Genes, Chromosomes, Cell division and Variation

Question 1

Where is DNA found ?

Answer 1

In the nucleus of a living cell

Question 2

What does DNA control ?

Answer 2

Cell functions and the instructions for building all proteins within an organism

Question 3

What is DNA’s structure ?

Answer 3

• double helix shape
• it has a sugar phosphate backbone
• has bases Adenine, thymine, guanine and cytosine

Question 4

Which bases complement each other ?

Answer 4

Adenine = thymine 
Guanine = cytosine

Question 5

What do the order of bases code for ?

Answer 5

Order of bases in the gene codes for the sequence of amino acid and protein. Three bases code for one amino acid-this is called a triplet

Question 6

What is a gene ?

Answer 6

A gene is a length of DNA which codes for protein

Question 7

What do the proteins made from a gene control ?

Answer 7

Chemical reactions, growth, colouration and all inheritable characteristics

Question 8

What are the structures called that DNA is wrapped up into ?

Answer 8

Chromosomes

Question 9

How many chromosomes does each person have ?

Answer 9

Two of each chromosome

Question 10

Where do people get their two chromosomes from ?

Answer 10

One of each pair comes from the father the other from the mother

Question 11

Where are genes for a specific characteristic situated on each homologous chromosome ? And what does this mean ?

Answer 11

They are situated at the same point on each homologous chromosome, therefore there is a pair of genes for each characteristic in every nucleus

Question 12

How many chromosomes does a human have ?

Answer 12

46 chromosomes, 23 pairs

Question 13

What does diploid mean ?

Answer 13

Two copies of each of their 23 chromosomes

Question 14

What does haploid mean ?

Answer 14

Only contain one copy of each chromosome

Question 15

What chromosomes are the sex chromosomes ?

Answer 15

The 23rd chromosomes

Question 16

What gender are you if you contain two X chromosomes ?

Answer 16

Female

Question 17

What gender are you if you have one X and one Y-chromosome ?

Answer 17

Male

Question 18

Given example of a human cell that is haploid ?

Answer 18

Egg and sperm cells. This is so when they fuse they form a diploid offspring

Question 19

What is DNA coiled around in chromosomes ?

Answer 19

Proteins called histones

Question 20

DNA is a macromolecule what is it made up of ?

Answer 20

Small units called nucleotide

Question 21

What does growth and reproduction require ?

Answer 21

Cell Division

Question 22

What are the two types of cell division ?

Answer 22

Mitosis and Meiosis

Question 23

What happens before a cell divides ?

Answer 23

The chromosomes replicate making an exact copy of themselves. This doubles the amount of DNA in the cell

Question 24

What is mitosis ?

Answer 24

• produces genetically identical daughter cells
• These cells are diploid
• Mitosis is used for growth, repair and asexual reproduction

Question 25

What is meiosis ?

Answer 25

* this produces gametes * they are genetically varied * meiosis is ONLY used to produce gametes for sexual reproduction

Question 26

Describe mitosis

Answer 26

* The two pairs of chromosomes each replicated itself to form chromatids * fibres appear in the cytoplasm and form a spindle * The chromosomes move to the equator of the spindle and spindle fibres shortening and appeared to pull the chromatids apart by centromeres * The chromatids are now chromosomes and have moved to opposite ends of the cell * The cell begins to divide * nuclear membrane forms again * after the cell divides it creates two identical daughter cells

Question 27

Describe meiosis

Answer 27

* chromosomes make identical copies of themselves * similar chromosomes pair up * sections of DNA get swapped * pairs of chromosomes divide * chromosomes divide * four haploid, genetically varied cells are produced

Question 28

How is variation in offspring produced ?

Answer 28

* genetic variation in gametes produced by meiosis | * Random fertilisation of ova by male gametes

Question 29

What Reproduction is meiosis used for ?

Answer 29

Sexual reproduction

Question 30

What reproduction is mitosis used for ?

Answer 30

Mitosis

Question 31

How many chromosomes are in the haploid cell after meiosis ?

Answer 31

23 chromosomes

Question 32

Why is variation important?

Answer 32

For evolution to occur

Question 33

How can variation occur ?

Answer 33

can be genetic, environmental or a combination of both

Question 34

Describe genetic variation

Answer 34

Following sexual reproduction or mutation, organisms will have different versions of genes to another individual

Question 35

Describe environmental variation

Answer 35

The environment can also affect the characteristics of an organism E.g. More sun = grow taller Less sun = shorter plant

Question 36

What is the mutation ?

Answer 36

Mutation is a change in the DNA

Question 37

How can a mutation occur ?

Answer 37

* often a mutation will cause a base in DNA to change. So when it is read by the RNA it is incorrect this is called substitution mutation * a cell can gain an extra chromosome or one part of the chromosome is stuck to another chromosome, this is called chromosomal mutation

Question 38

What three affects can mutations have ?

Answer 38

* neutral - like most sequence mutations * negative - most chromosomal mutations * positive - tiny minority of mutations could improve an organism survival chances

Question 39

What is a gene mutation ?

Answer 39

A single chromosome is changed as a result, a defective protein is produced. This can lead to a considerable change in characteristics, this can then be inherited.

Question 40

Why do mutations occur ?

Answer 40

They occur spontaneously

Question 41

What are mutagens ?

Answer 41

Factors that increase the rate of mutation

Question 42

What two mutagens can increase the rate of mutation ?

Answer 42

* Radiation - can damage DNA and cause mutation | * chemicals - Tobacco smoke and other chemicals can cause mutations

Question 43

What is a mutagen that causes uncontrolled cell division called ?

Answer 43

A caricinogen