Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

A-level Biology Longridge Towers School > Chapter 17 Inherited Change > Flashcards

Chapter 17 Inherited Change Flashcards

You may prefer our related Brainscape-certified flashcards:
AP® Biology flashcards Biology 101 flashcards
1
Q

What is a gene?

A

A section of DNA that codes for a single polypeptide or a protein.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

What name is given to the position of a gene on a chromosome?

A

Locus (plural - loci).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

What is an organism’s genotype?

A

The genetic constitution of the organism. Made up of the two alleles present for that particular gene. These are represented by letters.
Capital letter for a dominant allele. A

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What are homologous chromosomes?

A

Chromosomes that code for the same genes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

What is a phenotype?

A

The expression of an organism’s genotype, and it’s interaction with the environment

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

What is an allele?

A

A variation of a gene

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

What is a diploid organism?

A

An organism that has 2 sets of DNA. (one from mother, one from father).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

How many alleles are present for each characteristic?

A

2 for each gene.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

What are the variations of alleles?

A

Alleles can be dominant, recessive or codominant.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

What is a dominant allele?

A

A version of the gene which is always expressed when present in the genotype.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

What is a recessive allele?

A

A version of the gene that is only expressed when both alleles are recessive.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

What is a codominant allele?

A

This occurs when the alleles are different, both are dominant, and both expressed.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

What is the name given to the position of a particular gene on a chromosome?

A

A Locus

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

What does homozygous mean?

A

Homozygous is when the two alleles at a specific locus are the same. AA or aa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

What does heterozygous mean?

A

Heterozygous is when the two alleles at a specific locus are different. Aa

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

What does monohybrid mean?

A

Monohybrid is a description of a genetic cross, comparing one gene.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

What is a genetic cross?

A

A diagrammatic method of determining the potential genetic makeup of offspring when organisms reproduce.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

What do we use to represent the characteristic in a genetic cross?

A

A single letter. Typically the first letter of one of the contrasting features. Useful if the upper and lower case are different.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Which symbol represents dominant and which recessive?

A

Upper case - dominant; lower case - recessive. The letter must be the same for both versions of the characteristic.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

After selecting the symbol to use, what happens next in creating a monohybrid genetic cross?

A

The parent’s genotype is written using two symbols, one for each allele. The phenotype is described as well.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

After parents have been described, what happens next in creating a monohybrid genetic cross?

A

The individual gametes are described. They are single symbols, circled to indicate gametes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

After determining the gametes, what is the next step in creating a monohybrid genetic cross?

A

The male gametes and the female gametes are put into a Punnett square (a matrix), which, when filled in, shows the 4 different outcomes for the combining of gametes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

When the Punnett square has been filled in, what is the last step in creating a genetic cross?

A

The various outcomes are written out, dominant allele first. the phenotypes are described, and the number of each outcome given.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

What does pure-breed mean?

A

Both alleles for a particular characteristic are the same - homozygous. AA or aa.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

How are pure-breeding plants created?

A

By repeatedly breeding plants with the same characteristic, until the offspring are consistent for that characteristic.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

What is the F1 generation?

A

Offspring created by crossing 2 pure breeding (homozygous) plants. This will give heterozygous offspring.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

What is the F2 generation?

A

Offspring created by crossing 2 homozygous plants (F1 generation).

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

What ratio of offspring will be created in the F2 generation?

A

3:1 Dominant to recessive.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Studying the ratios given by different crosses led to the creation of the basic law of genetics - the law of segregation. What is this?

A

In diploid organisms, characteristics are determined by alleles which occur in pairs. Only one of each pair of alleles can be present in a single gamete.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
30
Q

What is meant by a ratio?

A

It is the relative measure of two groups, expressed as a proportion.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
31
Q

How are ratios often expressed for easy comparison?

A

By dividing the larger group by the smaller group. E.G. instead of a ratio of 7:5, we can write 1.4:1.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
32
Q

Why are the actual results of genetic crosses rarely the same as predicted results?

A

Statistical error. It is pure chance which allele is passed on to the offspring. Fertilisation is a random process so predicted ratios require large numbers of offspring.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
33
Q

What can be done to reduce the effect of statistical error when carrying out genetic crosses?

A

Use a large sample size, as the larger the number, the more likely it is that actual results will match theoretical ones.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
34
Q

What does dihybrid mean?

A

Dihybrid is a description of a genetic cross, comparing two genes located on different chromosomes.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
35
Q

What were the two main characteristics Gregor Mendel investigated in pea plants?

A

Seed shape (round or wrinkled) and seed colour (yellow or green).

36
Q

How did Mendel investigate dihybrid inheritance in pea plants?

A

He crossed 2 pure breeding types. One round and yellow seeds (dominant). One wrinkled and green seeds (recessive).

37
Q

When Mendel crossed Homozygous dominant and homozygous recessive pea plants, what were the genotypes of the offspring?

A

They were heterozygous.

38
Q

How are genotypes written for dihybrid crosses? Give an example of homozygous and heterozygous.

A

One gene after another. Eg RRGG for pure breeding round yellow peas, or rrgg for pure breeding wrinkled yellow peas. RrGg would be heterozygous for both.

39
Q

How are gametes written for dihybrid crosses?

A

One letter of each characteristic input in a circle. This is because each gamete has one set of each gene.

40
Q

What are the potential gametes created from heterozygous dihybrid inheritance. use these symbols: RrGg.

A

1 - RG; 2 - Rg; 3 - rG; 4 - rg.

41
Q

When heterozygous parents cross during dihybrid inheritance, what is the expected ratio of phenotypes?

A

9:3:3:1 - 9 dominant for both characteristics; 3 dominant for one; 3 dominant for the other; 1 recessive for both.

42
Q

The theoretical ratio of 9:3:3:1 has been shown in Mendel’s results. What law did it allow him to theorise?

A

The law of independent assortment.

43
Q

What is the law of independent assortment?

A

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

44
Q

What is codominance?

A

Where both alleles are expressed in the phenotype.

45
Q

What is meant by multiple alleles?

A

Where there are more than 2 versions of a gene that may be present at the loci of an individual’s homologous chromosomes.

46
Q

Why does codominance occur?

A

Instead of one allele being dominant and the other recessive, both alleles are equally dominant. they are both expressed.

47
Q

Give an example of codominance.

A

In flowers, one allele may code for red pigment, one allele may code for no pigment, the flower is white. If both alleles are present, the flower’s phenotype is pink.

48
Q

How are the symbols used in codominance crossing different to typical genetic crosses?

A

We don’t use upper/lower case letters as this indicates dominance. Instead a Letter is used for the particular gene, E.g. C for colour. The characteristics are described with superscript letters. E.g. R-red and W-white. CR CW

49
Q

What is a common example of a characteristic with multiple alleles?

A

Human blood groups.

50
Q

What are the different alleles associated with Human blood? How do they interact?

A
51
Q

What is sex linkage?

A

When a gene’s locus is on a sex chromosome. The gender of the organism may determine the possibility of carrying a specific trait.

52
Q

How many pairs of chromosomes does a human have?

A

23

53
Q

How many homologous chromosomes does a human have?

A

22, the remaining pair are the sex chromosomes. XX in females, XY in males.

54
Q

How is sex inherited in humans?

A

The sex chromosomes determine sex rather than a single gene.

55
Q

How are gametes different between men and women when describing the inheritance of sex?

A

Women only create gametes with an X chromosome. Men either have gametes with an X or gametes with a Y.

56
Q

Why is there not much of an equivalent homologous portion on the X chromosome to match the Y chromosome?

A

The Y chromosome is much shorter than the X chromosome.

57
Q

Why do recessive traits carried by the X chromosome appear more readily in males?

A

Because there isn’t the section on the Y chromosome to carry a dominant allele. Men only require 1 recessive allele rather than 2.

58
Q

What is an example of an X linked genetic disorder?

A

Haemophilia.

59
Q

What is haemophilia?

A

A disorder of the blood which inhibits clotting.

60
Q

Haemophilia has been selectively reduced in the population. How?

A

Those born with haemophilia die much younger, and therefore don’t pass on the genetic defect to the next generation.

61
Q

Why is haemophilia (X-linked, recessive) much more common in males?

A

They only require one allele to be present, and they only have one X chromosome. In women, there are two X chromosomes, therefore they would need 2 defective alleles to be present.

62
Q

From whom do males inherit haemophilia (x-linked genetic disorder).

A

From their mothers, as their father would have passed on the Y chromosome.

63
Q

If a haemophiliac male had children, who could he pass the defective allele on to?

A

Only his daughter, as the gene is X-linked. In passing on the y chromosome to his son, he would not pass on the haemophilia allele.

64
Q

What is linkage in terms of genetics?

A

When genes appear on the same chromosome. Any 2 genes on the same chromosome are said to be linked.

65
Q

What is the name given to chromosomes that are not sex chromosomes (X&Y)

A

Autosomes.

66
Q

What is the name given to the situation where two or more genes are carried by the same autosome?

A

Autosomal linkage.

67
Q

What does autosomal linkage mean for inheritance of the linked genes?

A

Those linked genes remain together through meiosis and pass together to gametes and therefore to the offspring together.

68
Q

What does autosomal linkage mean for Mendel’s Law of Independent Assortment.

A

The linked genes do not segregate.

69
Q

If 2 heterozygous genes (A and B) are on different chromosomes, what are the possible gametes?

A

AB; Ab; aB; ab.

70
Q

If 2 genes (A and B) are linked (on one chromosome). One dominant and one recessive, what are the possible gametes?

A

AB; ab.

71
Q

What might have happened during meiosis to stop autosomal linkage?

A

Crossover may separate the genes.

72
Q

What is epistasis?

A

Where the allele of one gene affects or masks the expression of another.

73
Q

When studying epistasis, what kind of genetic cross would be carried out?

A

A dihybrid cross.

74
Q

How can epistasis affect the characteristics of an organism?

A

1 - Two genes can control different factors of a particular characteristic. E.G. banding and colouring of hair.
2 - Two or more genes can be involved in a biochemical pathway, where the first enzyme coded for alters a starting molecule, and the second enzyme coded for alters the intermediary molecule to produce the end result.

75
Q

In epistasis of biochemical pathways, what happens if just one of the genes is faulty?

A

The end chemical will not be produced, as taking out any link in the pathway, no matter where it is will prevent the chain of reactions from occuring.

76
Q

What is the chi-squared test used for?

A

To test whether the observed results differ in a statistically significant amount from expected.

77
Q

What is the null hypothesis?

A

Is what is tested in a chi-squared test. It argues that there are no statistically significant differences between the observed and expected results. That any variation is due to chance.

78
Q

What 4 criteria are required for the chi-squared test to be valid?

A
  1. Sample size must be large (over 20)
  2. Data must be in discrete categories
  3. Only raw data, not averages or rates etc. can be used.
  4. It is used to compare experimental results with theoretical ones.
79
Q

What is the chi-squared formula? (You don’t have to remember this)

A
80
Q

What do the symbols in the chi-squared formula represent?

A

χ2 - Chi-squared
∑ - Sum of (add all the numbers together)
O - Observed results
E - Expected results

81
Q

When the chi-squared value has been determined, what is done next?

A

The value is read off a chi-squared distribution table in order to determine whether any deviation from expected results is significant or not.

82
Q

In order to use a chi-squared distribution table what do we need to know?

A

The degrees of freedom.

83
Q

What are the degrees of freedom for the chi-squared test?

A

The number of classes/categories minus one.

84
Q

When the chi-squared value and the degrees of freedom have been determined how do we ascertain if the result is significantly different or not?

A

We see whether the chi-squared value is greater or lower than the value at 0.05p. That is 5% probability that the result is due to chance.

85
Q

If the calculated chi-squared value is lower than that at 0.05p, what does this mean?

A

That the results are more than 5% probable to be due to chance, therefore the null hypothesis is accepted (any difference is due to chance and not significant)

86
Q

If the calculated chi-squared value is greater than that at 0.05p, what does this mean?

A

That the results are less than 5% probable to be due to chance, therefore the null hypothesis is rejected and the experimental hypothesis is accepted. The difference is significant.

A-level Biology Longridge Towers School (37 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions