Karteikarten
Variation, Inheritance and Evolution
Karten in diesem Stapel (48)
- 1How does variation occur?As a result of mutations - changes in the genetic code. Variation can also occur due to the organism's environment.
- 2What is chlorosis?When plants suffer from a condition that makes their leaves yellow as they don't produce the normal amount of chlorophyll. Because of this, they can't photosynthesis enough to make enough food.
- 3What factors cause chlorosis?Lack of light - they reduce their chlorophyll to conserve resources in the absence of light. Mineral deficiencies - for example, a lack of magnesium or iron as iron is cofactor for enzymes that make chlorophyll and magnesium is found in the chlorophyll molecule. Virus infections - viruses can interfere with the metabolism of cells.
- 4So what is reliable for the green colour of leaves?It is likely there is a gene that plays a part but the environment is also a big factor in the colouration of leaves
- 5How is body mass affected by environmental factors?The organisms body mass can depend on the amount of food, quality of food, amount of exercise and presence of disease.
- 6How is body mass affected by genetic factors?Chromosome 7 has been associated with body mass - a mutation can make the organism obese as it causes the pattern of fat deposition in the body to be altered. It has been tested on mice and mice who have the mutation grow 35-50% larger than normal mice.
- 7What creates genetic variance?The versions of the genes you inherit from your parents as for most genes there is a combination of possible alleles. The individual mixture of alleles an offspring inherits influences the characteristics they display.
- 8What is the genotype?The genetic make up of the organism
- 9What is the phenotype?The observable characteristics of the organism - this can be affected by both genetics and the environment
- 10What is the relationship between genotype and phenotype?If a person shows a dominant trait in their phenotype, we aren't sure what their genotype is as they could have two dominant alleles or a dominant and recessive. An organism that shows the recessive allele, however, we do know the genotype of as it must have two recessive alleles to express the characteristic.
- 11What does homozygous mean?They have two identical alleles for a characteristic - either homozygous dominant of homozygous receive
- 12What does heterozygous mean?They have two different alleles for a characteristic, and the dominant phenotype will be expressed
- 13What is continuous variation?A characteristic that can take any value within a range- it can be genetic and environmental and is controlled by a number of genes. Examples include the surface area of an organism, the mass and the skin colour.
- 14What is discontinuous variation?A characteristic that can only appear in specific values/ categories. It is mostly genetic and is controlled by one or two genes. Examples include blood group, albinism and the shape of the plant.
- 15What is monogenetic inheritance?When there are only two genes controlling something - the dominant and the recessive. Eg, G being dominant and for green pods and g being recessive and for yellow pods.
- 16What is codominance?When two different alleles occur for a gene but both are equally dominant. As a result, both of the alleles are expressed in the phenotype of the organism.
- 17What are common examples of codominance?The colour of flowers - there is an allele that codes for red flowers and an allele that codes for white flowers, but if both are present, they make a pink flower. White and red will both be homozygous but pink will he heterozygous.
- 18What does multiple alleles mean?There will be more than two alleles coding for a characteristic. Only two alleles will be present in the individual, but it is two from a range of more. An example for this is blood groups in humans.
- 19Explain how human blood groups workThe different alleles have different antigens on the surface of the red blood cells. There is Ia (antigen A), Ib (antigen b) or Io (neither antigen). Hence, there can be blood group A, B, AB or O. A and B can be heterozygous or homozygous, blood group AB is always heterozygous and blood group O is always homozygous.
- 20What are X and Y chromosomes?They are both sex determining chromosomes. X is larger and contains many genes that aren't involved in sexual development (some are). The Y chromosome is small and contains almost no genetic information besides a gene that codes for an embryo to develop as male.
- 21What is sex linkage?Some characteristics are determined by genes carried on the sex chromosomes.
- 22Which sex chromosome often carries the genetic disorders?The X allele - because if a genetic disorder is recessive, the males don't have another X allele to present to dominant allele to counteract it. If there is a recessive disorder on the X allele, the Y one can't stop it from presenting itself in the phenotype.
- 23What is haemophilia?A sex-linked disorder that causes sufferers to have extremely slow clotting blood which means there is prolonged bleeding if they get hurt and this can be potentially fatal. It is more common in males than females as they can't have the dominant allele to stop haemophilia from occurring. If females have the haemophilia allele, they will likely have the dominant allele on their other x chromosome to counteract the effect.
- 24What is autosomal linkage?When the genes that are linked are found on one of the other pairs of chromosomes
- 25What are linked genes?Genes that are inherited as one unit and there is no independent assortment during meiosis. The normal expected ratios for offspring will not apply if the genes are linked.
- 26What are recombinant offspring?Offspring with a new combination of alleles to either parents
- 27What is the recombination frequency and how is it measured?it is a measure of the amount of crossing over that has happened in meiosis and is calculated as followed:
Recombination frequency = number of recombinant offspring divided by the total number of offspring - 28How can we interpret recombinant frequency?A recombinant frequency of 50% indicates there is no linkage and the genes are on separate chromosomes. Less than 50% indicates that there is gene linkage and the random process of independent assortment has been hindered. As the degree of crossing over reduces, the recombinant frequency also gets smaller.
- 29What is epistasis?The interaction of genes at different loci. Gene regulation is a form of epistasis, such as the lac operon. The characteristics of plants and animals that show continuous variation involve multiple genes that interact through epistasis
- 30What does hypostatic and epistatic mean?Hypostatic means a gene that is affected by another gene and epistatic is when a gene affects the expression of another gene
- 31Show how genes can interact epistatically?
- 32What do we assume in Hardy Weinburg?It is a large population we are studying, that there is random mating, no advantage for a particular genotype, no mutations, no migration
- 33What are the two formulas to remember for Hardy Weinburg?p + q = 1
p2 + 2pq + q2 = 1 - 34What do they stand for?p = dominant allele
q = recessive allele
p2 = probability of dominant homozygous occurring
q2 = probability of recessive homozygous occurring
2pg = probability of dominant heterozygous occurring - 35What factors can affect evolution?Mutation, sexual selection leading to the increase in some alleles, gene flow (movement of alleles between populations), genetic drift (a new allele having a greater impact on smaller populations) and natural selection
- 36What is the impact on having a large population?There is a larger gene pool so lots of genetic diversity meaning more alleles. Smaller populations have a smaller gene pool so fewer alleles and less genetic diversity. They cannot adapt to change as easily.
- 37What limiting factors can limit the size of a population?Density dependent factors like competition, predatation, parasitism and communicable disease as well as density independent factors like climate change, natural disasters, seasonal change and human activities like deforestation
- 38What is a bottleneck?A large reduction in population size which lasts for at least one generation. It reduces the gene pool and genetic diversity and it takes thousands of years after a bottleneck to regain genetic diversity.
- 39Give an example of a small population that has to evolve a lot?A founder species/pioneer species as they have very few of their species so their gene pool is very low in the new area
- 40What is the difference between stabilising selection, directional selection and disruptive selection?Stabilising selection shows a normal distribution (bell-shaped), directional selections shows that the average veers more towards one extreme and in disruptive selection, the extremes are favoured more than the average
- 41What is allopatric speciation?It happens when members of the same group are divided from one another through physical barriers, like a body of water or divided land. A famous example of the Galapagos finches
- 42What is sympatric speciation?it is less frequent and happens when populations share the same habitat. It occurs when two members of different species breed and produce fertile offspring. This offspring is a new species as it cannot successfully mate with either of its parent species. This is more common in plants. It can also happen due to sexual selection.
- 43Give an example of sympatric speciation?Blind mole rats live in two different types of soil and mole rats that live in one kind of soil will only mate with the individuals from the same type of soil. Scientists have found this is already causing genetic differences even though there is no physical barrier.
- 44what is a 'wild type' allele?The allele that codes for the most common (or normal) characteristic. Other alleles that result from mutations are known as mutants.
- 45What is artificial selection?It works similarly to natural selection but the farmers or breeders will pair off animals to mate that have desirable characteristics to pass these characteristics on. Farmers have done this to animals and plants since before genes were discovered.
- 46What is inbreeding?The breeding of closely related individuals which reduces the frequency of alleles within the population and will eventually cause specialisation. Organisms that are closely related are often artificiality selected as they have the desirable characteristics.
- 47What issues are there with inbreeding?It reduces the gene pool which means the resulting organism will have issues with evolving and adapting to new situations as it has very few alleles to chose from. Lots of genetic disorders comes from recessive alleles and it is more common to get recessive alleles through inbreeding.
- 48How do we counteract the effects of artificial selection narrowing the gene pools of species?We keep things like seed banks where individuals showing lots of alleles are kept and frozen
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- A level Biology (Module 6) Karteikarten am Variation, Inheritance and Evolution , erstellt von Emma Lloyd am 18/06/2017.
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- Emma Lloyd
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