Topic 11-2 Flashcards
the cameo recissive mutation in female peacocks in a gene on the ______ leads to dull brown feathers
Z sex chr
in a ZZ-ZW system, females inherit ____ chromosome from their mother and ____ chromosome from their father
W, Z
in ZZ-ZW systems, traits that are dictated by the Y chr genes are called:
holandric traits
three main characteristics of holandric traits are:
1) present only in males
2) always inherited from the father
3) if father has trait, then every son will have it
human Y chr only have about ______ genes, and half of these encode for ______.
350, proteins
how many palindromic sequences on the human Y chr?
eight
can palindromic sequences on the human Y chr undergo recombination?
yes
lack of recombination b/w chr (like X and Y) would lead to:
accumulation of mutations and loss of genetic material on Y
what is intrachromosomal recombination?
occurs at the Y chr where arms of the Y chr crossover w/ each other. helps to prevent decay of the Y chr
dosage compensation equalizes:
protein levels
mechanisms to equalize the amount of protein produced by X-linked genes in males w/ respect to autosomal genes and X-linked genes in females
dosage compensation
if there is no dosage compensation in males, they will produce:
insuficient levels of certain proteins
in flies dosage compensation consists of:
increased expression of X-linked genes only in males
in placental mammals dosage compensation consists of:
increasing X-linked genes in males AND females, BUT one X in females is inactivated
who was the person who discovered what Barr bodies were?
Mary Lyon
what is the Lyon hypothesis?
wihin each female (placental mammals), one of the two X chr is inactivated, producing Barr bodies (dark spots in nucleus)
true or false: in placental mammal dosage compensation, the X chromosome that becomes inactivated is selected at random
true
due to random X-inactivation, female placental mammals are functionally _______ at the cellular level so that 50% of cells express one allele, and 50% of cells express another
hemizygous
random X-inactivation means that females are _____ for the expression of X-linked genes. and example of this is ______.
mosaics, calico cats
all cells produced from mitosis from one cell will have:
the same X chr inactivated as the parent cell
how does X-inactivation work w/ extra chr disorders?
if more than two chr, all but one X id inactivated and additional X’s become Barr bodies
why doesn’t dosage compensation prevent disorders like triple X disorder (XXX)?
probably bc some X-linked genes escape X-inactivation.
what are the two main steps for X-inactivation?
1) cell somehow counts how many X chr are present
2) one X chr is selected for inactivation
what is the mechanism for random X-inactivation? (five steps)
1) a gene called Xist becomes active in X chr chosen to be inactive
2) Xist makes a very long RNA molecule
3) Xist RNA molecules coat the X chr
4) Xist RNA molecules recruit protein complexes that alter chromatic structure making Barr bodies
5) other genes on the chosen “active” X chr repress the transcription of Xist and prevent RNA coating
is dosage compensation universal?
no!
