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biology > 4.3 inheritance > Flashcards

4.3 inheritance Flashcards

1
Q

define homozygous dominant
define homozygous recessive

A

genotype contains 2 copies of the dominant allele
genotype contains 2 copies of the recessive allele

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2
Q

what is a back cross?

A

crossing the organism with another that is homozygous recessive for the trait

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3
Q

what does a back cross determine?

A

whether an organism is homozygous or heterozygous

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4
Q

how would you know if the parent is heterozygous from doing a back cross?

A

if any of the offspring show the homozygous recessive trait in the phenotype

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5
Q

what is mendels 1st law of genetics?
define it

A

the law of segregation
the characteristics of an organism are determined by factors (genes) which occur in pair. only 1 member of a pair of factors can be represented in a single gamete

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6
Q

define monohybrid inheritance

A

the inheritance of a single pair of contrasting characters

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7
Q

define co-dominance

A

2 alleles which are both expressed in the phenotype

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8
Q

what is incomplete dominance?

A

phenotype of heterozygote is intermediate between the 2 parental phenotypes

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9
Q

define incomplete dominance in a simpler way
give an example

A

both alleles contribute to a blended phenotype
a red flower crossed with a white flower will make a pink flower

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10
Q

what does each allele code for in incomplete dominance?

A

one codes for an enzyme which catlyses something
the other codes for an enzyme without catalytic properties

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11
Q

define dihybrid inheritance

A

the inheritance of 2 separate genes which are unlinked

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12
Q

what is mendels 2nd law of genetics?
define it

A

the law of dominance
an organism with alternate forms of a gene will express the form that is dominant

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13
Q

what is mendels 3rd law of genetics?
define it

A

law of independent assortment
genes for different traits are sorted seperately from one another so that the inheritance of one trait is not dependent on the inheritance of another

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14
Q

what is the ratio for a heterozygous/dihybrid?

A

9:3:3:1

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15
Q

what are recombinants?

A

a new combination of alleles is produced from combining one allele from 1 chromo with 1 allele from another chromo

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16
Q

define sex linked inheritance

A

the inheritance of genes found on the sex chromosomes

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17
Q

what are non sex chromosomes called?
how many pairs do we have?

A

autosomes
we have 22 pairs

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18
Q

what are the 2 case studies for sex linked inheritance?

A

haemophilia
duchenne muscular distrophy (DMD)

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19
Q

what does haemophilia do?
who are the carriers?

A

impairs the body’s ability to control blood clotting
females

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20
Q

who is more likely to get haemophilia and why?

A

males as it’s an X chromosome disorder
males have XY so lack a ‘back up’ copy for the gene (another X)

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21
Q

what is DMD caused by and what does this do?

A

caused by a lack of dystrophin protein which is a component of the glycoprotein stabilising the cell membrane of muscle fibres
(causes the muscle fibres to break down)

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22
Q

what does DMD lead to?

A

a loss of muscle mass and weakness

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23
Q

define a mutation

A

a change in the amount, arrangement or structure of the DNA in an organism

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24
Q

what are the 2 types of mutations?

A

gene mutations
chromosome mutations

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25
Q

what can mutations do to a population?

A

increase variation

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25
Q

what do mutations do to a population?

A

increase variation

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26
Q

what are the 2 ways that can increase the rate of mutation?

A
  • ionising radiation
  • mutagenic chemicals e.g carcinogens cause cancer
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26
Q

what 2 things can increase the rate of mutation?

A

ionising radiation
mutagenic chemicals e.g carcinogens cause cancer

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27
Q

what are the 4 ways in which a mutation can occur?

A
  1. gene/point mutation
  2. chromosome mutation
  3. aneuploidy
  4. polyploidy
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27
Q

what are the 4 ways in which a mutation can occur?

A
  1. gene/point mutation
  2. chromosome mutation
  3. aneuploidy
  4. polyploidy
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28
Q

define gene/point mutation

A

changes in the base sequence occurs if DNA is not sopied correctly in S phase (synthesis phase - DNA replicates) before cell division

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28
Q

define a gene/point mutation

A

changes in base sequence occurs if DNA is not copied correctly in S phase (synthesis phase - DNA replicates) before cell division

29
Q

what can also happen in a gene/point mutation?

A

duplication - same base twice
inversion - DNA bases exchange positions

29
Q

what are the other 2 things that it can happen?
what happens during them?

gene/point mutation

A

duplication - same base twice
inversion - DNA bases exchange positions

30
Q

what is a silent mutation?

A

change in base doesn’t change the amino acid it codes for

30
Q

define a silent mutation

A

change in a base doesn’t change the amino acid it codes for

31
Q

what can the deletion of a base cause?
what is this?

A

a ‘frame shift’ - loss of single nucleotide

31
Q

what can the deletion of bases cause?
what is this?

A

‘frame shift’ - loss of a single nucleotide

32
Q

what kind of mutations may cause cancer?

A

somatic

32
Q

what kind of mutations may cause cancer?

A

somatic

33
Q

what are the only mutations that can be inherited and what are they called?

A

only those that occur in the formation of gametes - germ cell mutation

33
Q

define germ cell mutation

A

only those mutations which occur in the formation of gametes can be inherited

34
Q

what are germ cell mutations the basis of and why?

A

discontinuous variation as they cause sudden and distinct differences

34
Q

what are they the basis of?

germ cell mutation

A

discontinuous variation

35
Q

what is an oncogene?

A

a gene that, when mutated or expressed at high levels, can turn a normal cell into a tumour cell

35
Q

what is an oncogene?

A

a gene that, when mutated or expressed at high levels, can turn a normal cell into a tumour cell

36
Q

what are proto-oncogenes?

A

genes that if they mutate can become oncogenes

36
Q

what do they increase the rate of?

oncogenes

A

cell division

37
Q

what are tumour suppressor genes?

A

protective genes that control cell growth by suppressing cell division

37
Q

what is a proto-oncogene?

A

genes that if they mutate can become oncogenes

38
Q

what do oncogenes increase?

A

the rate of cell division

38
Q

what are tumour supressor genes?

A

protective genes that control cell growth by suppressing cell division

39
Q

what can mutations to oncogenes and tumour suppressing genes cause?

A

cancer

39
Q

what can mutations to tumour suppressor genes and oncogenes cause?

A

cancer

40
Q

what is an example of a point mutation?

A

sickle cell

40
Q

what is an example of a point mutation?

A

sickle cell

41
Q

what happens?

sickle cell

A

red blood cells deform and block capillaries when oxygen levels are low

41
Q

what happens?

sickle cell

A

red blood cells deform and block capillaries which causes low oxygen levels to certain parts of the body

42
Q

what is the gene called and what number chromosome is it on?

sickle cell

A

HBB gene on chromsome 11

42
Q

what gene is on what chromosome?

sickle cell

A

HBB gene on chromosome 11

43
Q

what does the mutation involve?
what does this change?

sickle cell

A

a substitution of an A for a T
this changes 1 amino acid

43
Q

what does the mutation involve?
what does this change?

sickle cell

A

a substitution of an A for a T
changes 1 amino acid

44
Q

what is the allele for normal haemoglobin?
what is the allele for mutant haemoglobin?

sickle cell

A

HbA
HbS

45
Q

what is the co dominant allele which reduces the ability of RBC to carry oxygen?
what can this lead to?

sickle cell

A

HbSHbS
lead to death

46
Q

what is the heterozygous co dominant allele?
if someone has this, what does it mean?

sickle cell

A

HbAHbS
they have at least 50% haemoglobin with trait less severe symptoms

47
Q

what is a chromosome mutation?

A

change in chromosome numbers

48
Q

what is this usually the result of?
what stage does it happen at?

chromo mutation

A

errors occuring during meiosis
happens at anaphase 1 or 2 when homologous chromos or chromatids fail to seperste correctly

49
Q

what autosome is down syndrome?

A

trisomy 21

50
Q

define aneuploidy
what does it result in?

A

the loss or gain of a single chromo
results in the formation of gametes with either one too many or one too few chromos

51
Q

define polyploidy

A

changes in the number of whole sets of chromosomes

52
Q

what 3 things can polyploidy be caused by?

A
  • a defect at the spindle (anaphase - too many chromatids move to a pole)
  • 2 diploid gametes fuse (tetraploid)
  • cytokinesis doesn’t happen - endomitosis
53
Q

define epigenetics

A

the control of gene expression by factors other than changes in the DNA base sequence

54
Q

DNA can be modified post - replication. explain this

A

this doesn’t change the DNA base sequence but changes the ability of a gene to be transcribed during protein synthesis

55
Q

what is DNA methylation?

A

the addition of methyl groups to bases prevents those bases from being recognised and reduces the ability of that gene to be expressed

56
Q

what are used to organise the DNA in a chromosome?

A

histone proteins

57
Q

how can histone proteins be modified?
(hint: coiling)

A

if the histone coils more tightly it can prevent gene expression or if it coils more loosely it can increase gene expression

58
Q

what is the chi2 test used for?

A

determining the validity of results of experiments by comparing observed and expected data

59
Q

during the chi2 test, how do you determine whether you accept or reject the null hypothesis?

A

if value is less than critical value (0.05) - accept as there’s no significant difference
if value is more than critical value - reject as there is significant difference and the probability is lower of it being due to chance

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