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IGCSE Biology > Topic 15 Inheritance > Flashcards

Topic 15 Inheritance Flashcards

1
Q

what do mutations form?

A

new alleles, which are alternative forms of genes, causing differences in inherited characteristics
eg gene for petal colour, one allele is red, one allele is yellow

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2
Q

what does dominant mean?

A

an allele that only needs to be inherited from one parent for it show in the phenotype of the organism

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3
Q

what does recessive mean?

A

an allele that only shows in physical characteristics of an organism when two copies are inherited, one from each parent

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4
Q

what does phenotype mean?

A

physical characteristics of an organism

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5
Q

what does genotype mean?

A

what alleles an organism has

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6
Q

what does homozygous mean?

A

when two alleles in an organism are the same

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7
Q

heterozygous

A

when two alleles in an organism are different

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8
Q

what is a carrier?

A

someone who is able to pass on a disease allele even though they are not suffering from disease

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9
Q

what is monohybrid inheritance?

A

characteristics involving a single gene

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10
Q

what is polygenic inheritance?

A

characteristics controlled by 2 or more genes working together

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11
Q

what kind of letter is the dominant allele given?

A

capital

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12
Q

what kind of letter is recessive allele given?

A

small letter

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13
Q

what is the allele pair for a phenotype called?

A

genotype

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14
Q

what is co dominance?

A

when both alleles within a genotype are expressed in the phenotype of an organism - neither allele is recessive, equally dominant

eg in a speckled hen, both black and white alleles are expressed in phenotype

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15
Q

what are most phenotypic features the result of?

A

polygenic inheritance rather than single genes

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16
Q

how to answer inheritance diagram questions

A
  1. show fully labelled working (parent genotypes, cross, offspring genotypes and phenotypes)
  2. show a conclusion with percentage chance
  3. do practice questions
17
Q

how to answer inheritance diagram questions

A
  1. show fully labelled working (parent genotypes, cross, offspring genotypes and phenotypes)
  2. show a conclusion with percentage chance
  3. do practice questions
18
Q

how to interpret family pedigrees

A
  • always write on the genotypes of the people with recessive phenotypes first eg. if they a disorder caused by a recessive allele, they must be homozygous recessive
  • for those with a dominant phenotype, you don’t know whether they are homozygous dominant or heterozygous dominant, so need to look at offspring -> only heterozygous individuals can pass on recessive allele to next generation
  • only recessive alleles can ‘skip a gen’ ie not visible in heterozygous individuals, but can be passed on to offspring
  • do practice question
19
Q

what is inheritance?

A

transmission of genetic information from generation to generation

20
Q

how is the sex of a person controlled?

A
  • one pair of chromosomes, XX in a female and XY in a male
21
Q

what is environmental variation?

A

variation caused by surroundings eg climate, diet, accidents, culture, lifestyle

22
Q

how is sex of offspring determined?

A
  • each male gamete may have an x or y chromosome, while each female gamete has an x chromosome
  • tend to draw circles round gametes before placing them in punnett square
23
Q

what is genetic variation?

A

inherited from parents due to genes recevied from sperm and egg (1/2 from each parent)

24
Q

what is a mutation?

A

rare, random change in genetic material that can be inherited

25
Q

what do mutations do?

A
  • alter sequence of abases in a gene, which causes different amino acids to be coded for, changing protein
  • adding extra base = insertion
  • deletion + substitution
  • this can affect phenotype
26
Q

why do most genetic mutations have no effect on the phenotype?

A
  • new codon codes for same amino acid
  • occurs in recessive alleles
  • mutation happens in a minor section of DNA
27
Q

why do most genetic mutations have no effect on the phenotype?

A
  • new codon codes for same amino acid
  • occurs in recessive alleles
  • mutation happens in a minor section of DNA
28
Q

what happens if a mutation occurs in a sex cell?

A

could be passed on to next generation

29
Q

what happens if a mutation occurs in a sex cell?

A

could be passed on to next generation

30
Q

What increases the incidence of mutations?

A
  • occur randomly
  • occur more often in ionising radiation, UV light, gamma and x rays
  • chemical mutagens eg chemicals in tobacco
31
Q

Explain how a mutation could lead to an enzyme failing to function?

A
  1. mutation occurs randomly, causing a change in DNA sequence and as a result the amino acid sequence
  2. active site of enzyme changes shape
  3. complementary substrate can no longer fit
  4. enzyme fails to function

(enzymes are proteins)

32
Q

what is evolution?

A

process by which different kinds of living organism are believed to have developed from earlier forms during history of earth

33
Q

what is darwin’s theory of evolution natural selection?

A
  1. each species reproduces and offspring show variation
  2. there is competition between these offspring for food, space, mates
  3. offspring with best adaptations to their environment survive, others die (survival of fittest)
  4. survivors pass on beneficial alleles to offspring
  5. over generations species will slowly change to become more suited to its environment
34
Q

how to answer natural selection questions?

A
  1. there is variation within a species for a characteristic due to random genetic mutations
    state what this variation is
  2. this advantageous phenotype leads to the individual outcompeting others of same species for …
    state what for
  3. this means the individual is more likely to survive and reproduce, passing their advantageous allele to offspring
  4. this accumulates over many generations leading to a new population of adapted individuals
35
Q

what are antibiotics and what do they do?

A
  • chemicals produced by fungi
  • kill bacteria by preventing cell wall formation and given to patients w bacterial infection
36
Q

how does antibiotic resistance occur?

A
  • mutation for antibiotic resistance prevents bacteria from being killed, whilst all non resistant bacteria are killed
  • this reduces levels of competition for resources (oxygen/glucose) for that bacteria
  • antibiotic resistant bacteria is therefore more likely to survive and reproduce, passing on gene for antibiotic resistance
  • creates population of antibiotic resistant bacteriA
37
Q

why is antibiotic resistance dangerous?

A
  • spread of infections we are unable to control
  • MRSA = super bug, dangerous as resistant to most antibiotics
  • to stop this, always avoid unnecessary use of antibiotics, and complete the full course (to kill all bacteria)!

IGCSE Biology (22 decks)

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