Topic 4: Genetic Diversity

Question 1

define meiosis

Answer 1

A type of nuclear division that produces 4 daughter cells, each with half (haploid) the number of chromosomes of the parent cell

Question 2

Purpose of meiosis

Answer 2

Produces genetically different daughter cells
Sexual reproduction results in genetic diversity in offspring
Survival advantage when environmental conditions change so individuals are more likely to survive

Question 3

What are gametes?

Answer 3

They are haploid and 2 fuse together to produce an offspring with diploid number of chromosomes

Question 4

Why are the chromosomes in homologous pairs similar?

Answer 4

One is from the male and one is from the female
They carry the same genes for the same polypeptides in the same positions (locus)

Question 5

What are produced in meiosis?

Answer 5

4 daughter cells that aren’t identical, they are genetically different and form gametes

Question 6

What is independent segregation?

Answer 6

It is a process of genetic variation
When homologous pairs line up on the equator , it is completely random as to which chromosomes from each pair end up together in daughter cells

Question 7

what is the result of independent segregation?

Answer 7

New combinations of paternal and maternal chromosomes in gametes

Question 8

When do independent segregation and crossing over occur?

Answer 8

During meiosis 1 when the homologous pairs line up

Question 9

What is crossing over?

Answer 9

When homologous pairs line up and become twisted to form a bivalent. The bivalent causes sections of the chromatids to be swapped- so alleles were swapped.
Produces recombinant chromatids

Question 10

define Chiasmata

Answer 10

Point where chromatids cross, break and rejoin

Question 11

Calculation for the possible combinations of chromosomes following meiosis

Answer 11

2^n

Question 12

2^n

Answer 12

How to calculate the possible combinations following meiosis

Question 13

How to calculate the possible combinations after random fertilisation of 2 gametes?

Answer 13

(2^n)2

Question 14

(2^n)2

Answer 14

How to calculate the possible combinations after random fertilisation of 2 gametes

Question 15

Life cycle exam questions

Answer 15

• may get given the life cycle of an unknown organism
• meiosis will be where a diploid has divided and become haploid
  Haploid to diploid is fertilisation
  If it stays the same= mitosis

Question 16

How many divisions are in meiosis?

Answer 16

2

Question 17

Describe prophase 1

Answer 17

Chromosomes are visible because they have condensed

Question 18

Describe metaphase 1

Answer 18

Homologous chromosomes line up at the equator, how they line up is random

Question 19

Describe anaphase 1

Answer 19

Homologous chromosomes are pulled to opposite poles

Question 20

Telophase 1

Answer 20

Cell prepares for first cell division

Question 21

Metaphase 2

Answer 21

Individual chromosomes line up at the equator

Question 22

Anaphase 2

Answer 22

Sister chromatids are separated to opposite poles

Question 23

Telophase 2

Answer 23

Each daughter cell is haploid

Question 24

What are chromosomes mutations?

Answer 24

Changes in structure or number of chromosomes

Question 25

What do chromosome mutations lead to?

Answer 25

Inherited conditions because errors are present in the gametes

Question 26

Polyploidy

Answer 26

Changes in whole sets of chromosomes- all homologous chromosomes fail to seperate properly
A diploid gamete is fertilised by a haploid gamete to give an organism 3 sets of chromosomes
May occur in plants

Question 27

Non-disjunction

Answer 27

Changes in the number of individual chromosomes- sometimes individual homologous chromosomes fail to seperate during meiosis

Question 28

What happens as a result of non-disjunction?

Answer 28

The resulting gamete has one more or one fewer chromosomes than it should
If a normal gamete fuses with this gamete, all resulting body cells will have the same number of chromosomes
This occurs in Down’s syndrome

Question 29

When is a mutation inherited?

Answer 29

They occur randomly, they are inherited if they occur in gametes but not if in somatic cells

Question 30

what are the causes of mutations?

Answer 30

They can occur randomly, but substances called mutagens can increase the natural mutation rate
Mutagens e.g ionising radiation, UV light, tobacco tar, mustard gas

Question 31

Are all mutations harmful?

Answer 31

No
They can be helpful by producing new alleles, and increasing variation in a population

Question 32

3 types of mutation

Answer 32

Addition
Deletion
Substitution

Question 33

What are addition and deletion known as?why?

Answer 33

Frameshift mutations
Because they can significantly alter the resulting polypeptide chain

Question 34

Addition

Answer 34

An extra nucleotide base is added

Question 35

Deletion

Answer 35

A nucleotide is removed

Question 36

Substitution

Answer 36

A nucleotide is replaced by one with a different base

Question 37

Why aren’t all base substitutions bad?

Answer 37

The degenerate nature of the genetic code means that not all base substitutions cause a change in sequence of encoded amino acids

Question 38

What is the effect of a mutation?

Answer 38

-The mutation causes a change in the sequence of bases in the dna
-this leads to a change in the mRNA
This leads to a change in the amino acid sequence in the polypeptide chain
This causes a change in the function of a protein because it has a different tertiary structure

Question 39

Give one example of a substitution mutation

Answer 39

Sickle cell anemia
Caused by a substitution of one dna base which alters one amino acid and changes the structure & function of haemoglobin

Question 40

What can mutations result in?

Answer 40

Differences in base sequences of alleles of a single gene may result in non-functional proteins, including non-functional enzymes