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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
What is translation?
When the RNA molecule serves as a code for the formation of an amino-acid chain
26
Although most body cells contain the same genes, why are many genes in a cell *not* expressed?
The cell only makes the specific proteins it needs
27
Define mitosis
Nuclear division giving rise to genetically identical cells
28
When cells divide, why do their chromosomes double?
It ensures that when the cell splits in two, each cell is still diploid
29
What is mitosis used for?
*growth, repair of damaged tissues, replacement of cells* and *asexual reproduction*
30
Define chromatid
One arm of a replicated chromosome
31
Before mitosis, what happens?
The unravelling of chromosomes and replication of DNA (doubling)
32
During mitosis, what happens?
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
During mitosis, what happens?
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
How do chromosomes seperate during mitosis?
Chromosomes line up along the centre of the cell where cell fibres pull them apart.
34
Define stem cells
Unspecialised cells that divide by mitosis to produce daughter cells that can become specialised for specific functions
35
What is the function of stem cells?
To produce new daughter cells that can become specialised within the tissue and be used for different functions
36
Define meiosis
A type of nuclear division that gives rise to cells that are genetically different
37
What is meiosis used for?
To produce gametes
38
What happens to the chromosome count after meiosis?
The chromosome count is halved from diploid to haploid
39
How many cells are produced by meiosis?
Four cells
40
How many cell divisions occur in mitosis and meiois?
In mitosis, one cell division occurs In meiosis, two cell divisions occur
41
What is the importance of meiosis?
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
Define inheritance
The transmission of genetic information from generation to generation
43
Define monohybrid inheritance
The inheritance of characteristics controlled by a single gene
44
What sort of diagram can be used to show monohybrid inheritance?
A punnet square genetic diagram
45
What does a punnet square show us?
The possible combinations of alleles that could be produced in the offspring: allowing us to figure out the ratio of combinations
46
Define dominant allele
An allele that is expressed if it is present in the genotype
47
Define recessive allele
An allele that is only expressed when there is no dominant allele of the gene present in the genotype
48
What is the genotype?
The genetic make-up of an organism determined by combinations of alleles
49
What is the phenotype?
The observable features of an organism
50
Define homozygous
Having two identical alleles of a particular gene
51
Define heterozygous
Having two different alleles of a particular gene
52
Define pure breeding
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
Two identical homozygous individuals that breed together will be __
Pure-breeding
54
How is a dominant allele shown?
With a capital letter
55
How is a recessive allele shown?
With a simple letter
56
In what order should a dominant and recessive allele be written together?
DOMINANT - recessive
57
What is a test cross used for?
To find out the genotype of an organism showing the dominant phenotype
58
How does a test cross work?
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
What are family pedigrees used for?
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
In pedigree diagrams, what shape indicates males and what shape indicates females?
Males: square Females: circle
61
In pedigree diagrams, what color are affected and unaffected individuals?
Affected: red Unaffected: blue
62
Horizontal lines between males and females in pedigree diagrams show...
That they have produced children (shown underneath each couple)
63
Define codominance
A situation in which both alleles in heterozygous organisms contribute to the phenotype
64
How are codominant alleles represented?
Both with uppercase letters, BUT with different letters used
65
What are the three alleles governing blood group?
IA, IB, IO
66
Which alleles for blood type are codominant?
IA, and IB
67
The alleles IA and IB are dominant to __
IO
68
What does the allele IA lead to?
Antigen A being produced in the blood
69
What does the allele IB lead to?
Antigen B being produced in the blood.
70
What does the allele IO lead to?
No antigens being produced in the blood
71
What are the possible phenotypes of blood type?
1. A 2. B 3. AB 4. O
72
Define sex-linked characteristic
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
Define sex-linked characteristic
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
Why are the alleles for sex-linked characteristics most commonly on X chromosomes?
X chromosomes are much larger than Y chromosomes
74
Why are females less likely to gain a sex-linked disease?
Females, having two copies of the X chromosome, are likely to inherit one dominant allele that masks the effect of the recessive allele
75
What do we call a female that has one recessive allele and one dominant allele for a sex-linked disease?
A carrier: they may not have the disease, but has a 50% chance of passing it to an offspring
76
What is an example of a sex-linked disease?
Red-green colorblindness
77
Define phenotypic ratio
A ratio comparing the possible outcomes for an organism based on physical appearance.

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