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GCSE Biology*** > Genes, Chromosomes, Cell division and Variation > Flashcards

Genes, Chromosomes, Cell division and Variation Flashcards

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1
Q

Where is DNA found ?

A

In the nucleus of a living cell

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2
Q

What does DNA control ?

A

Cell functions and the instructions for building all proteins within an organism

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3
Q

What is DNA’s structure ?

A
  • double helix shape
  • it has a sugar phosphate backbone
  • has bases Adenine, thymine, guanine and cytosine
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4
Q

Which bases complement each other ?

A 
Adenine = thymine 
Guanine = cytosine
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5
Q

What do the order of bases code for ?

A

Order of bases in the gene codes for the sequence of amino acid and protein. Three bases code for one amino acid-this is called a triplet

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6
Q

What is a gene ?

A

A gene is a length of DNA which codes for protein

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7
Q

What do the proteins made from a gene control ?

A

Chemical reactions, growth, colouration and all inheritable characteristics

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8
Q

What are the structures called that DNA is wrapped up into ?

A

Chromosomes

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9
Q

How many chromosomes does each person have ?

A

Two of each chromosome

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10
Q

Where do people get their two chromosomes from ?

A

One of each pair comes from the father the other from the mother

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11
Q

Where are genes for a specific characteristic situated on each homologous chromosome ? And what does this mean ?

A

They are situated at the same point on each homologous chromosome, therefore there is a pair of genes for each characteristic in every nucleus

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12
Q

How many chromosomes does a human have ?

A

46 chromosomes, 23 pairs

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13
Q

What does diploid mean ?

A

Two copies of each of their 23 chromosomes

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14
Q

What does haploid mean ?

A

Only contain one copy of each chromosome

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15
Q

What chromosomes are the sex chromosomes ?

A

The 23rd chromosomes

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16
Q

What gender are you if you contain two X chromosomes ?

A

Female

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17
Q

What gender are you if you have one X and one Y-chromosome ?

A

Male

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18
Q

Given example of a human cell that is haploid ?

A

Egg and sperm cells. This is so when they fuse they form a diploid offspring

19
Q

What is DNA coiled around in chromosomes ?

A

Proteins called histones

20
Q

DNA is a macromolecule what is it made up of ?

A

Small units called nucleotide

21
Q

What does growth and reproduction require ?

A

Cell Division

22
Q

What are the two types of cell division ?

A

Mitosis and Meiosis

23
Q

What happens before a cell divides ?

A

The chromosomes replicate making an exact copy of themselves. This doubles the amount of DNA in the cell

24
Q

What is mitosis ?

A
  • produces genetically identical daughter cells
  • These cells are diploid
  • Mitosis is used for growth, repair and asexual reproduction
25
Q

What is meiosis ?

A
  • this produces gametes
  • they are genetically varied
  • meiosis is ONLY used to produce gametes for sexual reproduction
26
Q

Describe mitosis

A
  • The two pairs of chromosomes each replicated itself to form chromatids
  • fibres appear in the cytoplasm and form a spindle
  • The chromosomes move to the equator of the spindle and spindle fibres shortening and appeared to pull the chromatids apart by centromeres
  • The chromatids are now chromosomes and have moved to opposite ends of the cell
  • The cell begins to divide
  • nuclear membrane forms again
  • after the cell divides it creates two identical daughter cells
27
Q

Describe meiosis

A
  • chromosomes make identical copies of themselves
  • similar chromosomes pair up
  • sections of DNA get swapped
  • pairs of chromosomes divide
  • chromosomes divide
  • four haploid, genetically varied cells are produced
28
Q

How is variation in offspring produced ?

A
  • genetic variation in gametes produced by meiosis

* Random fertilisation of ova by male gametes

29
Q

What Reproduction is meiosis used for ?

A

Sexual reproduction

30
Q

What reproduction is mitosis used for ?

A

Mitosis

31
Q

How many chromosomes are in the haploid cell after meiosis ?

A

23 chromosomes

32
Q

Why is variation important?

A

For evolution to occur

33
Q

How can variation occur ?

A

can be genetic, environmental or a combination of both

34
Q

Describe genetic variation

A

Following sexual reproduction or mutation, organisms will have different versions of genes to another individual

35
Q

Describe environmental variation

A

The environment can also affect the characteristics of an organism
E.g. More sun = grow taller
Less sun = shorter plant

36
Q

What is the mutation ?

A

Mutation is a change in the DNA

37
Q

How can a mutation occur ?

A
  • often a mutation will cause a base in DNA to change. So when it is read by the RNA it is incorrect this is called substitution mutation
  • a cell can gain an extra chromosome or one part of the chromosome is stuck to another chromosome, this is called chromosomal mutation
38
Q

What three affects can mutations have ?

A
  • neutral - like most sequence mutations
  • negative - most chromosomal mutations
  • positive - tiny minority of mutations could improve an organism survival chances
39
Q

What is a gene mutation ?

A

A single chromosome is changed as a result, a defective protein is produced. This can lead to a considerable change in characteristics, this can then be inherited.

40
Q

Why do mutations occur ?

A

They occur spontaneously

41
Q

What are mutagens ?

A

Factors that increase the rate of mutation

42
Q

What two mutagens can increase the rate of mutation ?

A
  • Radiation - can damage DNA and cause mutation

* chemicals - Tobacco smoke and other chemicals can cause mutations

43
Q

What is a mutagen that causes uncontrolled cell division called ?

A

A caricinogen

GCSE Biology*** (22 decks)

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