Basic genetics and genetic disease (should be in OP4103)

Question 1

what do chromosomes do?

Answer 1

store genetic information in the form of DNA through its unique base sequence

Question 2

What are diploid cells?

Answer 2

2 sets of chromosomes that are paired and homologous

Question 3

how many chromosomes do cells normally have?

Answer 3

46 chromosomes which include 22 pairs and 2 sex chromosomes

Question 4

what are the DNA bases?

Answer 4

adenine - thymine
cytosine -guanine

Question 5

Give the three steps to how a DNA and its associated protein form a chromosome:

Answer 5

1. The DNA double helix wraps around histone proteins forming the nucleosome
2. The DNA histone complex coils further and is then wrapped to form the chromosome
3. Once the chromosome is visible, the DNA and protein is describes as condensed chromatin

Question 6

what is the karyotype of a male?

Answer 6

46XY so 46 is the total chromosomes and XY is the male alleles

Question 7

how many genetic disorders can arise from a single gene mutation?

Answer 7

more than 3000

Question 8

What does sex linkage mean?

Answer 8

When a gene locus is on the X chromosome

Question 9

What is autosomal linkage?

Answer 9

When two genes are located on the same chromosome and not on the X and Y chromosome

Question 10

How does autosomal linkage affect the combination of alleles in gametes?

Answer 10

You can only have both alleles as dominant or both alleles as recessive e.g.
AB and ab

instead of AB Ab aB and ab

Question 11

What is base substitution?

Answer 11

Where a base is substituted for another and may result in a change of 1 amino acid because the base sequence is changed

Question 12

What is base deletion or insertion?

Answer 12

Where a base is deleted or inserted causing the number of bases to change

Question 13

Which type of mutation is more likely to produce a dysfunctional protein?

Answer 13

Base deletion or insertion is more likely to produce a dysfunctional protein than base substitution because it will affect multiple amino acids from the point of mutation causing the amino acid sequence of the polypeptide to be entirely different hence the polypeptide is unlikely to function correct because the sequence of bases in dna is read in triplets

Question 14

What is chromosome non-disjunction?

Answer 14

When individual nom homologous pairs of chromosomes fail to separate during meiosis

Question 15

what are the two different types of point mutation?

Answer 15

-missense
-nonsense
-frame shift (base deletion/ substitution

Question 16

what is a missense point mutation?

Answer 16

when a single base within a codon is swapped so a single amino acid is coded for instead

Question 17

what is a nonsense base mutation?

Answer 17

where there is a base change that causes the new codon to code for a stop codon and hence terminating the amino acid chain too early

Question 18

give some single gene mutation disorders and describe how for each one

Answer 18

-marfan syndrome due to a mutation to the structural protein of fibrillin
-familial hypercholesteremia due to a defect in the LDL receptor causing an accumulation of fat in the blood
-phenylketonuria due to defect in it’s enzyme protein phylalanine hydroxylase
-lysosomal storage disease due to a mutation in gene coding for lysosomal hydrolase causing an accumulation in the lysosomes
-neurofibromatosis
-haemophilia

Question 19

how are mitochondria different to other organelles in terms of dna?

Answer 19

as they have their own genome in the form of circular mtDNA and the genes code for mitochondrial proteins for oxidative phosphorylation

Question 20

what is mitochondrial disease and how does it come about?

Answer 20

it is a nuclear or mitochondrial mutation and comes about as mtDNA is more prone to mutation than nDNA

Question 21

what does mitochondrial disease refer to?

Answer 21

disorders caused by reduced atp production

Question 22

give the occular effects of mitochondrial disease

Answer 22

-drooping eyelids (ptosis)
-inability to move eyes side to side (external ophthalmoplegia)
-blindness (retinitis pigmentosa)

Question 23

why are mitochondria maternally inherited?

Answer 23

because the mitochondria in the sperm are lost during fertilisation

Question 24

how many still births are accounted for by chromosomal abnormalities?

Answer 24

45%

Question 25

Give two reasons for chromosomal disorders arising

Answer 25

-as they may have an abnormal structure
-there may be an abnormal number of chromosomes

Question 26

what is the basic structure of chromsomes?

Answer 26

the top bit which is the p arm
-the centromere
-the bottom bit which is the q arm

Question 27

why do structural abnormalities in chromosomes occur?

Answer 27

-due to exchange of genetic material, called translocation when it occurs between non homologous chromosomes
-deletion
-rearrangement

Question 28

what happens in chromosomal deletion?

Answer 28

theres a loss of genetic material as the chromosome has been shortened

Question 29

what happens in chromosomal inversion

Answer 29

where there are 2 breaks on a single chromosome and is pericentric is if its on opposite sides of the centromere and paracentric is its on the same arm

Question 30

what happens in ring formation in chromosomes?

Answer 30

where there are breaks at the telomeric end of the chromosome and acrocentric parts of the chromosome are deleted and the remaining chromosome fuses

Question 31

what happens in translocation of chromosomes? how is Robertsonian translocation different?

Answer 31

where genetic material is exchanged between non-homologous chromosomes and it can be balanced or unbalanced where chromatids are exchanged or not

in Robertsonian, there is a break near the centromere in 2 acrocentric chromosomes and so the long arms fuse to form a new chromosome made of q arms

Question 32

What does polyploid mean?

Answer 32

When organisms have three of more sets of chromosomes rather than the usual two causing a condition polyploidy mostly found in plants

Question 33

When do mutations in the number of individual chromosomes occur and what does this result in?

Answer 33

In chromosome non disjunction because it results in a gamete having either one more or one fewer chromosomes and if fertilised with a gamete that has the normal complement of chromosomes the resultant offspring have more or fewer chromosomes than normal.

Question 34

What is chromosome non-disjunction?

Answer 34

When individual non homologous pairs of chromosomes fail to separate during the anaphase 2 part of meiosis

Question 35

what is aneuploidy?

Answer 35

a non exact multiple of haploid set of 23 chromosome pairs

Question 36

what is monosomy?

Answer 36

a loss of a chromosome

Question 37

what is trisomy?

Answer 37

an extra copy of a chromosome

Question 38

name 3 autosomal chromosome disorders and their chromosomal name

Answer 38

-down syndrome = trisomy 21
-edwards syndrome = trisomy 18
-pateau syndrome = trisomy 13

Question 39

what is turners syndome? what are its affects clinically? how can a patient deal with the effects

Answer 39

where the X gamete in females has structural abnormalities or is not present

-cardiovascular anomalies
-fibrous ovaries which could mean sterile
-short height usually <5ft

growth hormones and oestrogen to lead a normal life

Question 40

what is teratology?

Answer 40

the study of congenital malformation which are morphological defects present at birth

Question 41

what are teratogens?

Answer 41

factors that can cause congenital defects:
-viruses e.g. rubella
-irradiation e.g. x-rays, beta, gamma
-chemicals like thalidomide and cytotoxic drugs

Question 42

what determines susceptibility of a teratogen in teratology?

Answer 42

the developmental stage of the foetus