lecture 4

Question 1

what percentage of a haploid genome is coding?

Answer 1

30%

Question 2

why do histones bind to DNA?

Answer 2

more than a 5th of their AAs are +ve charged

Question 3

what is a nucleosome?

Answer 3

DNA wound around 8 histones

Question 4

name some differences between mitosis and meiosis

Answer 4

mitosis:

• one division vs 2 in meiosis
• two identical daughter cells vs 4 haploid, genetically different cells in meiosis

Question 5

what occurs in each stage of the cell cycle? (mitosis)

Answer 5

interphase: DNA + cell components replicate
prophase: chromatin condenses to form chromosomes
prometaphase: nuclear envelope breaks down, microtubules connect kinetochores to centrosomes
metaphase: chromosomes line up against equator
anaphase: chromatids separate and move towards poles
telophase: separating chromosomes reach poles, nuclear envelope reforms

Question 6

what are the sources of genetic variation in meiosis?

Answer 6

independent assortment & crossing over

Question 7

explain independent assortment

Answer 7

the random orientation of homologous chromosomes at metaphase of Meiosis I allows each pair to sort its maternal and paternal homologs into daughter cells independently

Question 8

explain crossing over

Answer 8

produces recombinant chromosomes from chiasmata occurring during prophase I