Extensions of Mendelian Genetics

Question 1

Haplosufficiency?

Answer 1

50% of dominant allele is enough for a dominant phenotype in heterozygote.

Question 2

Types of loss of function mutations?

Answer 2

Null/Amorphic mutation - No functional product formed, homozygotes display mutant phenotype

Leakys/hypomorphic - Small amount of wild-type product made inheterozygotes, homozygotes make a mutant functional product making mutant phenotype.

Dominant negative mutation - Formations of multimeric proteins altered by mutant products interacting abnormally with products of other genes, leads to malformed multi-meric proteins. (osteogenesis imperfecta is due to formation of mutant collagen due to distorted trimer).

Question 3

What are the two types of gain of function mutations?

Answer 3

Hypermrphic mutation - Excessive expression of product leading to excessive gene action. May be more severe in homozygotes than heterozygotes.

Neomorphic mutation - Mutant has a novel function that produces a mutant phenotype in both heterozygotes and homozygotes. could be more severe in homozygotes.

Question 4

Incomplete dominance?

Answer 4

Neither completely dominant - phenotype is somewhere between the two.

Leads to same genotypic and phenotypic ratios

Question 5

What is incomplete penetrance? Example?

Answer 5

Dominant allele doesnt always penetrate to produce the phenotype.

Can skip generations

Polydactyly

Question 6

What is expressivity?

Answer 6

The extent to which the trait is expressed.

Question 7

What is overdominance? Example?

Answer 7

The heterozygote advantage.

Heterozygotes have a trait that is more beneficial than either homozygote

SICKLE CELL DISEASE

Heterozygote doesnt have disease and is malaria resistant while homozygous recessive have disease and resistant to malaria and homozygous dominant is neither

Question 8

What is codominance and a good example of this?

Answer 8

Heterozygotes express both traits equally due to both being dominant.

ABO blood typing is good example of this

Question 9

What is the bombay phenotype?

Answer 9

A mutation in the FUT-1 gene makes it not possible to properly make H substance to be made into A or B antigen, so even if their genotype is A or B they will have a phenotype that functions like O.

Question 10

What is sex-influenced inheritance and an example of this?

Answer 10

This is when an allele is dominant in one sex, but recessive in the other due to effects of hormones. Usually an autosomal trait. CAN OCCUR IN BOTH

Pattern baldness is an example of this.

Question 11

What is sex limited inheritance?

Answer 11

This is when a trait only occurs in one of the two sexes due to effect of sex hormones on gene expression. CANNOT OCCUR IN BOTH

Question 12

What is a lethal allele and an example of the two types? What is important when running a punnett square with these?

Answer 12

Have the potential to cause death:

Essential: without these an organism will die (phenotype is death)

Nonessential: not absolutely required for survival but may be beneficial (manx cat)

BE SURE TO ELIMINATE THOSE WITH LETHAL GENOTYPE FROM SQUARE AND NOT TO INCLUDE IN EQUATION IF THEY DONT NEED TO BE INCLUDED.

Question 13

What is pleiotropy? Example?

Answer 13

This is when a single gene results in multiple phenotypes due to:

1 - expression of single gene can affect cell function in more than one way

2. gene may be expressed in different cell in multicellular organism

3, gene may be expressed at different developmental stages

CF is an example of this.

Question 14

What is epistasis? epistatic vs hypostatic gene?

Answer 14

This is when the expression of one gene masks the expression of another.

Epistatic gene - the one that modifies

Hypostatic - the one that is masked

Question 15

What is complimentary gene interaction?

Answer 15

This is when genes interact in tandem with one another, so each dominant allele is complemented by another genes allele. In the case of pea plant color the dominant alleles prevented the formation of pigment when complimented by recessive other gene.

Question 16

What is duplicate gene action?

Answer 16

This is when two or more copies of similar genes exist resulting in gene redundancy, which allows for one gene to compensate for lack of expression of the other

Question 17

What is the difference between dominant and recessive epistasis?

Answer 17

Recessive - recessive allele is one that masks of reduces the expression (homozygous recessive)

Dominant - dominant allele suppresses expression of alleles at other gene

Question 18

What are some environmental factors that can effect phenotype?

Answer 18

Temperature - temp sensitive alles, siamese cats and himalayan rabits.

Nutrition - PKU, galactosemia, lactose intolerance

Chemicals - teratogens causing abnormalities in fetus, thalidomide caused Phocomelia (short limbs), which also is a PHENOCOPY (affect of chemical mimics effect of gene mutation) of roberts syndrome.

Question 19

What is huntington disease an example of?

Answer 19

Trinuceotide repeat expansion disorder, increasing amount of glutamine residues

Question 20

Describe genetic anticipation.

Answer 20

This is where the phenotype progresses at an earlier age of onset AND increases in severity from generation to generation.