III. Penetrance and Expressivity

Question 1

___ is the ability of a given gene or gene combination to be expressed phenotypically to any degree; the extent to which a particular gene or set of genes is expressed in the phenotypes of individuals carrying it, measured by the proportion of carriers showing the characteristic phenotype.

Answer 1

Penetrance

Question 2

___ refers to when most dominant and recessive genes in homozygous conditions and many completely dominant genes even in heterozygous conditions give their complete phenotypic expressions.

Answer 2

Complete Penetrance

Question 3

___ refers to when some genes in homozygous as well as in heterozygous conditions fail to provide complete phenotypic expression of them.

Answer 3

Incomplete Penetrance

Question 4

___ refers to the degree of the effect produced by a penetrant genotype; refers to variations in a phenotype among individuals carrying a particular genotype; determined by the proportion of individuals with a given genotype who also possess the associated phenotype.

Answer 4

Expressivity

Question 5

Identical twins are derived from ___ zygote that splits during development.

Answer 5

1

Question 6

Fraternal twins come from ___ different eggs fertilized separately at the same time.

Answer 6

2

Question 7

Differentiate monozygotic from dizygotic twins.

Answer 7

Monozygotic twins are identical and develop from one egg and one sperm that split into two embryos.

Dizygotic twins are non-identical and develop from two eggs and two sperm that form two separate zygotes.

Monozygotic twins share one placenta, while dizygotic twins have two placentas.

Question 8

___ is the probability that a pair of individuals will both have a certain characteristic, given that one of the pair has the characteristic.

Answer 8

Concordance

Question 9

___ is the degree of dissimilarity in a pair of twins with respect to the presence or absence of a disease or trait.

Answer 9

Discordance

Question 10

___ refers to when affected infants are considerably larger than normal (macrosomia) and tend to be taller than their peers during childhood.

Answer 10

Beckwith-Wiedemann Syndrome or Overgrowth Syndrome

Question 11

____ is a growth disorder characterized by slow growth before and after birth.

Answer 11

Russell-Silver Syndrome

Question 12

___ refers to genes on the same chromosome that are physically close to each other; they do not segregate independently but can be separated by recombination.

Answer 12

Linkage

Question 13

____ is a representation of the distribution of a set of loci within the genome.

Answer 13

Genetic Map

Question 14

___ is a method of mapping a gene to a particular band of the chromosome.

Answer 14

Cytogenetic Mapping

Question 15

____ means crossing over; can occur between any 2 genes on a chromosome.

Answer 15

Recombination

Question 16

___ refers to when 2 genes are on the same chromosome and are far enough apart that they undergo recombination at least 50% of the time.

Answer 16

Independent Assortment

Question 17

___ refers to when 2 genes show linkage with a recombination level greater than 0% and less than 50%.

Answer 17

Incomplete Linkage

Question 18

___ refers to two loci being so close together that alleles of these loci are virtually never separated by crossing over.

Answer 18

Complete Linkage

Question 19

What are the factors that affect recombination frequencies? (3)

Answer 19

1. Gender
2. Region of the Chromosome Involved
3. Increased Crossover Frequency

Question 20

____ is the establishment of the sex of an organism, usually by the inheritance at the time of fertilization of certain genes commonly localized on a particular chromosome; results in the development of individuals with characteristics that allow them to be identified as males, females, or in some cases, hermaphrodites.

Answer 20

Sex Determination

Question 21

____ is the phenotypic expression of an allele that is dependent on the gender of the individual and is directly tied to the sex chromosomes.

Answer 21

Sex Linkage

Question 22

In a ____, the transmission is from the mother to the son.

Answer 22

Recessive X Linkage (X-linked Recessive Traits)

Question 23

In ____, transmission is 100% to the daughters if only the father is affected and 100% to the sons if only the mother is affected.

Answer 23

X-linked Dominant Traits

Question 24

___ are traits that are carried on the Y chromosome.

Answer 24

Y-linked Traits (Holandric Traits)