Genetics: X-Linked Disorders and Recombination

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Questions and Answers

What is the mechanism responsible for recombination between linked genes on the same chromosome?

The random inactivation of X chromosomes

The condensation of Barr bodies

The independent assortment of chromosomes

The crossing over of homologous chromosomes (correct)

What term describes the offspring that exhibit phenotypes matching one of their parents?

Recombinant types

Heterozygous types

Parental types (correct)

Crossover types

Which of the following disorders is NOT caused by a recessive allele on the X chromosome?

Cystic fibrosis (correct)

Color blindness

Duchenne muscular dystrophy

Hemophilia

What is the term for genes located on the same chromosome that tend to be inherited together?

Linked genes Signup and view all the answers

During X inactivation in female mammals, what forms from the inactivated X chromosome?

Barr body Signup and view all the answers

What phenomenon describes the production of offspring with combinations of traits differing from either parent?

Genetic recombination Signup and view all the answers

Which characteristic of linked genes creates exceptions to Mendel's law of independent assortment?

They can produce nonparental phenotypes Signup and view all the answers

What is the expected frequency of recombination between two genes that are unlinked?

50% Signup and view all the answers

What does the chromosome theory of inheritance explain about Mendelian genes?

Mendelian genes have specific loci on chromosomes. Signup and view all the answers

Why are fruit flies often used in genetic studies?

They produce many offspring and have a short generation time. Signup and view all the answers

What was the outcome of Morgan's experiment when white-eyed male fruit flies were mated with red-eyed females?

The F2 generation showed a 3:1 red:white eye ratio. Signup and view all the answers

What conclusion did Morgan reach regarding the location of the white-eyed mutant allele?

It is located on the X chromosome. Signup and view all the answers

What characteristic of chromosomes allows them to explain Mendel's laws of inheritance?

Chromosomes undergo independent assortment and segregation. Signup and view all the answers

Which of the following best describes the meaning of the term 'mutant phenotype'?

Traits that deviate from the normal or wild-type form. Signup and view all the answers

Which type of inheritance did Morgan's findings about eye color in fruit flies help clarify?

Sex-linked inheritance. Signup and view all the answers

What observation led Morgan to support the chromosomal theory of inheritance?

The consistent inheritance patterns of traits linked to specific chromosomes. Signup and view all the answers

What is the significance of Morgan's discovery regarding the X chromosome in fruit flies?

It was the first evidence linking a gene to a specific chromosome. Signup and view all the answers

Which statement correctly describes linked genes?

They are inherited together due to their proximity on the same chromosome. Signup and view all the answers

In humans, what is the chromosomal configuration for males and females?

Males have XY and females have XX. Signup and view all the answers

Which gene is crucial for male sex determination and what does it code for?

SRY gene and it codes for a protein directing male anatomical development. Signup and view all the answers

Why are X-linked recessive disorders more common in males than in females?

Females can mask the disorder with one normal allele. Signup and view all the answers

What characterizes sex-linked genes compared to autosomal genes?

They can be influenced by the chromosomal sex determination system. Signup and view all the answers

For a recessive X-linked trait to be expressed in a female, what is necessary?

Two copies of the allele. Signup and view all the answers

What is a unique feature of genes found on the Y chromosome?

There are very few Y-linked genes compared to X-linked genes. Signup and view all the answers

Study Notes

X-Linked Recessive Disorders

Color blindness, Duchenne muscular dystrophy, and hemophilia can be caused by recessive alleles on the X chromosome.
Males are more likely to express these disorders than females.
Females need two copies of the recessive allele, while males only need one.

X Inactivation

In female mammals, one of the two X chromosomes in each cell is randomly inactivated during embryonic development.
The inactive X chromosome condenses into a Barr body.
This inactivation results in a mosaic pattern of gene expression for X-linked genes in females.

Linked Genes

Linked genes are located on the same chromosome and tend to be inherited together.
Genes on the same chromosome do not assort independently during meiosis.

Genetic Recombination

Recombination refers to the production of offspring with combinations of traits different from either parent.
Recombination can occur through crossing over, where homologous chromosomes exchange segments of DNA.
Recombination can also occur through independent assortment of chromosomes.

Sex Chromosomes

Humans have two sex chromosomes: X and Y.
Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).
The SRY gene on the Y chromosome determines male sex development.
The Y chromosome has fewer genes than the X chromosome.

Sex-Linked Genes

Genes located on sex chromosomes are called sex-linked genes.
Genes on the Y chromosome are Y-linked, while genes on the X chromosome are X-linked.
Many X-linked genes are not directly related to sex determination.
Inheritance patterns for X-linked genes are unique due to the difference in chromosome numbers between males and females.

Chromosome Theory of Inheritance

Genes are located on chromosomes.
The behavior of chromosomes during meiosis explains Mendel's laws of segregation and independent assortment.

Thomas Hunt Morgan's Experiments

Morgan's experiments with fruit flies provided evidence for the chromosome theory of inheritance.
The white-eyed mutation in fruit flies is X-linked.
Morgan's findings demonstrated that genes are located on specific chromosomes.

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Description

Explore the fascinating world of genetics with this quiz on X-linked recessive disorders, X inactivation, linked genes, and genetic recombination. Understand how these mechanisms affect inheritance patterns and gene expression. Test your knowledge and see how well you grasp these fundamental concepts in genetics.