2.4 Meiosis and Sexual Reproduction

Question 1

What is Meiosis

Answer 1

Form of cell division that gives rise to genetic variation

Question 2

Meiosis 1

Answer 2

Homologous pairs of chromosomes are separated
1) Chromosomes condense
2) Homologous chromosomes pair up + crossing over occurs
3) Homologous chromosomes line up at the equator
4) Spindle fibres pull the homologous chromosomes to opposite poles of the cell
5) Cytoplasm divides + 2 daughter cells are formed

Question 3

Meiosis 2

Answer 3

Pairs of chromatids are separated
1) Nucleolus disintegrates, chromosomes condense + spindle fibres are made
2) Chromosomes line up at the equator + each chromatid is independently assorted
3) Chromatids are pulled to the poles of the cell
4) Cytoplasm divides + 4 daughter cells are produced

Question 4

Crossing Over

Answer 4

Exchange of sections of DNA between homologous chromosomes

Question 5

Independent Assortment

Answer 5

Various combinations of maternal and paternal chromosome arrangement

Question 6

Translocation

Answer 6

A part of a chromosome switches places with a separate non homologous chromosome

Question 7

Non Disjunction

Answer 7

When homologous chromosomes fail to separate properly
1 gamete will have 2 copies of a chromosome + the other has none

Question 8

Chromosome Mutations

Answer 8

Deletion
Inversion
Duplication

Question 9

Deletion Mutation

Answer 9

An entire region of a chromosome is deleted

Question 10

Inversion Mutation

Answer 10

A part of a chromosome will break, then before rejoining invert itself due to a change in a sequence

Question 11

Duplication Mutation

Answer 11

Regions of a chromosome can be duplicated

Question 12

Aneuploidy

Answer 12

Cell contains to many chromosomes

Question 13

Monosomy

Answer 13

Only 1 of a pair of chromosomes is present in a cell

Question 14

Polysomy

Answer 14

A cell contains 3 or more rather than 2 copies of a chromosome

Question 15

Down Syndrome

Answer 15

An extra chromosome 21
Polysomy

Question 16

Turners Syndrome

Answer 16

Only affects females
Only 1 X chromosome
Y chromosome determines maleness so if missing child will be female

Question 17

Spermatogenesis

Answer 17

1) Diploid germ cell divides by mitosis twice to give spermatogonia
2) They grow until they are primary spermatocytes
3) Divide by meiosis to give 2 haploid secondary spermatocytes
4) Undergo 2nd meiosis to give 4 haploid spermatids
5) Differenciate into spermatozoa

Question 18

Sperm Adaptations

Answer 18

Acrosome
Haploid Nucleus
Mitochondria
Flagellum

Question 19

Acrosome

Answer 19

Storage of enzymes to digest outer layer of the ovum

Question 20

Haploid Nucleus

Answer 20

Contains 23 highly condensed chromosomes

Question 21

Mitochondria

Answer 21

Release energy for the flagellum to move

Question 22

Flagellum

Answer 22

Has microtubules which move the flagellum

Question 23

Oogenesis

Answer 23

1) Diploid germ cell divides by mitosis twice to form a diploid oogonia
2) Grows to form a diploid primary oocyte
3) Undergoes meiosis to form a haploid secondary oocyte + a polar body
4) Ovulation occurs
5) 2nd meiotic divison occurs
6) Haploid secondary oocyte divides by meiosis which forms an ovum
7) Polar bodies disintegrate

Question 24

Egg Adaptations

Answer 24

Haploid Nucleus
Cytoplasm
Corona Radiata
Zona Pellucida
Cortical Granules

Question 25

Haploid Nucleus

Answer 25

23 highly condensed chromosomes

Question 26

Cytoplasm

Answer 26

Has Food Reserves

Question 27

Corona Radiata

Answer 27

Protective barrier around the ovum

Question 28

Zona Pellucida

Answer 28

Layer that initiates the acrosome reaction

Question 29

Cortical Granules

Answer 29

Blocks additional sperm from reaching the egg

Question 30

Animal Fertilisation

Answer 30

1) Sperm reaches the zona pellucida and acrosme reaction occurs 2) Sperm head fuses with egg cell membrane which allows sperm nucleus to enter the egg cell 3) Cortical reaction occurs which causes the zona pellucida to harden and prevents polyspermy 4) Nucleus fuse together creating a diploid zygote

Question 31

Sorophyte generation

Answer 31

Diploid + produces spores by meiosis

Question 32

Gametophyte Generation

Answer 32

Haploid + produces gametes by mitosis

Question 33

Pollen Formation

Answer 33

1) Diploid microspore mother cells in the anther undergo meiosis and form 4 haploid microspores 2) Haploid microspores undergo mitosis to mature into pollen grains This contains a generative + pollen tube nucleus

Question 34

Ovum Formation

Answer 34

1) Diploid megaspore mother cells in the ovule undergo mitosis This forms an ootid 2) Ootid undergoes 3 miotic divisions to form an embryo sac This has 2 polar nuclei, an egg cell, 2 synergids + 3 antipodal cells

Question 35

Plant Fertilisation

Answer 35

1) Pollen Grain sticks to the stigma where it germinates 2) Pollen tube grows down the style via the secretion of digestive enzymes 3) Pollen tube grows through the micropyle into the embryo sac 4) Generative nucleus divides by mitosis and produces 2 sperm cells 5) Double Fertilisation occurs

Question 36

Double Fertilisation

Answer 36

1) A diploid zygote 2) Triploid Endosperm which act as nutrients