16.1 Passage of information from parent to offspring

Question 1

Inheritance

Answer 1

the transmission of genetic information from generation to (the next) generation.

Question 2

Chromosome

Answer 2

a thread of DNA, made up of a string of genes.

Question 3

Allele

Answer 3

any of two or more alternative forms of a gene.

Question 4

Homologous Chromosomes

Answer 4

A pair of chromosomes in a diploid cell that have the same structure as each other, with the same genes (but not necessarily the same alleles of those genes) at the same loci, and that pair together to for a bivalent during the first division of meiosis

Question 5

Types of nuclear division

Answer 5

1) Mitosis - growth

2) Meiosis (reduction division) - sexual reproduction

Question 6

Meiosis

Answer 6

A type of cell division in which a diploid cell divides to form four haploid cells, in which different combinations of alleles are present. It involves 2 divisions, so 4 daughter cells are formed.

Question 7

In Meiosis what do the cells have?

Answer 7

• Only half the chromosomes as the parent cell

- Different combinations of alleles from each other and from the parent cell

Question 8

What does meiosis produce in animals and plants?

Answer 8

Gametes

Question 9

How many pairs chromosomes are there in a cell?

Answer 9

• 23 pairs
• so 2 sets of chromosomes
• 22 matching pairs
• 1 non-matching pair labelled X and Y

Question 10

Sex Chromosomes

Answer 10

X and Y non-matching chromosomes

Y chromosome has portions missing so is shorter than the X chromosome

Question 11

Autosomes

Answer 11

All other chromosomes besides the sex chromosomes

Question 12

Gene

Answer 12

a length of DNA that is the unit of heredity and codes for a specific protein. A gene may be copied and passed on to the next generation

Question 13

Locus

Answer 13

The position at which a particular gene is found on a particular chromosome; the same gene is always found at the same locus

Question 14

Each chromosome has a characteristic set of

Answer 14

genes that code for different features

Question 15

abbreviation n =

Answer 15

the number of chromosomes in one set

of chromosomes.

Question 16

Diploid

Answer 16

A cell that possesses two complete sets of chromosomes; the abbreviation for diploid is 2n

Question 17

Haploid

Answer 17

A cell that possesses one complete set of chromosomes; the abbreviation for haploid is n

Question 18

Centrosome

Answer 18

• produce the spindle fibers that are required during metaphase of mitosis.
• Each centrosome consists of two centrioles that are orientated at right-angles to each other.
• Each centriole is a cylindrical array of 9 microtubules

Question 19

Importance of Meiosis

Answer 19

• Sexual Reproduction - introduces genetic variation into the gametes and therefore the zygotes that are produced.

Question 20

Meiosis Divisions

Answer 20

1) Interphase
2) Meiosis I is a reduction division, resulting in two daughter nuclei with half the number of chromosomes of the parent nucleus.
3) In Meiosis II, the chromosomes behave as in mitosis, so that each of the two haploid daughter nuclei divides again. Meiosis therefore results in a total of four haploid nuclei.

Question 21

Meiosis Steps

Answer 21

1) Prophase I
2) Metaphase I
3) Anaphase I
4) Telophase I and Cytokinesis
6) Prophase II
7) Metaphase II
8) Anaphase II
9) Telophase II and Cytokinesis

Question 22

Prophase I

Answer 22

• Centrosomes divide and are involved in spindle formation
• Chromosomes begin to condense
• The spindle continues to form
• Homologous chromosomes pair up. This process is called synapsis.
• Each pair is called a bivalent
• Nuclear envelope breaks up as in mitosis
• Nucleolus disappears
• Crossing over of Chromatids may occur

Question 23

Metaphase I

Answer 23

• Bivalents line up across equator of spindle, attached by centromeres
• spindle formed, as in mitosis

Question 24

Anaphase I

Answer 24

• Centromeres do not divide, unlike in mitosis.

- Whole chromosomes move towards opposite ends of spindle, centromeres first, pulled by microtubules

Question 25

Telophase I and Cytokinesis

Answer 25

• Animal cells usually divide before entering meiosis II.
• Chromosomes partly unwind
• Spindle disappears and the nuclear envelopes form
• Many plant cells go straight into meiosis II with no reformation of nuclear envelopes or nucleoli.

Question 26

Prophase II

Answer 26

• nuclear envelope and nucleolus disperse

- centrosomes and centrioles replicate and move to opposite poles of the cell

Question 27

Metaphase II

Answer 27

chromosomes line up separately across equator of spindle

Question 28

Anaphase II

Answer 28

centromeres divide and spindle microtubules pull the chromatids to opposite poles

Question 29

Telophase and Cytokinesis

Answer 29

• This is like telophase of mitosis, but in meiosis
  telophase II four haploid daughter cells are formed
• Spindles Disappear
• Nuclear envelopes reappear
• Chromosomes unwind

Question 30

3 sources of Genetic Varation

Answer 30

• Crossing Over (Meiosis)
• Independent Assortment (Meiosis)
• Fusion between random gametes at fertilisation

Question 31

Crossing Over

Answer 31

• Occurs at Prophase I
• The two homologous chromosomes lie side by side and their chromatids form links called chiasmata (singular chiasma) with each other
• When they move apart, a piece of chromatid from one chromosome may swap with a piece from the other chromosome. This is called Crossing Over
• It results in each chromosome having different combinations of alleles than it did before

Question 32

Independent Assortment

Answer 32

• Shuffles the alleles like Crossing Over
• Occurs at Metaphase I
• The pairs of homologous chromosomes line up on the equator before being pulled to opposite poles of cell
• Each pair behaves independently from every other pair, so there are many different combinations that can end up together
• In a human there are 23 pairs, so there is a huge number of different possibilities