3B Sexual Reproduction and Meiosis

Question 1

sexual reproduction (3)

Answer 1

• the production of a new individual resulting from the joining (fusion) of two specialized cells known as gametes.
• produces individuals that are not genetically the same as either of their parents, but contain genetic information from both
• occurs when two haploid nuclei fuse to form a new diploid cell called a zygote

Question 2

what is the great advantage of sexual reproduction? (2)

Answer 2

• increases genetic variation because gametes from two different individuals are fused together
• in a changing environment, this gives a greater chance that one or more of the offspring will have a combination of genes that improves their chance of surviving and reproducing

Question 3

diploid (2n)

Answer 3

a cell with a nucleus containing two full sets of chromosomes

Question 4

haploid (n)

Answer 4

a cell with a nucleus containing one complete set of chromosomes

Question 5

zygote

Answer 5

the cell formed when two haploid gametes fuse at fertilization

Question 6

male types of tissue and whether they are diploid or haploid (3)

Answer 6

body tissue = diploid
testis tissue = diploid
sperm in testis = haploid

Question 7

female types of tissue and whether they are diploid or haploid (4)

Answer 7

body cells = diploid
ovary tissue = diploid
ovum in ovary = haploid
zygote tissue = diploid

Question 8

gonads

Answer 8

the sex organs in animals

Question 9

ovaries (2)

Answer 9

• the female sex organ in both animals and plants

- they produce the female gametes called ovules in plants and ova in animals

Question 10

anthers

Answer 10

male sex organs in plants that produce the male gametes contained in the pollen

Question 11

ovules (2)

Answer 11

• the haploid female gametes in plants

- made in the ovaries

Question 12

pollen

Answer 12

the spore which contains the haploid male gametes of plants

Question 13

testes

Answer 13

the male sex organs in animals that produce the male gametes (sperm or spermatoza)

Question 14

ova

Answer 14

the haploid female gametes in animals (singular=ovum)

Question 15

sperm/spermatoza (2)

Answer 15

• the haploid male gametes in animals

- usually much smaller than the female gametes, but produced in larger quantities

Question 16

why must meiosis occur? (2)

Answer 16

• when the gametes are being formed, the chromosome number needs to be halved to give the necassary haploid nuclei
• occurs only in the sex organs

Question 17

difference between meiosis in animals and flowering plants (2)

Answer 17

• in animals, the gametes are formed directly from meiosis
• , while in flowering plants meiosis forms special male cells called microspores and female cells called megaspores, which develop into gametes

Question 18

meiosis (2)

Answer 18

• two nuclear divisions produce four haploid daughter cells, each with its own unique combination of genetic material
• similar to mitosis, the contents of the cell are replicated in interphase, before it enters meiosis

Question 19

Prophase 1 (3)

Answer 19

• each chromosome appears in condensed form with two chromatids
• homologous pairs of chromosomes associate with eachother
• crossing over occurs

Question 20

Metaphase 1 (2)

Answer 20

• spindle forms

- the pairs of chromosomes line up on metaphase plate

Question 21

Anaphase 1 (3)

Answer 21

• the centromeres do not divide
• one chromosome (pair of chromatids) from each homologous pair moves to each end of the cell
• now the number of chromosomes in each cell is halved

Question 22

Telophase 1 (3)

Answer 22

• nuclear membrane reforms
• cells begin to divide
• in some cells there may now be cytokinesis and maybe a period of interphase (but no further DNA replication)

Question 23

Prophase 2 (3)

Answer 23

• new spindles are formed
• chromosomes condense
• difference to prophase 1= daughter cells only have one copy of homologous chromosomes

Question 24

Metaphase 2 (2)

Answer 24

• chromosomes randomly line up on metaphase plate

Question 25

Anaphase 2 (2)

Answer 25

• centromeres divide

- chromatids move to opposite ends of cell

Question 26

Telophase 2 (3)

Answer 26

• nuclear envelopes reform
• the chromosomes return to their interphase state
• cytokinesis occurs, giving four daughter cells each with half the chromosome number of the orginal diploid cell

Question 27

homologous pairs

Answer 27

matching pairs of chromosomes in an individual which both carry the same genes, although they may have different alleles

Question 28

difference between the two divisions (1 and 2) in meiosis (2)

Answer 28

• in the first division, the homologous chromosomes (each consisting of two chromatids) separate
• in the second division, the individual chromatids separate

Question 29

What are the main ways in which genetic variation is introduced to species? (3)

Answer 29

• crossing over (recombination)
• independant/random assortment
• mutation

Question 30

crossing over (recombination) (3)

Answer 30

• occurs in prophase 1
• large multi-enzyme complexes ‘cut and join’ bits of the maternal and paternal chromatids together
• the points where the chromatids break are called chiasmata

Question 31

Why is crossing over so important? (2)

Answer 31

• this exchange of genetic material leads to added genetic variation
• errors in the process lead to mutation, which is a further way of introducing new combinations into the genetic makeup of the species

Question 32

Independant/random assortment (3)

Answer 32

• occurs during metaphase 1, when the chromatids line up on metaphase plate
• the maternal and paternal chromosomes are distributed into the gametes at random
• example= each gamete gets 23 chromosomes, any number from 0 to 23 can come from either the maternal or paternal chromosomes

Question 33

chiasmata

Answer 33

the points where the chromatids break during crossing over

Question 34

Explain how meiosis produces genetic variation in gametes (from exam) (3)

Answer 34

• independant/random assortment and crossing over
• independant assortment gives rise to new combinations of paternal and maternal chromosomes
• crossing over involves swapping of sections of chromatids

Question 35

Why can offspring (for example twins) be genetically different, even thought hey are from the same father and mother? (3)

Answer 35

• because each zygote is formed from different gametes, so through random fertilisation
• each gamete contains different combinations of alleles
• this is due to independant assortment or crossing over during meiosis

Question 36

mutation

Answer 36

a permanent damage in the DNA of an organism