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Biology IB HL > 3.1 Genes > Flashcards

3.1 Genes Flashcards

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1
Q

What is DNA?

A

DNA is the genetic blueprint which codes for, and determines, the characteristics of an organism

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2
Q

What features does DNA code for (3)?

A

This includes the physical, behavioural and physiological features of the organism

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3
Q

What is DNA packaged into?

A

DNA is packaged and organised into discrete structures called chromosomes

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4
Q

What is a gene?

A

A gene is a sequence of DNA that encodes for a specific trait (traits may also be influenced by multiple genes)

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5
Q

What is a locus?

A

The position of a gene on a particular chromosome is called the locus (plural = loci)

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6
Q

What are alleles?

A

Alleles are alternative forms of a gene that code for the different variations of a specific trait

For example, the gene for eye colour has alleles that encode different shades / pigments

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7
Q

What similarities do alleles have?

A

As alleles are alternative forms of one gene, they possess very similar gene sequences

Alleles only differ from each other by one or a few bases

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8
Q

What is a gene mutation?

A

A gene mutation is a change in the nucleotide sequence of a section of DNA coding for a specific trait

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9
Q

What does mutation form?

A

New alleles are formed by mutation

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10
Q

What three “types” of gene mutation can there be (in terms of how they affect the organism)?

A

Gene mutations can be beneficial, detrimental or neutral

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11
Q

What do beneficial mutations do?

A

Beneficial mutations change the gene sequence (missense mutations) to create new variations of a trait

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12
Q

What do detrimental mutations do?

A

Detrimental mutations truncate the gene sequence (nonsense mutations) to abrogate the normal function of a trait

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13
Q

What do neutral mutations do?

A

Neutral mutations have no effect on the functioning of the specific feature (silent mutations)

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14
Q

What is an example of a disorder caused by a gene mutation?

A

Sickle cell anaemia is an example of a disorder caused by a gene mutation

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15
Q

How did the mutation in sickle cell anaemia arise?

A

The disease allele arose from a base substitution mutation – where a single base was changed in the gene sequence

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16
Q

What is the cause of sickle cell anaemia? (in the DNA)

A

Sickle cell anaemia results from a change to the 6th codon for the beta chain of haemoglobin

17
Q

How is the DNA sequence different in a person with sickle cell?

A

DNA: The DNA sequence changes from GAG to GTG on the non-transcribed strand (CTC to CAC on the template strand)

18
Q

How is the mRNA sequence different in a person with sickle cell?

A

mRNA: The mRNA sequence changes from GAG to GUG at the 6th codon position

19
Q

How is the polypeptide different in a person with sickle cell?

A

The sixth amino acid for the beta chain of haemoglobin is changed from glutamic acid to valine (Glu to Val)

20
Q

What does the change in the polypeptide result in people with sickle cell?

A

The amino acid change (Glu → Val) alters the structure of haemoglobin, causing it to form insoluble fibrous strands

21
Q

What does the insolubility of Hb lead to?

A

The insoluble haemoglobin cannot carry oxygen as effectively, causing the individual to feel constantly tired

22
Q

What does the fibrous nature of the Hb lead to?

A

The formation of fibrous haemoglobin strands changes the shape of the red blood cell to a sickle shape

23
Q

What may the sickle cells form?

A

The sickle cells may form clots within the capillaries, blocking blood supply to vital organs and causing myriad health issues

24
Q

What is another disadvantage of sickle cells?

A

The sickle cells are also destroyed more rapidly than normal cells, leading to a low red blood cell count (anaemia)

25
Q

What is the genome?

A

The genome is the totality of genetic information of a cell, organism or organelle

26
Q

What does the genome include?

A

This includes all genes as well as non-coding DNA sequences (e.g. introns, promoters, short tandem repeats, etc.)

27
Q

What was the Human Genome Project?

A

The Human Genome Project (HGP) was an international cooperative venture established to sequence the human genome

28
Q

What did the HGP show?

A

The HGP showed that humans share the majority of their sequence, with short nucleotide polymorphisms contributing diversity

29
Q

What were the 4 (general) outcomes of the HGP?

A

mapping
screening
medicine
ancestry

30
Q

What was the outcome of the HGP in terms of mapping?

A

The number, location, size and sequence of human genes is now established

31
Q

What was the outcome of the HGP in terms of screening?

A

This has allowed for the production of specific gene probes to detect sufferers and carriers of genetic diseases

32
Q

What was the outcome of the HGP in terms of medicine?

A

The discovery of new proteins have lead to improved treatments (pharmacogenetics and rational drug design)

33
Q

What was the outcome of the HGP in terms of ancestry?

A

Comparisons with other genomes have provided insight into the origins, evolution and migratory patterns of man

34
Q

Will the number of genes present differ between species?

A

YES!!!
The number of genes present in an organism will differ between species and is not a valid indicator of biological complexity

35
Q

How is the number of genes in a genome predicted?

A

The number of genes in a genome is usually predicted by identifying sequences common to genes

36
Q

What may the identifying regions be include?

A

These identifying regions may include expressed sequence tags (ESTs) or sequences that are homologous to known genes

37
Q

What makes the counts of unique gene numbers difficult?

A

The presence of pseudogenes and transposons make accurate counts of unique gene numbers very difficult

38
Q

Why may gene estimations greatly vary?

A

As scientists may use different approaches to predicting gene numbers, final estimations can vary significantly

For instance, the number of genes in rice (Oryza sativa) is estimated as being between 32,000 – 50,000
The number of genes in humans is estimated as being between 19,000 – 25,000

39
Q

What can be used to compare gene sequences from two different species?

A

Gene sequences from different species can be identified and then compared using two online resources:

GenBank – a genetic database that serves as an annotated collection of DNA sequences
Clustal Omega – an alignment program that compares multiple sequences of DNA

https://ib.bioninja.com.au/standard-level/topic-3-genetics/31-genes/gene-comparisons.html

Biology IB HL (56 decks)

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