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Ib biology > Topic 3 > Flashcards

Topic 3 Flashcards

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1
Q

What is a brief explanation of meiosis?

A
  • 1 diploid cell to 4 haploid
  • Meiosis 1 and 2
  • Described as reduction division as chromosome number is halved
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2
Q

What is the definition of diploid cell?

A

2 chromosomes of each type

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3
Q

What is the definition of haploid cell?

A

1 chromosome of each type

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4
Q

What feature of meiosis allows there to be a sexual life cycle?

A

Chromosome numbers are halved

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5
Q

What is a sexual life cycle?

A

The differences between the chromosomes of offspring and parents

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6
Q

Why does the chromosome number need to be halved at some point of the life cycle?

A

Fertilisation occurs and it doubles the chromosome number each time

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7
Q

When can meiosis only occur in animals?

A

Making of gametes

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8
Q

The orientation of pairs of homologus chromosomes are what?

A

Random

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9
Q

How many poles is each chromosome attached to?

A

1

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10
Q

Does the orientation of one bivalent impact the other?

A

NO

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11
Q

Are 2 homologus chromosomes in a bivalent attached to the same pole?

A

no

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12
Q

What halves the chromosome number?

A

Separation of homologus chromosomes in meiosis 1

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13
Q

What is disjunction?

A

The separation of homologus chromosomes

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14
Q

How does disjunction occur?

A

1 chromosome from each bivalent moves to opposite poles of the cell which halves the chromosome number

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15
Q

What three processes promote genetic variation?

A

Crossing over, fertilisation and random orientation of bivalents

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16
Q

How does crossing over promote genetic diversity?

A

Allows linked genes to produce new allele combinations and increases the number of allele combinations generated by meiosis

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17
Q

How does random orientation of bivalents promote genetic diversity?

A
  • Promotes genetic variation among genes that are on different chromosomes
  • n of allele combinations = 2 to the power of n ( n = haploid number)
  • For every bivalent the number of combinations doubles
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18
Q

Why does fertilisation promote genetic diversity?

A

It is the start of new life, allows alleles from 2 different individuals to be combined into 1, combination of alleles are unlikely to have been seen before

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19
Q

What is non- disjunction?

A

When pairs of homologus chromosomes fail to separate

20
Q

When the chromosomes fail to separate where would they move to?

A

Both to one pole and neither to the other pole

21
Q

What is trisomy 21?

A
  • When there are 3 of chromosome 21
  • lead to hearing loss, heart and vision disorders
  • down syndrome
22
Q

What else can there be an abnormal number of?

A

Sex chromosomes

  • Klinefelter’s syndrome = XXY
  • Turner’s syndrome = X
23
Q

What is the correlation between maternal age and non disjunction?

A

Strong positive correlation with the risk of chromosome abnormalities increasing after the age of 30

24
Q

DNA replication

A
  • during interphase

- so that all the chromosomes consist of 2 sister chromatids

25
Q

We know that DNA replication is accurate because two chromatids are intitally genetically what?

A

Identical

26
Q

What happens to the chromatids during meiosis?

A
  • 1 diploid nucleus where each consists of 2 chromatids divides twice to produce 4 haploid nuclei which consist of 1 chromatid
27
Q

What is it called when homologus chromosomes pair up?

A

Bivalent

28
Q

What is the process in which the homologus chromosomes pair up called?

A

Synapsis

29
Q

After the chromosomes have paired up what happens?

A

Crossing over

30
Q

Describe the process of crossing over

A
  • A junction is created where one chromatid in each of the homologus chromosomes breaks off and rejoins with another
  • occurs anywhere along the chromosome
  • there is a mutual exchange of genes as crossing over occurs at the same position in each chromatid
31
Q

What are the two ways that you can maintain cells from a fetus?

A

-amniocentesis ( passing a needle from the mothers abdomen wall and using it to withdraw a sample of amniotic fluid)
-chronic vilus sampling ( sampling tool that enters through the vagina and obtains cells from the chronion)
CHRONION = MEMBRANE THAT THE PLACENTA DEVELOPS IN

32
Q

Stages of meiosis

A

PMAT 1 + PMAT 2

33
Q

Prophase 1

A
  • 2n chromosomes
  • homologus chromosomes pair up
  • crossing over occurs
34
Q

Metapahse 1

A
  • spindle fibres move the chromosomes to the equator of the cell
  • orientation is random
35
Q

Anaphase 1

A
  • the homologus pairs are separated ( one chromosome of each pair moves to each pole)
36
Q

Teleophase 1

A
  • chromosomes uncoil
  • chromosomes go from diploid to haploid
  • cytokinsesis occurs
37
Q

Prophase 2

A
  • chromosomes condense and become more visible
38
Q

Metaphase 2

A
  • chromosomes line up at the equator
39
Q

Anaphase 2

A
  • chromosomes separate and the chromatids are pulled to opposite poles
40
Q

Teleophase 2

A
  • chromatids reach opposite poles
  • nuclear envelope forms
  • cytokinesis occurs
41
Q

Bacterial chromosomes

A
  • Prokaryotes that have 1 chromosome consisting of a circular DNA molecule
  • Naked DNA
  • 1 copy of a gene
  • Two copies after replication
42
Q

Features of plasmids

A
  • Small and circular
  • Contain genes that may be useful to the cell but not genes needed for basic processes ( like genes for antibiotic resistance)
  • may be multiple copies
43
Q

Why can there be multiple copes of plasmids?

A

They are not replicated the same time as the chromsomes

44
Q

How can plasmids be spread through a population?

A

The copies are transferred from one cell to another

45
Q

How can plasmids cross the species barrier?

A

Plasmid released when a prokaryotic cell dies and is absorbed the cell of another species

Ib biology (11 decks)

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