Mitosis And Meiosis

Question 1

What disease is due to trisomy of chromosome 21?

Answer 1

Down syndrome

Question 2

Outline the structure of a chromosome

Answer 2

p (short) +q (long) arm
Telomere at end of chromosomes

Question 3

What are the locations of centromeres?

Answer 3

metacentric - centre
submetacentric - between top and middle
acrocentric - closer to top (1 very short + 1 very long arm)
telocentric - very end

Question 4

What are telomeres, what is their function and where are they found?

Answer 4

• DNA sequence - TTAGGG
• Protect chromosomes from degradation + limit the number of times mitosis occurs
• Ends of chromosomes

Question 5

What condition is caused by one X chromosome missing?

Answer 5

Turner syndrome

Question 6

Outline karyotyping

Answer 6

• method of describing chromosome composition
• chromosome number , gender + mutations

e.g.
46,XX - normal female
47,XY,+21- male with trisomy 21 (downs)

Question 7

What are the phases of mitosis?

Answer 7

Prophase
Prometaphase
Metaphase
Anaphase
Telophase

Question 8

What happens in prophase?

Answer 8

• chromosomes condense
• spindle fibres develop

Question 9

What happens in prometaphase?

Answer 9

• nuclear envelope + nucleolus dissolves
• spindle fibres attach to centromere

Question 10

What happens in metaphase?

Answer 10

Chromosomes align at centre

Question 11

What happens in anaphase?

Answer 11

Sister chromatids pulled to opposite poles

Question 12

What happens in telophase?

Answer 12

• nuclear envelope reforms
• cytoplasm starts to cleave (splitting in cytokinesis)

Question 13

What is non-disjunction?
Name a condition that occurs from this

Answer 13

Failure of one or more pairs of sister chromatids to separate normally&raquo_space; gain/loss of a chromosome

Down syndrome - trisomy of chromosome 21

Question 14

Stages of meiosis

Answer 14

Meiosis I - same as mitosis
Meiosis II - same step occur without DNA replication
- chromosomes separate to form chromatids
- four haploid daughter cells

Question 15

What is aneuploidy?
What is it caused by?

Answer 15

• Condition of having an abnormal number of chromosomes in a haploid organism
• Caused by non-disjunction in mitosis or meiosis

Question 16

How does meiosis create genetic diversity?

Answer 16

• crossing over
• independent assortment
• random segregation

Question 17

What is crossing over?
When does it occur?

Answer 17

• Exchange of regions of DNA at the chiasmata between 2 homologous chromosomes due to twisting
• Occurs in meiosis I

Question 18

What is a chiasmata?

Answer 18

Point at which crossing over of chromosomes occurs in meiosis

Question 19

What is independent assortment?

Answer 19

The random organisation of chromosomes along the midline of the cell

Question 20

What is random segregation?

Answer 20

Random distribution of alleles among the 4 gametes

Question 21

Outline spermatogenesis

Answer 21

• 1 spermocyte (2n) > 4 mature sperm (n)
• over 60 days

Question 22

Outline oogenesis

Answer 22

• 1 oocyte (2n) > 1 egg (n) + 3 polar bodies
• over 12-50 years

Question 23

Impact of missegregation in meiosis

Answer 23

• infertility
• miscarriage
• mental retardation

Question 24

What is the karyotype of Turner’s syndrome?

Answer 24

45, XO

Question 25

What is the karyotype of Down syndrome?

Answer 25

47, XX/XY +21

Question 26

What are the phases of the cell cycle?
What are their function?

Answer 26

• G1: cellular contents duplicated
• S: DNA synthesis replicates genetic material > w sister chromatids per chromosome
• G2: cell double checks for errors before mitosis
  + makes repairs
• M: mitosis - nuclear division
• cytokinesis: cell division

Question 27

What three conditions have trisomy > 47 chromosomes?
What are their karyotype in females?

Answer 27

• Downs: 47, XX +21
• Edward’s: 47, XX + 18 - infant mortality
• Patau’s: 47, XX +13

Question 28

What disease is due to trisomy of chromosome 18?

Answer 28

Edward’s syndrome

Question 29

What disease is due to trisomy of chromosome 13?

Answer 29

Patau’s syndrome