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Image: “Graphic decomposition of a chromosome (found in the cell nucleus), come the bases pair that the DNA” by KES47. License: CC through 3.0


Also known as the Boveri–Sutton chromosome theory, the chromosome theory of inheritance says that chromosomes space the communication of all genetic inheritance. It describes how genes are inherited in accordance with Mendel’s law. Every gene is situated on a certain location, recognized as loci, on particular chromosomes. The is the habits of chromosomes throughout meiosis that defines why gene inherit in accordance through Mendel’s law.

You are watching: The chromosome theory of inheritance states that

During meiosis, chromosomes undergo 2 things:

SegregationIndependent assortment

Linking Genes and also Chromosomes ~ above the basis of Morgan’s occupational with Fruit Flies


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Image: “Results from reciprocal crosses between red-eyed (Red) and white-eyed (White) Drosophila in Morgan’s experiments. W + = red allele (wild-type allele) and w = white (mutant allele). In sex-linked inheritance, alleles ~ above sex chromosomes (XY) space inherited in predictable patterns. Drosophila sex-chromosomes.” through YassineMrabet. License: CC BY-SA 3.0


Morgan’s experiment through fruit paris is verification of chromosome theory. A mutation in the gene coding because that the shade of the eye in a fruit fly causes the white shade of the eye, instead of the regular red color.

The eye color gene in fruit flies is situated on the X chromosome.

During his experiment, Morgan discovered that once a red-eyed woman (wild-type) crosses with a white-eyed male, every offspring (F1) are red-eyed. When F1 flies space crossed v each other, every the F2 females are red-eyed, and half of the F2 males room white-eyed. This indicates that the white eye color gene inherits in the pattern of the X chromosome and also is recessive; whereas, the red-eye color is a leading trait.

Sex determination in Humans

All offspring inherit one X chromosome indigenous the mother; therefore, the sex the a person being is constantly dependent top top the kind of sex chromosome they get from the father. If the is a Y, the gender is a male, and also if that is an X, gender is a female.

SRY gene is vital in sex determination. That encodes one SRY protein which is responsible for masculine sex decision initiation.

Y chromosome outcomes in testes formation. If Y chromosome is absent, gonads would differentiate into ovaries.

Difference in different Species


Species

Females

Males

Humans, Drosophila

XX

XY

Grasshoppers

XX

XO

Honeybees

Diploid

Haploid

Birds

ZW

ZZ


Sex-Linked Human genetic Disorders

Human hereditary disorders have the right to be sex-linked.

Color blindness

It is more prevalent in males compared to females since it is an X-linked recessive trait.

A cross between a carrier female and also an affected male will result in the following:

25% influenced sons25% affected daughters25% carrier daughter25% normal sons

A cross in between an impacted mother and normal father would an outcome in:

50% impacted sons50% transport daughters

Hemophilia

It is one X-linked recessive disease in which the body’s ability to do blood coagulation is impaired. It results in prolonged bleeding after ~ an injury and easy bruising that the skin.Since females have actually two X chromosomes, they do not suffer unless both chromosomes carry the mutation. A cross in between an influenced father and also carrier mrs would an outcome in:

25% affected sons25% carrier daughters25% affected daughters25% regular sons

A cross in between an impacted mother and also normal dad would result in:

50% impacted sons50% transport daughters

Duchenne muscular dystrophy

This is a rarely X-linked recessive disease and among the most constant genetic problems affecting muscles.

Epidemiology

The condition affects every 1 in 3,500 males born all over the world. The an illness mainly manifests in the age of 3-6 years.

Etiology

The disease arises indigenous mutations the the DMD gene situated on the X chromosome. This is the gene the regulates production dystrophin, a protein discovered in association through the inside membrane the the membrane that skeletal and cardiac muscle cells.

Presentation

Patients through this disease experience weak muscles and also atrophy the the muscle of the pelvic area and shoulder region due to a lack of sarcolemma function in the myocytes of these muscles. The condition may progress to involve other parts the the body.

Complications

They incorporate cardiomyopathies and also respiratory distress because of the involvement of respiratory muscles.

Amelogenesis imperfect (AI)

It is a dental disorder in which over there is a defect in the enamel formation. Resultantly, the teeth space small, discolored, pitted, and also easily worn. AI is an X-linked leading trait.

A cross between an impacted female and unaffected masculine will an outcome in:

25 % influenced sons25 % regular daughters25 % impacted daughters25 % regular sons

A cross in between an unaffected female and impacted male will result in:

50 % influenced daughters50 % regular sons

X-inactivation

One that the X chromosomes gets inactive in woman mammals v the process of X-inactivation. Guys possess only one copy the the X chromosome, therefore this phenomenon actually prevents females indigenous having twin X chromosome gene products. The an option of X chromosome selected for silencing is random, and also once this X chromosome is inactive, it stays so because that the rest of the life on an organism. The inactivated chromosome has actually heterochromatin, a transcriptionally inactive structure, and also becomes a bar body.


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Image: “A calico cat has different colored fur on miscellaneous patches.” by dmgreen44. License: CC0 1.0


Tortoiseshell and also Calico cats have a different color on your fur. This is a manifestation that X-inactivation. In this cats, the black and also orange alleles i m sorry express fur shade are located on X chromosomes. Orange and also black fur have pigment, and white fur has no colours in cats.

In one area whereby the fur is black, the allele for orange hair is inactive.

On the job where fur is orange, the allele because that black hair is inactive.

White fur, top top the other hand, has no pigment.

Exceptions to a chromosomal theory

There are two exceptions come this theory.

Organelle inheritance

Traits that are controlled by the genes outside the cell core come under organelle inheritance. The gene expressing these traits are dubbed extra-nuclear or cytoplasmic genes.

It is a uniparental inheritance. Mitochondria in a zygote indigenous an egg cell does not come from sperm throughout fertilization. The expression of those genes included in this mitochondria is because of this exclusive come maternal inheritance. Similarly, in plants, the chloroplast is regularly inherited from the mother.

Genomic imprinting

Genomic imprinting is the hereditary phenomenon in which only the non-imprinted allele from any type of one the the parental is expressed. The imprinted allele is silenced throughout the process, avoiding it indigenous expressing itself.

The procedure of imprinting is done utilizing nuclear enzymatic mechanisms that preserve the parental epigenetic markings.

For example, a mouse inherits a mutated recessive allele native the father and also normally a dominant allele native the mother; however, the computer mouse grows to express the mutated gene. It is because the normal dominant allele was silenced during genomic imprinting.

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Epigenetic factors

Epigenetics involves the scientific research of changes in organisms due to the changes in gene expression rather than the alters in the coded DNA material. These factors influence gene expressions.


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“Exceptions to Chromosome Theory. Epigenetic determinants influences gene expression” Image created by jajalger2018.org


Specific changes in the following epigenetic components can reason the gene to express in different way in the kind of certain diseases:

DNA packingDNA methylationDietary impactsEnvironmental impactsTransposable elementsRegulatory genesIndividual lifestyle

Epigenetic transforms can cause a hold of disorders. The complying with are instances of together disorders:

CancersMental retardation linked disordersImmune disordersPediatric disordersNeuropsychiatric disorders