Genetics: Gene Linkage and Recombination

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Questions and Answers

Which disorder is NOT caused by a recessive allele on the X chromosome?

Duchenne muscular dystrophy

Hemophilia

Sickle cell anemia (correct)

Color blindness

What happens to one of the X chromosomes in female mammals during embryonic development?

It is duplicated.

It is removed.

It is expressed fully.

It is inactivated. (correct)

Which gene becomes active on the chromosome that will be inactivated?

Histone

Mosaic

BARR

XIST (correct)

What term describes genes that are located on the same chromosome and tend to be inherited together?

Linked genes Signup and view all the answers

In Morgan's experiments with fruit flies, what did he conclude about the inheritance of traits?

Some genes are inherited together. Signup and view all the answers

What phenomenon allows traits from two parents to be separated in offspring?

Genetic recombination Signup and view all the answers

Which of the following statements is true about the X chromosome in female mammals?

One X chromosome is randomly inactivated in each cell. Signup and view all the answers

Which trait was NOT a factor in Morgan's dihybrid cross experiments?

Eye color Signup and view all the answers

How many X chromosomes do female flies have?

Two Signup and view all the answers

What is the role of the SRY gene on the Y chromosome?

Responsible for development of testes Signup and view all the answers

In which scenario would a female express an X-linked recessive trait?

Being homozygous for the allele Signup and view all the answers

Which type of gene only has 78 identified genes coding for about 25 proteins?

Y-linked genes Signup and view all the answers

What does it mean for a male to be hemizygous concerning X-linked traits?

He has only one copy of the X chromosome Signup and view all the answers

Which statement about X-linked recessive disorders is correct?

They are much more common in males than in females Signup and view all the answers

What does the chromosome theory of inheritance primarily suggest?

Genes located on chromosomes are responsible for inheritance patterns. Signup and view all the answers

Which aspect of inheritance makes X-linked genes unique?

Males require only one copy of the recessive allele. Signup and view all the answers

What is the result when genes that are far apart on the same chromosome have a recombination frequency near 50%?

They behave as if found on different chromosomes. Signup and view all the answers

What primary evidence was used to support that genes are located on chromosomes in Drosophila?

Linkage maps of fruit fly genes. Signup and view all the answers

What is the consequence of nondisjunction during meiosis?

Gametes end up with an abnormal number of chromosomes. Signup and view all the answers

Which of the following statements is true regarding aneuploidy?

It results from fertilization of gametes with abnormal chromosome numbers. Signup and view all the answers

What characterizes a monosomic zygote?

It has one copy of a particular chromosome. Signup and view all the answers

How does polyploidy affect organisms compared to aneuploidy?

Polyploids are generally more normal in appearance than aneuploids. Signup and view all the answers

Which of the following describes triploidy?

An organism has three complete sets of chromosomes. Signup and view all the answers

What is often a consequence of large-scale chromosomal alterations in mammals?

Increased likelihood of spontaneous abortion. Signup and view all the answers

What type of chromosomal alteration involves removing a segment of a chromosome?

Deletion Signup and view all the answers

Which condition is characterized by the presence of three copies of chromosome 21?

Down syndrome Signup and view all the answers

What is a common characteristic of individuals with Klinefelter syndrome?

They have an extra X chromosome in males Signup and view all the answers

Which aneuploidy condition results from nondisjunction of sex chromosomes but does not exhibit any syndrome?

XYY males Signup and view all the answers

What chromosomal change results in the reversal of orientation of a segment within a chromosome?

Inversion Signup and view all the answers

Which syndrome is caused by a specific deletion in chromosome 5?

Cri du chat syndrome Signup and view all the answers

What is a unique characteristic of XXX females?

They are at risk for learning disabilities Signup and view all the answers

Which type of chromosomal alteration moves a segment from one chromosome to another?

Translocation Signup and view all the answers

What is the phenomenon called when the phenotype depends on which parent passed along the alleles?

Genomic imprinting Signup and view all the answers

Which of the following statements about genomic imprinting is true?

The silencing of genes occurs depending on parental origin. Signup and view all the answers

What type of DNA is found within mitochondria and chloroplasts?

Circular DNA Signup and view all the answers

How are extranuclear genes typically inherited?

Maternally Signup and view all the answers

What is the primary effect of mutations in mitochondrial genes?

Deficiencies in ATP production Signup and view all the answers

Which gene was one of the first identified to show genomic imprinting?

Igf2 Signup and view all the answers

What methylation of which nucleotide is thought to be involved in the process of genomic imprinting?

Cytosine nucleotides Signup and view all the answers

What type of patterns do mitochondrial genes follow in terms of inheritance?

Extranuclear inheritance patterns Signup and view all the answers

Study Notes

Genetic Linkage and Recombination

Genes located far apart on the same chromosome can have a recombination frequency of nearly 50%, indicating they are genetically unlinked.
Sturtevant utilized recombination frequencies to create linkage maps of fruit fly genes, uncovering four groups of linked genes.
Linkage maps, alongside the four chromosomes in Drosophila, supported the theory that genes are situated on chromosomes.

Chromosomal Alterations and Disorders

Large chromosomal alterations often lead to miscarriages or various developmental disorders in mammals, while plants are more tolerant of these changes.
Nondisjunction occurs when homologous chromosomes fail to separate correctly during meiosis, leading to gametes with abnormal chromosome numbers.
Aneuploidy arises from the fertilization of gametes affected by nondisjunction, resulting in offspring with an abnormal chromosome count.
Monosomic zygotes have one copy of a chromosome, whereas trisomic zygotes have three copies.
Polyploidy, the presence of more than two complete sets of chromosomes, is prevalent in plants and involves triploidy (3n) and tetraploidy (4n).

Sex-Linked Genes and Inheritance

Morgan linked the white-eyed mutant allele to the X chromosome, confirming the chromosome theory of inheritance.
Males possess one X and one Y chromosome (XY), while females have two X chromosomes (XX), influencing sex determination.
In mammals, the SRY gene on the Y chromosome directs the development of male characteristics.
Sex-linked genes, particularly X-linked genes, exhibit distinct inheritance patterns and recessive disorders are more common in males, as a single recessive allele suffices for expression.

Inactivation of X Chromosomes in Females

In female mammals, one of two X chromosomes gets randomly inactivated during embryonic development, forming a Barr body.
Heterozygous females become mosaics for characters linked to the X chromosome due to this random inactivation.
The XIST gene plays a crucial role in the inactivation process of X chromosomes.

Linkage and Genetic Recombination

Linked genes tend to be inherited together because they reside close to each other on the same chromosome.
Morgan's experiments with fruit flies showed that specific traits did not assort independently, indicating linkage.
Genetic recombination can separate linked traits, producing nonparental phenotypes.

Structural Chromosomal Alterations

Chromosome breakage can result in deletions, duplications, inversions, or translocations.
Altered chromosome structure can lead to serious disorders, with some types of aneuploidy allowing individuals to survive birth.
Down syndrome (Trisomy 21) typically arises from an extra copy of chromosome 21, affecting 1 of 830 children and correlating with maternal age.

Disorders from Chromosomal Alterations

Klinefelter syndrome (XXY) and Turner syndrome (X0) are examples of aneuploidy related to sex chromosomes.
Cri du chat syndrome is caused by a deletion on chromosome 5, leading to severe intellectual disabilities.
Certain cancers, such as chronic myelogenous leukemia, result from chromosome translocations.

Exceptions to Mendelian Inheritance

Genomic imprinting influences phenotype based on the parent of origin, involving the silencing of certain genes.
Imprinting is often due to the methylation of specific nucleotides and most notably impacts genes essential for embryonic development.

Inheritance of Organelle Genes

Extranuclear genes, or cytoplasmic genes, are inherited maternally and reside in organelles like mitochondria and chloroplasts.
Mitochondrial disorders can impair ATP production and affect muscular and nervous system functions, exemplified by mitochondrial myopathy and Leber’s hereditary optic neuropathy.

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Description

Explore the fascinating concepts of gene linkage and recombination frequency in this quiz. Learn about how Sturtevant used recombination frequencies to create linkage maps for fruit fly genes and understand the implications of physical and genetic linkage. Test your knowledge on linkage groups and chromosomes.