AGR3303 Exam3

List the chromosome types based on the position of the centromere.

Metacentric (centromere in the middle), Submetacentric (centromere slightly off center), Acrocentric (centromere near one end), Telocentric (centromere at the end).

Differentiate sister chromatids and homologous chromosomes.

Sister chromatids are identical copies of the same chromosome joined at the centromere. Homologous chromosomes are a pair of chromosomes (one from each parent) with the same genes but possibly different alleles.

What are the stages of the cell cycle in somatic cells?

G1 (cell growth), S (DNA replication), G2 (preparation for division), M (mitosis and cytokinesis).

What are the phases of mitosis?

Prophase, Metaphase, Anaphase, Telophase, followed by Cytokinesis.

What are the final products of mitosis?

Two genetically identical diploid daughter cells.

How do chromosomes change during mitosis?

Chromatin condenses into visible chromosomes made of sister chromatids; chromatids separate during anaphase and move to opposite poles.

How does chromosome number change during mitosis?

The chromosome number stays the same; diploid cells produce diploid daughter cells.

How do DNA copies change during mitosis?

DNA replicates in S phase; sister chromatids separate during mitosis so each daughter cell receives one copy.

What are the phases of meiosis?

Meiosis I: Prophase I, Metaphase I, Anaphase I, Telophase I.Meiosis II: Prophase II, Metaphase II, Anaphase II, Telophase II.

What are the final products of meiosis?

Four genetically different haploid gametes.

What is characteristic of meiosis I?

Homologous chromosomes pair and separate, reducing chromosome number from diploid to haploid.

What is characteristic of meiosis II?

Sister chromatids separate, similar to mitosis.

How does chromosome number change during meiosis?

Meiosis I reduces chromosome number from diploid (2n) to haploid (n); meiosis II maintains the haploid number.

What is crossing over?

Exchange of DNA segments between non-sister chromatids of homologous chromosomes during prophase I.

How does crossing over increase genetic diversity?

It creates new combinations of alleles on chromosomes.

What is random assortment of homologous chromosomes?

Homologous chromosome pairs align randomly during metaphase I and separate independently.

How many chromosome combinations can result from meiosis?

2ⁿ combinations, where n is the haploid number (number of chromosome pairs).

How does random separation of homologous chromosomes influence genetic variation?

Different combinations of maternal and paternal chromosomes are distributed into gametes, producing genetically unique offspring.

chromosome morphological parts

1 centromere, 2 arms, 2 telomeres

the centromere is a constricted region of the chromosome where

the kinetochores form and the spindle microtubules attach

Chromosome arms (p vs q)

The p arm is the short arm on top of the chromosome, and the q arm is the long arm on the bottom.

Metacentric chromosome

The centromere is in the middle, so the p and q arms are about equal in length (p = q).

Submetacentric chromosome

The centromere is slightly off center, so the p arm is shorter than the q arm (p < q).

Acrocentric chromosome

The centromere is very close to one end, making the p arm much shorter than the q arm (p << q).

telocentric chromosome

the centromere is at the very end of the chromosome, so there is essentially no p arm (p = 0).

Telomere

The protective tip at the end of a chromosome.

Centromere

The constricted region of a chromosome where two sister chromatids are connected after DNA replication.

What are the four phases of the somatic cell cycle?

G1, S, G2, and M.

What happens during G1 (Gap 1)?

The cell grows and prepares for DNA replication; it is the longest phase of the cell cycle.

What happens during the S phase?

DNA replication occurs and chromosomes are duplicated.

What happens during G2 (Gap 2)?

The cell prepares for cell division.

What is interphase?

The combined stages of G1, S, and G2 when the cell grows and replicates DNA.

What happens during the M phase?

Mitosis and cell division occur, separating duplicated chromosomes into two daughter cells.

What are the daughter cells produced by mitosis?

Two genetically identical cells that are identical to the parent cell.

How does DNA amount change during the cell cycle?

G1: normal amount of DNA; S: DNA doubles; G2: DNA remains doubled; M: DNA is separated into two daughter cells.

What is the difference between mitosis and meiosis in terms of genetic material?

Mitosis produces daughter cells with the same amount of genetic material as the parent cell, while meiosis produces daughter cells with half the genetic material.

What type of cells undergo mitosis?

Somatic (body) cells.

What type of cells undergo meiosis?

Gamete-producing cells that form sperm or eggs.

What is a diploid cell?

A cell that contains two sets of chromosomes, one from each parent (2n).

Where do the two chromosome sets in diploid cells come from?

One set is inherited from the male parent and the other from the female parent.

What are homologous chromosomes?

Two chromosomes that have the same genes, gene order, structure, and centromere placement, with one inherited from each parent.

What is a homologous pair?

The pair of corresponding chromosomes (one maternal and one paternal) that carry the same genes at the same locations.

What is the total chromosome number (2n)? duplicate sorry

The total number of chromosomes in an organism's somatic cells.

What is the human total chromosome number?

Humans have 2n = 46 chromosomes.

What is the haploid number (n)? duplicate sorry

The number of chromosomes in a gamete; it is half the total chromosome number.

What is the human haploid number?

Humans have n = 23 chromosomes in gametes.

What is a locus? duplicate sorry

the specific location of a gene on a chromosome (plural: loci).

How many copies of each gene does a diploid organism have?

Two copies, one on each homologous chromosome.

What are alleles?

Alternative forms of a gene located at the same locus.

How can alleles differ at a locus?

the alleles may be identical or different and determine variations in traits.

What does the word meiosis mean?

It comes from the Greek word "meioum," meaning "to reduce."

What happens during meiosis?

Two successive nuclear divisions occur to produce gametes, reducing the chromosome number by half.

What is the result of the two meiotic divisions?

Four daughter cells are produced.

What type of chromosomes do the cells produced by meiosis contain?

each cell contains only one chromosome from each homologous pair (haploid).

What happens before meiosis begins?

Interphase occurs and DNA (chromosomes) replicate.

What are the two main divisions of meiosis?

Meiosis I and Meiosis II.

What is another name for Meiosis I?

Reduction division because the chromosome number is reduced by half.

What are the phases of Meiosis I?

Prophase I, Metaphase I, Anaphase I, and Telophase I.

What is another name for Meiosis II?

Equational division because sister chromatids separate similar to mitosis.

What are the phases of Meiosis II?

Prophase II, Metaphase II, Anaphase II, and Telophase II.

What happens during Prophase I of meiosis?

Chromosomes condense and become more visible, homologous chromosomes pair, and crossing over occurs.

How long can Prophase I last?

It can last several days and includes five sub-stages.

What is synapsis?

The pairing of homologous chromosomes during Prophase I.

What are bivalents?

Paired homologous chromosomes during Prophase I.

What is crossing over (slides)

The exchange of genetic material between non-sister chromatids of homologous chromosomes.

What is a chiasma?

The visible point where crossing over occurs between non-sister chromatids.

What is crossing over (slides again sorry idk)

Physical exchange of genetic material between chromatids of homologous chromosomes, creating chromosomes that are mosaics of maternal and paternal DNA.

What happens during Metaphase I of meiosis?

Tetrads (paired homologous chromosomes) align on the metaphase plate.

What happens during Anaphase I of meiosis?

Homologous chromosomes separate and move to opposite poles; centromeres do not divide

What happens during Telophase I?

Haploid sets of chromosomes reach each pole, cytoplasm divides, and chromosomes relax; each chromosome still has two sister chromatids.

What is interkinesis?

The period between meiosis I and II when the nuclear membrane reforms and chromosomes relax; no DNA replication occurs.

What happens during Meiosis II?

Sister chromatids separate, resembling mitosis; chromosome number remains the same (equational division).

What is the result of Meiosis II?

Each gamete contains one member of each homologous chromosome pair (haploid).

What is random separation of homologous chromosomes?

Homologous chromosome pairs align randomly in Metaphase I, and their independent separation in Anaphase I creates genetic variation.

How many gamete combinations are possible from three chromosome pairs?

Eight combinations (2³ = 8).

How does haploid number (n) relate to gamete combinations?

Number of combinations = 2ⁿ, where n = haploid number of chromosome pairs.

How many possible gametes can a human produce due to random assortment alone?

2²³ = 8,388,608 possible gamete combinations.

Aneuploidy

A condition in which the number of chromosomes is not an exact multiple of the haploid set.

Types of aneuploidy:

Monosomy: loss of a single chromosome (2n − 1)

Nullisomy: loss of both chromosomes of a homologous pair (2n − 2)

Trisomy: gain of a single chromosome (2n + 1)

Tetrasomy: gain of two homologous chromosomes (2n + 2)

Polysomy: gain of more than two chromosomes beyond the haploid set

Origin of aneuploidy - Nondisjunction

Failure of homologous chromosomes or sister chromatids to separate properly during meiosis or mitosis, resulting in gametes or cells with abnormal chromosome numbers.

Products of nondisjunction

Meiosis I: two gametes with n + 1, two gametes with n − 1

Meiosis II: one gamete with n + 1, one with n − 1, two normal gametes with n

Polyploidy

The presence of more than two complete sets of chromosomes in a cell.

Basic chromosome number (x)

The number of distinct chromosomes in a single complete set.

Differences between x, n, and 2n

x: basic chromosome number of a species

n: number of chromosomes in a gamete (haploid)

2n: number of chromosomes in a somatic cell (diploid)

Determine ploidy level

Ploidy level = total chromosome number ÷ basic chromosome number (2n ÷ x).

Determine basic chromosome number

x = total chromosome number ÷ ploidy level

Autopolyploid

- Multiple chromosome sets from same species

- Forms via genome duplication (e.g., 2n → 4n)

- Chromosomes are all homologous

Allopolyploid

- Chromosome sets from different species hybridizing

- Forms via interspecies hybridization

- Chromosomes are homeologous (similar but not identical)

Chromosomal aberrations - types:

- Deletion: loss of a chromosome segment

- Duplication: repeated segment of a chromosome

- Inversion: segment of a chromosome is reversed

- Translocation: segment of one chromosome moves to another non-homologous chromosome

Effects of deletions, duplications, and inversions

- Deletions: loss of gene function; often lethal or causes disorders

- Duplications: extra copies can increase gene dosage; may lead to abnormal traits

- Inversions: may disrupt gene function; can cause problems during meiosis due to improper pairing

What are chromosomal variations?

Variations in chromosome number or chromosome structure.

What are the two main types of chromosomal number changes?

Aneuploidy (change in individual chromosomes) and polyploidy (change in whole chromosome sets).

What is aneuploidy?

A condition where an organism gains or loses one or more chromosomes but not an entire set.

What is monosomy?

Loss of a single chromosome (2n − 1).

What is nullisomy?

Loss of both chromosomes of a homologous pair (2n − 2).

What is trisomy?

Gain of one extra chromosome, resulting in three homologous copies (2n + 1).

What is tetrasomy?

Gain of two extra homologous chromosomes, resulting in four copies (2n + 2).

What is polysomy?

Presence of more than two copies of a particular chromosome (2n + x)

What is polyploidy?

A condition where an organism has more than two complete sets of chromosomes.

What is disjunction?

Normal separation of homologous chromosomes or sister chromatids during cell division.