PATTERNS OF INHERITANCE 6.1.2 OCR A LEVEL BIOLOGY

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  • Created by: Davina1st
  • Created on: 06-11-21 19:06
What is a gene?
A section of DNA that codes for a particular polypeptide.
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What is an allele?
An alternative version of a gene. (different version of the same gene).
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What is a chromosome?
A long section of DNA that is made up of many genes.
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What is a homologous pair?
A pair of chromosomes that carry the same genes but different alleles.
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What is a phenotype?
An observable characteristic of an organism (doesn't have to be visible) .
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What causes phenotypic variation?
The phenotype is determined by the interaction between the genotype and the environment.
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What is interspecific variation, describe the variation?
Genetic variation between species, as different species have different genes, the bigger the difference in phenotype, the fewer genes they share.
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What is intraspecific variation, describe the variation?
Genetic variation within the same species, members of the same species have the same genes, just different versions (alleles), the small difference in sequences leads to different proteins being produced.
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What is a monogenic trait?
It is controlled by a small number of genes with few/no alleles e.g. freckles/dimples. Shows discontinuous patterns where the phenotypes fit into distinct categories.
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What is discontinuous variation?
The traits fit into distinct categories, like blood group, freckles, dimples, round and wrinkled pea shape.
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What is a polygenic trait?
Controlled by many genes with many alleles, e.g. height, length and skin colour. Alleles often have additive/cumulative effect. It is influenced by the environment and shows continuous variation.
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What is continuous variation?
Variation that can be caused by both your genotype and the environment, it doesn't fit into distinct categories, e.g. height and leaf surface area
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What is chlorosis?
When a plant doesn't produce enough chlorophyll so appears yellow. Chlorotic plants have the correct genotype for making chlorophyll, but environmental factors prevent expression.
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What is chlorosis caused by?
Lack of light, magnesium deficiency and virus infection
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What is etiolation?
Plants grown in the dark appear yellow and spindly.
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How is animal body mass affected by your genotype and environment?
Your genotype might code for a lower body mass, but without the right nutrients, diet and regular exercise, your body mass can end up being larger.
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What is a dominant allele?
An allele that is always expressed if present
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What is a recessive allele?
An allele that is only expressed if there is no dominant allele present
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What does homozygous and heterozygous mean?
Homo - a genotype that has two of the same alleles for one gene, hetero - a genotype that has two different alleles for a gene.
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What is the locus of a chromosome?
The position of a gene on a chromosome.
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What is the F1 generation?
The first familial generation, the offspring cross between two parents
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What is the F2 generation?
The second familial generation, the offspring of a cross between two of the f1 generation
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What is pure breeding?
An organism that consistently produces offspring showing the same phenotype and therefore is homozygous for the trait.
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What is the ratio for a heterozygous cross of a monogenic trait?
3:1
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What is a codominant allele?
Co-dominant alleles have equal dominance, this means they are both expressed in the phenotype of the heterozygote.
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Give an example of a co-dominant allele
Allele for a red coat C^R and allele for a white coat is C^W. (horse coat colour)
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What does it mean if a gene has multiple alleles?
When a gene has more than two versions, as an organism only carries two versions of the gene (one on each homologous chromosome), only two alleles can be present in the individual.
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What is a dihybrid inheritance?
The inheritance of two or more monogenic traits simultaneously. A dihybrid cross is used to show the simultaneous inheritance of two characteristics.
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A dihybrid cross assumes the alleles are independently assorted in meiosis, what does this mean?
Alleles of two or more different genes get sorted into gametes independently of each other. Independent assortment of the alleles for two genes on separate chromosome of a heterozygous parent = 25% of the gametes having each of the 4 possible combo's
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If a dihybrid cross of two parents heterozygous for both traits is carried out, what is the phenotypic ratio?
9:3:3:1
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If a co-dominant trait of two heterozygous parents is carried out, what is the expected phenotypic ratio?
1:2:1
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Why could the results of a cross not match up with the expected phenotypic ratio?
There are only a small number of offspring so the sample isn't representative / genes are linked.
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What does sex-linkage mean?
The characteristics inherited are determined by genes carried on the sex chromosomes.
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How does sex-linkage work? (the X and Y chromosomes)
The Y chromosome is shorter than the X, and is missing some genes, the gene-loci is found on the non-homologous region of the X = males only carry one allel for sex linked traits.
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What is the part of the chromosome present on both the X and Y called?
The homologous region.
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When drawing the notation of sex-linked traits, what is different?
The Y chromosome never carries an allele because it is missing the non-homologous region, so is always written as just Y
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How do you work out the expected number for a chi-squared, from the phenotypic ratio?
If the ratio is 9:3:3:1, you add these up = 16. You then do 9/16 x the total frequency. or 3/16 x total frequency.
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Why is chi-squared useful in genetic experiments?
Due to random fertilisation, the actual number of offspring of each phenotype is unlikely to match the expected ratio perfectly. Allows to see if the difference is significant between observed and expected.
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What does it mean if the calculate x squared value is greater than the critical value value?
The null hypothesis is rejected as there is less than 5% probability that the difference was due to chance.
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What are autosomes?
Chromosomes which are not involved in sex determination.
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What is autosomal linkage?
Two or more genes located on the same non-sex chromosome
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What happens to unlinked genes in meiosis?
Chromosomes (metaphase 10 and chromatids (metaphase 2) are independently assorted. Gametes with each possible combination are made = equal proportions of each combination of alleles.
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What happens to linked genes during meiosis?
They are inherited as one unit, there is no independent assortment during meiosis unless crossing over occurs. This means expected ratios will not be produced. There will be more allele combinations the same as the parent, and fewer recombinant.
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What happens if the genes are close together on the chromosome during autosomal linkage?
Crossing over can only occur in a small region, the less likely they are to be separated = fewer recombinant offspring produced.
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How do you work out recombination frequency?
number of recombinant offspring/total number of offspring x100
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What is epistasis?
The interaction between pairs of genes at different loci. It often involves he pair of alleles at one locus masking the effects of the alleles at the other locus.
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What is the epistatic gene and the hypostatic gene?
Epistatic - the gene that masks the expression of another gene, hypostatic - the gene that is masked by the epistatic gene.
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What is recessive epistasis?
The homozygous recessive genotype at the one locus masks the effect of the pair of alleles at the second.
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What is dominant epistasis?
The heterozygous dominant or homozygous recessive genotype masks the effect of the pair of alleles at the second locus.
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What does the hardy Weinberg principle state?
In a stable population with no disturbing factors, the allele frequencies will remain constant from one generation to the next and there will be no evolution.
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What is the Hardy-Weinberg principle expressed as? (don't need to know)
p2 + 2pq + q2 = 1
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What does p and q stand for in the Hardy Weinberg expression?
P2= frequency of homozygous dominant genotype in the population. Q2= frequency of homozygous recessive genotype in the population. 2PQ= frequency of heterozygous genotype in the population.
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For the Hardy Weinberg expression to be true, what conditions have to be true?
No natural selection, no sexual selection, no mutations, large population size and no gene flow
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What does population mean in genetics?
A group of species living in the same place at the same time.
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What are the five factors affecting evolution?
Mutation, sexual selection, gene flow, genetic drift and natural selection.
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Small populations are less likely to become extinct, true or false?
False - more likely
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Limiting factors increase/decrease population size, what are the two types?
Density dependant - dependant on population size (competition, predation, parasitism, disease). Density independent - affect populations of all sizes in the same way (climate change, natural disaster, human activities)
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What is variation?
Difference sbwteen organisms in the same species (intraspecific) and a different species (interspecific)
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What is natural selection?
Individuals with a characteristic that increases their chnace of survival breed together, leading to the frequency of alleles coding for that characteristic increasing.
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What is the gene pool?
Sum total of all the alleles in a population.
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What is genetic drift?
Occurs in small populations, a change in allele frequency due to the random nature of a mutation, Appearance of a new allele is more likely to have a larger impact.
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What is gene flow? What is the founder effect?
Movement of alleles between population e.g. immigration and emigration. Founder effect - new colonies created by isolated individuals.
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What is allopatric and sympatric speciation?
Allopatric - when member of a population separated by physical barrier (river/sea) environments different=founder effect+genetic drift. Sympatric-within population that shares a habitat(plants)
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What is speciation?
The formation of a new species, organisms of the new species will no longer be able to interbreed and produce fertile offspring.
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What is artificial selection/sexual selection?
Human selection of organisms with desirable characteristics to interbreed which leads to increase in frequency of alleles which code for characteristics that improve mating success.
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What is directional selection?
When there is a chnage in the environment and the normal (most common) phenotype is no longer the most advantageous. Organsims whcih are lesson common and have more extreme phenotypes are positively selected.
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What is disruptive selection?
The extremes are selected for and the norm selected against.
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What are some problems caused by inbreeding?
Limits gene pool, decreasing genetic diversity=reduced chance of inbred population surviving changes of environment. Organisms closely related=more likely to have recessive alleles=greater chance of being homozygous recessive. (cystic fibrosis)
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What is a gene bank?
Store biological samples, other than seeds, such as sperm or eggs (usually frozne). Gene banks can increase the allele frequency and genetic diversity of a population if inbreeding causes problems.
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Other cards in this set

Card 2

Front

What is an allele?

Back

An alternative version of a gene. (different version of the same gene).

Card 3

Front

What is a chromosome?

Back

Preview of the front of card 3

Card 4

Front

What is a homologous pair?

Back

Preview of the front of card 4

Card 5

Front

What is a phenotype?

Back

Preview of the front of card 5
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