Inheritances and Mutations

Question 1

Define:
Homozygous
Heterozygous
Hemizygous

Answer 1

Homozygous: alleles on both chromosomes are the same
Heterozygous: alleles on both chromosomes are different
Hemizygous: allele on the X-chromosome is missing on the Y-chromosome (only occurs in males)

Question 2

Describe the co-dominance exerted by bloody type

Answer 2

Isoglutamin gene codes for glycoproteins on erythrocytes surface
Ia and Ib are equally dominant over Io
When Heterozygous with Ia and Ib —> AB blood type
Only have O blood type when homozygous with Io

Question 3

Explain how blood type determines he antibodies present in the blood and how that blood type can be transfused

Answer 3

A - anti-B in blood (give: A,AB take: A,O)
B - anti-A in blood (give: B,AB take: B,O)
AB - none (give: AB take: A,B,AB,O)
O - anti-A and anti-B in blood (give: A,B,AB,O take: O)

Question 4

Who is affected by
Autosomal
X-linked
Y-linked

Answer 4

Autosomal: males and females equally
X-linked: hemizygous males and females
Y-linked: males only

Question 5

What are dominant genes?

What are recessive genes?

Answer 5

Dominant:
Allele that determines phenotype, usually heterozygous (homozygous is very rare)
Any carriers affected
Recessive:
Allele that determines phenotype when homozygous
Carriers are unaffected (allows generation skipping)

Question 6

What is frequency of recombination?

Answer 6

Rate at which new phenotypes present

Recombinant frequency = Recombinant phenotypes / All phenotypes (Recombinant + Original Parental)

Question 7

What are linked/non-linked genes and what are their recombinant frequency?

Answer 7

Linked genes: Genes within short distance (on the same chromosome) recombinant frequency less than 50%
Non-linked genes: Genes further away (on different chromosomes) recombinant frequency less than or equal to 50%

Question 8

What is a transposable element?

Answer 8

A sequence of DNA that can change its position within the genome

Question 9

Describe the outcomes if elements are transposed onto:
Introns
Exons
Transcription start sites/Transcription termination sites
Non-homologous Chromosomes

Answer 9

Introns: No effect
Exons: Absent/Abnormal protein
TSS/TTS: Abnormal protein transcription (could affect translation)
Non-homologous Chromosomes: No effect

Question 10

What are micro-mutations, the types and the outcomes?

Answer 10

Single nucleotide changes on one strand:
Deletion/Insertion: Frameshift
Substitution: No Frameshift

Question 11

What are macro-mutations, the types and where they occur?

Answer 11

Fragments of code changes on both strands:
Deletion (same chromosome)
Insertion (same chromosome)
Inversion (same chromosome) - para- (1 arm), peri- (both arms)
Substitution (different homologous chromosome)
Translocation (different non-homologous chromosome)

Question 12

Describe these single-base mutations:
Transitions
Transversions
Missense
Nonsense
Silent

Answer 12

Transitions: change to the same type base
Transversions: change to a different type base
Missense: change to a different amino acid
Nonsense: change to a stop-codon
Silent: change to the same amino acid

Question 13

Describe the outcomes of mutations

Answer 13

Gain of function mutations
No effect (silent/synonymous, recessive)
Change gene products (missense/non-synonymous)
Change the amount of gene (transcription/translation affected)
Change the length of the protein (frameshift, nonsense, missense of stop-codon)

Question 14

What effect does Nitrous acid have on bases?

Answer 14

Removes amine groups (deamination), changing:
Adenine —> Hypoxanthine (bonds to C) - Transversion
Cytosine —> Uracil (bonds to A) - Transversion
Guanine —> Xanthine (bonds to C) - Transition

Question 15

What is the result of germ-line mutations?

What is the result of somatic mutations?

Answer 15

Germ-line: occurs in gametes, affects all somatic cells and is passed onto offspring

Somatic: occurs in somatic cells, affects cell line and is not passed onto offspring

Question 16

Where can somatic and germ-line mutations occur simultaneously?

Answer 16

Mitochondrial DNA

Only mothers affected will pass it onto the offspring

Question 17

What is a spontaneous mutation?

Answer 17

Mutation that occurs in the first affected individual (all somatic mutations)

Question 18

How do primordial germ cells develop in males?

Answer 18

Foetus:
Mitotic proliferation
Mititic arrest
Birth:
Mitotic proliferation
Puberty:
Meiotic proliferation

Question 19

How do primordial germ cells develop in females?

Answer 19

Foetus:
Mitotic proliferation
Meiotic proliferation
Meiotic arrest (P1)
Birth:
Follicle formation
Puberty:
Meiotic proliferation
Meiotic arrest (M2)
Fertilisation:
Completion of meiosis

Question 20

What is the difference between mosaicism and chimerism?

Answer 20

Mosaicism: 1 zygote with more than 1 cell lines (mis-matched genomes)
Chimerism: 2 zygotes with at least 2 cell lines (different genomes)

Question 21

What is the difference between mosaicism and non-mosaicism?

Answer 21

Mosaicism: more than 1 cell line forms during division after the first-post zygotic division
Non-mosaicism: only 1 cell line forms during the first-post zygotic division

Question 22

What is Turner syndrome?

Answer 22

Monosomy (loss of the X chromosome in females)

Question 23

What are the 3 common trisomies and the chromosome number they affect?

Answer 23

Down syndrome (+21)
Patau syndrome (+13)
Edwards syndrome (+18)

Question 24

What is polyploidy and what is the most common cause?

Answer 24

Loss/Gain of whole genome

Polyspermy (fertilisation by more than 1 sperm)

Question 25

What is triploidy?

Answer 25

Gain of a haploid set of chromosomes (3n)

Question 26

What are the types of chromosomal translocations and do they affect gene expression?

Answer 26

Reciprocal translocation: Exchange of segments of chromosome between non-homologous chromosomes
Non-reciprocal translocation: Movement of segments of chromosome from one to another
Robertsonian translocation: Joining of two acrocentric chromosomes to form a single chromosome
Does not affect gene expression

Question 27

What happens to chromosomes that have translocated during Meiosis?

Answer 27

Depending on the segregation of the chromosomes, the gametes formed will either be:
Normal (contain normal chromosomes)
Balanced (contain the correct amount of chromosomes but incorrect number of chromosomes)
Unbalanced (contain abnormal amount of chromosomes or number of chromosomes)