Meiosis and Development

Question 1

Meiosis

Answer 1

• Cell division to create germ-line cells (sperm + eggs)
• Occurs in reproductive cells (testes and ovaries)

Question 2

Gamete Formation

Answer 2

• Formation of eggs and sperm in the reproductive organs - by meiosis
• Eggs in ovaries and sperm in testes

Question 3

Reduction Division

Answer 3

• Produces 4 daughter cells that have half of the DNA of the original cell
• This happens in meiosis
• Starts with a diploid cell (46 chromosomes)
• Ends with 4 haploid daughter cells (23 chromosomes)

Question 4

Homologous Chromosomes

Answer 4

• Carry different versions of the same genes
• 1 from mum and one from dad

Question 5

Sister Chromatids

Answer 5

• Exact replicates of each chromosome

Question 6

Crossing-over

Answer 6

• Homologous chromosomes exchange genetic information
• Increases genetic diversity
• Leads to recombination

Question 7

Recombination

Answer 7

• A mixture of genes from maternal and paternal chromosomes
• Increases genetic diversity

Question 8

Steps of Meiosis

Answer 8

• Interphase – DNA replicated (only time this occurs in meiosis)
• Prophase I
• Metaphase I
• Anaphase I
• Telophase I
• Prophase II
• Metaphase II
• Anaphase II
• Telophase II

Question 9

Anaphase I

Answer 9

• Homologous chromosomes separate
• Sister chromatids stay together
• This is where genes from Mum and Dad are separated
• Only one set being passed onto offspring

Question 10

Result of Meiosis I

Answer 10

• 2 daughter cells
• 23 homologous chromosomes in each cell (unpaired)

Question 11

Anaphase II

Answer 11

• Sister chromatids separate into daughter cells
• One chromatid in each daughter cell

Question 12

Result of Meiosis II

Answer 12

• 4 daughter cells
• 23 homologous chromosomes
• Haploid daughter cells – 1 chromatid in each

Question 13

Mitosis vs Meiosis

Answer 13

• Mitosis occurs in somatic cells: non-reproductive cells (muscle cells, bone cells etc.)
• Meiosis occurs in germ cells: cells that become sperm and eggs
• Somatic cells are diploid: 2 copies of every chromosome (one from Mum and one from Dad)
• Germ cells are haploid: 1 copy of every chromosome

Question 14

Stages of development for new organisms

Answer 14

• Fertilization: sperm + egg
• Cleavage: mitosis cell division
• Gastrulation: cell layers develop (early tissues)
• Organ formation: tissues interact to form organs
• Growth and specialization: organs develop, begin to function

Question 15

Fertilization

Answer 15

• Fusion of one haploid male sperm and haploid female egg
• Produce one diploid zygote

Question 16

Cleavage

Answer 16

• Series of rapid miotic cell divisions
• Convert a single-cell zygote into a solid ball of 16 cells (Morula)
• Cleavage ends when the solid morula develops into a solid blastula

Question 17

Blastula

Answer 17

• Ball of cells with a fluid-filled cavity (blastocoel)
• Consists of 100-1000 cells, depending on the organism

Question 18

Gastrulation

Answer 18

• Cells move and form germ layers of the gastrula
• The round blastula becomes flat on one side
• Some of the cells on the flat side begin to move into the blastocoel, creating a hole (blastopore) on that side
• The leading edge of the cells moving inside, continues until it reaches the other side of the ball
• Forms a second opening
• Results in a tube from one side to the other
• Eventually forms the alimentary canal
• At the same time, some cells break away and migrate to form a third layer

Question 19

Protostomes

Answer 19

• Some animals (invertebrates), where during gastrulation the blastopore forms the mouth

Question 20

Deuterostomes

Answer 20

• Species where the blastopore form the anus during gastrulation
• Happens in humans
• E.g., Sea stars, sea urchins etc.

Question 21

Organ Formation

Answer 21

• The mature gastrula is composed of 3 germ layers
• These 3 layers will form different organs in the future

Question 22

Ectoderm

Answer 22

• Outer layer of cells
• Skin and nervous tissue
• E.g., brain, spinal cord

Question 23

Endoderm

Answer 23

• Inner layer of cells
• Digestive tract and lungs
• E.g., Stomach and intestines

Question 24

Mesoderm

Answer 24

• Middle layer of cells
• Arises later from cells which grow/ bud from the endoderm
• Muscles, skeleton (bones), connective tissue, circulatory, urinary (kidney), and reproductive systems (ovary)

Question 25

Growth and Tissue Specialization

Answer 25

- Involves 4 basic processes 1. Mitosis and cell growth 2. Cell differentiation 3. Cell Migration 4. Cell suicide

Question 26

Cell Differentiation

Answer 26

- formation of cells with specialized shapes and functions through the activation of unique gene combinations

Question 27

Cell Migration

Answer 27

- Movement of cells to appropriate locations - E.g., Peripheral nerve cells move towards outside of developing organism

Question 28

Cell Suicide (Apoptosis)

Answer 28

- Sometimes, cells intentionally die off - Apoptosis: programmed cell death - Important in sculpting of body parts - Example: formation of paws in mice

Question 29

Tissue Formation

Answer 29

- Cell differentiation, migration, and apoptosis lead to tissues - Tissue: A group of cells with a similar function - E.g., Muscles, fat, bone, skin, etc. - Together tissues form organs and systems