LECTURE 5 (Factors affecting euk gene expression)

Question 1

Are mendelian ratios fixed?

Answer 1

No, genotype is not always manifested to the same extent in offspring bc there’re deviations.

Question 2

Does the external environment affect the genotype?

Answer 2

yes. the biggest example is color of the fur in some animals. The C gene has different alleles determining the different fur color. C>c Dark fur is dominant over albino, himalayan and chinchilla colors.
the pathway is as follows;
colorless —— tyrosinase (melanin) : warm temp active enzyme
colorless ——- no tyrosinase (no melanine): cool temp inactive enzyme

The dark ones have C gene therefore tyrosinase is produced tyrosine is produced making the dark color (this happens in cool temp)
In warm temperatures the enzyme tyrosinase is not functional therefore light color (no melanin)

The himalayan is a special case, usually the coolest parts in the body are ears, mouth, snout therefore tyrosinase will be active and produce a dark color whereas in other parts pale color (himalayan is taches)

Albino complete loss of function

Question 3

What effects of the internal environment affect the genotype?

Answer 3

Gender
Age
Maternal effect genes

Question 4

Why does gender affect the genotype? give examples

Answer 4

sometimes the expression of some genes depend on the hormonal environment (sex limited traits)
e.g Hen: there are two types of feathers hen and cock. in all the genotypes the females show hen whereas in homozygous males show cock. if we remove the ovaries of the females the homozygous will also be Hen but they’re under hormone control.

e.g lactation in female cattle the males carry genes for the expression of milk however they don’t express them bc of testosterone. if we remove male hormones then they’ll express milk

Question 5

What are sex limited traits?

Answer 5

They’re genes that depend on the hormonal environment.

Question 6

What are maternal effect genes? give an example

Answer 6

The mother has a genotype and a phenotype, regardless what the genotype of the offspring is, they’re gonna show the mother’s phenotype
e.g shell coiling : D(dextral)>d(sinistral)
F (dd) x M(DD)
F(Dd)–> phenotype is sinistral rather than dextral due to mum

F (Dd) x M (Dd)
dd Dd Dd DD –> all of them show dextral due to mum’s genotype

conclusion: offspring phenotype determined by mother’s genotype.

Question 7

Why does age affect gene expression? example

Answer 7

basically the newborns appear normal and they develop the disease more and more with aging
e.g hunting tons disease: brain deterioration up to 38 yr it’s a trinucleotide repeat when 36: disease is manifested autosomal dominant disease

Question 8

What’s genetic anticipation?

Answer 8

When heritable disorders exhibit a progressively earlier age of onset and an increased severity in successive generations
This has been observed in hunting tons.

Question 9

What’s genomic imprinting?

Answer 9

one maternal or paternal gene is switched off this is due to methylation

Question 10

What causes genomic imprinting?

Answer 10

Methylation

Question 11

give an example of genomic imprinting

Answer 11

insulin growth factor 2 in mouse giving normal and dwarf offspring when imprinting

Question 12

explain what’s happening in imprinting green card.

Answer 12

basically the mum is normal bc she inherited that from the dad and the off is dwarf bc inherited from the mum and in this case mum: switched off dad: active.

Question 13

What’s an epistatic gene?

Answer 13

a gene that masks another gene

Question 14

What’s a hypostatic gene

Answer 14

a gene whose expression is masked by another

Question 15

Whats a modifier

Answer 15

sth that reduces or enhances the expression of a gene but do not mask

Question 16

give an example of modifier

Answer 16

black and brown color Black> brown
B-D- black B-dd dilute black bbD- brown bbdd diluted brown
dd is a modifier bc it dilutes the color

Question 17

example of modifier in nature

Answer 17

drosophila if. a mutation in the eyes homo severe hetero just problems

eld: enhances the mutagenic effect and makes it worse
emc: represses the mutagenic effect and reverts to WT

Question 18

What’s heterodimer suppresion

Answer 18

two polypep are formed by two genes that form an heterodimer; modified ratio

Question 19

Describe heterodimer suppresion

Answer 19

card

Question 20

What’s CFTR?

Answer 20

it’s a pleiotropic gene many unrelated effects +ve or -ve CFTR is modified by the environment or other genes

Question 21

What’s a +ve effect of CFTR?

Answer 21

resistance to cholera and other infections if heterozygous

Question 22

what’s a pleiotropic gene

Answer 22

it means that it has pleiotropic effects which means that they affect more than one phenotypic trait to increase or reduce fitness. consequently a mutation in a pleiotropic gene may have an effect on some or all traits simultaneously

Question 23

what’s oligogenic disease

Answer 23

oligogenic disease are conditions produced by the combination of two three or four defective genes

Question 24

what’s monogenic disease?

Answer 24

monogenic diseases are those in which defects in a single gene produces a disease e.g Alzheimer

Question 25

What are the three types of disease

Answer 25

oligogenic monogenic and polygenic

Question 26

is CF a monogenic disease?

Answer 26

in theory yes cause by CFTR however since it’s modified by other genes it can be seen as oligogenic