7A: Inheritance Flashcards

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1
Q

Define gene

A

A sequence of bases on a DNA molecule that codes fr a protein which results in a characteristic e.g eye colour

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2
Q

Define allele

A

A different version of a gene.

  • There can be many different alleles on a single gene, but in diploid organisms (e.g humans) only 2 are carried.
  • The order of bases on each allele is slightly different –> they code for different versions of the same characteristic
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3
Q

Define genotype

A

The genetic constitution of an organism - the alleles it has

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4
Q

Define phenotype

A

The expression of the genetic constitution and its interaction with the environment

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5
Q

Define dominant

A

An allele whose characteristic appears in the phenotype even when there’s only one copy. Shown by a capital letter

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6
Q

Define recessive

A

An allele whose characteristic only appears in the phenotype if 2 copies are present. Shown by a lower case letter

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7
Q

Define codominant

A

When alleles are both expressed in the phenotype - neither one is recessive

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8
Q

Define locus

A

The fixed position of a gene on a chromosome. Alleles of a gene are found at the same locus on each chromosome in a pair

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9
Q

Define homozygote

A

An organism that carries 2 copies of the same allele, e.g BB or bb

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10
Q

Define heterozygote

A

An organism that carries two different alleles, e.g Bb

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11
Q

Define carrier

A

A person carrying an allele which is not expressed in the phenotype but can be passed to the offspring

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12
Q

What are diploid organisms?

A

They carry 2 sets of chromosomes

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13
Q

Define gametes

A

Sex cells

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14
Q

Define monohybrid inheritance

A

The inheritance of a characteristic controlled by a single gene

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15
Q

In the F1 generation of a monohybrid cross, what ratio of phenotypes would you expect to see in the offspring?

A

In F1 of a monohybrid cross, a homozygous dominant organism is bred with a homozygous recessive. This will produce offspring that are all heterozygous dominant

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16
Q

In the F2 generation of a monohybrid cross, what ratio of phenotypes would you expect to see in the offspring?

A

2 heterozygotes (F1) are crossed. In F2, you’d expect a ratio of 3:1 dominant to recessive phenotypes

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17
Q

Define dihybrid inheritance

A

When 2 different genes, on different chromosomes are inherited together

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18
Q

In the F2 generation of a dihybrid cross, what would be the expected phenotypic ratio? (providing no linkage/ epistasis is involved)

A

The expected ratio would be 9 : 3 : 3 : 1

Both dominant : Dominant 1st recessive 2nd : Recessive 1st Dominant 2nd: both recessive

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19
Q

In the F1 generation of a dihybrid cross, what ratio of phenotypes would you expect to see in the offspring?

A

In F1 of a dihybrid cross, a homozygous dominant organism is bred with a homozygous recessive. This will produce offspring that are all heterozygous dominant

20
Q

What is codominance?

A

When both alleles are expressed in the phenotype, neither one is recessive

21
Q

In the F1 generation of a codominant cross, what ratio of phenotypes would you expect to see in the offspring?

A

In F1 of a codominant cross, a homozygous dominant organism is bred with a homozygous recessive. This will produce offspring that are all heterozygous dominant

22
Q

In the F2 generation of a codominant cross, what ratio of phenotypes would you expect to see in the offspring?

A

The expected ratio would be 1 : 2 :1

homozygous for 1 allele : heterozygous for the other allele

23
Q

What is an example of a gene having multiple alleles?

A

In humans, there are 3 alleles for blood group (ABO)

24
Q

What are the alleles for blood group in humans?

A

Io = Group O
IA = Group A
IB = Group B
IB IA = Group AB

25
Q

Describe the alleles for blood group

A

Io = recessive

IA and IB are codominant

26
Q

If someone has the alleles ‘IA IB’ what blood group will they be?

A

Group AB

27
Q

Describe the offspring of a cross between a heterozygote of blood group A and a heterozygote of blood group B

A
Any offspring could have 1 of the 4 blood types. 
IA IB = AB 
IA Io = A 
IB Io = B 
Io Io = O
28
Q

What would a person’s genotype be if they were Heterozygous blood group A?

A

IA Io

29
Q

What chromosomes do females have?

A

XX

30
Q

What chromosomes do men have?

A

XY

31
Q

Describe what ‘sex linkage’ means

A

When an allele is located on a sex chromosome

32
Q

Give an example of sex linkage, what chromosome is this disorder carried on?

A

Colour blindness - carried on the X chromosome

33
Q

What is meant by autosomal gene linkage?

A

Genes on the same autosome are said to be linked - because they’ll stay together during independent segregation in meiosis 1 and their alleles will be passed on to their offspring together

34
Q

What process may stop autosomally linked genes from being passed on together?

A

Crossing over

35
Q

The what effect does the closeness of two genes on the autosome have on their chances of being inherited together?

A

The closer they are together the more closely they are said to be linked - because crossing over is less likely to split them up

36
Q

What is an autosome?

A

Any chromosome that is NOT a sex chromosome

37
Q

Describe epistasis

A

When one gene masks the expression of another gene

38
Q

If two genes are autosomally linked, you won’t get the expected phenotypic ratio. What does this allow you to do?

A

You can use the predicted phenotypic ratio to identify autosomal linkage

39
Q

What is the chi squared test used for?

A

To see if the results of an experiment support a theory.

40
Q

What is a null hypothesis?

A

The null hypothesis is always that there is no significant difference between the observed and expected results (if there is a small difference that it is due to chance, not your theory being wrong)

41
Q

In a chi-squared test, what do these values stand for?
O =
E =
Σ =

A
O = Observed results
E = Expected results
Σ = Sum of...
42
Q

What is the critical value in a chi-squared test?

A

The value that you compare your calculated (chi-squared) value to.

43
Q

In a chi-squared test, in what circumstance do you reject the null hypothesis?

A

If your calculated value is larger than or equal to the critical value (this means there IS a significant difference between O and E)

44
Q

In a chi-squared test, in what circumstance do you accept the null hypothesis?

A

If your calculated value is smaller than the critical value (this means there is NOT a significant difference between O and E)

45
Q

How do you calculate degrees of freedom?

A

No. of classes - 1