3 Meiosis 4 Gen Div and Adaptation 5 Classification Flashcards
What is meiosis, what does it result in
Why does it happen (4 main uses)
What is the formula to work out all possible combinations during meiosis?
Difference between diploid and haploid
What: Meiosis produces genetically unique daughter cells
Meiosis involves 2 nuclear divisions and creates 4 haploid daughter cells from a single diploid parent.
Why: 1) Producing gametes
2) Chromosome number maintenance in offspring
- Therefore when male and female gametes fuse to form zygote – diploid
3) Genetic variation
- Crossing over of chromosomes
4) Evolution – new species
2n (n= no. of pairs of homo chromosomes)
Diploid: full set of chromosomes In humans = 46 2n Haploid:Cell with half the number of chromosomes In humans = 23 n
How is genetic variation introduced? In which of the three stages of meiosis?
Meiosis 1
Crossing Over: 1) Chromatids of each pair become twisted around each other
2) Tension created breaks off equal portions of the chromatids
4) Broken portions rejoin with chromatids of its homologous partner (recombination)
5) New genetic combinations of paternal and maternal alleles are produced
Independent segregation (random assortment)
1) Homologous chromosomes arrange randomly along equator
2) One of each pair passes to the daughter cell (depends on how they’re lined up)
3) Combination of chromosomes in daughter is random
Compare Mitosis and Meiosis
Number of daughter cells Genetic diversity between daughter cells Genetic diversity between parent and daughters Chromosome number Nuclear divisions Crossing over Separation of homologous pairs
2 4
Genetically identical Genetically different
Identical to parents Different to parents
Diploid Haploid
One 🡪 2 offspring Two 🡪 4 offspring
No Yes
Do not get separated in mitosis Do get separated in meiosis
What are the stages of Meiosis? In detail (inlcuding the stages in each stage)
Interphase G1, S, G2
Mitosis I Production of two haploid daughter cells
(Describe prophase, metaphase, anaphase, telophase, cytokinesis in depth)
Meiosis II Production of four haploid daughter cells
(Describe prophase, metaphase, anaphase, telophase, cytokinesis in depth)
Study tips: How to work out no. of chromosomes, number of DNA, when DNA molecules increase and decrease
Number of chromosomes – count number of centromeres
Number of DNA = count number of chromatids
Number of DNA molecule increases only when DNA is replicated in S phase
DNA molecule decrease only when cell divides
A mule is a cross between a horse (64 chromosomes) and a donkey (62 chromosomes). Mules have 63 chromosomes – from your knowledge of meiosis – suggest why mules cannot produce gametes and are therefore sterile.
During meiosis, homologous chromosmes line up along the equator of the cell and are seperated, 63 is odd so it means one chromosome will remain unpiared so can’t be seperated(?)
How to tell Meiosis on a life cycle?
Always directly after 2n
2n divides to haploid- in between is meiosis
Difference between sister chromatids and homologous chromosomes? Which are split at which meiosis stage?
Main difference between those two that is crucial and not so hard to remember.
Sister chromatids are formed during DNA replication therefore they are identical, that is, they are literally copies of each other - the same genes AND the same alleles. Split during Meiosis II
Homologous chromosomes are paired up after fertilisation, so one is from you mum and one is from your dad, therefore even though they carry the same genes (that’s why they pair up) they have different variations of them - alleles. Split during Meiosis I
Define the following
Population Species Genetic Diversity
What does a greater number of alleles mean?
A group of organisms of one species living in a particular habitat
Group of similar organisms that can breed together to form fertile offspring
Total number of different alleles of genes in a population
Greater number of different alleles = greater genetic diversity
Four main aspects/ steps in natural selection, definition of natural election, some key words, then steps in natural selection
1)Variation 2)Competition 3)Survival of the fittest 4)Reproduction
Niche Species Compete Natural selection Fittest Better adapted Survive Advantageous genes Evolution
1) Species which share the same niche compete with each other. The idea that better adapted species survive is the basis of natural selection.
2) Natural selection is the process in which fitter individuals who are better adapted to the environment survive and pass on the advantageous genes to future generations.
3) Evolution is the process by which the frequency of alleles in a gene pool changes over time as a result of natural selection.
Any exam question about natural selection: 6 part answer
1) Existing variation in population
2) Mutation
3) Organisms with specific allele survive/ grow
4) Decrease in non-advantageous allele
5) Adapted organisms reproduce
6) Increase in frequency of allele
Define and give examples
Behavioural adaptations vs physiological vs anatomical which increase an organism’s chance of survival
Behavioural adaptations - the way an organism acts to increase its chance of survival (e.g: hibernation, migration and instincts).
Innate behaviour - doesn’t have to be learned, instinctive behaviour
Learned behaviour - Change in behaviour as a result of experience, modified to suit changing conditions
Fish swim in groups (schools) for protection.
Hippos spend most of their day in water to help them lose heat.
Birds fly south in the winter as they can find more food there
Grizzly bears enter a den and hibernate through the winter when their food is unavailable (e.g: covered by snow). Hibernating lowers their heart rate, body temperature and need for energy. Grizzly bears are able to live off fat they stored in their body in the summer and autumn when hibernating.
Physiological- Changes in metabolism and the way an animal functions
Can adapt to tolerate aridity, chemical pollution, extreme temperatures, altitude, and fire
Developing means for protection, body temperature regulation, and predation
Snakes production of venom to catch prey
Ability of mammals to maintain constant body temperature
Antifreeze proteins in cold environments
Hibernation
Anatomical- The physical feature of an organism’s body that helps it to survive/reproduce.
The Emperor Penguin- lives in the Antarctic environment which is very cold. The ground is covered in ice and snow and food is only available in the sea.
Adaptation: Short stiff tail- can lean backwards and balance on their heels and their tail. This reduces heat loss from their feet to the ground. The colour of body- camouflage it when it is swimming.
Camel- lives in hot, dry desert
Adaptation: Long lashes- protects eyes from sand Hump to store fat- Storing in just one location instead of all over body, prevents overheating Giraffe- herbivore, eats from tall trees
Adaptation: Long neck so it can reach leaves on tall trees
Cacti- grow in hot, dry environments
Adaptation: Hairs/ spikes- reduce water loss, protect from animals Thick, succulent stems- store
What is the bottleneck effect (with real examples) (and what is genetic drift), how different from natural selection
What, cause, how (example), effect
What?
A type of random genetic drift (a random change of allele frequency in a gene pool).
In contrast to natural selection, there are no heritable traits that would allow some organisms to survive better than others, nor does the population become better suited for its environment.
If most members of a population suddenly die, genetic variation decreases and the frequency at which different alleles are found in that population changes.
Illustrated through… → only a small proportion of an original population being able to pass through the narrow neck of a bottle. The resulting random population would then have completely different genetic diversity.
Cause?
A drastic decrease in population resulting from natural disaster (earthquake, volcanic eruption) or human activity (over-hunting, deforestation, pollution) that alters the ecosystem.
How? (e.g: New Zealand black robin)
The original population of black robins had genetic variation with the different “red” and “blue” genotypes.
Humans caused a population bottleneck for these birds by introducing non-native predators and destroying their natural habitat.
Over time, the black robin population shrank until there were only five birds left.
In the aftermath of the bottleneck event, and with the help of conservation scientists, the remaining few birds were able to reproduce and slowly increase their population size. BUT the new population is descended from just a few individuals, so the genetic diversity of the species is greatly reduced.
Effect?
Because only some members of the population survive, only their alleles survive as well. The chance disaster leads to a loss of genetic diversity within the population, and though the population is able to increase to its original size, it will not have the same genetic diversity it did before the disaster. The more genetically diverse a population is, the healthier it is considered to be. This is the main reason why bottleneck events are so detrimental to populations.
Founder effect
What, how it happens, examples (human and animal)
The founder effect is a case of genetic drift - when a small group of organisms becomes isolated from the larger population
Usually when the group becomes separated geographically (such as due to migration) so cannot breed with the original population
The organisms that separate from the original population have less genetic diversity so the founder effect will cause that smaller group to become genetically distinct from the original population
This can result in a new subspecies or even a new species
One of the most well known examples is Darwin’s finches (or the Galápagos finches)
Darwin’s finches are a group of around 18 species of birds located on several small islands. They resemble mainland finches, but with various differences
It is thought that small colonies of finches were established on each of the islands and, due to the founder effect, these evolved into different species
Another example is the Amish in Pennsylvania
Their community was founded by around 200 individuals who immigrated from Germany
They typically marry within their own community, creating an isolated group with little genetic diversity, so genetic mutations are more common
What is non disjunction? What are the two different types of daughter cell it can result in? What diseases can it cause?
The failure of homologous pairs to separate during anaphase (meiosis I) or of sister chromatids to separate (meiosis II). The result of this error is a cell with an imbalance of chromosomes.
Such a cell is said to be aneuploid
Loss of a single chromosome (2n-1), in which the daughter cell(s) with the defect will have one chromosome missing from one of its pairs, is referred to as a monosomy.
Gaining a single chromosome, in which the daughter cell(s) with the defect will have one chromosome in addition to its pairs is referred to as a trisomy
In the event that an aneuploidic gamete is fertilized, a number of syndromes might result.
Monosomy:
Turner Syndrome
a condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing. Can cause a variety of medical and developmental problems, including short height, failure of the ovaries to develop, and heart defects
Trisomy:
Down Syndrome- non-disjunction during Meiosis I/II to chromosome 21.
Leads to one cell have two copies of chromosome 21, n+1.
During fertilisation, if this fuses with a normal n cell, there are now 3 copies of chromosome- 2n+1 which results in down’s syndrome
Edward Syndrome
Patau Syndrome
