Biochemistry - Mendelian Inheritance Iii & Iv

Front 1

do males pass on their X chromosome to sons or daughters? Y chromosome?

Back 1

daughters; sons

Front 2

true or false. The X and Y sex chromosomes are approximately the same size.

Back 2

false, the X chromosome has 155Mb while the Y chromosome has only 23Mb

Front 3

what is the name for the product formed in the process of X-inactivation, an effort to equilbrate the amount of genetic material in males and females?

Back 3

Barr body

Front 4

at which point in development does X inactivation occur? Is one X normally chosen over the other for X-inactivation?

Back 4

early in embryogenesis; no, both are inactivated without discretion in each cell

Front 5

can the X chromosome chosen for a Barr body change with DNA replication and cell division?

Back 5

no

Front 6

do all cells in the female have the identical genetic identity?

Back 6

no; they either have one X chromosome activated or the other. This is usually restricted to regions but is completely random

Front 7

will a female heterozygous for an X-linked recessive disease gene manifest the disease?

Back 7

usually not since each tissue in a woman's body will contain some cells that express the disease gene and others that do not (due to Barr bodies)

Front 8

what appears to be the mechanism behind X-inactivation?

Back 8

DNA methylation

Front 9

what is the name for the gene in females which is present on the Barr body and is not present in males?

Back 9

XIST

Front 10

is the XIST transcript translated into protein? What is its role?

Back 10

no; it is thought to induce inactivation through recruitment of unidentified silencing factors

Front 11

genes in which region of the Barr body remain activated? What is the name for this region?

Back 11

distal tip of the short arm; pseudoautosomal region 1 (PAR1)

Front 12

what role does PAR play during meiosis?

Back 12

X and Y chromosomes pair during meiosis at PAR

Front 13

what must occur in females for them to have a phenotype for an X-linked recessive disease?

Back 13

they must have the gene copy on each X chromosome defected

Front 14

what is the term used for males in relationship to their X chromosome?

Back 14

hemizygous

Front 15

sex-linked recessive genes pass through the maternal or paternal side?

Back 15

maternal since the males receive their X chromosome from the mother.

Front 16

are males or females more commonly afflicted with a sex-linked recessive disease?

Back 16

males

Front 17

what percentage of the daughters of a man affected with a sex-linked recessive disease will be carriers for the gene? The daughter's sons?

Back 17

none; 50%

Front 18

can male-to-male transmission of sex-linked recessive disease occur?

Back 18

no

Front 19

are x-linked dominant disease more or less common than x-linked recessive disorders?

Back 19

less

Front 20

by how much are x-linked dominant diseases more common in females than in males?

Back 20

two times

Front 21

what is an example of a disease with a y-linked inheritance pattern?

Back 21

there are none

Front 22

what is heteroplasmy?

Back 22

the fact that each mitochondrion contains multiple copies of DNA and that there are multiple mitochondria per cell and that mutations in DNA may only occur in one copy of DNA in one mitochondrion

Front 23

how many genes are encoded by the mitochondrial genome? Does the mt genome have introns?

Back 23

37; no

Front 24

which tissues are usually most heavily affected by mitochondrial mutations?

Back 24

tissues that require a higher level of mitochondrially produced ATP for normal function

Front 25

what are 4 common mitochondrial diseases?

Back 25

encephalopathy, myopathy, ataxia, and retinal degeneration

Front 26

what is a new mutation?

Back 26

when a child is born with a genetic disease and there is no previous history of the disease -- most prevalent with autosomal dominant diseases

Front 27

what is mosiacism?

Back 27

when a mutation occurs in an embryonic cell but not in all embryonic cells and the disease is thus limited to certain tissues in the body and not others

Front 28

what is the implication of having part of the germ cells that have a mutation while having all somatic cell normal?

Back 28

the individual is at risk for having more than one affected offspring while not expressing the disease him/herself

Front 29

what is incomplete penetrance? What is an example of this?

Back 29

when an individiual has the genotype for a disease but does not exhibit the disease phenotype at all although he/she can transmit the disease to the next generation; retinoblastoma

Front 30

what is delayed age of onset?

Back 30

when a disease is not expressed until adulthood which makes it difficult to assess the mode of inheritance

Front 31

what is variable expressivity?

Back 31

situation in which penetrance is complete but the severity of the disease may vary greatly among affected individual members of the same family who have the same mutation

Front 32

what is locus heterogeneity?

Back 32

a disease that can be caused by mutations at different loci in different families

Front 33

what is allelic heterogeneity?

Back 33

situation in which different mutations in the same gene result in variable phenotypes. These differences can be either minor or quite significant

Front 34

which disease results from the unstable or dynamic mutations resulting from trinucleotide repeats?

Back 34

Fragile X syndrome

Front 35

as the number of trinucleotides increases in a person with fragile X mutation, does the likelihood of passing on the gene with a disease phenotype increase or decrease? Does the age of onset of the disease increase or decrease with each generation of Fragile X? what is the term used to describe this phenomenon?

Back 35

increase; decrease; genetic anticipation

Front 36

what is genetic imprinting?

Back 36

when the maternal and paternal copies of the same gene are expressed differently