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IGCSEs > Biology πŸƒ | Inheritance | 17 > Flashcards

Biology πŸƒ | Inheritance | 17 Flashcards

1
Q

Define inheritance

A

The transmission of genetic information from generation to generation

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2
Q

Define DNA

A

Deoxynucleic acid, the chemical containing genetic information from which genes and chromosomes are made.

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3
Q

Define chromosomes

A

Thread-like structures of DNA, carrying genetic information in the form of genes

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4
Q

Where are chromosomes located?

A

In the nuclei of cells

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5
Q

Define gene

A

A short length of DNA found on a chromosome that codes for a specific protein

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6
Q

Define allele

A

An alternate form of the same gene

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7
Q

How does DNA control cell function?

A

By controlling the production of proteins, including enzymes, membrane carriers and receptors for neurotransmitters

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8
Q

Nuclei with two sets of chromosomes are known as __

A

Diploid nuclei

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9
Q

In which chromosome is sex determined?

A

In the 23rd chromosome

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10
Q

What sex chromosome do females have?

A

XX

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11
Q

What sex chromosome do males have?

A

XY

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12
Q

Whhich parent is responsible for determining the sex of a child?

A

The father, as only he can pass on a Y chromosome

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13
Q

All egg cells carry a _ chromosome

A

An X chromosome

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14
Q

Sperm cells carry _ chromosome

A

Sperm cells have a 50% chance to carry an X chromosome, and a 50% chance to carry a Y chromosome

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15
Q

What diagram can we use to show sex inheritance?

A

A punnet square or genetic diagram

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16
Q

What does the sequence of bases in a gene determine?

A

The sequence of amino acids used to make a specific protein

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17
Q

How are proteins made?

A

Proteins are made by ribosomes with the sequence of amino acids controlled by the sequence of bases contained within DNA

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18
Q

Why can’t DNA directly travel into ribosomes?

A

DNA is far too big to pass through a nuclear pore

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19
Q

What does mRNA stand for?

A

Messenger RNA

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20
Q

Since DNA can’t travel out of the nucleus, what is used to send genetic information to ribosomes?

A

mRNA

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21
Q

What is mRNA?

A

A copy of a gene in the DNA, made in the nucleus, that moves to the ribosome

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22
Q

How do mRNA molecules send information to ribosomes?

A
  1. They move out of the nucleus and attach to a ribosome
  2. The ribosome β€˜reads’ the mRNA in groups of three
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23
Q

How do ribosomes know which amino acids to create?

A

Each triplet of bases on mRNA codes for a specific amino acid. Thus, the ribosome translates the sequence of bases into a sequence of amino acids that make up a protein

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24
Q

What is transcription?

A

When the sequence of one gene is replicated in an mRNA molecule

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25
Q

What is translation?

A

When the RNA molecule serves as a code for the formation of an amino-acid chain

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26
Q

Although most body cells contain the same genes, why are many genes in a cell not expressed?

A

The cell only makes the specific proteins it needs

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27
Q

Define mitosis

A

Nuclear division giving rise to genetically identical cells

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28
Q

When cells divide, why do their chromosomes double?

A

It ensures that when the cell splits in two, each cell is still diploid

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29
Q

What is mitosis used for?

A

growth, repair of damaged tissues, replacement of cells and asexual reproduction

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30
Q

Define chromatid

A

One arm of a replicated chromosome

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31
Q

Before mitosis, what happens?

A

The unravelling of chromosomes and replication of DNA (doubling)

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32
Q

During mitosis, what happens?

A

The copies of chromosomes separate to opposite sides of the cell, maintaining the chromosome number in each daughter cell. Then, the cell divides into two.

32
Q

During mitosis, what happens?

A

The copies of chromosomes separate to opposite sides of the cell, maintaining the chromosome number in each daughter cell. Then, the cell divides into two.

33
Q

How do chromosomes seperate during mitosis?

A

Chromosomes line up along the centre of the cell where cell fibres pull them apart.

34
Q

Define stem cells

A

Unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions

35
Q

What is the function of stem cells?

A

To produce new daughter cells that can become specialised within the tissue and be used for different functions

36
Q

Define meiosis

A

A type of nuclear division that gives rise to cells that are genetically different

37
Q

What is meiosis used for?

A

To produce gametes

38
Q

What happens to the chromosome count after meiosis?

A

The chromosome count is halved from diploid to haploid

39
Q

How many cells are produced by meiosis?

A

Four cells

40
Q

How many cell divisions occur in mitosis and meiois?

A

In mitosis, one cell division occurs
In meiosis, two cell divisions occur

41
Q

What is the importance of meiosis?

A

Meiosis produces variation by forming new combinations of maternal and paternal chromosomes every time a gamete is made, meaning that when gametes fuse randomly at fertilisation, each offspring will be different from any others

42
Q

Define inheritance

A

The transmission of genetic information from generation to generation

43
Q

Define monohybrid inheritance

A

The inheritance of characteristics controlled by a single gene

44
Q

What sort of diagram can be used to show monohybrid inheritance?

A

A punnet square genetic diagram

45
Q

What does a punnet square show us?

A

The possible combinations of alleles that could be produced in the offspring: allowing us to figure out the ratio of combinations

46
Q

Define dominant allele

A

An allele that is expressed if it is present in the genotype

47
Q

Define recessive allele

A

An allele that is only expressed when there is no dominant allele of the gene present in the genotype

48
Q

What is the genotype?

A

The genetic make-up of an organism determined by combinations of alleles

49
Q

What is the phenotype?

A

The observable features of an organism

50
Q

Define homozygous

A

Having two identical alleles of a particular gene

51
Q

Define heterozygous

A

Having two different alleles of a particular gene

52
Q

Define pure breeding

A

A type of breeding in which all of the offspring carry the same phenotype as the parents.

OR, an individual is homozygous for a particular characteristic

53
Q

Two identical homozygous individuals
that breed together will be __

A

Pure-breeding

54
Q

How is a dominant allele shown?

A

With a capital letter

55
Q

How is a recessive allele shown?

A

With a simple letter

56
Q

In what order should a dominant and recessive allele be written together?

A

DOMINANT - recessive

57
Q

What is a test cross used for?

A

To find out the genotype of an organism showing the dominant phenotype

58
Q

How does a test cross work?

A

Crossing the unknown individual with an individual showing the recessive phenotype – if the individual is showing the recessive phenotype, then its genotype must be homozygous recessive.
~
By looking at the ratio of phenotypes in the offspring, we can tell whether the unknown individual is homozygous dominant or heterozygous

59
Q

What are family pedigrees used for?

A

Used to trace the pattern of inheritance of a specific characteristic (usually a disease) through generations of a family, to work out the probability that someone in the family will inherit the genetic disorder

60
Q

In pedigree diagrams, what shape indicates males and what shape indicates females?

A

Males: square
Females: circle

61
Q

In pedigree diagrams, what color are affected and unaffected individuals?

A

Affected: red
Unaffected: blue

62
Q

Horizontal lines between males and females in pedigree diagrams show…

A

That they have produced children (shown underneath each couple)

63
Q

Define codominance

A

A situation in which both alleles in heterozygous organisms contribute to the phenotype

64
Q

How are codominant alleles represented?

A

Both with uppercase letters, BUT with different letters used

65
Q

What are the three alleles governing blood group?

A

IA, IB, IO

66
Q

Which alleles for blood type are codominant?

A

IA, and IB

67
Q

The alleles IA and IB are dominant to __

A

IO

68
Q

What does the allele IA lead to?

A

Antigen A being produced in the blood

69
Q

What does the allele IB lead to?

A

Antigen B being produced in the blood.

70
Q

What does the allele IO lead to?

A

No antigens being produced in the blood

71
Q

What are the possible phenotypes of blood type?

A
  1. A
  2. B
  3. AB
  4. O
72
Q

Define sex-linked characteristic

A

A feature in which the gene responsible is located on a sex chromosome and that this makes the characteristic more common in one sex than in
the other

72
Q

Define sex-linked characteristic

A

A feature in which the gene responsible is located on a sex chromosome and that this makes the characteristic more common in one sex than in
the other

73
Q

Why are the alleles for sex-linked characteristics most commonly on X chromosomes?

A

X chromosomes are much larger than Y chromosomes

74
Q

Why are females less likely to gain a sex-linked disease?

A

Females, having two copies of the X chromosome, are likely to inherit one dominant allele that masks the effect of the recessive allele

75
Q

What do we call a female that has one recessive allele and one dominant allele for a sex-linked disease?

A

A carrier: they may not have the disease, but has a 50% chance of passing it to an offspring

76
Q

What is an example of a sex-linked disease?

A

Red-green colorblindness

77
Q

Define phenotypic ratio

A

A ratio comparing the possible outcomes for an organism based on physical appearance.

IGCSEs (68 decks)

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