Genetics: Chromosomes and Genes

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Questions and Answers

What genetic trait did Morgan discover through his experiments with Drosophila melanogaster?

Eye color mutation (correct)

Wing size variation

Body color change

Tail length alteration

What characteristic of Drosophila melanogaster made it particularly suited for genetics research?

It can survive in various environments.

It produces a large number of offspring quickly. (correct)

It has a high mutation rate.

It has numerous and complex traits.

In Morgan's experiments, which allele was identified as recessive for eye color?

w+ (wild type)

W (white)

R (red)

w (mutant) (correct)

What was the outcome when mutant white-eyed male Drosophila were crossed with wild-type females?

All progeny had red eyes. Signup and view all the answers

What segregation pattern was noted in the progeny of Morgan’s eye color experiment?

All daughters had red eyes, and sons were equally divided between red and white eyes. Signup and view all the answers

What did Morgan conclude regarding the location of the gene for eye color?

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

What were the phenotypes studied by Morgan in his experiments?

Red and white eyes Signup and view all the answers

What indicates that a gene was unambiguously linked to a chromosome?

The pattern of transmission reflects the chromosome's behavior. Signup and view all the answers

What was the outcome when white-eyed females were crossed with red-eyed males in the experiment?

All daughters had red eyes and all sons had white eyes Signup and view all the answers

What term describes the failure of chromosomes to disjoin during meiosis as explained by C.B. Bridges?

Nondisjunction Signup and view all the answers

Which of the following best explains Morgan's findings about the inheritance of eye color in Drosophila?

The eye color gene is located on the X chromosome Signup and view all the answers

What significant contribution did C.B. Bridges make to genetics?

He provided proof of the chromosome theory Signup and view all the answers

What genetic disorder is caused by mutations in the dystrophin gene?

Duchenne Muscular Dystrophy Signup and view all the answers

Why are males predominantly affected by Hemophilia A?

The factor VIII gene is located on the X chromosome Signup and view all the answers

What concept describes the transmission of properties of chromosomes that explains Mendel’s principles?

Chromosome Theory of Heredity Signup and view all the answers

What may cause nondisjunction during meiosis?

Faulty chromosome movement Signup and view all the answers

What type of complex is formed by DNA and proteins in eukaryotic cells?

Chromatin Signup and view all the answers

What is the consequence of chromosome packing during cell division?

Distinctive shapes and numbers of chromosomes become visible Signup and view all the answers

Which of the following describes the basic chromosome number for humans?

23 chromosomes Signup and view all the answers

What is the term used for cells that contain four sets of chromosomes?

Tetraploid Signup and view all the answers

What field of genetics involves the microscopic examination of chromosomes?

Cytogenetics Signup and view all the answers

How many chromosomes do most human somatic cells contain?

46 chromosomes Signup and view all the answers

What happens to the chromosomal composition during cell division?

It is packed into a small volume. Signup and view all the answers

What do we call the set of chromosomes that defines the haploid genome?

Haploid set Signup and view all the answers

What type of chromosome do female grasshoppers possess that male grasshoppers do not?

Extra X chromosome Signup and view all the answers

What is the expected ratio of male to female zygotes produced during fertilization in grasshoppers?

1:1 male to female Signup and view all the answers

In humans, what chromosome pairs with the X chromosome during meiosis in males?

Y chromosome Signup and view all the answers

Which of the following statements is true regarding the structure of the human Y chromosome?

It is shorter than the X chromosome Signup and view all the answers

What characterizes the chromosomes in grasshoppers compared to other animals, including humans?

Females have additional chromosomes Signup and view all the answers

What type of chromosomes are X and Y classified as?

Sex chromosomes Signup and view all the answers

How many types of sperm are produced during meiosis in males regarding sex chromosomes?

Two types, X-bearing and Y-bearing Signup and view all the answers

In the context of heredity, what did many biologists suspect by 1910?

Genes were situated on chromosomes Signup and view all the answers

What is Mendel’s Principle of Independent Assortment associated with?

The random alignment of chromosomes at metaphase Signup and view all the answers

In autosomal dominant inheritance, how many copies of the abnormal gene are required to display a trait?

One copy Signup and view all the answers

Which condition exemplifies autosomal dominant inheritance?

Huntington’s Disease Signup and view all the answers

What is the probability of a child inheriting both defective copies of a gene if both parents are carriers of an autosomal recessive trait?

25% Signup and view all the answers

What is the function of the protein produced by the CFTR gene, related to cystic fibrosis?

Regulates the movement of ions in and out of cells Signup and view all the answers

Which of the following statements regarding carriers of autosomal recessive traits is true?

Carriers can pass the gene to their offspring Signup and view all the answers

What genetic alteration is responsible for Huntington’s Disease?

An excessive number of CAG repeats in the HTT gene Signup and view all the answers

How do autosomal dominant and autosomal recessive traits differ in terms of expression?

Dominant traits can skip generations while recessive traits cannot Signup and view all the answers

Study Notes

Chromosomes and Genes

Chromosomes are structures within cells that contain the genetic material.
Genes are physically located within chromosomes.
Each chromosome contains a long DNA segment and proteins.
In eukaryotic cells, the complex of DNA and proteins is called chromatin.

Cytogenetics

The study of chromosomes using microscopes.
Examines the chromosomal composition of cells.
Chromosomes are best seen when cells are dividing.

Karyotype

A complete set of chromosomes from a single cell.
Diploid human cells have two complete sets of chromosomes, or a karyotype.

Chromosome Number

Most species have an even number of chromosomes.
The basic number of chromosomes in humans is 23.
Most human cells are diploid (2n), meaning they have two of each chromosome.
Some cells are tetraploid (4n), with four of each chromosome.
Cells with eight of each chromosome are octoploid (8n).

Sex Chromosomes

In many species, males and females have different chromosome numbers.
In grasshoppers, females are XX and males are XO.
In humans, males are XY and females are XX.
The X chromosome is larger than the Y chromosome.

X and Y Chromosome Transmission

During meiosis in females, the two X chromosomes separate, producing eggs containing a single X chromosome.
During meiosis in males, the X and Y chromosomes separate, producing X-bearing and Y-bearing sperm.
When sperm and egg unite, XX zygotes develop into females and XY zygotes develop into males.

Autosomes

All chromosomes other than sex chromosomes are autosomes.

The Chromosome Theory of Heredity

This theory states that genes are located on chromosomes.
Thomas H. Morgan's experiments with fruit flies provided evidence for the chromosome theory.
He discovered a gene for eye color in Drosophila.

Morgan’s Experiment

Morgan discovered a mutant male fruit fly with white eyes.
When crossed with wild-type females, all offspring had red eyes.
When these offspring were intercrossed, only half of the male offspring had white eyes.
This pattern suggested that the inheritance of eye color was linked to the X chromosome.

Morgan’s Additional Experiments

He crossed heterozygous F1 females with white-eyed males, resulting in half of each sex having white eyes.
He crossed white-eyed females with red-eyed males, resulting in all daughters with red eyes and all sons with white eyes.

Nondisjunction

C.B. Bridges showed that exceptions to inheritance rules could be explained by chromosome behavior.
Nondisjunction - when chromosomes fail to separate during meiosis.

Duchenne Muscular Dystrophy (DMD)

Caused by mutations in the dystrophin gene, which is essential for maintaining muscle cell integrity.
Results in progressive muscle weakness and degeneration.
Largely affects males.

Hemophilia A

Caused by mutations in the factor VIII gene, which is crucial for blood clotting.
Results in prolonged bleeding.
Females are typically carriers.

Mendel's Principle of Independent Assortment

This principle states that different pairs of chromosomes align randomly at metaphase.

Autosomal Inheritance

Refers to inheritance patterns of traits on autosomes (chromosomes 1-22).

Autosomal Dominant Inheritance

Occurs when one defective gene is necessary for a trait to appear.
A parent with an autosomal dominant condition has a 50% chance of passing the gene to their offspring.

Autosomal Dominant Example: Huntington's Disease

Caused by mutations in the HTT gene.
Mutations result in an abnormal huntingtin protein that damages brain cells.
Inherited as a dominant trait, anyone who inherits the mutated gene will eventually develop the disease.

Autosomal Recessive Inheritance

Requires two copies of an abnormal gene to be present for a trait to appear.
Individuals with only one defective gene are carriers.
When two carriers have a child, there is a 25% chance that the child will inherit both defective genes and express the trait.

Autosomal Recessive Example: Cystic Fibrosis

Caused by mutations in the CFTR gene, which regulates ion movement in cells.
Mutations result in defective protein causing thick mucus buildup in organs.

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Description

Explore the fundamental concepts of chromosomes and genes in this quiz. Learn about the structure of chromosomes, the role of genes, and how cells are studied in cytogenetics. Understand key terms like karyotype and chromosome number in the context of human genetics.