Heredity, Probability, Linkage, and Mapping

Question 1

What are transmission genetics?

Answer 1

• the study of how genes are transmitted from parents to offspring
• principles are derived from Mendel’s experimentation

Question 2

What does a monohybrid cross examine?

Answer 2

one pair of contrasting traits

Question 3

What does a dihybrid cross examine?

Answer 3

two pairs of contrasting traits

Question 4

What are Mendel’s 4 Postulates?

Answer 4

1. unit factors in pairs
2. dominance, recessiveness
3. segregation
4. independent assortment

Question 5

What is Mendel’s monohybrid ratio?

Answer 5

3:1

Question 6

What is Mendel’s dihybrid ratio?

Answer 6

9:3:3:1

Question 7

What does a trihybrid cross examine?

Answer 7

three contrasting traits

Question 8

What is Mendel’s trihybrid ratio?

Answer 8

27:9:9:9:3:3:3:1

Question 9

How does independent assortment contribute to genetic variation?

Answer 9

• the possible number of gametes is 2^n
• n=haploid number
• humans: n=23. 2^23=8x10^6. there are over 8 million types of gametes possible through independent assortment
• from two parents each, 64x10^12 potential genetic offspring combinations

Question 10

What is the product law?

Answer 10

• the probability of two or more independent events occuring simultaneously is equal to the product of their individual probabilities

e.g. if you toss a penny and nickel at the same time there are four combos:
PhNh:(1/2)(1/2)=1/4
PtNh:(1/2)(1/2)=1/4
PhNt:(1/2)(1/2)=1/4
PtNt:(1/2)(1/2)=1/4

Question 11

What is the sum law?

Answer 11

the probability of obtaining any single outcome, where that outcome can be acheived by two or more events, is equal to the sum of the individual probabilities of all such events
* adding the probabilities together

e.g. what is the probability of tossing a penny and nickel and obtaining one head and one tail?
1/4 + 1/4 = 1/2

Question 12

What is a wild-type allele?

Answer 12

the allele we desginate as normal.
(often but not always dominant)

Question 13

What is a loss-of-function mutation?

Answer 13

a mutation that causes the discrimination or loss of a specific wild-type function

Question 14

What is a gain-of-funciton mutation?

Answer 14

a mutation that affects the regulation of transcription of a gene, resulting in an increasing quantity of the gene product

Question 15

What is a neutral mutation?

Answer 15

the gene product presents no change to either the phenotype or the evolutionary fitness of the organism

Question 16

What is incomplete dominance?

Answer 16

a cross between parents with constrasting traits that generate an intermediate phenotype. neither parent is dominant
e.g. cross between red and white flower making a pink, incomplete dominance

Question 17

Explain multiple alleles and give a real-life example.

Answer 17

multiple alleles can be present on the same gene and create a unique mode of inheritance.
Example: ABO Blood group
* characterized by presence of anitgens on the surface of red blood cells
* combinations of alleles in ABO system exhibits a mode of inheritance
* each individual has either:
* A antigen (A phenotype)
* B antigen (B phenotype)
* The A and B antigens (AB phenotype)
* or neither antigen (O phenotype)

Question 18

What is a lethal allele?

Answer 18

mutations resulting in the synthesis of a gene product that is nonfunctional
* heterozygotes can often tolerate
* recessive lethal alleles will cause the homozygous recessive individuals to die
* death depends on when the product is needed
* dominant lethal allele: Huntington disease. Allele causes onset and eventual death in heterozygotes (later in adulthood)

Question 19

What is a gene interaction?

Answer 19

describes the idea that several genes influence a particular characteristic
* cellular function of numerous gene products can contibute to a common phenotype

Question 20

What is epigenesis?

Provide an example.

Answer 20

each step of development increases the complexity.
e.g. formation of inner ear in mammals
* during formation, many genes influence intricate developmental events
* mutations that interrupt any of the steps of ear development can lead to hereditary deafness
* in humans, over 50 genes are involved in development of ability to discern sound

Question 21

What is epistasis?

Answer 21

A phenomenon where the expression of one gene or gene pair modifies the expression of another gene or gene pair
* a gene can mask other genes
* can be dominant, recessive, or complementary, or create a novel phenotype

Question 22

What is pleiotropy?

Answer 22

a phenomenon in which a single gene has multple phenotypic effects

Question 23

What is X-linkage?

Provide an example.

Answer 23

genes presence on the X chromosmoe exhibit unique patterns of inheritance
* males cannot be hetero/homozygous, they only have one X chromosome. They can be hemizygous
* example: Colour-blindness. Mother passes trait to her sons but not her daughters

Question 24

What is Penetrance and Expressivity?

Answer 24

Penetrance: the percentage of individuals who show at least some degree of expression of a mutant genotype
Expressivity: the range of expression of the mutant genotype

Question 25

What is the linkage ratio?

Answer 25

a unique ratio results in the F2 offspring if complete linkage exists between two genes (because of close proximity) and orgaisms heterozygous at both loci are mated
the 1:2:1 ratio is characteristics of complete linkage