Genomics

Question 1

Allelic vs non-allelic

Answer 1

Same gene (allelic)
Different gene (non-allelic)

Question 2

Law of segregation

Answer 2

The two alleles from each parent separate during meiosis

Question 3

Monohybrid cross

Answer 3

One gene which gives phenotypic ratio of 3:1

Question 4

How do you find out if a phenotype is caused by a recessive/dominant mutant gene

Answer 4

Cross a mutant with a wild-type individual; if the mutant is dominant then F1 will contain mutants, if if it recessive then it will be seen in F2

Question 5

Law of Independent assortment

Answer 5

Different traits assort independently of each other

Question 6

Dihybrid cross

Answer 6

Independent assortment; 9:3:3:1

Question 7

Mutation in amino acid

Answer 7

Results in related proteins with some differences in function

Question 8

Mutation in gene regulation

Answer 8

Changes the amount of gene product or/and changes when and where the gene is expressed

Question 9

Mutation in intron and exon

Answer 9

Results in proteins with different functional domains present/absent

Question 10

Recessive loss of function mutation

Answer 10

Partial loss of gene: leaking or hypomorphic mutation
Complete loss of gene: null mutation

Question 11

Haplo-sufficient mutation

Answer 11

One wild-type allele provides enough normal gene to produce a phenotype because mutation is recessive

Question 12

Haplo-insufficient mutation

Answer 12

A wild-type allele cannot provide enough normal gene product to produce a phenotype because mutation is dominant

Question 13

Gain of function mutation

Answer 13

Increase in functional gene product - Hypermorphic mutation
New function - neomorphic mutation

Question 14

Allelic series

Answer 14

Genes in order of dominance according to the phenotypes expressed

Question 15

Conditional Mutants

Answer 15

Mutated phenotype occurs under certain environments
Restrictive condition: mutant phenotype
Permissive condition: wild-type phenotype

Question 16

Penetrance

Answer 16

The proportion of individuals of a specific genotype that exhibit the corresponding phenotype
Incomplete penetrance: not everyone displays the mutant

Question 17

Lethal alleles

Answer 17

Dominant lethal alleles
Homozygous mutant
Offspring ratio = 2:1

Recessive lethal alleles
F1 intercross of heterozygotes - ¼ of offspring will die
Offspring ratio = 1

Lethal alleles result in altered 3:1 ratios = dominant (2:1) or recessive (3:0)

Question 18

Pleiotropic

Answer 18

A single gene with more than one phenotype

Question 19

The complementation test

Answer 19

Determines whether recessive mutants are from the same gene or two different genes

Two homozygous mutants with the same phenotype are mated
If the F1 is the wild-type, the two mutations complement each other and represent two different genes
If the F1 is a mutant, the two mutations fail to complement and represent two different alleles of the same gene.

Question 20

Gene interactions

Answer 20

Complementary gene interaction: the activity of both genes is needed for the final phenotype - 9:7

Duplicate gene interaction: either gene can carry out the biological process (redundancy) - 15:1

Dominant gene interaction: two genes with the same phenotype interact additively - 9:6:1

Question 21

Epistasis

Answer 21

One gene masks the phenotype of another

Recessive epistasis: the recessive genotype of one gene blocks the phenotype controlled by another gene - 9:3:4 ratio

Question 22

Mitosis

Answer 22

somatic cells - chromosomes replicate and divide, chromosome number is maintained

Question 23

Meiosis

Answer 23

Germline cells - chromosomes replicate and undergo 2 rounds of division, chromosome number is halved

Question 24

The chromosome theory of Inheritance

Answer 24

Sutton & Boveri (1902): The behaviour of chromosomes during meiosis can explain why genes are inherited according to Mendel’s Laws

Question 25

Sex chromosomes

Answer 25

X and Y
X if greatly bigger and has more genes
Heterogametic sex: the sex with different sex chromosomes
Homogametic sex: the sex with the same sex chromosomes
Human sex chromosomes:
Biological males are hetero (XY)
Females are homogametic (XX)

Question 26

ATP-binding cassette (ABC) transporters

Answer 26

transmembrane proteins that use ATP to transport molecules across membranes

The white gene of the Drosophila eye colour is an ABC transporters

Question 27

Why do drosophila’s have white eyes

Answer 27

The white gene is an ABC transporter and because the Xw mutation blocks the transport of pigment precursors guanine and tryptophan, it leads to white eyes

Question 28

Drosophila notation

Answer 28

For a recessive trait with allele e:
- Wild type allele: e+
- Homozygotes: ee, e+e+
- Hetero with genetype e+e would be the wildtype

For a dominant trait with allele B:
- Wild type: B+
- Homozygotes: BB, B+B+
- Hetero with genotype B+B would be mutant

For a sex-linked trait with allele a:
- Wild type allele Xa+
- Homo: XaXa, Xa+Xa+
- Hetero: Xa+Xa would be wildtype
- Hemizygotes with XaY would be mutant
- Hemizygotes: with only one copy of an allele present instead of two (XY males for X-linked genes). This phenotype is present regardless of dominance

Question 29

Reciprocal crosses

Answer 29

Used to determine sex linkage: two crosses are performed, where the genotypes of the male and female parents are swapped

If offspring ratios differ, this indicates that the trait is sex-linked

Question 30

Criss cross inheritance

Answer 30

Trait goes from mum to son

Question 31

X linked

Answer 31

Appears more in males, mothers are carriers

Question 32

Pedigrees

Answer 32

Family tree - female: circle, male: square

Question 33

Autosomal recessive inheritance

Answer 33

• Individuals who have the disease are often born to parents who do not
• If only one parent has the disorder, the risk that a child will have it depends on the genotype of the other parent
• If both parents have it, all children will have it
• The gender ratio of affected offspring is expected to be equal
• The disease is not usually seen in each generation but if an affected child is produced by unaffected parents then the risk to subsequent children is ¼
• If the disease is rare, unaffected parents of affected children are likely to be related to one another

Question 34

autosomal dominant inheritance

Answer 34

• Each individual who has the disease has at least one affected parent
• Males and females are affected in equal numbers
• Either gender can transmit the disease
• In crosses where one parent is affect, approximately half the offspring will have the disease
• Two unaffected parents will not have any children with the disease
• Two affected parents may produce unaffected children

Question 35

Autosomal mutants

Answer 35

Autosomal dominant: one mutant allele is sufficient
Autosomal recessive: two mutant alleles result in trait
X-linked: hemizygous males express the trait

Question 36

Y-Linked inheritance

Answer 36

• Only impact males
• Occurs in all sons of affected males
• Females will not be carriers

Question 37

X linked dominant

Answer 37

• Trait is present in hemizygous males
• Each affected individual has at least one affected parent (except in the case of de-novo - new- mutations that may have occurred in the germline)
• Affected hetero females mated to unaffected males transmit the disease to half their sons and daughters
• Affected hemi males transmit to all their daughter

Question 38

X linked recessive

Answer 38

• Present in hemi males
• Present in homo females
• Most affected individuals are male
• May skip generations (such as the criss cross inheritance)
• Unaffected parents with a female carrier will give no affected females but half affected males
• Affected males mated to unaffected females will have no affected offspring, but all their daughters are carriers
• Affected females mated to unaffected males will have all affected sons and no affected daughters, but their daughters are carriers
• XX carriers have half of their cells inactivated the mutant X, while half have inactivated wild-type which is why they’re ok
• If XX individuals are ‘mosaic’ for a disease, then the products of both heterozygous alleles are expressed and sufficient to prevent full manifestation of X-linked recessive traits
• Hemizygote: Only produce mutant allele in this case
• X-inactivation skewing: sometimes non-random proportion of X’s of one type are inactivated