FUNBIO 18 - Transmission genetics: Chromosomes, Meiosis

Question 1

How did Flemming contribute to the discovery of chromosomes?

Answer 1

Flemming provided the first clear drawings of chromosomes in the nucleus during division.

Question 2

How did Morgan contribute to the discovery of chromosomes?

Answer 2

Morgan proposed that genes are linearly arranged on chromosomes.

Question 3

How did Watson and Crick contribute to the discovery of chromosomes?

Answer 3

Watson and Crick proposed the structure of the DNA molecule and won the Nobel Peace Prize.

Question 4

How did Gamow contribute to the discovery of chromosomes?

Answer 4

Gamow discovered the triplet of three nucleotide bases (the codon) forms the genetic code.

Question 5

Describe the structure of chromatin.

Answer 5

Chromatin fibers are composed of DNA, non-histone chromosomal proteins and histone chromosomal proteins. Two H2A, H2B, H3, and H5 histones make up the positively charged histone octamer called the nucleosome. The H1 and H5 histones, along with the negatively charged core and linker DNA wrap around the nucleosome. The DNA helix making 1.8 turns per nucleosome.

Question 6

What does a chromosome consist of?

Answer 6

• p arm
• centromere
• q arm

Question 7

Describe the different names given to chromosomes based on centromere location.

Answer 7

Metacentric: centromere in the middle of chromosome
Submetacentric: centromere between the middle and end of chromosome
Acrocentric: centromere close to the end of the chromosome
Telocentric: centromere at the end of the chromosome

Question 8

Explain the steps of Mitosis.

Answer 8

Interphase: cell carrying out regular life activity and chromosomes become duplicated.
Early Prophase: Nuclear envelop disappears and chromatin condenses into chromosomes
Late Prophase: Spindle fibers start to form from centrioles at the poles and the spindle fibers attach to kinetochores of chromosomes
Metaphase: Chromosomes line up along the midplane
Anaphase: Chromatids are separated.
Telophase: Cytokinesis occurs and nuclear envelope forms around chromosomes at each pole.

Question 9

Define homologous chromosomes.

Answer 9

A set of one maternal and one paternal chromosome that pair up with each other inside a cell during meiosis.

Question 10

Define Meiosis.

Answer 10

The division of gamete-producing cells in which the nucleus splits twice, resulting in four sex cells each processing half the number of chromosomes as the original cell.

Question 11

Explain the steps of Meiosis.

Answer 11

Interphase: cell carrying out regular life activity and chromosomes become duplicated.
Prophase 1:
- Leptotene: chromosomes condense
- Zygotene: homologous chromosomes synapse
- Pachytene: a tetrad forms and homologous recombination occurs and DNA is exchanged between non-sister chromatids
- Diplotene: Synapse ends and the chiasmata are visible
- Diakinesis: Chromatids contract maximally, centrioles move to poles, nucleoli and nuclear envelope disappear
Metaphase 1: Spindle fibers attach to kinetochores and tetrads line up along midplane.
Anaphase 1: Chromosomes are pulled to the poles of the cell. Centromere remains intact.
Telophase 1: Chromosomes reach the poles, spindle fibers break down, cytokinesis occurs, nuclear envelope forms and two haploid daughter cells are created.
Prophase 2: Shortening and thickening of chromatids
Metaphase 2: Centrioles move to the poles and spindle fibers attach to the kinetochores and the haploid chromosomes line up on the midplane.
Anaphase 2: Centromere breaks and the sister chromatids separate to opposite poles of the cell
Telophase 2: Nuclear envelope forms, nucleoli reappear, chromosomes condense to chromatin, cytokinesis occurs to form 4 haploid daughter cells.