Because the identity of the __ chromosomes in an individual could be inferred by observing the sex of the fly, the behavior of the two members of the pair of __ chromosomes could be correlated with the behavior of the two __ of the eye color gene.
In humans and other mammals, there are two varieties of sex chromosomes, designed __ and __.
-- The __ is much smaller than the __.
- A person with ___ is a female; a person with __ is a male.
two X chromosomes
an X and a Y
Short segments at either end of the __ chromosome are the only regions that are homologous with corresponding regionsof the __.
-- These ___ allow the __ and __ chromosomes in males to pair and behave like __ during meiosis in the __.
In both teh testes and ovaries, the two sex chromosomes __ during meiosis, and each receives one.
X and Y
__ is a matter of chance- 50%
There are three other chromosomal systems besides the human X-Y system.
- name the first one in grasshoppers and cockroaches
- only one type of sex chromosome, the X-Females are XX
-males are X0
-SEx of the offspring is determined by whether the sperm cell contains an X or no sex chromosome
Name the chromosomal system in birds and fishes, etc.
- sex chromosome in the egg determines the sex of offspring.
- Sex chromosomes are Z and W
- Females: ZW/ Males: ZZ
Name the chromosomal system in bees and ants.
- no sex chromosoems.
-females develop from fertilized eggs and are diploid
-males- from unfertilized eggs are haploid- have no fathers
In humans, the anatomical signs of __ begin to emerge when the embryo is about __ months old.
- Before then, the rudiments of the __ are generic- they can develop into either __ or __, depending on whether a __ is present.
In 1990, a British research team identified a gene on the _ chromosome required for the development of the __.
-- In the absence of __, the gonads develop into ovaries.
-- The biochemical, physiological, and anatomical features that distinguish males and females are complex and many genes are involved in their development. In fact, __ codes for a protein that regulates other genes.
SRY- sex-determining region of Y
Researchers have sequenced the human __ chromosome and have identified __ genes, which code for about __ proteins (some genes are duplicates). ABout 1/2 of these genes are expressed only in the testis, and some are required for normal __ functioning. In their absence, an __ individual is male, but doesn't produce normal sperm.
In addition to their role as carriers of genes that determine sex, these chromosomes, especially X chromosomes, have genes for many characters unrelated to sex.
-- A gene located on either sex chromosome is called a __, although in humans the term has historically referred specifically to a gene on the __ chromosome. __ in humans follow the same pattern of inheritance as the fruit flies eye-color.
Fathers pass __ to all of their daughters but to none of their sons.
In contrast, mothers can pass __ to both sons and daughters.
sex-linked alles x2
If a __ is due to a __ allele, a female will display the phenotype onyl if she is a __.
Males don't use homo and heterozygotes. These use __.
-- Any male receiving the __ from his mother will express the trait. For this reason, far more males than females have sex-linked recessive disorders.
-- However, even though the chance of a female inheriting a double dose of the __ is much less than the probability of a male inheriting a single does, there are females with sex linked disorders.
__- affects about one of every 3500 males born in the US; characterized by a progressive weakening of the muscles and loss of coordination; affected individuals rarely live past their early 20s; researchers have traced the disorder to the absence of a key muscle protein calle ddystrophin and have mapped the gene for this protein to a specific locus on teh X chromosome
Duchenne muscular dystrophy
__- sex-linked recessive disorderdefined by the absence of one or more of the proteins required for blood clotting. When a person with this is injured, leeding is prolonged because a firm clot is slow to form. Bleeding in the muscles or joints, unlike a small cut, can be painful and can lead to serious damage
One X chromosome in each cell in females becomes almost completely inactivated during __.
- As a result, the cells of females and males have the same effective dose (one copy) of these genes. The __ X in each cell of a female condenses into a compact object called a __, which lies along the inside of the nuclear envelope.
- Most of the genes of the X chromosome that forms the __ are not expressed. In the ovaries, __ chromosomes are reactivated in the cells that give rise to eggs, so every female gamete has an __.
__ demonstrated that selection of which X chromosome will form the __ occurs randomly and independently in each embryonic cell present at the time of X __.
-- As a consequence females consist of a mosaic of two types of cells: those with the __ derived from the father and those from the mother.
After an X chromosome is inactivated in a particular cell, all mitotic descendents of that cell have the same inactive X.
- Thus, if a female is __for a __, about half her cells will express one allele, while the others wll express the alternate.
In humans, __ can be observed in a recessive X-linked mutation that prevents the development of sweat glands. A woman who is eterozygous for this trait has patches of normal skin and patches of skin lacking sweat glands.
Inactivation of an X chromosome involves modification of the DNA, including attachmeent of __ groups to one of the __ of DNA __.
Researchers have also discovered an X chromosome gene called __ for __ that is active only on the __ chromosome.
X- inactive- specific- transcript
Multiple copies of the __ product of this gene apparently attach to the X chromosome on which they are made, eventually almost covering it.
-- Interaction of this __ with the chromosome seems to initiate __, and regulation of this process by other genes is still being researched.
Chapter 15: The Chromosomal Theory of Inheritance (2)