7a Genes and chromosomes

Question 1

What is the structure of a chromosome?

Answer 1

DNA: Chromosomes are composed of DNA molecules, which contain genetic information.
Histones: DNA wraps around histone proteins, forming nucleosomes, which help package the DNA into a compact structure.
Nucleotide: The basic unit of DNA, consisting of a sugar, phosphate group, and a nitrogenous base.

Question 2

What is DNA?

Answer 2

Definition: DNA (Deoxyribonucleic Acid) is the molecule that carries genetic instructions for the development, functioning, growth, and reproduction of all living organisms.
Structure: It consists of two strands forming a double helix, with each strand made up of nucleotides.

Question 3

What is a nucleotide?

Answer 3

Definition: A nucleotide is the basic building block of DNA and RNA.
Components: Each nucleotide consists of a sugar (deoxyribose in DNA, ribose in RNA), a phosphate group, and a nitrogenous base (Adenine, Thymine, Cytosine, Guanine in DNA).

Question 4

What is a histone?

Answer 4

Definition: Histones are proteins that DNA wraps around to form nucleosomes.
Function: They help in packaging DNA into a compact structure and play a role in gene regulation.

Question 5

What is chromatin?

Answer 5

Definition: Chromatin is a complex of DNA and proteins (mainly histones) found in the nucleus of eukaryotic cells.
Function: It packages DNA into a more compact, denser shape, and plays a role in gene regulation and DNA replication.

Question 6

What is a chromatid?

Answer 6

Definition: A chromatid is one-half of a duplicated chromosome.
Function: During cell division, chromatids separate and are distributed to the daughter cells.

Question 7

What is a centromere?

Answer 7

Definition: The centromere is the region of a chromosome that links sister chromatids.
Function: It is essential for the proper distribution of chromosomes during cell division.

Question 8

What is a gene? Give an example.

Answer 8

Definition: A gene is a segment of DNA that contains the instructions for building a specific protein or set of proteins.
Example: The BRCA1 gene is associated with an increased risk of breast cancer.

Question 9

What is an allele? Give an example.

Answer 9

Definition: An allele is a variant form of a gene.
Example: The gene for eye color has different alleles, such as one for blue eyes and another for brown eyes.

Question 10

What is a genome?

Answer 10

Definition: A genome is the complete set of genetic material in an organism, including all of its genes.
Function: It contains all the information needed for the growth, development, and functioning of an organism.

Question 11

What are homologous chromosomes?

Answer 11

Definition: Homologous chromosomes are pairs of chromosomes that have the same structure and carry the same genes, though they may have different alleles.
Function: They pair during meiosis and are important for genetic diversity.

Question 12

How many homologues are there in human cells?

Answer 12

Human cells have 23 pairs of homologous chromosomes, for a total of 46 chromosomes.

Question 13

What is a gene loci?

Answer 13

Definition: A gene loci (plural: loci) is the specific location or position of a gene on a chromosome.
Function: It is used to identify the location of genes within the genome.

Question 14

What are autosomes?

Answer 14

Definition: Autosomes are chromosomes that are not involved in determining the sex of an individual.
Human Example: Humans have 22 pairs of autosomes.

Question 15

What are sex chromosomes? Give examples.

Answer 15

Definition: Sex chromosomes determine the biological sex of an organism.
Examples: In humans, the sex chromosomes are X and Y. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

Question 16

How do chromosomes vary in size and how are they numbered?

Answer 16

Size Variation: Chromosomes vary in size based on the amount of genetic material they carry.
Numbering: They are numbered from 1 to 22 based on size, with chromosome 1 being the largest. The sex chromosomes are labeled as X and Y.

Question 17

What is a karyotype?

Answer 17

Definition: A karyotype is the complete set of chromosomes in an individual, displayed in a systematic arrangement.
Use: It is used to study chromosome abnormalities and to determine the chromosome number of an individual.

Question 18

How are chromosomes organized in a karyotype?

Answer 18

Organization: Chromosomes are arranged in pairs and ordered by size, from largest to smallest, with the sex chromosomes placed last.

Question 19

How do you see an abnormality in a karyotype? Give an example of a chromosomal abnormality.

Answer 19

Detection: Abnormalities can be identified by changes in chromosome number or structure.
Example: Down syndrome (trisomy 21) is caused by an extra copy of chromosome 21.

Question 20

How do you tell the difference between a male and female when looking at a karyotype?

Answer 20

By examining the sex chromosomes. Females have two X chromosomes (XX), while males have one X and one Y chromosome (XY).

Question 21

Define the term, haploid

Answer 21

Definition: Haploid cells contain one complete set of chromosomes.
Example: In humans, gametes (sperm and egg cells) are haploid, containing 23 chromosomes.

Question 22

Define the term, diploid

Answer 22

Definition: Diploid cells contain two complete sets of chromosomes, one from each parent.
Example: Human somatic cells are diploid, containing 46 chromosomes.

Question 23

What is the difference between 2n and n?

Answer 23

2n (Diploid): Represents cells with two sets of chromosomes.
n (Haploid): Represents cells with one set of chromosomes.

Question 24

What is Polyploidy?

Answer 24

Definition: Polyploidy is the condition of having more than two complete sets of chromosomes.
Example: Some plants, like wheat, are polyploid.

Question 25

What is Aneuploidy? How do you recognize aneuploidy in a karyotype?

Answer 25

Definition: Aneuploidy is the presence of an abnormal number of chromosomes in a cell.
Recognition: In a karyotype, aneuploidy is seen as extra or missing chromosomes (e.g., trisomy or monosomy).

Question 26

What is trisomy 21 and how does it occur?

Answer 26

Definition: Trisomy 21, also known as Down syndrome, is a condition where there are three copies of chromosome 21.
Cause: It occurs due to nondisjunction during cell division, leading to an extra chromosome 21.

Question 27

What is nondisjunction?

Answer 27

Definition: Nondisjunction is the failure of chromosomes to separate properly during cell division.
Consequence: It can result in an abnormal number of chromosomes in the daughter cells, leading to conditions like trisomy 21.