WEEK 11 (Meiosis)

Question 1

What is Reproduction?

Answer 1

The process by which organisms give rise to offspring

Question 2

What are the two basic types of reproduction?

Answer 2

Asexual reproduction & Sexual reproduction

Question 3

What is the advantage of sexual reproduction?

Answer 3

Produces genetic variation in the offspring

Question 4

What does Sexual reproduction involve?

Answer 4

The production of haploid gametes by MEIOSIS followed by FERTILISATION and the formation of a diploid zygote

Question 5

Do sperm and egg contribute equally to the genetic character of the offspring? (YES/NO)

Answer 5

YES

Explanation: Despite their huge difference in size, sperm and egg contribute equally to the genetic character of the offspring

Question 6

What is the difference between Germ-line cells and Somatic cells?

Answer 6

GERM-LINE CELLS = Give rise to haploid gametes by meiosis and the gametes spread genetic information into the next generation

SOMATIC CELLS = Form the body of the organism and are necessary to support sexual reproduction but themselves leave no progeny

Question 7

What is the history of Meiosis?

Answer 7

In 1888 Theodor Boveri noted that the fertilised egg of a PARASITIC ROUNDWORM contains four chromosomes, whereas the worm’s gametes contain only two

Question 8

What does meiosis involve?

Answer 8

One round of DNA replication followed by two rounds of cell division

Explanation: Mitosis and Meiosis both begin with a round of chromosome duplication and the reduction in chromosome number after meiosis occurs because a single round of duplication is followed by two successive cell divisions without further DNA replication

Question 9

How long does Mitosis and Meiosis II take compared to Meiosis I?

Answer 9

• MITOSIS & MEIOSIS II = within hours
• MEIOSIS I = Last, months or even years
  [Because of the long time spent in Prophase]

Question 10

What is pairing?

Answer 10

Each duplicated paternal chromosome first locates and then attaches itself to the corresponding duplicated maternal homolog

Question 11

What do duplicated homologous chromosomes do before lining up on the meiotic spindle?

Answer 11

Duplicated homologous chromosomes pair before lining up on the meiotic spindle to form BIVALENTS

Question 12

Describe what happens in Crossing over

Answer 12

Non-sister chromatids in each bivalent exchange segments of DNA which is facilitated by the formation of a SYNAPTONEMAL COMPLEX

Question 13

Describe how the Synaptomenal complex helps in Crossing over

Answer 13

As the duplicated homologs pair, the Synaptomenal complex
- Helps to hold the bivalent together
- Aligns the homologs so that strand exchange can readily occur between the non-sister chromatids

Question 14

Multiple crossovers can occur between the duplicated homologous chromosomes in a bivalent (TRUE/FALSE)

Answer 14

TRUE

Question 15

What is the importance of Chiasmata?

Answer 15

• CROSSOVER EVENTS create CHIASMATA between non-sister chromatids in each bivalent
• Chiasmata hold homologous chromosomes together during prophase I -> Chiasmata help ensure that the maternal and paternal homologs will segregate from one another correctly at the FIRST MEIOTIC DIVISION -> Allow for separation in Meiotic Anaphase I

Question 16

What is a Kinetochore?

Answer 16

A disc-shaped protein structure associated with duplicated chromatids in eukaryotic cells where the spindle fibers attach during cell division to pull sister chromatids apart

Question 17

What happens in Meiosis I?

Answer 17

• Pairing
• Crossing over

Question 18

What is the difference in Metaphase of Meiosis I and Meiosis II?

Answer 18

• MEIOSIS I = Kinetochore microtubules of sister chromatids point in the SAME DIRECTION -> Arms of sister chromatids become unglued, allowing the duplicated homologs to separate
• MEIOSIS II = Kinetochore microtubules on each sister chromatid function INDEPENDENTLY -> allowing two sister chromatids to be pulled to opposite poles

Question 19

Describe Meiosis II

Answer 19

• METAPHASE = The kinetochores of the sister chromatids point in opposite directions
• ANAPHASE = Cohesins holding the sister chromatids together at the centromere are degraded -> Allows kinetochore microtubules to pull the two sister chromatids to opposite poles

Question 20

What can errors in chromosome segregation during meiosis result in?

Answer 20

Gametes with incorrect numbers of chromosomes

Question 21

What is Non-disjunction?

Answer 21

The failure of homologous chromosomes or sister chromatids to separate properly during cell division

Question 22

What is Down syndrome?

Answer 22

Down syndrome is a condition when an individual has an extra chromosome on chromosome 21

DIAGNOSIS:
- The first trimester ultrasound shows increased nuchal translucency and hypo plastic nasal bone
- Markers for Down syndrome are increased hCG and increased inhibin

CAUSES:
- Nondisjunction
- Unbalanced Robertsonian translocation
- Post Fertilisation mitotic error

SYMPTOMS:
- Intellectual disability
- Flat face
- Small ears
- Slanting eyes
- Small mouth
- Low muscle tone and loose joints
- Short neck, arms and legs

Question 23

What is the most important risk factor for Trisomy?

Answer 23

Maternal age

Question 24

What are the three most common types of autosomal trisomy?

Answer 24

• Trisomy 21 (Down syndrome)
• Trisomy 18 (Edwards syndrome)
• Trisomy 13 (Patau syndrome)

[Trisomy = The gain of a chromosome]

Question 25

What is Edwards Syndrome and what are the symptoms?

Answer 25

Babies with Edwards' syndrome have more of chromosome 18 in some or all of the cells in their body. It is also known as Trisomy 18. SYMPTOMS: - Abnormally shaped head - Rocker-bottom feet - Intellectual disability - Nondisjunction - Clenched fists with overlapping fingers - Low-set ears - Micrognathia (small jaw) - Congenital heart disease - Death usually occurs by age 1

Question 26

What is Patau syndrome and what are the symptoms?

Answer 26

Patau's syndrome is a serious rare genetic disorder caused by having an additional copy of chromosome 13 in one or all of the body's cells. It's also called trisomy 13. SIGNS AND SYMPTOMS: - Severe intellectual disability - Small head - Heart defects - Cleft palate - Extra fingers - Small or missing eyes - Death usually occurs by 1

Question 27

What is Klinefelter syndrome and what are the symptoms?

Answer 27

Klinefelter syndrome is when boys are born with an extra X chromosome (XXY). To compensate for the extra X chromosome, one X chromosome will be inactivated (Barr body). SYMPTOMS: - Taller than average structure - Longer legs due to delayed epiphyseal closure which leads to increased bone length - Absent, delayed or incomplete puberty - After puberty, less muscle and less facial and body hair compared with other teens - Small, firm testicles (TESTICULAR ATROPHY) - Small penis - Enlarged breast tissue (GYNECOMASTIA) - Abnormal Lydia cell function - decrease testosterone and increase LH and oestrogen

Question 28

What is Triple X syndrome?

Answer 28

Also known as Trisomy X is characterised by the presence of an extra X chromosome in each cell of a female SYMPTOMS: - Taller than average - Learning difficulties - Decreased muscle tone - Seizures - Kidney problems

Question 29

What is Turner syndrome (Monosomy X)

Answer 29

Turner syndrome, a condition that affects only females, results when one of the X chromosomes (sex chromosomes) is missing or partially missing (XO) Sex chromosome (X, or rarely Y) is loss often due to NONDISJUNCTION during meiosis or mitosis. Meiosis errors usually occur in paternal gametes (sperm missing the sex chromosome) and Mitosis errors occur after zygote formation (loss of sex chromosome in some but not all cells) SYMPTOMS: - Short stature - Lymphatic defects resulting in WEBBED NECK - 1st degree amenorrhea (late period) - menopause before even starting period (pregnancy possible using IVF & Progesterone) - decrease in oestrogen leads to increase in LH & FSH - No Barr body - Shield chest

Question 30

What is Mosaicism?

Answer 30

A chromosomal change in only some of the cells [Women with Turner syndrome caused by X chromosome mosaicism are said to have MOSAIC TURNER SYNDROME]

Question 31

What is the difference between Meiosis I and Meiosis II?

Answer 31

- MEIOSIS I = separates homologous chromosomes - MEIOSIS II - separates sister chromatids

Question 32

Where does Pairing of homologous chromosomes occur, Meiosis or Mitosis?

Answer 32

Meiosis Explanation: In Mitosis there is no pairing of homologous chromosomes

Question 33

Where does Crossing over occur, Meiosis or Mitosis?

Answer 33

Meiosis Explanation: In Mitosis crossing over does not occur

Question 34

What is Asexual Reproduction?

Answer 34

Involves one parent and produces offspring that are genetically identical to each other and to the parent

Question 35

What is Sexual reproduction?

Answer 35

Involves two parents and produces offspring that are genetically unique

Question 36

What is Meiosis?

Answer 36

The type of cell division that produces gametes