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GCSE Biology > Inheritance, Variation and Evolution > Flashcards

Inheritance, Variation and Evolution Flashcards

1
Q

what is DNA?

A

a chemical that all of the genetic material in a cell is made up from, containing coded information, basically all the information needed to put an organism together and make it work

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2
Q

what does DNA stand for?

A

Deoxyribonucleic acid

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3
Q

where is DNA found?

A

the nucleus of animal and plant cells in really long structures called chromosomes, which normally come in pairs

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4
Q

describe the structure of DNA

A

a polymer - made up of two strands coiled together in the shape of a double helix

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5
Q

what is a gene?

A

a small section of DNA found on a chromosome

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6
Q

what does each gene code for?

A

a particular sequence of amino acids which are put together to make a specific protein

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7
Q

how many amino acids are used to code for how many proteins?

A

20 amino acids used to code for thousands of proteins

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8
Q

what does DNA determine about a cell?

A

what kind of protein it makes (eg haemoglobin, keratin ) and that in turn determines what type of cell it is ( eg red blood cell, skin cell)

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9
Q

what is a genome?

A

a term meaning the entire set of genetic material in an organism

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10
Q

how does the understanding of the human genome help us understand and combat disease?

A
  • it allows scientists to identify genes in the human genome that are linked to different types of disease
  • knowing which genes are linked to inherited diseases could help us to understand them better and could help us develop effective treatments for them
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11
Q

“scientists can look at the genomes to trace the migration of certain populations of people around the world”

elaborate on this point :D

A

All modern humans are descended from a common ancestor who lived in Africa, but humans can now be found all over the planet.
The human genome is mostly identical in all individuals, but as different populations migrated away from Africa, they gradually developed tiny differences in their genomes.
By investigating these differences, scientists can work out when new populations split off in a different direction, and what route they took

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12
Q

DNA is a POLYMER what is the name for the repeating units in this polymer?

A

nucleotides

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13
Q

describe DNAs nucleotides structure …

A

each nucleotide consists of:
- one sugar molecule
- one phosphate molecule
- one ‘base’
The sugar and phosphate molecules in the nucleotides form a ‘backbone’ to the DNA strands. The sugar and phosphate molecules alternate. One of four different bases joins together each sugar. Each base links to a base on the opposite side in the helix.

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14
Q

what are the 4 bases that hold the nucleotides together?

A

A, T, C, and G

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15
Q

what are the complimentary base pairs?

A

A & T , C & G

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16
Q

what do the order of bases in a gene determine?

A

the order of amino acids in a protein

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17
Q

each amino acid is coded for by a sequence how many bases per gene?

A

3 bases

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18
Q

what do non-coding parts of DNA do?

A

switch genes on and off, and so control if the gene is expressed

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19
Q

what does it mean if a gene is expressed?

A

if a gene if used to make a protein or not

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20
Q

where area proteins made?

A

cytoplasm anf ribosomes

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21
Q

how do ribosomes make proteins?

A

they use the code in the DNA. The DNA is found in the cell nucleus and cannot move out of it because its too big, so the DNA is transported from the nucleus to the ribosomes using a transport molecule called mRNA.

mRNA copies the code from the DNA, the mRNA acts as a messenger betweed the DNA and the ribosome - carrying the code between the two

the correct amino acids are brought to the ribosomes in correct order by carrier molecules

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22
Q

what does a proteins unique shape mean?

A

it determines which task the protein is made to perform

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23
Q

give some examples of proteins…

A

enzymes - biological catalysts to speed up chemical reactions
hormones - used to carry messages around the body
structural proteins - physically strong ( eg collagen strengthens connective tissues)

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24
Q

what is a mutation?

A

a random change in an organisms DNA

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25
Q

give an example of a spontaneous mutation?

A

when a chromosome is not replicated properly

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26
Q

how can the chances of a mutation occurring increase?

A

by exposure to certain substances or some types of radiation

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27
Q

what happens when a mutation occurs?

A

the sequence of DNA bases in the gene change which produces a genetic variant . SAS the sequence of DNA bases codes for the sequence of amino acids that make up a protein, mutations to a gene sometimes lead to changes in the protein that it codes for

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28
Q

how do mutations effect a protein?

A
  • most mutations have very little, or no effect on the protein, some will change it to such a small extent that its function or appearance is unaffected
  • some mutations seriously affect a protein, because sometimes the mutation will code for an altered protein with a change in its shape, causing it to lose its ability to perform its function
  • mutations in non-coding DNA can alter how genes are expressed
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29
Q

explain how a change in shape of a protein ( due to mutation) could affect its ability to perform its function…

A
  • if the shape of the enzymes active site has changed it’s substrate may no longer be able to bind to it
  • structural proteins like collagen could lose their strength if their shape is changes, meaning they can no longer provide structure and support
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30
Q

what are the 3 types of mutations?

A

insertions, deletions and substitutions

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31
Q

what is an insertion mutation?

A

where a new base is inserted into the DNA base sequence where it shouldn’t be, so an insertion changes the way the groups of three bases are ‘read’, which can change the amino acids that they code for - they change more than one amino acids as they have a knock-on-effect on the bases further on in the sequence

32
Q

what is a deletion mutation?

A

when a random base is deleted from a DNA sequence, like insertions they change the way that the base sequence is read and have knock of effects further down the sequence

33
Q

what is sexual reproduction?

A

where genetic information from two organisms ( a father and mother) is combined to produced offspring which are genetically different to either parent

34
Q

what do mother and father cells produce in meosis?

A

gametes - eg egg and sperm cells in humans

35
Q

how many chromosomes does a human gamete have?

A

23 chromosomes - half the number of chromosomes in a normal cell ( instead of having two of each chromosome, a gamete has just one of each)

36
Q

what happens to the egg and sperm cell in sexual reproduction?

A

they fuse together to form a cell with the full number of chromosomes

37
Q

why is there variation of the offspring of sexual reproduction?

A

it receives genetic information from both its parents, so inherits different features

38
Q

what is asexual reproduction?

A

reproduction that only involves one parent, and produces genetically identical offspring

39
Q

how does asexual reproduction happen?

A

mitosis - an ordinary cell makes a new cell by dividing in two

40
Q

what is it called when a cell is genetically identical?

A

a clone ;)

41
Q

what kind of organisms reproduce asexually?

A

bacteria, plants and animals

42
Q

in humans where are the only 2 places that meiosis takes place ?

A

ovaries in female and testes in men

43
Q

what happens in a cell before it starts to divide in meiosis?

(replication, arrangement)

A

the cell duplicates its genetic information, forming two armed chromosomes - one arm of each chromosome is an exact copy of the other arm. After replication, the chromosomes arrange themselves into pairs.

44
Q

describe the division stages of meiosis

(division)

A
  • in the first division the chromosome pairs line up in the centre of the cell
  • the pairs are then pulled apart so each new cell only has one copy of each chromosome. Some of the fathers chromosomes and some of the mothers chromosomes go in each cell
  • in the second division, the chromosomes line up again in the centre of the cell, the arms of the chromosomes are pulled apart
45
Q

what is substitution mutation?

A

substitution mutations are when a random base in the DNA base sequence is changed to a different base

46
Q

describe the gametes produced in meiosis

A

you get four gametes, each with only a single set of chromosomes in it, each of the games is genetetically different from the others because the chromosomes all get shuffled up during meiosis and each gamete only gets half of them, at random

47
Q

what happens to the gametes produced by meiosis?

A
  • after the two gametes have fused during fertilisation the resulting new cell divides by mitosis to make a cop of itself
  • mitosis repeats itself many times to produce lots of new cells in an embryo
  • as the embryo develops these cells then start to differentiate into different types of specialised cells that make an organism
48
Q

what can we use to speed up natural selection?

A

selective breeding - where individuals with desirable characteristics are bred to produce offspring that have desirable characteristics too

49
Q

how could selective breeding be used to increase food production?

A

by breeding animals that produce a lot of meat

50
Q

how many PAIRS of chromosomes are there in every human body cell?

A

23 PAIRS ( so 46 chromosomes per cell )

51
Q

what are the human’s 23 pairs of chromosomes labelled?

A

XY or XX

52
Q

give some examples of characteristics controlled by single genes?

A

mouse fur colour, red-green colour blindness

53
Q

all genes exist in different versions - what are these versions called?

A

alleles

54
Q

how many alleles do we have for every gene in our body?

A

2 versions - one on each chromosome in a pair

55
Q

what does it mean if an organism is homozygous for a particular trait ?

A

if the organism has two alleles for that particular gene that are the same

56
Q

what does it mean if a gene is heterozygous

A

if two alleles for a particular gene are different

57
Q

what is a dominant allele?

A

in heterozygous the two alleles are different, but only one can determine what characteristic is present - the allele for the characteristics that’s shown is called the dominant allele

58
Q

what kind of letter is used to represent a dominant allele?

A

CAPITAL LETTERS

eg CC or Cc - because the dominant allele overrules the recessive one

59
Q

when does an organism display recessive characteristics?

A

both alleles must be recessive - even if there is one dominant and one recessive the dominant will always overrule the recessive

60
Q

how do we represent recessive alleles?

A

lower caps

eg ‘cc’

61
Q

define genotype?

A

the alleles an organism has for a particular characteristic

62
Q

define phenotype

A

the visible characteristics of an organism that occurs as a result of its genes

63
Q

what is cystic fibrosis?

A

a genetic disorder of the cell membrane, that results in the body producing a lot of thick sticky mucus in the air passages and in the pancreas

64
Q

what allele causes cystic fibrosis?
how common is it to carry this allele?

A

a recessive allele ‘f’ carried by about 1 in 25 people

65
Q

what does it mean if someone is a carrier of cystic fibrosis?

A

if a person has one copy of the allele, and so doesn’t have the disorder ( because it is recessive)

66
Q

what are the chances of a child having the disorder if both parents are the carriers?

A

1 in 4

67
Q

what is polydactyly

A

a genetic disorder where a babys born with extra fingers or toes

68
Q

what kind of allele is polydactyly caused by?

A

Dominant ‘D’ - so can be inherited if just one parent carries the defective allele

69
Q

what are the chances a child will develop polydactyly if one parent has a ‘D’ allele?

A

50%

70
Q

how is an embryo in IVF genetically screened?

A

they remove a cell and analyse its genes

71
Q

how is a baby genetically screened before it is born?

A

DNA is removed from the embryo in the womb and that can be tested for disorders

72
Q

give some reasons against embryonic screening…

A
  • it implies people with genetic problems are ‘undesirable’ which could lead to an increase in prejudice
  • it may come to the point where everyone wants to screen their embryos to find the most ‘desirable’ one
  • screening is expensive
73
Q

give some reasons for embryonic screening…

A
  • it will help people to stop suffering
  • there are laws to stop it going far, eg cannot select sex of their baby
74
Q

what causes genetic variation?

A

where genes are passed on in gametes from the mother and father, which contains genes that code for your characteristics - meaning you will have some similar characteristics as both parents

75
Q

give some examples of characteristics that are only contained by genes?

A

eye colour, blood group, inherited disorders

76
Q

how do mutations introduce variation?

A
  • mutations are changes to the sequence of bases in the DNA
  • mutations can cause changes in the protein that a gene codes for
  • most mutations have no effect on the organisms phenotype
  • some have a small influence on phenotype and so alter the characteristics slightly
  • in rare occasions mutations can result in a new phenotype being seen in a species

GCSE Biology (8 decks)

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