Ib Biology Topic 10

Front 1

Meiosis

Back 1

a reduction division of the nucleus to form haploid gametes

Front 2

When does DNA replication occur?

Back 2

In the S-phase of interphase before meiosis

Front 3

Crossing over

Back 3

the exchange of DNA material between non-sister homologous chromatids

Front 4

What does crossing over do?

Back 4

It produces new combinations of alleles on the chromosomes of haploid cells

Front 5

Chromatid

Back 5

one of the replicated chromosomes still connected to the other by the centromere

Front 6

How are bivalents formed?

Back 6

Homologous pairs (attached to their replications) associate with each other via synapsis during prophase I

Front 7

Chiasma (pl. chiasmata)

Back 7

the X-shaped, microscopically visible region representing non-sister homologous chromatids that have exchanged genetic material through crossing over during meiosis

Front 8

What must happen for crossing over to function correctly?

Back 8

Identical breaks must occur at exactly the same position in adjacent non-sister chromatids

Front 9

When do homologous chromosomes separate?

Back 9

Meiosis I (Anaphase I)

Front 10

When do sister chromatids separate

Back 10

Meiosis II (Anaphase II)

Front 11

What does random orientation refer to?

Back 11

The behaviour of homologous chromosomes (meiosis I) or pairs of sister chromatids (meiosis II)

Front 12

What does independent assortment refer to?

Back 12

The behaviour of alleles of unlinked genes as a result of gamete production

Front 13

When are gene loci considered linked?

Back 13

When they are on the same chromosome

Front 14

How do linked genes work?

Back 14

The linked genes are on the same chromosome and are close together, reducing the chance of them being separated in crossing over. This means they are more likely to be inherited together.

Front 15

Mendel's Law of Independent Assortment

Back 15

The presence of an allele of one of the genes in the gamete has no influence over which allele of another gene is present.

Front 16

Name an example of discrete variation

Back 16

Dry versus wet earwax

Front 17

Name an example of continuous variation

Back 17

Human height

Front 18

What are polygenic characteristics?

Back 18

Characterisitics influenced by multiple genes

Front 19

Do phenotypes of polygenic characteristics tend to show continuous or discrete variation?

Back 19

Continuous

Front 20

What is Drosophila?

Back 20

A genus of fruit fly

Front 21

Why did Morgan use Drosophila in his experiments?

Back 21

They reproduced quickly - every two weeks

Front 22

What did Morgan discover?

Back 22

His results showed non-Mendelian ratios, and from them he discovered linked genes

Front 23

What can also influence polygenic traits?

Back 23

Environmental factors

Front 24

Gene pool

Back 24

the total collection of different alleles in an interbreeding population OR all the genetic information present in the reproducing members of a population at a given time

Front 25

Large gene pool

Back 25

Lots of variation

Front 26

Small gene pool

Back 26

Little variation

Front 27

Allele frequency

Back 27

a measure of the proportion of a specific variation of a gene in a population

Front 28

What is allele frequency expressed as?

Back 28

A proportion or a percentage