Brainscape's Knowledge GenomeTM

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


See full index

IB biology sl > unit 3 > Flashcards

unit 3 Flashcards

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

what is a gene?

A

a heritable factor that consists of a length of DNA and influences a specific characteristic.

  • a gene occupies a specific position on a chromosome.
  • the various specific forms of a gene are alleles.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

what is an allele?

A

one specific form of a gene, differing from other alleles by one or only a few bases and occupying the same gene locus as other alleles of the gene.

  • new alleles are formed by mutation
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

what is a genome?

A

the whole of the genetic information of an organism.

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

what is a gene mutation?

A

a change to the base sequence of a gene

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

what is sickle cell anaemia?

A

a genetic disease that affects red blood cells in the body

  • caused by a single base mutation on the Hb gene which codes for a polypeptide which is part of haemoglobin. GAG found in the normal Hb gene is mutated to GTG - A is replaced by T

this results in a change to the sequence of a polypeptide in haemoglobin during translation: causes glutamic acid to be substituted by valine as the 6th AA.

= results in the formation of the abnormal haemoglobin (S) in red blood cells instead of the normal haemoglobin A.

effects the phenotype as instead of normal donut shaped red blood cells being produced some of the red blood cells will be sickle-shaped.

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

what are the consequences of sickle cell anaemia?

A
  • sickle-shaped red blood cells cannot carry oxygen as efficiently as normal red blood cells would.
  • symptoms = fatigue and shortness of breath - the sickle haemoglobin causes the red blood cells to become less flexible and may get stuck in the small blood capillaries causing pain.
  • homozygous has lethal sickle cell anaemia whereas heterozygous carry the trait and half of the red blood cells would be sickled.
  • heterozygotes are more resistant to malaria.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

describe the chromosomes of prokaryotes

A
  • 1 chromosome
  • not enclosed in a nuclear membrane; found in the nucleoid region
  • consist of a circular DNA
  • DNA is naked as it doesn’t attach to proteins
  • have plasmids
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

describe the chromosomes of eukaryotes

A
  • many chromosomes
  • enclosed in a nuclear membrane.
  • consist of linear chromosomes
  • DNA is associated with histone proteins.
  • don’t have plasmids
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

how many chromosomes do humans have?

A

46 - 23 homologous pairs

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

what are homologous chromosomes?

A

are the same size and carry the same sequence of genes but not necessarily the same alleles of those genes.

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

characteristics of a diploid nucleus

A
  • 2 sets of chromosomes in a nucleus
  • have pairs of homologous chromosomes - each parent contributed one of the pair
  • e.g skin cell
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

characteristics of a haploid nucleus

A
  • 1 set of chromosomes in a nucleus
  • have one chromosome of each pair
  • e.g gametes
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

what is a karyogram and what are its uses?

A
  • a photograph that shows the chromosomes of an organism in homologous pairs of decreasing length.

used to:

  • deduce sex
  • diagnose chromosomal abnormalities such as Down syndrome in humans.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

what is a karyotype?

A

a property of a cell - the number and type of chromosomes present in the nucleus

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

what is meiosis?

A
  • 1 diploid nucleus divides by meiosis to produce four haploid nuclei.
  • the halving of the chromosome number allows a sexual life cycle with fusion of gametes.
  • involves two divisions
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

what happens before meiosis?

A
  • cells have an interphase stage before the start of meiosis I which is similar to mitosis. It includes G1, S and G2 phases.
  • DNA is replicated so that all chromosomes consist of two sister chromatids.
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

compare mitosis and meiosis

A

mitosis:
- produces somatic cells
- 2 diploid cells
- no crossing over
- centromere splits
- produced cells are identical

meiosis

  • produces gametes
  • 4 haploid cells
  • crossing over in prophase I
  • centromere splits in anaphase II only
  • produced cells are genetically varied
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

what is crossing over?

A
  • is the exchange of genetic material between non-sister chromatids which results in genetic variation
  • allows DNA from a person’s maternal chromosomes to mix with DNA from paternal chromosomes
  • occurs in prophase I
How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

what is random allocation

A
  • how the homologous pairs of chromosomes line up at the centre of the cell during metaphase 1
  • increases variation because the way they line up with by chance
20
Q

what is non-disjunction

A
  • when the chromosomes do not separate properly during meiosis, either in anaphase I or anaphase II

in anaphase I – the homologous chromosomes pair fail to separate properly - results in the formation of 4 abnormal cells.
in anaphase II – the sister chromatids fail to separate properly - resulting in the formation of 2 abnormal cells.

causes the production of gametes that either has a chromosome too many or too few. Gametes with a missing chromosome usually die quite fast however gametes with an extra chromosome can survive

21
Q

what causes down syndrome?

A
  • also called trisomy 21
  • chromosomes failed to separate properly during meiosis leading to three chromosomes of type 21 instead of two.
  • a person with the condition has a total of 47 chromosomes instead of 46.
  • Down syndrome leads to many complications and also the risk of having a child with the condition increases with age.
  • symptoms include malformations of the digestive system, physical and mental problems.
22
Q

how are cells obtained for karyotyping?

A

Karyotyping is performed using cells collected by chorionic villus sampling (CVS) or amniocentesis, for prenatal diagnosis of chromosome abnormalities.

Amniocentesis: involves using a hypodermic needle to extract some of the amniotic fluid around the developing baby. Inside the amniotic fluid, some of the fetal cells can be found.

CVS: taking a sample from the chorionic villus which will contain some fetal cells.

23
Q

what are a genotype and phenotype

A

genotype = the alleles of a gene carried by an organism.

phenotype = the expression of the gene; the characteristics of an organism.

24
Q

what are dominant and recessive alleles?

A

dominant = an allele that affects the phenotype when present in the homozygous or heterozygous state - mask the effects of recessive alleles.

recessive = an allele that affects the phenotype only when present in the homozygous state.

25
Q

what are codominant alleles?

A

pairs of alleles which are both expressed when present.

co-dominant alleles have joint effects.

26
Q

what are homozygous and heterozygous alleles/genes?

A

homozygous = having two identical alleles of a gene.

heterozygous = having two different alleles of a gene.

27
Q

what is a carrier?

A

an individual that has one copy of a recessive allele that causes a genetic disease in individuals that are homozygous for this allele.

28
Q

what are multiple alleles?

A

when some genes have more than 2 alleles

such as blood type

29
Q

what are the 3 alleles that control the ABO blood groups?

A
  • the allele IA corresponds to blood group A
    (genotype IAIA)
  • the allele IB corresponds to blood group B (genotype IBIB)
  • blood group O has the genotype ii
  • the allele i is recessive to both IA and IB so if you have the genotype IAi you will have blood group A and if you have the genotype IBi you will have blood group B.
30
Q

codominant alleles (blood type)

A

co-dominant alleles have joint effects.
both of IA and IB are dominant alleles and so if IA and IB are present together they form blood group AB (genotype IAIB).

31
Q

genetic diseases in humans

A
  • many are due to recessive alleles of autosomal genes, although some genetic diseases are due to dominant or co-dominant alleles.
  • some genetic diseases are sex-linked.
32
Q

sex chromosomes

A
  • sex chromosomes determine gender (X and Y chromosomes)
  • females have two X chromosomes whereas males have one X and one Y chromosome.
  • if the male passes on the X chromosome then the growing embryo will develop into a girl. If the male passes on the Y chromosome then it will develop into a boy = gender depends on whether the sperm which fertilizes the egg is carrying an X or a Y chromosome.
  • the X chromosome is relatively large compared to the Y (which is much smaller)
  • some genes are present on the X chromosome and absent from the shorter Y chromosome in humans.
33
Q

what is sex linkage?

A

when the gene controlling the characteristic is located on the sex chromosome and so the characteristic is associated with gender.

most of the time sex-linked genes are carried on the X chromosome = females have 2 copies of the gene, males only have 1

34
Q

what are 2 examples of sex-linked diseases carried on the X chromosome

A
  • red-green colour blindness

- haemophilia

35
Q

haemophilia genes/allele

A

XH is the allele for normal blood clotting and is dominant over Xh which is recessive and causes haemophilia.

36
Q

why are males more likely to have haemophilia?

A
  • haemophilia is a sex-linked recessive disease
  • the gene is carried on the X chromosome
  • for a male to be affected (Xh Y), it is enough to inherit one affected allele from the mother. A male can’t be a carrier.
  • for a female to be affected (Xh Xh ), she must inherit both affected alleles from both parents; she must be homozygous recessive. If she inherits one affected allele, then she is normal but a carrier XH Xh (heterozygous).
37
Q

what is cystic fibrosis and what causes it?

A
  • an autosomal recessive genetic disease
  • caused by a mutation of the CFTR gene on chromosome 7
  • the CFTR gene codes for a Chloride ion channel protein that transports Ch ions into and out of cells.
  • the flow of Ch ions via channel proteins helps control the movement of water in tissues, which is necessary for the production of mucus.
  • mutations in the CFTR gene disrupt the function of the Ch channels, preventing them from regulating the flow of Ch ions and water across cell membranes.
    = cells that line the passageways of the lungs, pancreas, and other organs produce mucus that is unusually thick and sticky.
  • this mucus clogs the airways and various ducts, causing the characteristic signs and symptoms of cystic fibrosis.
38
Q

what is Huntington’s disease and what causes it?

A
  • an autosomal dominant genetic disease.
  • due to a mutation in the Huntington gene (HTT)
  • this mutation results in a repetition of a CAG sequence in the gene encoding for the protein Huntington (Htt).
    = leads to the formation of an abnormal protein with repetitive glutamate amino acid.
  • the repetitive glutamates in the Htt change the shape of the brain cells, affecting their function = brain cell damage.
  • Huntington’s disease is a neurodegenerative genetic disorder that affects muscle coordination and leads to mental decline and behavioural symptoms
39
Q

how to know if a disorder is sex-linked through a pedigree chart

A
  • if most of the males in the pedigree are affected the disorder is X-linked.
  • if it is a 50/50 ratio between men and women the disorder is autosomal.
40
Q

how to know if a disorder is recessive or dominant through. a pedigree chart

A
  • if the disorder is dominant, one of the parents must have the disorder.
  • if the disorder is recessive then neither of the parents has to have the disorder as they can be heterozygous.
41
Q

What is a PCR and how does it work?

A
  • PCR can be used to amplify small amounts of DNA.
  • can be useful when only a small amount of DNA is available but a large amount is required to undergo testing.
  • we can use DNA from blood, semen, tissues and so on from crime scenes for example.
  • this is done by DNA replication
  • Taq DNA polymerase enzyme is used (extracted from bacteria) as it can withstand high temperature without denaturing.
  • PCR requires cycles of heating and cooling:
  • heating to breakdown the hydrogen bond between the two DNA strand
  • cooling as primers bind to DNA sequences at low temp.
42
Q

what is gel electrophoresis?

A
  • is used to separate proteins or fragments of DNA according to size.
  • gel electrophoresis of DNA is used in DNA profiling.
43
Q

what is the process of gel electrophoresis?

A
  1. DNA (long fragment) is cut up with restriction enzymes.
  2. sample of fragmented DNA is placed in one of the wells on the gel.
  3. an electrical current is passed across the gel.
  4. fragment separation is based on size.
  5. large fragments move slowly.
44
Q

what is the process of DNA profiling?

A
  • DNA is copied using PCR
  • it is cut up into small fragments using restriction enzymes.
  • gel electrophoresis separates fragmented pieces of DNA according to their size and charge. This gives a pattern of bands on a gel which is unlikely to be the same for two individuals.
  • The DNA banding patterns are compared.
45
Q

explain the gene transfer of insulin into bacteria

A
  1. the desired gene that codes for insulin is extracted from a human pancreatic cell that produces insulin.
  2. the desired gene is cut with restriction enzymes (endonucleases) to produce sticky ends.
  3. at the same time, a plasmid (a circular DNA) is removed from a bacterium cell.
  4. the selected plasmid is cut and cleaved using the same restriction enzymes which cut the DNA at specific base sequences and produce corresponding sticky ends.
  5. the desired gene is then added to the open plasmid and loose ends are joined (spliced) with DNA ligase.
  6. the plasmid with the desired human insulin gene is now called recombinant plasmid.
  7. the recombinant plasmid formed can then be inserted into a new host cell (e.g a bacterium).
  8. host cells are then cloned.
  9. desired gene product; insulin is produced.
46
Q

what is required for gene transfer?

A
  1. desired gene
  2. plasmid
  3. host cell
  4. enzymes ( restriction enzymes and DNA Ligase)

IB biology sl (6 decks)

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