Module 5: Heredity Flashcards
What is reproduction?
Production of offspring. Can be either sexual or asexual.
What is sexual reproduction?
Involves a male and female parent from the same species.
Each parent provides half of the genetic material for their offspring, in the form of sex cells. In fertilisation, these two sex cells fuse to form a diploid cell that will develop into a new organism.
What is asexual reproduction?
Involves one parent, thus offspring are genetically identical.
Pros (2) and cons (2) of external fertilisation, like spawning?
Pros
- Doesn’t require mates to meet
- Lots of offspring can be produced
Cons
- Low change of survival due to being prone to environmental factors
- Waste of resources
List methods of asexual reproduction in plants
Runners: side branches with clumps of leaves called plantlets, that run along the ground and dig roots into the ground to establish more plants, like strawberries.
Bulbs: Bulbs grow underneath the plant underground, which grow buds which develop into new plants, like the daffodil.
Budding: Growths develop on the sides of the parent and grow before detaching, creating a new organism, like cacti.
How does sexual reproduction occur in plants?
Pollination, insects birds or wind transport pollen, which is produced in the stamen, to flowers, which contain carpels containing ovules, female plant sex cells. The flowers will develop fruits, and the ovules turn into seeds.
How do fungi reproduce?
Depends on environmental conditions. Good environmental conditions will have them reproduce asexually, through budding, releasing spores. In bad conditions, spores can fuse to form a new fungus with characteristics from both parents, reproducing sexually.
How do bacteria reproduce?
Bacteria are prokaryotic and unicellular. Most reproduce asexually through binary fission, where it copies its DNA, grows to twice its original size, before dividing into two separate organisms.
How do protists reproduce?
Protists are eukaryotic, unicellular organisms who mostly reproduce through binary fission, or budding.
Pros (2) and Cons (2) of Internal fertilisation:
- Relatively much higher survival rate
- Does not waste resources
- Reproductive rate is low
- Mates must physically meet
Pros (1) and cons (2) of sexual reproduction with example
Pros
- Increases genetic diversity, thus able to adapt to environmental changes
Cons
- Time, energy and resourcefully expensive
- Often have a slower reproductive rate
The Galapagos finches, found in South America. Initially there was an abundance of food sources, so finches all had different beak types as none was particularly beneficial, high genetic diversity. Over time, islands containing the finces broke off to form islands, and the food sources became more restricted, creating a selection pressure that made certain beak types more beneficial than others.
Pros and cons of asexual reproduction with example.
More resource, time and energy efficient relative to sexual reproduction.
Rapid reproductive rate
Results in populations with low genetic diversity, making population more vulnerable to selection pressures.
An example is the Irish Potato Famine, where during the mid-1800s, potatoes were the sole food source for a third of the population. As all the potatoes were grown through vegetative propagation, genetic diversity was very low, resulting in the devastating impact that a new fungal disease called Phytophthora infestans had on the potatoes, wiping out all of the plants and causing widespread famine.
Steps of Fertilisation?
Ovary releases egg
Egg travels to fallopian tube
Semen travels to fallopian tube and fuses with an egg cell
Zygote forms a strong outer membrane to prevent more sperm from entering
What happens during implantation?
Fertilised egg (zygote) attaches and envelops itself within the lining of the uterus.
Develops into an embryo
What are the important hormones of reproduction?
Oestrogen and Progesterone
What is oestrogen?
Hormone which stimulates ovulation, aids blood flow to the embyro, aids organ development and stimulates the production of progesterone.
What is the placenta?
An organ that forms in the uterus during pregnancy that provides oxygen and nutrients, as well as removing waste.
What is the aminiotic sac?
Sac containing the embryo, that contains fluid that maintains optimal temperature and provides cushioning.
What are hormones?
The body’s chemical messengers, created by endocrine glands and travel through the bloodstream to coordinate organ function and various body processes.
What is progesterone?
Progesterone stimulates the thickening of the endometrium to provide a healthy environment for embryo development, and strengthens pelvic floor muscles to support labour. Progesterone is produced by the corpus luteum throughout the first 8-10 weeks of pregnancy before the placenta develops. The placenta causes progesterone levels to gradually rise, reaching a peak in the third trimester, before a drastic drop disables the suppression of oxytocin, generating contractions in preparation for lavour.
How does asexual reproduction occur in plants?
Through budding, vegetative propagation or fragmentation.
Artificial insemination:
A type of selective breeding, where sperm is taken from a male animal with specific desirable traits, and inserted into the female’s reproductive tract.
Artificial pollination:
A type of selective breeding where pollen is taken from one flower and deposited into another.
Selective breeding:
Purposeful manipulation of mating to create organims with desirable characteristics
Cloning:
a genetically identical copy of an organism is produced
Advantages of manipulating agriculture
- Increased sales
- Improved food quality
- Increased resistance to pests and disease
- Decreased medicine and pesticide use as organims can be manipulated to be resistant to pests and disease.
Downsides of manipulating agriculture
- Reduced biodiversity
- increased likelihood for genetic disorders
- Leaves organisms more susceptible to changes in environment
What is DNA structure?
Eukaryote:
- Double-helix structure, with DNA wrapped around histone proteins
- Linear chromosomes
- Found inside nucleus
Prokaryote:
- Less DNA
- Unbound DNA
- Singular, circular chromosome, no nucleus
What is a nucleuotide and its components?
Builiding blocks of DNA, consisting of a phosphate group, a deoxyribose sugar and a nitrogenous base.
Structure and purpose of RNA?
RNA is single stranded, consiting of nucleotides, which contain a ribose sugar, phosphate and nitrogenous base instead of Thymine, they have Uracil. Used in protein synthesis.
What is a karyotype?
An image displaying a complete set a person’s 46 chromosomes. They are usually taken during Metaphase.
How are chromosomes counted?
Counted by the number of centromeres present.
What are chromosomes made up of?
Chromatin, which is 40% DNA highly condensed and wrapped around 60% histone proteins.
What is a chromosome?
Intensely packed units of DNA, organised for easy transporation and configuration during cell division.
Prokaryote vs Eukaryote?
What are the steps of DNA replication?
Unravelling DNA
Building a new DNA strand
Forming the DNA backbone
What is a telomere?
End of a chromosome that protects fraying. As individuals age, the telomeres become slightly shorter.
How is DNA replicated?
The enzyme DNA helicase unzips by breaking hydrogen bonds, splitting the double helix into two strands. As it unravels, SSB proteins and topo-isomerase keeps the DNA from supercoiling and binding back together.
While it is unraveling, the enzyme DNA primase lays RNA primers on both strands, where DNA polymerase will build the new strands of DNA.
What is semi-conservative?
During DNA replication, each copied strand is directly derived from a strand from the parent molecule, reducing the chance of copying a strand incorrectly
What is the leading and lagging strand?
As DNA polymerase builds in the 5’ to 3’ direction, there will be a continuous strand, called the leading strand, building in the direction of the helicase, and a lagging strand, that needs to be repeatedly primed and built as the helicase unravels the DNA. Ligase is needed to seal the Okazaki fragments together.
What is the direction of DNA?
5 prime to 3 prime, each strand is antiparallel to each other.
What are the steps of meiosis I?
Interphase
Prophase I - Chromatin condenses into chromosomes. Next, crossing over occurs, where homologous chromosomes pair up through the process of synapsis, and lie parallel to each other. Next, the chromatids will overlap each other at different set points, called chiasmata. The segments of maternal and paternal genetic info are exchanged at the chiasmata, and the homologous pairs separate, forming recombinant chromosomes. Lastly, nuclear membrane dissolves and centrioles release spindle fibres.
Metaphase I - Pairs of recombinant chromosomes line up on the equatorial plane, while centrioles release spindle fibres on each polar end of the, attaching to the kinetochores.
Anaphase I - The homologous pairs are pulled apart, not split apart, with one random chromosome from each pair being moved to each pole.
Telophase I - Chromosomes reach the pole, the nuclear membrane forms and cytokinesis splits the cytoplasm.
We have half the number of chromosomes in each cell, so Meiosis I is known as a reduction division.
What is mitosis and its importance?
The process in which somatic cells divide to create two genetically identical daughter cells. These new cells are required for growth and repair.
What are the phases of Mitosis?
IPMAT
Interphase - Everything that happens outside of mitosis
Prophase - DNA condenses from chromatin to form chromosomes, as the nuclear membrane begins to break down.
Metaphase - Nuclear membrane dissolves, as chromosomes align on the equatorial plane of the cell. Centrosomes (with two centrioles) line up at the polar ends of the cell and release spindle fibres, which attach to the kinetochores of the chromosomes.
Anaphase - Spindle fibres separate the chromatids, which are pulled to the poles of the cell.
Telophase and Cytokinesis - Nuclear membrane forms around each pole containing the chromosomes, and the cell is split into two through cytokinesis.
What is meiosis?
When a parent germ cell (spermatocyte or oocyte) divides twice to produce 4 genetically non-identical daughter cells (gametes).
What is the importance of crossing over?
Crossing over is essential as it contributes to genetic variety of offspring. If crossing over did not occur, the resulting gametes would inherit chromosomes with the same allele combination of the parents.
What is independent assortment and random segregation?
Independent assortment is during Metaphase I, where the homologous pairs of chromosomes line up in a random order.
Random segregation happens during Anaphase I and II, where as a result of independent assortment, the sets of chromosomes segregated to each daughter cell is random.
What are the source of genetic variation in sexual reproduction?
Crossing over, Independent assortment, Random segregation and fertilisation.
During fertilisation, a parental gamete and a maternal gamete fuse to form a zygote. Since every parent produces a large amount of unique gametes as a result of meiosis, the number potential combinations of maternal and paternal genetic information is immense.
What are the steps of Meiosis II?
Prophase II - Chromatin condenses into chromosomes, and the nuclear membrane breaks down.
Metaphase II - Chromosomes align on the equatorial plane of the cell. Centrioles in the centrosomes go to each pole of the cell and release spindle fibres which attach to the kinetochores of the chromosomes.
Anaphase II - Spindle fibres split the chromosomes into two chromatids, and pull the chromatids to each pole.
Telophase II - With 23 chromosomes on each end of the pole, the nuclear membrane forms and the chromosomes unravel and cytokinesis splits the cytoplasm.
Advantages and disadvantages of models?
Models are useful in visualising processes that are difficult to understand or objects that are difficult to see.
They are also cheaper and easier to use, relative to actually observing the process/object.
To communicate ideas, models must be made less complex, losing accuracy of them model.
E.g. Ball and stick models represent atoms, but don’t include everything scientists know about the structure of atoms.
Models approximate, as they cannot show the true detail of the things they represent.
E.g. Solar system models approximate distance between planets, not to scale.
What is the cell cycle?
The processes in which cells perform cell division. It’s a 4 step process:
1. Gap 1 (G1)
Cell increases in size, and organelles are duplicated.
2. Synthesis (S)
DNA is replicated.
3. Gap 2 (G2)
Cell, organelles and proteins grows more in preparation for cell division.
4. Mitosis (M)
G1, S and G2 makes up what we call Interphase.
There is also a G0 phase, also known as the resting phase, when the cell is neither dividing nor preparing to divide. This may occur because it it not necessary for the cells to divide, or due to a lack of the nutrients that are necessary for the cells to divide.
How does genotype and environment affect phenotype? with examples
When an individual’s genotype is expressed through protein synthesis, the phenotype is affected, for example blue eyes.
The environment, such as temperature and nutrient availability can also alter the expression of phenotype. For example, individuals growing up in places of lower socio-economic status may have their height stunted due to lack of access to food and nutrients.
What is a protein?
Complex molecules made up of amino acids. They are the only biological molecules that contain nitrogen. All proteins make up the ‘proteome’ of a cell.
What are codons?
A specific set of three nitrogen bases in DNA which each code for a different amino acid. However, as there are 64 different types of amino acids, different codons can code for the same amino acid. This quality of our genetic code is referred to as ‘degenerate’. Some codons also serve as ‘stop’ codons, which indicates the end of the gene, stopping RNA polymerase from further unzipping the DNA molecule.
What are the stages of protein synthesis?
Transcription - Occurs in the nucleus, where DNA is ‘transcribed’, an mRNA copy being made using DNA as a template. RNA polymerase attached to DNA at the desired gene and separates the strands, just for a single gene.
Free floating nucleotides will be paired by RNA polymerase, forming H-bonds with their complementary bases, forming a strand of RNA, while the DNA strands rejoin behind the process so they aren’t left exposed, until a terminator sequence is reached. The process has been completed for prokaryotes. In eukaryotes, introns are then spliced out of the strand, as they do not code for proteins, and exons are stuck together to form the final mRNA strand.
Translation:
mRNA will break out of the nucleus, and attach to a ribosome to begin translation. Free floating tRNA molecules with specific anti-codon sequences will pair up with its complementary codon on the mRNA molecule. Every tRNA molecule has a specific anticodon and amino acid, so specific codons will only code for specific amino acids. As more tRNA molecules bond with the mRNA, the ribosome catalyses the formation of a peptide bond between the amino acids attached to the tRNA molecules, and the tRNA molecule is released. This process continues until a stop codon is reached, where only a single tRNA molecule remains, signalling for the release of the polypeptide chain.
GIve an example of structural protein.
Structural proteins provide cells and tissues with their structural properties, such as collagen, which provides skin and bone with its flexibility.
What are multiple alleles?
When there are more than two alleles for one gene.
What are autosomes vs sex chromosomes
Humans have 22 pairs of autosomes, which code for non-sexual characteristics, while sex chromosomes code for sexual characteristics (but not solely). Males have 2 dissimilar chromosomes (XY) while females have 2 similar (XX).
Codominance vs incomplete dominance
Codominance: Where two different dominant alleles can both be expressed in the phenotype. The DNA has NOT mixed, its just some cells are expressing one allele, while some are expressing the other. Example, roan cattle, or human blood type.
Incomplete dominance: Dominant allele is only partially expressed, so a bit of the recessive allele is expressed too. The heterozygous phenotype is an intermediate between the homozygous phenotypes. Example: Snapdragons, red dominant and white recessive makes pink.
Examples of autosomal diseases
Huntington’s disease, caused by autosomal dominant inheritance. Causes breakdown of brain nerve cells
Phenylketonuria: Autosomal recessive inheritance. Causes people to not be able to process the phenylalanine amino acid, which is toxic and leads to brain damage.
What is the hardy-weinberg equation?
Allows us to calculate the number of organims with a certain genotype and phenotype if we know allele frequencies.
p^2 (Homozygous) +2pq (heterozygous)+ q^2 (homozygous) = 1
Where p is frequency of dominant alllele (the decimal)
q is the frequency of the recessive allele.
Why are men more susceptible to sex-linked disease?
As men only have one copy of the X and Y chromosome, they must express all of their chromosome alleles, as recessive traits can’t be masked by a dominant X or Y allele. Thus, X-linked recessive traits will affect men more than woman, as there is a higher chance of men inheriting one faulty X chromosome than women inheriting two fault X chromosomes.
Examples of Sex-linked diseases
Red-green colour blindness - X linked recessive
Haemophilia - X linked recessive - causes blood to not clot properly, making it hard to control bleeding.
Vitamin D rickets disorder - X linked dominant which causes bone disorders
What are the assumptions of the Hardy-Weinberg model?
Assumes that no evolutionary processes are taking place.
Doesn’t consider natural selection
Assumed all individuals had the same chance of breeding.
Hardy Weinberg assumed the absence of gene flow.
What is GWAS?
Genome-Wide Association Studies, in which DNA is taken from a person, bases that are known to be highly variable are searched for, called single nucleotide polymorphisms (SNPS). By comparing SNPs, we can figure out which SNPs are associated with disorder.
What is population dynamics?
The study of genetic variation within or between populations and how it can be improved.
What are the limitations of Genome Wide Association Studies?
Population Stratification - When disorders are more common in people of a particular ethnicity. This is because people of shared ethnicity are more likely to share certain SNPs, which skews research as these SNPs are not necessarily linked with disease. Thus, ancestry must be controlled when taking sampling for GWAS.
What is a cladogram?
Graph that shows how long ago different species’ shared a common ancestor.
What is PCR?
Polymerase Chain Reaction is a technique used to amplify DNA, (making lots of copies of a specific region of DNA).
Steps of Polymerase Chain Reaction?
Mixture of the DNA sample template, free nucleotides, heat-stable DNA polymerase, primers and buffer are placed inside of a thermal cycler so it can be heated or cooled in a controlled method.
The mixture is first heated to 95 degrees in denaturation, to denature the DNA and split into two strands.
Next, the reaction is cooled to 55 degrees in the process of annealing, allowing primers to anneal onto the template DNA.
Lastly, in extension, the reaction is heated to 72 degrees and DNA Polymerase synthesises new DNA on the template. The process is then repeated to create more copies of DNA.
What is Gel electrophoresis?
As DNA molecules have a negative charge due to their phosphate groups, gel electrophoresis uses this aspect to determine the size of DNA fragments, as it is attracted by positive electrodes. Through determining the size, DNA profiles can be constructed.
What are the steps of Gel electrophoresis?
Liquid agarose gel is poured into a mold, and a well comb is placed inside before it sets, creating a row of holes on one end.
Gel is placed inside a box with a positive electrode on one end, and a negative electrode on the end where the wells are.
Next, the gel is immersed in a buffer that can conduct electricity.
DNA samples are then transferred into each well with dye that stains the DNA fragments, as well as a DNA ladder, which is made up of known DNA fragments with known sizes.
Next, a current is run through the gel, and the DNA molecule are attracted to the positive electrode. As the gel is a matrix, having pores, smaller DNA fragments are able to fit through the pores more easily.
What is DNA sequencing?
Process of determining the base sequence of a DNA sample. The whole idea of the Sanger sequencing reaction is that there are 4 ‘special’ PCRs performed, with each test tube containing a chain terminating nucleotide. All PCRs are then put into gel electrophoresis.
What is DNA profiling?
Analysing genetic markers for identification, which are normally 2-5 bases long. These are:
- Short tandem repeats (STRs)
- Single nucleotide polymorphisms (SNPs)
How does DNA profiling work?
Primers bind on each side of an STR, and these STRs are amplified using PCR. STRs are all the same repeating unit, and occur in the same place in the genome, but they vary in length. As your genome comes half from each of your parents, your STRs should be present in both of your parents.
Reproduction in Animals?
Almost all reproduce sexually, male sperm and female egg fuse during fertilisation to form a new organism. It can either be external, the sex cells are released into the environment or internal, fusing within the female’s reproductive tract.
Is eukaryotic fungi unicellular or multicellular?
Both!
What is a protist?
Eukaryotic, unicellular organism that doesn’t classify as an animal, plant, fungus or bacteria. Many don’t have much in common.
In favourable conditions, how do plants and fungi reproduce?
Asexually, as the process is faster, and allows the organism to take advantage of the environment. Also, genetic variety is less of a concern in a favourable, and thus less harsh, environment.
What is the umbilical cord?
Connects the baby’s abdomen to the placenta so substances can move between the two.
What is natural breeding?
Animals with favourable characteristics are placed close in an enclosed environment, and waiting for them to mate.
Chromatin vs Chromosomes
- Chromatin consists of DNA and histone proteins, which is thin and thread-like, condensed for gene transcription
- Chromosomes compact, tightlt wound units of genetic material, which condenses DNA into 23 pairs in preparation of cell replication
What does DNA polymerase do?
Pairs free-floating nucleotides to the exposed template strand, building an identical copy of the DNA strand. DNA also stitches the newly joined nucleotides togehter by catalysing the condensation reaction that forms the sugar-phosphate backbone of DNA.
What happens during Interphase?
What is genotype?
An organism’s entire genetic makeup.
What is phenotype?
An organism’s physical expression for a particular characteristic. Determined by genotype and environment
What is the individual’s genotype?
Aa Bb Gg
What is an amino acid?
Molecules made up of an amino group, a carboxyl group, hydrogen atom and an R group, all connected to a central carbon atom.
What is the R group of amino acids?
Just means the rest of the molecule, which varies between amino acids and differentiates each one. There are 20 different R groups so 20 different amino acids.
Function of Proteins?
There are different classifications of proteins, structural proteins, enzymes, hormones and
Strucutral proteins maintain cell shape and connective tissues, important for growth, repair and maintenance of tissue. Example is collagen which increases the flexibility of skin and bone.
Enzymes are biological catalysts, speeding up chemical reacitions in cells. They act on a specific siubstrate to either break it down or combine them. Sucrase breaks sucrose down into glucose and fructose while DNA polymerase bonds nucleotides together.
Hormones are proteins that are secreted into blood by endocrine glands. They travel to ‘target cells’, where they cause a change in activity. For example, insulin regulates blood glucose levels.
Some proteins help with immunity, such as antibodies, which react with antigens and remove them from the body.
How do you test for proteins?
The biuret test, where sodium hydroxide is added to make the solution basic. Next, copper (II) sulfate is added to the solution, which will either stay blue or change purple, indicating a protein is present.
What is a peptide?
Multiple amino acids in a chain.
Terminator sequence vs stop codon?
A terminator sequence is a nucleic acid sequence that causes RNA polymerase to stop its activity. It marks the end of a gene, therefore stopping transcription. A stop codon is an mRNA nucleotide sequence that signals the end of the newly formed polypeptide chain during translation.
What is a genetic locus?
A locus is where on a chromosome a specific gene is.
Examples of characteristics coded for by sex chromosomes
Breast development in women
Adam’s apple development in men
Keep in mind sex chromosomes do not exclusively code for sexual characteristics, but all sexual characteristics are coded for by them.
Examples of characteristics coded for by autosomal
Eye Colour
Blood Type
Hair colour
How does co-dominance work with human blood type?
Every allele codes for the production of glycoproteins on the outer memebrane of RBC. AB is co-domiannt, so A and B glycoproteins appear on the surface of RBC. O occurs when there is a homozygous recessive ii, where there are no glycoproteins on the outer memebrane.
Give examples related to our understanding of how inheritance works.
- Artificial pollination: Mendel’s Laws
- X-ray crystallography: structure of DNA (Rosalind Franklin)
- CRISPR technology can precisely modify a piece of DNA in the human body for biomedicinal use
Things to look for on pedigrees?
Double affected parents - think recessive
Double unaffected parents - think dominant
Affected Mothers - Look at the sons
Unaffected Fathers - Look at the daughters
Number of affected females to males ratio
How to calculate allele frequency?
Number of a specific allele in population/Total number of alleles in population
Define the Hardy Weinberg equilibrium
It states that allele frequencies in a population will stay stable between generations in the absence of evolutionary pressure.
Examples of measuring extinction risk
Measuring population genetics to calculate risk of extinction
Galapagos finches, where heavy rains impacted the size of seeds produced by cacti. Thus, finches with smaller beaks could more easily eat the smaller seeds. If the population was no genetically diverse, it could have led to the extincition of the species.
Monitoring Inbreeding
In 2016, population of Chough birds in Scotland had started to inbreed, resulting in the population plummeting. Closely related individuals have similar ancestors, and as unhealthy alleles are often recessive, offspring of inbreeding are more likely to inherit two of the same unhealthy alleles, which would thus be expressed in their phenotype. By comparing the genomes of a random population sample, we can determine how closely related the population members are, and measure the allele frequencies for unhealthy mutations.
What is speciation?
Refers to a formation of a new species. Even if two species are extremely similar, if they do not interbreed in the wild, they are separate species. It typically occurs when there is a barrier to gene flow (movement of genes in or out of a population).Cryptic species are species orginally thought to be the same, but are actually different.
Levels of protein structure
Primary, secondary, tertiary and quarternary.
Primary refers to the exact ordering of amino acids forming their chains.
Secondary refers to chains that are folded, which occurs in long polypeptide chains, in alpha helices and beta pleated sheets, which are largely due to H-bonds.
Tertiary refers to 3D folding of the whole polypeptide.
Quaternary is folding of multiple polypeptides to form a protein e.g. haemoglobin made up of 4 polypeptides
