Final Exam III

Question 1

What are the two kinds of ancestors an individual has?

Answer 1

biological ancestors and genetic ancestors

Question 2

if two current day siblings receive copies of the same allele of a region of a genome from one of the chromosomes in one of their parents, then that parental allele is the______________

Answer 2

most recent common ancestor (MRCA)

Question 3

mitochondrial DNA (mtDNA)

Answer 3

passed directly form mother to their oddspring with no contribution from the fathers

Question 4

the DNA on the ______is passed directly from fathers to sons

Answer 4

Y chromosome

Question 5

What are Barr bodies?

Answer 5

inactive X chromosomes

Question 6

facultative heterochromatin

Answer 6

an entire X chromosome becomes nearly completely heterochromatic in some cells, while other copies of this same X chromosome remain euchromatic in other cells

Question 7

What does the X inactivation center (XIC) do?

Answer 7

it mediates dosage compensation

Question 8

Xist genes product

Answer 8

unusually long noncoding RNA (nCRNA) that never leaves the nucleus and is never translated into a protein. It triggers the inactivation of the X chromosome from which it is transcribed.

Question 9

What are B lymphocytes?

Answer 9

specialized white blood cells that make more than a billion different varieties of antibodies (immunoglobins)

Question 10

Each light and each heavy chain has a ______ and ______?

Answer 10

constant (C) domain and a variable (V) domain

Question 11

The C domain of the heavy chain determines?

Answer 11

whether the antibody falls into one of five major classes (IgM, IgG, IgE, IgD, and IgA) which influences where and how an antibodu functions

Question 12

What is the function of the V domain?

Answer 12

V domains of the light and heavy chains come together to form the antigen-binding site, which defines an antibody specificity

Question 13

What helps create the hypervariable regions?

Answer 13

Each gene’s DNA elements are joined imprecisely, which is perpetrated by cutting and splicing enzymes that sometime trim DNA from or add nucleotides to the junctions of segments they join Imprecise joining creates the hypervariable regions.

Question 14

What are the two enzymes that interact with DNA sequences in antibody genes to help catalyze rearrangements in B-lymphocytes?

Answer 14

RagI and RagII

Question 15

What causes the uncontrolled B-cell division that leads to a cancer known as Burkitt lymphoma?

Answer 15

Enzymes sometimes make a mistake that results in a recipricol translocation between human chromosomes 8 and 14. After this translocation, the enhancer of the chromosome 14 heavy-chain gene lies in the vicinity of the unrelated c-myc gene from chromsome 8. The translocated antibody-gene enhancer accelerates expression of c-myc, causing B cells containing the translocation to divide out of control, which leads to cancer.

Question 16

Dosage compensation

Answer 16

to compensate for female cells having two copies of each X-linked gene, and male cells having only one, XX cells inactivate one of their two chromosomes

Question 17

Sex-limited traits

Answer 17

affects a structure or process that is found in one sex but not the other

Question 18

A second method by which cells can regulate transcription initiation is through the control of DNA methylation. What is DNA methylation?

Answer 18

A biochemical modificaton of DNA itself in which a methyl (-CH3) group is added to the fifth carbon of the cytosine base in a 5’ CpG 3’ dinucleotide pair on one strand of the double helix

Question 19

What enzyme catalyzes the methylation of cytosines in CpG dinucleotides?

Answer 19

DNA methyl transferases

Question 20

What is one of the most important function of DNA methylation?

Answer 20

It controls the expression of housekeeping genes in vertebrates, and also plats a roe in regulating some cell-type specific genes

Question 21

epigenetic phenomenon

Answer 21

DNA methylation can alter gene expression heritably without changing the base sequence of DNA

Question 22

genomic imprinting

Answer 22

the epigenetic phenomenon in which certain genes are express in a parent-of-origin manner. If the alleles inherited from the father is imprinted,it is thereby silences, and only the allele from the mother is expressed.

Question 23

CpG islands

Answer 23

DNA sequences that may be a few hundred or a few thousand bp long, and within which the frequency of CpG dinucleotides is much higher than that of the rest of the genome.

Question 24

What happens when the CpG islands in the vicinity of a gene’s promoter are unmethylated? What happenes when they are methylated?

Answer 24

The chromatin is “open” and the gene is transcriptionally active. Methylation of the CpG islands “closes” the chromatin and represses transcription.

Question 25

Why are CpG island’s usualy unmethylated?

Answer 25

Proteins that activate transcription by binding to CpG islands prevent DNMTs (DNA methyltransferases) from methylating these islands.

Question 26

silencing

Answer 26

long term repressions through DNA methylation

Question 27

genomic imprinting

Answer 27

the unusual phenomenon in which the expression of an allele depends on the parent that transmits it. In genomic imprinting, the copy of a gene an individual inherits from one parent is transcriptionally inactive while the copy inherited from the other parent is active.

Question 28

imprinting control region (ICRs)

Answer 28

sex-specific methylation of certain DNA sequences

Question 29

paternally imprinted genes

Answer 29

allele from the mother is transcribed

Question 30

maternally imprinted genes

Answer 30

the allele inherited from the mother is not transcribed and all of the mRNA for this genes is made from the paternal allele

Question 31

epigenetic changes

Answer 31

modifications to genes that later gene expression without changing the base pair sequence and that are inherited directly through cell divisions

Question 32

What types of epigenetic change is responsible for genomic imprinting?

Answer 32

Sex specific DNA methylation of CpG dinucloetides found in specific ICRs (imprinting control regions)

Question 33

What two ways can ICR methylation influence gene expression?

Answer 33

1) inculator mechanisms–> ICR contains an insulator whose function is controlled by DNA methylation
2) noncoding RNA (ncRNA) mechanism –> in the vicinity of some imprinted genes, the ICR encodes an ncRNA whose transcription is controlled by a CpG island