Sex linkage

Sex Linkage

	Email		Print
	Bookmark		Link

Sex linkage

Sex linkage is the phenotypic

Phenotype

A phenotype is any observable characteristic or trait_ of an organism: such as its morphology , development, biochemical or physiological properties, or behavior....
expression of an allele

Allele

An allele is one member of a pair or series of different forms of a gene. Usually alleles are coding region, but sometimes the term is used to refer to a junk DNA....
that is related to the chromosomal sex of the individual. This mode of inheritance is in contrast to the inheritance of traits on autosomal

Autosome

An autosome is a non-sex chromosome. It is an ordinarily paired type of chromosome that is the same in both sexes of a species . For example, in humans, there are 22 pairs of autosomes....
chromosomes, where both sexes have the same probability of expressing the trait. Since, in humans, there are many more genes on the X than there are on the Y, there are many more X-linked traits than there are Y-linked traits.

In mammal

Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
s, the female

Female

Female is the sex of an organism, or a part of an organism, which produces mobile ovum . The ova are defined as the larger gametes in a heterogamous reproduction system, while the smaller, usually motile gamete, the spermatozoon, is produced by the male....
is the homogametic sex, having two X chromosome

X chromosome

The X chromosome is one of the two sex determination system chromosomes in many animal species, including mammals . It is a part of the XY sex-determination system and X0 sex-determination system....
s (XX), while the male is heterogametic, having one X and one Y chromosome (XY).

Discussion

Ask a question about 'Sex linkage'

Start a new discussion about 'Sex linkage'

Answer questions from other users

Full Discussion Forum

Encyclopedia

Sex linkage is the phenotypic

Phenotype

A phenotype is any observable characteristic or trait_ of an organism: such as its morphology , development, biochemical or physiological properties, or behavior....
expression of an allele

Allele

Autosome

Mammal

Mammals are a class of vertebrate animals whose name is derived from their distinctive feature, mammary glands, with which they feed their young....
s, the female

Female

X chromosome

Linkage overview

X-linked recessive

X-linked recessive is a mode of Mendelian inheritance in which a mutation in a gene on the X chromosome causes the phenotype to be expressed in males and in females who are Zygosity for the gene mutation ....
traits expressed in all heterogametics, but only in those homogametics that are homozygous

Zygosity

In genetics, zygosity refers to the similarity or dissimilarity of the DNA sequences in specific coding segments, or genes, on the homologous chromosomes chromosomes of a zygote, or fertilisation ovum....
for the recessive allele. For example, an X-linked recessive allele in humans causes hemophilia. Haemophilia is much more common in males than females because males are hemizygous

Zygosity

In genetics, zygosity refers to the similarity or dissimilarity of the DNA sequences in specific coding segments, or genes, on the homologous chromosomes chromosomes of a zygote, or fertilisation ovum....
- they only have one copy of the gene in question - and therefore express the trait when they inherit one mutant allele. In contrast, a female must inherit two mutant alleles, a less frequent event since the mutant allele is rare in the population.

The incidence of recessive X-linked phenotypes in females is the square of that in males (squaring a proportion less than one gives an outcome closer to 0 than the original). If 1 in 20 males in a human population are green color blind

Color blindness

Color blindness, a color vision deficiency, is the inability to perceive differences between some of the colors that others can distinguish. It is most often of genetic nature, but may also occur because of eye, nerve, or brain damage, or due to exposure to certain chemicals....
, then 1 in 400 females in the population are expected to be color blind (¹/₂₀)*(¹/₂₀).

X-linked traits are maternally inherited from carrier mothers. Each son born to a carrier mother has a 50% probability of inheriting the X-chromosome carrying the mutant allele. There are a few Y-linked traits; these are inherited from the father.

In classical genetics, a reciprocal cross

Reciprocal cross

In genetics, a reciprocal cross is a breeding experiment designed to test the role of parental sex on a given inheritance pattern. All parent organisms must be true breeding to properly carry out such an experiment....
is performed to test if a trait is sex-linked.

Types of links

Diseases well known for their X-linked recessive inheritance are Haemophilia

Haemophilia

Haemophilia is a group of heredity genetic disorders that impair the body's ability to control blood clotting or coagulation, which is used to enclose cuts on your skin....
(types A and B), and color blindness

Color blindness

X-linked recessive

X-linked inherited diseases occur far more frequently in males because they only have one X chromosome. Females must receive a copy of the gene from both parents to have such a recessive disease. However, they will still be carriers if they receive one copy of the gene. Recessive genes on the X chromosome that cause serious diseases are usually passed from female carriers to their ill sons and carrier daughters. This is because males, who always have the disease and are not just carriers, would have to father a daughter to pass on the gene. This is unlikely because severe genetic diseases often cause death in childhood or early adulthood. Even those males who survive childhood are unlikely to father children because a sickly male will be less likely to find a mate

Mate

Mate and similar may refer to:* One of a pair of animals involved in mating* Mate , a colloquialism used to refer to a friend* Mahte, a goddess in Latvian mythology, also spelled Mate...
. However, if the disease shows up late in life, or is not severe, he will pass the gene to all of his daughters. He can not pass it to his sons because a male receives his X chromosome from his mother. A mother with one copy of the gene has a 50% chance of passing it to her children of both sexes, but her daughters will just be carriers of the gene unless their father has it, too.

X-linked dominant

There are few examples of X-linked dominant diseases; the best known in this category is vitamin D resistant rickets.

Incontinentia pigmenti
Incontinentia pigmenti

Incontinentia Pigmenti is a genetic disorder that affects the skin, hair, teeth, and nails. It is also known as Bloch-Sulzberger disease, Bloch Siemens syndrome, melanoblastosis cutis and naevus pigmentosus systematicus....
CHILD
Child

A child is a human being between the stages of birth and puberty. The legal definition of "child" generally refers to a minor , otherwise known as a person younger than the age of majority....

Y-linked

Various failures in the SRY
SRY

SRY is a sex-determining gene on the Y chromosome in the therians .This intronless gene encodes a transcription factor that is a member of the high mobility group -box family of DNA-binding proteins....
genes

Sex-linked traits in other animals

Calico or tortoiseshell cat
Tortoiseshell cat

Tortoiseshell describes a coat coloring found in cats. Cats of this color are mottled, with patches of red and black, chocolate, or cinnamon. They are sometimes called torties for short....
s, those which have orange-and-black fur.
White
White (mutation)

white was the first sex-linked mutation ever discovered in Drosophila melanogaster. In 1910 Thomas Hunt Morgan, collected a single male white-eyed mutant from a population of Drosophila melanogaster fruit flies, which usually have bright red eyes....
eyes in Drosophila melanogaster
Drosophila melanogaster

Drosophila melanogaster is a two-winged insect that belongs to the Diptera, the Order of the Fly. The species is commonly known as the Drosophilidae or vinegar fly, and is one of the most commonly used model organisms in biology, including studies in genetics, physiology and Life history theory....
flies, the first sex-linked gene
Gene

A gene is the basic unit of heredity in a living organism. All living things depend on genes. Genes hold the information to build and maintain their cell and pass genetic trait to offspring....
ever discovered.