder to their offspring if their partner also has an allele for cystic fibrosis - disorder of the cell membranes that prevents diffusion of certain substances in/out of the cell
[] mucus secreted by cells becomes very thick and sticky, and often clogs up organs (especially the lungs and pancreas), affecting their function - many with cystic fibrosis are infertile
- treated with physiotherapy, antibiotics and replacement enzymes if the pancreas is clogged
[] no cure yet, though scientists hope that genetic engineering will be able to cure the disorder as well as genetic disorders generally
What is amniocentesis ?
- method of genetic screening of embryos carried out at 15-16 weeks of pregnancy
- fluid from the amniotic sac containing foetal cells is retrieved using a needle
- these foetal cells can be genetically screened for disorders
What is chorionic villus sampling (CVS) ?
- method of genetic screening of embryos, carried out at 10-12 weeks of pregnancy
- two methods: transabdominal (cells retrieved using a needle through the abdomen), and transcervical (cells retrieved using a catheter through the cervix and into the uterus)
- both methods involve taking a sample of foetal cells from the developing placenta to be genetically screened for disorders
Where can cells be taken from to be genetically tested for disorders during embryo screening ?
- embryo external to the patient (eg. IVF embryos)
- placenta
- amniotic fluid
How is genetic screening carried out generally ?
DNA isolated from the cell(s)’ nucleus and tested for specific disorders
Give the advantages and disadvantages of embryo screening
disadvantages:
- screening increases the risk of miscarriage, which is emotionally and physically stressful for the parent(s)
- can sometimes give a false positive or negative
[] healthy embryos thus may be discarded or aborted mistakenly, or disordered embryos may be allowed to develop and be born
- if the embryo tests positive for a disorder, couples have to make the decision to either abort or continue with the pregnancy; emotionally stressful
- screening is expensive
[] at the moment, is only offered to those with a family history of genetic disorders or older parents whose children are more at risk of genetic disorders
- ethical concerns about eugenics or “designer” babies
advantages:
- people with genetic disorders are more expensive for the government or parents long-term as treatment is often intensive or highly specialised
- allows parents who don’t want to terminate the pregnancy if the embryo tests positive for disorder to make preparations and accommodations for the child in advance
- if the parents cannot afford to raise a child with a genetic disorder, allows them to abort the pregnancy or not implant that embryo and try again for a healthy baby
