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The Chromosomes present in the diploid cells of the majority of the sexually reproducing animals are of two types: autosomes bearing genes for somatic characters and sex chromosomes bearing genes for sex. Sex chromosomes also carry some genes for non-sexual characters such as colour blindness and haemophilia. Such genes which are always associated with sex chromosomes are called sex-linked genes. In man and Drosophila the sex chromosomes (X and Y) are unequal in size and shape, X being larger and rod shaped whereas Y is small and slightly curved. In birds and butterflies the sex chromosomes (Z and W) are also unequal in shape and size, Z being larger than W. In Mendelian pattern of inheritance, the genes for contrasting characters were located on autosomes but not on the sex chromosomes. Secondly, the result of reciprocal cross is same as normal cross which is not the case with sex linked inheritance. There are three types of sex-linked genes depending upon their association with particular chromosome.
Some important points of sex linked inheritance are as follows:
- It is a criss-cross inheritance as the father passes its sex-linked character to his daughter who in turn passes it to the grandson.
- Daughter does not express the recessive trait but act as carrier in the heterozygous condition.
- Female homozygous for recessive trait expresses the trait.
- Any recessive gene borne by the X chromosome of male is immediately expressed as Y chromosome has no allele to counteract.
Sex linked inheritance : examples in men
Colour Blindness
Colour blindness is an example of sex linked character. Those who suffer from red green colour blindness cannot distinguish between red and green colour. The gene for this defect is located on X chromosome.
When a normal woman is married to a colour blind man, their children (daughters and sons) have normal colour vision. But when their daughters were married to normal man, 50% of their sons are colour blind and the remaining 50% are normal, while the daughters were all normal.
If a colour blind woman marries a normal man, their daughters are normal but all their sons are colour-blind. When these F1 daughters are married to colour blind men, colour blind sons and daughters are born in equal number.
Haemophilia
Haemophila is another popular example of sex linked inheritance in human beings. It is caused by a mutant gene (h) present in X chromosome and recessive to normal gene and is, therefore, suppressed in heterozygous condition. Individuals suffering from this disease lack a factor responsible for clotting of blood. So in the absence of blood clotting substance, a minor cut or injury may cause prolonged bleeding leading to death. This disease in man is generally restricted to male members.,
Sex-linked inheritance is a type of inheritance in which a gene is located on a sex chromosome. In humans, there are two sex chromosomes: X and Y. Females have two X chromosomes, while males have one X chromosome and one Y chromosome.
X-linked recessive inheritance is a type of sex-linked inheritance in which the gene for the trait is located on the X chromosome. If a female inherits one copy of the gene from her father, she will be a carrier of the trait, but she will not show any symptoms of the disease. However, if she passes the gene on to her son, he will have the disease.
X-linked dominant inheritance is a type of sex-linked inheritance in which the gene for the trait is located on the X chromosome. If a female inherits one copy of the gene from her father, she will show symptoms of the disease. However, if a male inherits the gene from his mother, he will not show any symptoms of the disease, but he will be a carrier of the trait.
Y-linked inheritance is a type of sex-linked inheritance in which the gene for the trait is located on the Y chromosome. Only males can inherit Y-linked genes, and the trait will be passed down from father to son.
Mitochondrial inheritance is a type of inheritance in which the genes are located in the mitochondria, which are the energy-producing organelles in cells. Mitochondrial genes are inherited only from the mother, because the sperm cell does not contribute any mitochondria to the fertilized egg.
Sex-limited inheritance is a type of inheritance in which a gene is expressed only in one sex. For example, the gene for baldness is sex-limited, and it is only expressed in males.
Sex-influenced inheritance is a type of inheritance in which a gene is expressed more strongly in one sex than in the other. For example, the gene for height is sex-influenced, and it is expressed more strongly in males than in females.
Genomic imprinting is a type of epigenetic inheritance in which certain genes are expressed differently depending on whether they are inherited from the mother or the father. For example, the gene for Prader-Willi syndrome is imprinted, and it is only expressed if it is inherited from the father.
Sex-linked inheritance is a complex topic, and there are many different types of sex-linked inheritance. However, all types of sex-linked inheritance involve genes that are located on sex chromosomes.
Here are some frequently asked questions about genetics and their short answers:
What is genetics?
Genetics is the study of genes and heredity. Genes are the basic units of heredity and are passed down from parents to offspring. They are located on chromosomes, which are found in the nucleus of every cell.What are chromosomes?
Chromosomes are structures in the nucleus of cells that contain genes. They are made up of DNA, which is the molecule that contains the genetic code.What is DNA?
DNA is a molecule that contains the genetic code. It is made up of four types of nucleotides: adenine (A), thymine (T), guanine (G), and cytosine (C). These nucleotides are arranged in a double helix structure.What is the genetic code?
The genetic code is the sequence of nucleotides in DNA that codes for proteins. Proteins are the building blocks of cells and are responsible for many of the functions of the body.What are genes?
Genes are the basic units of heredity. They are located on chromosomes and are passed down from parents to offspring. Genes code for proteins, which are the building blocks of cells and are responsible for many of the functions of the body.What is heredity?
Heredity is the passing down of traits from parents to offspring. Traits are characteristics that are passed down from parents to offspring. They can be physical traits, such as eye color, or behavioral traits, such as Personality.What is a mutation?
A mutation is a change in the genetic code. Mutations can be caused by errors in DNA replication, exposure to radiation or chemicals, or viruses. Mutations can be harmful, beneficial, or neutral.What is a genetic disorder?
A genetic disorder is a condition that is caused by a mutation in a gene. Genetic disorders can be inherited from parents or they can be caused by new mutations. Some genetic disorders are mild, while others are severe.What is genetic counseling?
Genetic counseling is a process that helps people understand and manage genetic risks. Genetic counselors can help people understand their family history, genetic testing, and reproductive Options.What is genetic testing?
Genetic testing is a process that looks for changes in genes. Genetic testing can be used to diagnose genetic disorders, to screen for genetic risks, or to determine paternity.What is gene therapy?
Gene therapy is a process that uses genes to treat or prevent disease. Gene therapy can be used to replace a mutated gene, to turn off a gene, or to deliver a gene to a specific cell.What is stem cell therapy?
Stem cell therapy is a process that uses stem cells to treat or prevent disease. Stem cells are cells that have the ability to develop into different types of cells. Stem cell therapy can be used to replace damaged cells, to regenerate Tissues, or to treat cancer.What is cloning?
Cloning is a process that creates a genetically identical copy of an organism. Cloning can be used to create animals, Plants, or even humans.What is gene editing?
Gene editing is a process that changes the genetic code of an organism. Gene editing can be used to correct genetic defects, to improve crops, or to create new medicines.What is the future of genetics?
The future of genetics is very promising. Genetics is a rapidly growing field with many potential applications. Genetics can be used to diagnose and treat diseases, to improve crops, and to create new medicines.
Question 1
Which of the following is not a type of inheritance?
(A) Autosomal dominant inheritance
(B) Autosomal recessive inheritance
(C) Sex-linked dominant inheritance
(D) Sex-linked recessive inheritance
Answer
(C) Sex-linked dominant inheritance is not a type of inheritance.
Question 2
In autosomal dominant inheritance, the affected individual must have one copy of the mutated gene.
(A) True
(B) False
Answer
(A) True. In autosomal dominant inheritance, the affected individual must have one copy of the mutated gene. The mutated gene is dominant over the normal gene, so the individual will express the trait even if they only have one copy of the mutated gene.
Question 3
In autosomal recessive inheritance, the affected individual must have two copies of the mutated gene.
(A) True
(B) False
Answer
(A) True. In autosomal recessive inheritance, the affected individual must have two copies of the mutated gene. The mutated gene is recessive to the normal gene, so the individual will only express the trait if they have two copies of the mutated gene.
Question 4
In sex-linked dominant inheritance, the affected individual must be male.
(A) True
(B) False
Answer
(B) False. In sex-linked dominant inheritance, the affected individual can be either male or female. The mutated gene is located on the X chromosome, so if a female inherits one copy of the mutated gene, she will be affected. If a male inherits one copy of the mutated gene, he will also be affected.
Question 5
In sex-linked recessive inheritance, the affected individual must be female.
(A) True
(B) False
Answer
(B) False. In sex-linked recessive inheritance, the affected individual can be either male or female. The mutated gene is located on the X chromosome, so if a female inherits two copies of the mutated gene, she will be affected. If a male inherits one copy of the mutated gene, he will not be affected because he has a Y chromosome that will mask the effects of the mutated gene.
Question 6
Which of the following is an example of a genetic disorder that is caused by autosomal dominant inheritance?
(A) Huntington’s disease
(B) Sickle cell anemia
(C) Color blindness
(D) Duchenne muscular dystrophy
Answer
(A) Huntington’s disease is an example of a genetic disorder that is caused by autosomal dominant inheritance. The mutated gene responsible for Huntington’s disease is located on chromosome 4. If an individual inherits one copy of the mutated gene, they will develop the disease.
Question 7
Which of the following is an example of a genetic disorder that is caused by autosomal recessive inheritance?
(A) Cystic fibrosis
(B) Tay-Sachs disease
(C) Sickle cell anemia
(D) All of the above
Answer
(D) All of the above are examples of genetic disorders that are caused by autosomal recessive inheritance. Cystic fibrosis is a genetic disorder that affects the lungs and Digestive System. Tay-Sachs disease is a genetic disorder that affects the nervous system. Sickle cell anemia is a genetic disorder that affects the blood.
Question 8
Which of the following is an example of a genetic disorder that is caused by sex-linked dominant inheritance?
(A) Hemophilia
(B) Duchenne muscular dystrophy
(C) Color blindness
(D) None of the above
Answer
(A) Hemophilia is an example of a genetic disorder that is caused by sex-linked dominant inheritance. The mutated gene responsible for hemophilia is located on the X chromosome. If a female inherits one copy of the mutated gene, she will be a carrier of the disorder. If a male inherits one copy of the mutated gene, he will develop the disorder.
Question 9
Which of the following is an example of a genetic disorder that is caused by sex-linked recessive inheritance?
(A) Hemophilia
(B) Duchenne muscular dystrophy
(C) Color blindness
(D) All of the above
Answer
(D) All of the above are examples of genetic disorders that are caused by sex-linked recessive inheritance. Hemophilia is a genetic disorder that affects the blood. Duchenne muscular dystrophy is a genetic disorder that affects the muscles. Color blindness is a genetic disorder that affects the ability to see certain colors.