Chromosomes, genes and inheritance

Question 1

List the 3 components of chromosomes

Answer 1

Telomeres at the tip
Centromere
Chromatin (Euchromatin + heterochromatin)

Question 2

Describe a telomere

Answer 2

Protects end of chromosome from deterioration or fusion with neighbouring chromosomes

Question 3

What is DNA packaged with in chromosomes

Answer 3

histone proteins

Question 4

How many histones in a nucleosome (further wrapping)

Answer 4

8

Question 5

Describe euchromatin

Answer 5

Open and under active transcription

Question 6

Describe heterochromatin

Answer 6

tightly packed, dense and silenced

Question 7

What is the purpose of packaging DNA

Answer 7

negatively charged DNA neutralised by positive histones
DNA takes up less space
Inactive DNA can be folded into accessible locations until required

Question 8

Define genotype and phenotype

Answer 8

Genotype - Full genome of individual (even if not expressed)
Phenotype - Physical manifestation eg appearance, behaviour

Question 9

How many geneotypes are there in the population

Answer 9

800AA + 190Aa + 10aa = 1000

Question 10

How many alleles are there in the population

Answer 10

1600AA + (190A + 190a) + 20aa = 2000

Question 11

What is the genotype frequency

Answer 11

p2 + 2pq + q2

Question 12

What is the allele frequency

Answer 12

p:q

Question 13

Do gene frequencies change

Answer 13

No they remain constant

Question 14

What factors does the HWE equation assume

Answer 14

Ignores mutation
Migration is negligible
Mating is random
There is a large population
Allele frequencies are equal in sexes

Question 15

What does the HWE equal

Answer 15

AA: Aa : aa =1

Question 16

Define fitness of alleles

Answer 16

Relative ability to survive and pass on genes

Question 17

Does Autosomal dominant inheritance skip generations

Answer 17

NO

Question 18

Does autosomal dominant inheritance favour a generation

Answer 18

No equal in male and females

Question 19

What is a childs chance of inheriting an autosomal dominant disease?

Answer 19

50%

Question 20

Do affeceted parents have affected children in autosomal recessive inheritance

Answer 20

No, the children are carriers.

Question 21

Can autosomal recessive skip generations?

Answer 21

yes

Question 22

Can heterozygous parents have affected kids in autosomal recessive

Answer 22

Yes, if child innherits both mutated alleles.

Question 23

Who is most commonly affected in X-linked inheritance?

Answer 23

males - they only inherit one X

Question 24

Can X-linked inheritance skip generations?

Answer 24

yes

Question 25

What type of transmission does not occur in X-linked inheritance

Answer 25

Male to male

Question 26

Describe factors of non mendelian inheritance

Answer 26

• incomplete penetrance
• genomic imprinting (different mutated chromosomes)
• environmental factors
• genetic modifiers

Question 27

Give examples of non- mendelian inheritance

Answer 27

triple repeat disorders

mitochondrial mutations

Question 28

Give examples of Autosomal dominant diseases

Answer 28

Huntingtons (neuro-degenerative)

Achondroplasia - dwarf

Question 29

Give examples of X-linked diseases

Answer 29

Duchene muscular dystrophy (degeneration of muscle tissue)
Hemophilia - disorder of blood clotting
Red/ green colour blindness

Question 30

Define gene point mutations and list examples

Answer 30

Minor change, affecting 1 amino acid - protein may still function
Substitution, Missense, Nonsense, Silent

Question 31

Describe silent mutations

Answer 31

Replaced nucelotide codes for same amino acid

eg. CGA (Arg) –> CGC (Arg)

Question 32

Describe substitution mutations

Answer 32

Nuclotide is replaced with another (changes codon)

Question 33

Describe missense mutations

Answer 33

Altered codon codes for a different protein

Question 34

Describe Nonsense mutations

Answer 34

Altered codon acts as a stop codon so protein can’t function

Question 35

Explain degeneracy

Answer 35

amino acids are coded for by more than one codon (20 amino acids)
So if single mutations occur (esp. 3rd base - wobble) protein will not be altered

Question 36

What are the exceptions to degeneracy

Answer 36

methionine and tryptophan

Question 37

Describe deletion chromosome mutations

Answer 37

Chromosome breaks in 2 places, losing a section and forming a shorter chromosome

Question 38

Describe insertion chromosome mutations

Answer 38

Segment becomes reversed (broken off, turned, reattached) - Balanced rearrangements

Question 39

What are balanced rearrangements

Answer 39

Mutations where although the shape of the chromosome is altered all the genetic information is still there

Question 40

Describe insertion chromosome mutations

Answer 40

Gains segment from another chromosome

Question 41

Describe translocation chromosome mutations

Answer 41

Segment breaks off and is added to another chromosome

Question 42

Describe reciprocal translocation chromosome mutations

Answer 42

2 new derivative chromosomes formed

Question 43

Describe robertsonian translocation chromosome mutations

Answer 43

Fusion of two acrocentric chromosomes

Question 44

Give examples of autosomal chromosome mutations

Answer 44

Trisomy 21 - Down’s syndrome
trisomy 13 - Patau (non-dysjunction)
trisomy 16 - Edwards

Question 45

Give examples of sex related chromosome mutations

Answer 45

(45, X) 45 chromosomes, one X - Turners syndrome (females)

47, XXY - Klinefelter syndrome

Question 46

Describe de novo mutations

Answer 46

New mutation occurs in germ cell of parent and passes to of spring
No family history of cancer

Question 47

List ways of chromosome mutation testing

Answer 47

PCR
gel electrophoresis (electric field seperates fragments by size)
RFLP 
ARMS
DNA sequencing

Question 48

Describe the process of PCR

Answer 48

1. denature DNA (90-95)
2. Anneal primers (50-70)
3. Extension- polymerase adds nucleotides to 3’ end(70-75)

Question 49

How much DNA does one cycle of PCR produce

Answer 49

doubles it - amplify