B11.1 and 2 : Chromosomes, Genes, and Cell division

Question 1

Types of cell division

Answer 1

1. mitosis

2. meiosis

Question 2

Meiosis

Answer 2

1. This results in the formation of four genetically non-identical daughter cells.
2. Meiosis is used in sexual reproduction.
3. Shares out the chromosomes so that each new cells gets only one of each type
4. Meiosis leads to genetic variation because because the cells will get a mixture of the mothers DNA and the fathers DNA.
5. e.g. a sperm cell could contain a chromosome 1 from the man;’s father and a chromosome 2 from his mother, and so on. There are all sorts of different possible combinations
6. reduction division in which the chromosome number is halved from diploid to haploid, resulting in genetically different cells
7. starts with a diploid (usually a specialised cell in the ovaries or testes - gonads) and ends with 4 haploid cells

Question 3

Mitosis

Answer 3

1. This results in the formation of two genetically identical daughter cells.
2. Mitosis is used in asexual reproduction, growth, and for replacing damaged cells.
3. The way in which any cell - plant or animal - divides when an organism is growing, or repairing a damaged part of its body.
4. e.g. if you cut yourself, new skin cells will be made by mitosis to help to heal the wound
5. Nuclear division giving rise to genetically identical cells
6. It starts with a diploid and ends with a diploid

Question 4

haploid

Answer 4

a cell with a single set of chromosomes, such as a gamete

Question 5

homologous chromosomes

Answer 5

1. two chromosomes of a pair

Question 6

Cells before mitosis

Answer 6

1. Just before mitosis takes place, the chromosomes in the parent cell are copied
2. Each copy remains attached to the original one, so each chromosome is made up of two identical threads joined together
3. The two threads are called chromatids and the point where they are held together is called the centromere

Question 7

centromere

Answer 7

the point where the chromatids are held together

Question 8

gametes chromosomes

Answer 8

1. gametes have only half the number of chromosomes of a normal body cell
2. They have one set of chromosomes instead of two
3. This is so that when they fuse together, the zygote formed has two sets of chromosomes

Question 9

Human gametes cell division

Answer 9

1. Human gametes are formed by the division of cells in the ovaries and testes
2. The cells divide by a special type of cell division called meiosis
3. Meiosis shares out the chromosomes so that each new cell gets only one of each type

Question 10

Cytokinesis

Answer 10

The cell membrane pinches in and eventually divides into two daughter cells.

Question 11

Cancer cells

Answer 11

1. Cells grow then divide by mitosis only when we need new ones. This is when we’re growing or need to replace old or damaged cells.
2. When a cell becomes cancerous, it begins to grow and divide uncontrollably. New cells are produced even if the body does not need them.
3. A group of cancerous cells produces a growth called a tumour.

Question 12

Types of tumors

Answer 12

1. benign

2. Malignant

Question 13

Benign tumor

Answer 13

1. Grow slowly.
2. Usually grow within a membrane, so can easily be removed.
3. Do not invade other parts of the body.

Question 14

Malignant tumor

Answer 14

1. Grow quickly.
2. Invade neighbouring tissues and can spread to other parts of the body in the bloodstream.
3. As the tumour grows, cancer cells detach and can form secondary tumours in other parts of the body.
4. This process is called metastasis.

Question 15

Stem Cells

Answer 15

1. Many tissues in the human body contain a small number of unspecialised cells
2. These are called stem cells and their function is to divide by mitosis and produce new daughter cells that can become specialised within the tissue and be used for different functions

Question 16

Synapsis

Answer 16

1. Synapsis is the pairing of two homologous chromosomes that occurs during meiosis.
2. It allows matching-up of homologous pairs. it is the exchanging/swapping of genes between 2 cells
3. Synapsis takes place during prophase I of meiosis.

Question 17

Genomes

Answer 17

1. The genome is all the genetic material of an organism, inherited (passed down) from parents to offspring.
2. Within a genome, there are lots of levels of organisation

Question 18

DNA

Answer 18

1. DNA is double helix polymer, which means it is a polymer (a large molecule made up of many subunits) made up of two strands forming a twisted, ladder shape.
2. DNA molecule marries a code that instructs the cell about which kinds of proteins it should make

Question 19

Genes

Answer 19

1. A gene is a small section of DNA. Genes code for a sequence of amino acids, which combine to give a specific protein.
2. Every cell in your body has an exact copy of all of your genes. Besides an identical twin, there is no one else in the world with exactly the same combination of genes that you have
3. Genes make u unique
4. Genes on ur chromosomes determine all sorts of things about you - colour eyes, hair, genetic disease etc

Question 20

Chromosomes

Answer 20

1. Long strands of DNA are coiled up to form chromosomes. Each chromosome will carry instructions for making many different proteins
2. Chromosomes contain many genes.
3. Human body cells contain 23 pairs of chromosomes, one of each pair coming from each parent.
4. The human body has 46 chromosomes
5. Usually chromosomes are too thin to be seen except with an electron microscope. But when a cell is dividing, they get shorter and fatter so they can be seen with a light microscope

Question 21

Three levels of organisation of a genome

Answer 21

1. DNA
2. Genes
3. Chromosomes

Question 22

Organisation of Genetic Material

Answer 22

1. The nucleus of eukaryotic cells contains chromosomes made of DNA molecules.
2. Each chromosome contains a large number of genes.
3. Each gene tells how a specific protein should be made.

Question 23

Gene Vs DNA (size)

Answer 23

1. A gene is a segment of DNA.
2. But there can be fragments of DNA that are smaller than a gene.
3. This question is like asking whether a city or a community is bigger.
4. They are kind of the same depending on how you define them.

Question 24

Polymer

Answer 24

1. Polymers are very large, chain-like molecules, which often extend for hundreds and thousands of atoms
2. The atoms in a polymer molecule are joined by a strong covalent bond