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Biology > Topic 3 (Genetics) > Flashcards

Topic 3 (Genetics) Flashcards

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1
Q

Meiosis - diploid cells

A

diploid cells have pairs of chromosomes/a full set of chromosomes
In humans body cells have 46 chromosomes (23 pairs)

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2
Q

Meiosis - haploid cells

A

haploid cells have one of each pair of chromosomes/half the number of chromosomes
sex cells are haploid
in humans the sex cells have 23 chromosomes

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3
Q

meiosis defined

A

Type of cell division that produces sex cells/gametes (sperm + egg in animals / pollen + egg in plants)

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4
Q

meiosis produces:

A

4 daughter cells
each with half the number of chromosomes as the original cell and one of each pair of chromosomes (haploid cells)
this ensures that at fertilisation, the zygote is diploid
CELLS PRODUCED ARE GENETICALLY DIFFERENT ensuring variety of zygotes

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5
Q

mitosis vs meiosis

A

DRAW A TABLE

mitosis / meiosis
produces genetically identical cells / produces genetically different cells
produces diploid cells / produces haploid cells
produces 2 cells / produces 4 cells
divides once / divides twice
produces body cells / produces sex cells

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6
Q

chromosome

A

found in nucleus of cells and made of dna

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7
Q

gene

A

a section of dna that codes for a specific protein

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8
Q

allele

A

alternative form of a gene

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9
Q

phenotype

A

physical or chemical expression of your genotype

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10
Q

genotype

A

alleles present in nuclei of cells

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11
Q

dominant allele

A

if present it is always expressed in phenotype

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12
Q

recessive allele

A

only expressed if dominant allele is absent

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13
Q

homozygous/pure breeding

A

both alleles for a characteristic are the same

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14
Q

heterozygous

A

two alleles for a characteristic are different

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15
Q

gamete

A

a sex cell

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16
Q

zygote

A

a fertilised egg cell
cell produced when sperm and egg fuse

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17
Q

what case letter for dominant

A

uppercase eg M

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18
Q

what case letter for recessive

A

lowercase eg m

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19
Q

using letter m homozygous dominant

A

MM

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20
Q

using letter m homozgyous recessive

A

mm

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21
Q

using letter m heterozygous

A

Mm

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22
Q

Why might you not get the expected ratio of phenotypes

A
  1. It is a matter of chance which sperm fuses with which egg: random fusion of gametes.
  2. There are only a small number of offspring/small sample size so patterns less likely to be clearly seen/more affected by chance
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23
Q

What are genetic diseases caused by?

A

a faulty allele that can be inherited

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24
Q

define a carrier

A

heterozygous therefore dont have the condition but can pass the recessive allele to their offspring

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25
Q

what chromosomes determine sex

A

X and Y

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26
Q

male sex chromosomes

A

X and Y: XY genotype

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27
Q

female sex chromosomes

A

X and X: XX genotype

28
Q

Diagram to show genetic sex

A

/ X / Y
X / XX / XY
X / XX / XY
XX = female
XY = male
50/50 chance

29
Q

How does the male determine the sex of the child?

A

Because if his sperm is (Y), when fuses with the (X) egg, the child is male and genotype Y but if his sperm is (X), when it fuses with the (X) egg, the child is a female and genotype XX

30
Q

How to set out genetic diagram?

A

phenotype
genotype
gametes
diagram
label diagram
expected ratio if needed

31
Q

Why are there differences in the inherited characteristics as a result of alleles? (4)

A

A gene is a section of DNA that codes for a specific protein
An allele is an alternative form of a gene
Therefore different alleles lead to the production of different proteins
Therefore leading to the production of different phenotypes eg different eye colours

32
Q

Phenotypes caused by multiple genes (2)

A

Some phenotypes caused by one gene eg:
presence/absence of earlobes
eye colour
blood group
rolling tongue

most phenotypes caused by multiple genes eg:
height
weight

33
Q

Mendel crossed together pure breeding pea plants with purple flowers and pure breeding pea plants with white flowers. Offspring’s flowers were all purple. Explain this result

A

The purple flowers are dominant as the HETEROzygous offspring were purple so it must be dominant.
This allele is present in offspring and expressed in phenotype therefore dominant

34
Q

Family pedigree shows inheritance of sickle cell disease thru three generations. Caused by recessive allele.
X has heterozygous parents and unaffected- homozygous dominant
Y is heterozygous one parent heterozygous one homozygous dominant.
Z is heterozygous one parent heterozygous, one parent homozygous recessive.
Why should X, Y and Z have pedigree analysis done before having children?

A
  1. Pedigree analysis should be carried out on X, Y and Z and their parents.
  2. Would show likelihood of offspring inheriting disorder
  3. X is homozygous dominant and doesn’t have disease/not a carrier so will not pass allele for disease to his offspring. If partner is carrier 50% chance of child being carrier.
  4. Y and Z are carriers of sickle cell allele/heterozygous so have 50% chance of passing the allele for SCD to offspring.
  5. If partners also carriers, 25% chance children have SCD and 50% chance of them being carriers.
35
Q

Why do we look similar to our parents?

A

All our alleles are inherited from them- 50% from Mum, 50% from Dad : all our genotypes are result of father sperm fusing w mother egg and so we share physical characteristics/phenotypes.

36
Q

Why are we not identical to our parents?

A

Mutations cause differences in alleles and random fusion of gametes at fertilisation means alleles can be combined in many different ways.
Also half from mum and half from dad so cannot look identical to both

37
Q

Mutation (5)

A
  • A mutation is a rare random change to the base sequence of DNA
  • When they occur this results in a new allele of a gene and therfore the gene produces a different protein
  • Most mutations have no effect on the phenotype
  • Some have a small effect on the phenotype eg a mutation may cause a cat’s fur to be slightly longer
  • Very rarely, a mutation may have a big effect on phenotype. This might be because the protein maybe no longer produced or might no longer carry out its function. Can cause genetic diseases eg cystic fibrosis
38
Q

one word definition of variation

A

differences

39
Q

Interspecific variation

A

Variation between species (1)
Species vary from one another due to them having different genes (3)

40
Q

Intraspecific variation

A

Variation within a species

41
Q

Intraspecific variation causes

A

Genetic differences
Environmental (acquired characteristics)
Genetic + environmental

42
Q

genetic as a reason for intraspecific variation

A

mutations cause differences in alleles (because they cause a change in the base sequence of a gene)
random fusion of gametes at fertilisation so alleles can be combined in many different ways

43
Q

environmental (acquired characteristics) as a reason for intraspecific variation

A

eg scars
plant growing in dark room will have yellow leaves instead of green leaves

44
Q

genetic + environmental as a reason for intraspecific variation

A

some characteristics purely due to differences in allele ie genetic differences eg blood group and tongue rolling
but some due to genetics (alleles you have) + environmental influences eg height ie if you are malnourished you wont reach full height or eg intelligence ie if you are not stimulated intellectually as a child then even if you are genetically predisposed to be intelligent you will not be as intelligent as you could have been

45
Q

interspecific variation

A

variation between species

46
Q

interspecific variation

A

variation between species

47
Q

Genetic differences show what variation

A

Discontinous

48
Q

Discontinuous variation

A

CAused by one gene
IE only a few discreet possibilities

49
Q

Genetic and envirionmental iffernces show what variation

A

Continuous

50
Q

Continuous variation

A

Caused by multiple genes
Ie can be any value between two extremes

51
Q

Discontinuous variation bar chart

A

Random distribution

52
Q

Continuous variation bar chart

A

Arc-like shape
Smooth-ish peak and trough

53
Q

IF answer says use diagram/has letters, what do you do?

A

USE DIAGRAM AND LETTERS

54
Q

Why does a large sample size improve investigation

A

Random fusion of gametes often greatly affected by small sample size
Large sample size allows anamolies to be identified more easily and allows pattern/ratio to be seen more clearly
More likely to get theoretical ratios

55
Q

Genome

A

Entire DNA of an organism

56
Q

HGP acronym

A

Human Genome Project

57
Q

HGP starting and ending date

A

1990-2003

58
Q

What did the HGP do?

A

Identified all 25,000 genes in human DNA
and mapped them ie found out what chromosomes they were on and worked out base sequence of these genes

59
Q

medical applications of HGP

A
  • prediction and prevention of disease
  • testing and treatment for inherited disorders
  • new and better medicines
60
Q

genetic mutation(2)

A

Genetic mutations are rare randomchanges to the base sequence of your dna
happen during cell division when yourcells make copies of themselves.

61
Q

why are called inherited disorders

A

Sincegenes are passed from parent to child, any changes to the DNA within a gene are also passed.
If this causes a condition, it is called an inherited disorder

62
Q

Example of mutations in human genes that affect the phenotype: sickle-cell anemia

A

Here, a normalhemoglobingene may be converted into a sickle-cell haemoglobin gene by changing a singlenucleotidein the gene encoding the protein of the haemoglobin.

63
Q

Brief history of genetics

A

1856: Mendel discovers basic principles of genetics
1869: Miescher discovers DNA
1953: double helix dna structure discovered
1990: HGP starts
2003: HGP ends

64
Q

Ethical legal social implications of HGP

A

Increased stress: eg if someone knew from early age they were likely to develop nasty brain disease could panic everytime they got a headache

People with genetic problems could be under pressure not to have children

Discrimination by employers and insurers could occur: eg life insurance could become impossible to get or be very expensive if you were likely to develop a serious disease + employers might discriminate against those likely to develop a serious disease

65
Q

Prediction and prevention of disease HGP

A

If doctors know what genes predispose people to what disease everyone can get individually tailored advice on best diet and lifestyle to avoid likely problems and doctors can check regularly to ensure early treatment if we develop the diseases that we are susceptible to

66
Q

Testing and treatment for inherited disorders HGP(3)

A

Some diseases eg cystic fibrosis are caused by recessive alleles.
Due to HGP scientists able to identify alleles that are suspected of causing an inherited disorder much more quickly
People can be tested to see if they have this allele and may be possible to develop better treatments or even a cure.

67
Q

new and better medicines HGP

A

HGP highlighted some common genetic variations (diff between alleles) between people.
Some affect how our individual bodies will react to certain diseases and their possible treatments
Scientists can use this knowledge to design new drugs that are tailored to people with a particular genetic variation
Can also determine how well an existing drug will work for an individual
Tests can already identify whether or not someone with breast cancer will respond to a particular drug and what dosage is best for certain drugs in certain patients
In general, knowing how a disease affects us on a molecular level should make it possible to design more effective treatment with fewer side effects

Biology (2 decks)

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