Inherited change Flashcards

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1
Q

What is the genotype?

A

The genetic constitution of an organism.
It describes all the alleles that an organism has.

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2
Q

How is the genotype affected?

A

It may determine that a human baby could grow to be 1.8m tall, but the actual height that this individual reaches is affected by other factors, such as diet.
A lack of an element, like calcium, at a particular stage of development could mean that the individual never reaches their potential maximum height.

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3
Q

What is the phenotype?

A

The observable characteristics of an organism.
It is the result of interaction between the expression of the genotype and the environment.
The environment can alter an organism’s phenotype.

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4
Q

What is a gene?

A

A length of DNA - a sequence of nucleotide bases - that normally code for a particular polypeptide.
This polypeptide may be an enzyme that is needed in the biomechanical pathway that leads to the production of the characteristic (e.g. codes for a brown pigment in the iris).
The locus is the position of a gene on a particular DNA moleucle.

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5
Q

What is an allele?

A

Genes exist in two or more different forms called alleles.

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6
Q

What are homologous chromosomes?

A

Only one allele of a gene can occur at the locus of any one chromosome.
However, in diploid organisms, the chromsomes occur in pairs called homologous chromosomes.
There are therefore two loci that each carry one allele of a gene.

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7
Q

What is homozygous?

A

When the allele on each chromosome is the same.
If the two alleles are different, then the organism is heterozygous for the characteristic.

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8
Q

What is recessive and dominant?

A

Dominant alleles are always expressed in the phenotype.
Recessive are only present if no dominant alleles are present.

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9
Q

What is codominance?

A

When two alleles contribute to the phenotype.
In this situation, when both alleles occur together, the phenotype is either a blend of both features, or both features are represented.

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10
Q

What are multiple alleles?

A

Sometimes a gene has more than two allelic forms.
However, as there are always only two characteristics in a homologous pair, it follows that only two of the three or more alleles in existence can be present in a single organism.
Multiple alleles occur in the human ABO blood grouping system.

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11
Q

What is pure-breeding?

A

Example of Mendel’s peas:
If green pod peas are bred repeatedly with each other so they consistently give rise to green pod plants, it’s pure breeding for green pods.
The organisms are homozygous for that particular gene.

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12
Q

What happens when the F1 generation is bred?

A

The heterozygous plants are crossed with one another, the offspring, F2, are in approximate ration of 3:1 of green to yellow.

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13
Q

Why are actual results of genetic crosses different to predicted results?

A

It is chance which gametes fuse with which.
The larger the sample, the more likely the actual results are to come near to matching the theoretical ones.
It is therefore important to use large numbers of organisms in genetic crosses if representative results are to be obtained.

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14
Q

What is an example of codominance?

A

In the snapdragon plant, one allele codes for an enzyme that catalyses the formation of a red pigment in flowers.
The other allele codes for an enzyme that lacks catalytic activity and so does not produce pigment.
This produces three colours as it is codominant.

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15
Q

What are the different phenotypes of the snapdragon?

A

In homozygous red, both alleles code for the enzyme, and hence the pigment production, so produce red flowers.
Homozygous white, both alleles produce no enzyme or pigment, so produces white flowers.
Heterozygous plants produce pink flowers.

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16
Q

What are the ratios in monohybrid?

A

Predicted ratio of phenotype in offspring is 3:1.
Predicted ratio of genotype 1:2:1

17
Q

What are dihybrid crosses?

A

How two different characteristics, determined by two different genes on different chromosomes (so the genes should be separated) are inherited.
The theoretical ratio is 9:3:3:1.

18
Q

What is the law of independent assortment?

A

Each member of a pair of alleles may combine randomly with either of another pair.

19
Q

What is the example of multiple alleles?

A

The three alleles of gene I lead to the presence of different antigens on the cell-surface membrane of red blood cells:
Allele I^A produces antigen A.
Allele I^B produces B.
Allele I^O does not produce either.
Only 2 alleles can be present, as there are only 2 gene loci.
A and B are codominant, O is recessive.

20
Q

What is the cross of ABO alleles?

A

Cross between O and AB produces only individuals of group A and B.
Individuals of A with individuals of B may have any of the blood groups. (When the parent is IA, IO, and the other IB and IO.)

21
Q

What are sex chromosomes?

A

Females have 2 X chromosomes, so all the gametes contain a single X chromosome.
Males have 1 X and 1 Y, so produce 1 X gamete and 1 Y gamete.

22
Q

What are sex-linked genes?

A

Any gene carried on the X or Y chromosome.
X is much longer than Y, so many genes aren’t found on Y.
This means, if the allele is recessive, men only have 1 X chromosome, so only need 1 copy for it to be expressed, and are more likely to have the recessive allele.

23
Q

What is haemophilia?

A

The blood clots slowly and there is persistent internal bleeding. It is found on the X chromosome.
It mainly is confined to males, as any females who have it die at puberty.

24
Q

What is haemophilia caused by?

A

A recessive allele with an altered sequence of DNA bases that codes for a faulty protein, involving in clotting.
The gene can now be manufactured and given to haemophilics.

25
Q

How is haemophilia inherited?

A

Males can only obtain the X chromosome from the mother, and they may be heterozygous and carry the allele, so pass it on to the son.
Males do not pass their X chromosome to sons, so cannot pass it on to them.
They can pass it to daughters, who would become a carrier.

26
Q

What is autosomal linkage?

A

Genes on the same chromosome are linked.
Non-sex chromosomes are autosomes.
So when 2 or more genes are carried on the same autosome are sex-linked.
During meiosis, the linked genes remain together.
Not linked, there’s 4 possible gametes, linked there is 2, assuming no crossing over.

27
Q

What is epistasis?

A

When the allele of one gene affects the expression of another in the phenotype.

28
Q

What is chi-squared test?

A

Used to test the null-hypothesis, which assumes there will be no statistically significant difference between two sets of observations, and any different is due to chance.

29
Q

When is chi-squared used?

A

The sample size must be over 20.
The data must fall into discrete categories.
Only raw counts and not percentages can be used.
It compares experimental results with theoretical ones.

30
Q

What is the formula for chi-squared?

A

sum of [observed numbers (O) - expected numbers (E)] squared / expected numbers (E)

31
Q

What are the degrees of freedom?

A

The value is read off a distribution table to determine whether deviation is significant or not.
The degree of freedom is the number of classes - 1 and is needed to read the table.

32
Q

When is chi-squared accepted?

A

If the probability that the deviation is due to chance is equal or more than 0.05, then the null hypothesis is accepted, and is due to chance.
If the probablity is less than 0.05, the null hypothesis is rejected, and the difference is significant.