Sex Chromosome Biology in the Mammalian Kingdom All biological
... Sex Chromosome Biology in the Mammalian Kingdom
All biological differences between women and men originate from the sex chromosomes. Some 160
million years ago, the X and Y chromosomes were very similar, but since then the Y chromosome
has lost most of its genes, whereas the present X chromosome con ...
Test 4 Review
... him to stud. In looking over the stud book,
however, you discover that the horse’s
grandfather exhibited a rare disorder that
causes brittle bones. The disorder is
hereditary and results from homozygosity
for a recessive allele. If your horse is
heterozygous for the allele, it will not be
possible t ...
... can be a perfectly normal female.
If the SRY gene becomes translocated to
another chromosome, an XX individual
can be a phenotypically normal (but
Lyonization - National Foundation for Ectodermal Dysplasias
... (the term lyonization is in honor of Mary Lyon, the scientist who first offered this explanation for gene dosage
compensation). This inactivation process does not occur in males because they have only one X chromosome.
This process is most often random. The specific X turns off in each cell is an ac ...
X n Y
... Sex influenced traits
• The gene is NOT on a
sex chromosome, but
SEX affects the
• Ex-baldness-dominant in
males, recessive in
– If ‘B’ represents bald
and ‘b’ is hairy then
Men must be bb to keep
Women can be Bb or bb
to keep hair
Mutations and Genetics Test Review 1. What percentage of human
... change the number of sets of
chromosomes found in cells.
change eukaryotic plants into
frequently cause mutations, which create
new alleles and genes.
insert foreign DNA into plant
4. Which of the following would require the use of
... of the disorder. A carrier is a person who
a. does not have the disorder but can pass it on to offspring.
b. can develop the disorder later in life but cannot pass it on.
c. has a dominant normal allele that has been inactivated.
d. passes the disorder to offspring on the Y chromosome only.
4. Genes ...
Genetics - the science of heredity and variation
... Allele - one of a pair of genes that occupy the same location on homologous
chromosomes and affect the same trait in animals
Diploid - refers to paired chromosomes in body cells
Gametes - male or female reproductive cells
Genes - the smallest unit of inheritance; a portion of a DNA molecule, occur i ...
... Dissociator caused the chromosomes to break and
effected neighbouring genes when the activator was
Later, in 1948, she found that Ds and Ac could
transpose on the chromosome.
By changing the colouration of the kernels over each
generation, by using controlled crosses, she concluded
that Ac ...
... the inner cell mass, and in these cells both X chromosomes become active again.
Sex-linked genes, genes located on one of the sex chromosomes (X
... red-green colorblindness. Hemophilia is the failure (lack of
genetic code) to produce certain substance needed for proper
blood-clotting, so a hemophiliac’s blood doesn’t clot, and (s)he
could bleed to death from an injury that a normal person might
not even notice.
Patterns of Inheritance 4. Sex-linked Recessive C. Nondisjunction
... B. Sex-linked (X-linked)
1. Genes located on sex chromosomes
2. Males (XY)
a. Only inherit 1 allele because they only have 1 X
b. The one allele comes from their mom
3. Females (XX)
a. Inherit 2 alleles
b. 1 allele from each parent
c. X-chromosome inactivation
i. A process that “turns off ...
Lecture #6 Date ______
... sex chromosome
Linked genes: genes located on
the same chromosome that tend
to be inherited together
outline File - selu moodle
... Males and females express the same levels of certain genes found on the X chromosome Dosage compensation
In females one X chromosome is randomly selected for modification
13.3 Exceptions to the Chromosomal Theory of Inheritance
Mitochondrial and chloroplast DNA is inherited only from the egg cell.
Genes & Chromosomes
... Autosomes: Chromosomes that are the same
in males and females.
Sex-Linked: Trait that is determined by a gene
located on a sex chromosome.
X-chromosome inactivation: molecular mechanism and genetic
... M., Tonlorenzi, R. and Willard, H. F. (1991). A gene from the region of
the human X inactivation centre is expressed exclusively from the inactive
X chromosome. Nature 349, 38-44.
Migeon, B. R. (1994). X-chromosome inactivation: molecular mechanisms
and genetic consequences. Trends Genet 10, 230-235 ...
... 4. Telomeric and centromeric regions
Features of Facultative Heterochromatin
1. Referred to as silent chromatin
2. Potential to become heterochromatic (Barr body)
Genetics of Sex - University of San Francisco
... genes shared between the two
In the Y chromosome, the shutting
down of X–Y crossing over during
evolution triggered a monotonic
decline in gene function
PAR1 homology maintained by
recombination in male meiosis,
genes in this region not subject to
Changes in Chromosome Number
... inserted into the
*Tests are not
due to risk of
Skewed X chromosome inactivation occurs when the inactivation of one X chromosome is favored over the other, leading to an uneven number of cells with each chromosome inactivated. It is usually defined as one allele being found on the active X chromosome in over 75% of cells, and extreme skewing is when over 90% of cells have inactivated the same X chromosome. It can be caused by primary nonrandom inactivation, either by chance due to a small cell pool or directed by genes, or caused by secondary nonrandom inactivation, which occurs by selection. Most females will have some levels of skewing. It is relatively common in adult females; around 35% of women have skewed ratio over 70:30, and 7% of women have an extreme skewed ratio of over 90:10. This is of medical significance due to the potential for the expression of disease genes present on the X chromosome that are normally not expressed due to random X inactivation. X chromosome inactivation occurs in females to provide dosage compensation between the sexes. If females kept both X chromosomes active they would have twice the number of active X genes than males, who only have one copy of the X chromosome. At approximately the time of implantation (see Implantation (human embryo), one of the two X chromosomes is randomly selected for inactivation. The cell undergoes transcriptional and epigenetic changes to ensure this inactivation is permanent. All progeny from these initial cells will maintain the inactivation of the same chromosome, resulting in a mosaic pattern of cells in females.