Inheritance Of Genes

Question 1

Chromosomes

Answer 1

Before replication one chromosome = one DNA molecule
After replication one chromosome = two DNA molecules

Sister chromosomes - Both from mother/father
Non-sister chromosomes - one from father and one from mother

Question 2

Mitosis

Answer 2

Cell division for somatic cells
Production of two identical daughter cells (diploid)
Mitotic growth necessary for some tissue (epidermis, mucosae, home marrow, spermatogonia)

Question 3

Mitosis

Answer 3

Prophase - chromosomes condense
Prometaphase - spindle fibres attached to chromosomes
Metaphase - chromosomes align
Anaphase - sister chromatids move to opposite poles
Telophase - nuclear membrane reforms, chromosomes decondense
Cytokinesis - cytoplasm divides - 2 identical daughter cells

Question 4

Meiosis

Answer 4

Cell division for gametes - egg and sperm
Production of four non-identical daughter cells (haploid cells)
One round of replication followed by two rounds of division (meiosis I and II)

Question 5

DNA replication

Answer 5

Helicase opens helix - location determined by DNA sequence
Requires a kickstart by primase
Replicates from 3’ to 5’ (DNA polymerase can only extend a 3’end)
Leading strand - copied continuously
Lagging strand - copied in sections (Okazaki fragments)
DNA ligase joins fragments

Question 6

Meiosis

genetic diversity

Answer 6

Random assortment of chromosomes

Crossing over of genetic material (recombination during chiasmata)

Question 7

Spermatogenesis

takes ~ 48 days

Answer 7

2n spermatogonium
2n primary spermatocyte
n (x4) spermatids
n (x4) mature sperm

Question 8

Oogenesis

12-50 years

Answer 8

2n oogonium
2n primary oocyte (arrested here until puberty)
n (one cell and three polar bodies)
n mature ovum - meiosis only completes at fertilised

Question 9

Consequences of faulty meiosis

Answer 9

1/3 of all identified miscarriages
Infertility
Leading cause of mental retardation