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A Level - Biology > 17: Inherited change > Flashcards

17: Inherited change Flashcards

1
Q

Define a gene

A

A small section of DNA that codes for a specific protein

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2
Q

Define a genotype

A

Genetic makeup of an organism

All the genes an animal can express

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3
Q

Define a phenotype

A

Observable or biochemical characteristics of an organism

Can be altered by the environment

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4
Q

What does an organisms genotype define?

A

The limits of the characteristics which an organism can develop
E.g lack of something could mean a person could not grow to max height

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5
Q

Define locus

A

The position of a gene on a DNA molecule

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6
Q

Define an allele

A

One of the different forms of a gene

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7
Q

How many alleles can be present at one locus?

A

One

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8
Q

How many copies of a gene are found in homologous chromosomes?

A

Two loci each carry one allele of a gene

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9
Q

Define homozygous

A

When alleles on each of the homologous chromosomes are the same

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10
Q

Define heterozygous

A

When alleles on each of the homologous chromosomes are different

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11
Q

Define a dominant allele

A

Allele of a heterozygote that expresses itself in the phenotype

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12
Q

Define a recessive allele

A

Allele of a heterozygote that does NOT expresses itself in the phenotype

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13
Q

Define homozygous dominant

A

Homozygous organism with two dominant alleles

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14
Q

Define homozygous recessive

A

Homozygous organism with two recessive alleles

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15
Q

Define codominant

A

Two alleles which are both expressed in the phenotype

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16
Q

When is an organism said to have multiple alleles?

A

Genes that have two allelic forms

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17
Q

What can cause multiple alleles to occur?

A

Random mutations which occur over long periods of time

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18
Q

Define monohybrid crossing

A

Crossing of one gene

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19
Q

What is F0, F1, F2?

A

F0 - parent
F1 - offspring
F2 - offspring of F1 interbred

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20
Q

Define the law of segregation

A

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

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21
Q

Define a ratio

A

Measure of the relative size of two classes

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22
Q

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

A

Predicted results are just predictions of what will occur, does not necessarily occur

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23
Q

Define dihybrid inheritance

A

Crossing of two different genes located on different chromosomes, result is inherited

24
Q

What is the standard ratio caused by the breeding of two heterozygous organisms with dihybrid inheritance?

A

9:3:3:1

25
Q

What is the law of independent assortment

A

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

26
Q

What are the alleles present which determine blood group?

A 
IA - produces antigen A on cell surface
IB - produces antigen B on cell surface
IO - does not produce any antigen on cell surface
IA and IB are codominant
IO is recessive to both
27
Q

What is the gene combination for blood types?

A

A - IAIA or IAIO
B - IBIB or IBIO
AB - IAIB
O - IOIO

28
Q

Why might you not trust the dihybrid inheritance ratio 9:3:3:1?

A

Alleles are on the same chromosome therefore not independently assorted

29
Q

What does a 9:7 ratio suggest?

A

Not 3:1, but probably 9:3:3:1 which is common for a dihybrid

30
Q

What are the sex chromosomes?

A

23rd pair of chromosomes
XX in females
XY in males

31
Q

What is a Y chromosome?

A

A smaller and different shaped chromosome only found in males

32
Q

What gametes form from males and females?

A

Female - All gametes have single X chromosomes

Male - one has X chromosome other has Y

33
Q

What is a sex-linked gene?

A

Any gene that is carried on either the X or Y chromosome

34
Q

What does the extra length of the X chromosome mean?

A

The corresponding Y chromosome has no equivalent homologous portion
Only one copy of a gene present in males

35
Q

How do recessive alleles on the non-homologous X chromosome change in frequency?

A

Recessive X chromosomes will appear more frequently as no homologous portion on Y chromosome could be dominant

36
Q

What is haemophilia?

A

Recessive allele on X chromosome which codes for a faulty protein that doesn’t function
Means blood cannot clot

37
Q

What is standard notation for looking at males and females in genetic diagrams?

A

Empty square - normal male
Empty circle - normal female
Filled shape - affected

38
Q

What is an autosome?

A

All chromosomes other than the sex chromosomes

39
Q

What are linked genes?

A

Any two genes that occur on the same chromosome are linked

Linked genes remain together in meiosis, pass onto gametes together

40
Q

Why are linked genes not separated in meiosis?

A

They do not segregate by independent assortment

41
Q

If the question presents you with the genotypes hhgg and HhGg, which alleles go together?

A

h always goes with g

Diagram is hg hg gametes crossed with HG hg gamets

42
Q

What is the difference between sex or autosomal linkage?

A

Sex linkage occurs when a gene is not found on the Y chromosome but is found on X
Autosomal works on the non-sex chromosomes, so no Y chromosomes present

43
Q

What process in meiosis could cause varieties in ratios when sex-linked genes are crossing?

A

Crossing over may have occurred

44
Q

Define epistatis

A

The allele of one gene affects or masks the expression of another in the phenotype

45
Q

What is the classic example of epistatis?

A

Black, agouti, and albino mice

46
Q

What genes are found in the different colours of mice?

A 
A - agouti
a - black
B - production of melanin
b - no production of melanin
If bb is present, the mouse is albino
47
Q

What is the standard format of a ratio?

A

A:1

48
Q

Why would some people not like to take part in testing?

A

Some embarrassed about

Cannot decide which phenotype is present, as it is subjective

49
Q

What shows that a phenotype is caused by a recessive allele?

A

Parents can be carriers but unaffected by the disease

50
Q

How many different gametes can be produced from Bb Cc Dd?

A

2^3 = 8

Due to 1 allele from each pair

51
Q

How many antigen-determining alleles will be preset in a white blood cell?

A

2 - white blood cells are diploid cells

52
Q

What is the standard ratio when two AaBb mice mate?

A

9 - agouti
4 - albino
3 - black

53
Q

What are the steps in the chi squared test?

A

Observed (O) and Expected values (E)
Sum of (O-E)^2 / E
If this value is larger than the critical value, then there is enough data to reject H0

54
Q

When should the chi-squared test be used?

A

If: the data is in categories
Sample size is large to be representative
Data indicates absolute numbers

55
Q

If a question asks about a gene coding for enzymes with colours, how do you answer the question?

A

Gene X allows for the production of the enzyme

Enzyme causes chemical to made, giving the phenotype

A Level - Biology (22 decks)

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