Chapter 9 - Genetic Diversity

Question 1

Gene mutation
What is it?

Answer 1

A gene mutation is a change in the DNA base sequence.
/ change in the base sequence of a chromosome

Question 2

How do mutations occur?

Answer 2

Gene utations occur spontaneously during DNA replication if DNA is misread during DNA replication.

Question 3

Factors that increase risk of mutation?

Answer 3

Mutagenic agents/mutagens
Ultraviolet or ionising radiation, chemicals and viruses can increase the rate of mutations.

Question 4

What are the two types of mutation?

Answer 4

Base substitution and base deletion

Question 5

What is substiution?

Answer 5

Type of gene mutation in which a nucleotide in a DNA molecule is replaced by another nucleotide that has a different base
A substitution mutation is when a base is swapped out for a different one.
This mutation may change the amino acid sequence coded for by the gene.
One amino acid is changed

Question 6

What is deletion?
Why is it more harmful?

Answer 6

1.Deletion - One base is removed from the sequence - a nucleotide is lost from the DNA sequence
2. Deletions are much more likely to change the amino acid sequence because they cause a frameshift which means the enitre amino acid sequence will be different, not just one.

Question 7

Why might a mutation not lead to a change in the amino acid sequence?

Answer 7

1. Substiution mutation may lead to new triplet coding for the same amino acid as the original triplet because genetic code is degenerate and mutation will have no effect
2. Mutation may occur in a non coding region (intron)

Question 8

What are chromosome mutations?

Answer 8

changes to the structure or number of whole chromosomes

Question 9

What are the two types of chromosome mutations?

Answer 9

1. Polyploidy- Changes in whole sets of chromosomes
2. Non-disjunction - changes in the number of indivudal chromosomes

Question 10

What is polyploidy chromosome mutation?
Where is this mostly found?

Answer 10

When organsims have three or more sets of chromosomes rather than 2. when organisms have more than two sets of chromosomes,
Occurs mostly in plants

Question 11

What is non-disjunction chromosome mutation and how does it occur?

Answer 11

This occurs when homologous chromosomes fail to separate in meiosis which results in gametes having either one more or one fewer chromosome, and leads to individuals with extra or missing chromosomes in all cells.
E.g Down’s syndrome

Question 12

Diploid and haploid cells
What is the difference?

Answer 12

Haploid cells have half the amount of chromosomes than diploids
Diploid cells have a full set of chromosomes
Gamtes - sex cells are haploid cells and have 23 chromosomes
Diploid number in humans is 46
Two haploid gametes sperm and egg fuse at fertilisation and form the diploid number

Question 13

What does meiosis produce?

Answer 13

4 daughter cells each with half the number of chromosomes as the parent cell - Meiosis produces haploid cells from diploid cells

Question 14

Meiosis involves two divisions(Meiosis 1 and Meiosis 2)
Overview of what happens in each division?

Answer 14

Meiosis I - Homologous chromosomes are separated into different cells
Meiosis II - Chromatids move apart and are separated into four cells
Meiosis I - Prophase I, metaphase I, anaphase I, and telophase I.
Meiosis II - Prophase II, metaphase II, anaphase II, and telophase II.

Question 15

Meiosis 1 - Describe process
Remember that cells have already replicated their DNA during interphase and each chromosome is made up of two identical sister chromatids.

Answer 15

Homologous chromosomes pair up and thier chroamtids wrap around each other.
Equivalent portions of these chromatids may be exh=changed in crossing over
Chromosomes line up along the equator of the cell in their homologous pairs (so in humans, 23 pairs line up).
Each chromosome attaches to the spindle by their centromere.
Homologous chromosome pairs are separated and pulled to opposite poles of the cell (chromatids stay joined together).
Cell divides into two, one chromosome from each pair into one of the two daughter cells

Question 16

Meiosis 2 -Describe process

Answer 16

The sister chromatids move apart and at the end of meiosis four cells have been formed, each containing 23 chromosomes in humans

Question 17

Compare Mitosis and Meiosis
How do they differ?

Answer 17

Mitosis produces 2 daughter cells genetically identical, Meiosis produces 4 genetically different daughter cells
Mitosis 1 division, Meiosis 2 divisions
Functions: Mitosis growth and repair, Meiosis production of gametes

Question 18

Meiosis and genetic variation
Two main roles of meiosis?

Answer 18

Production of haploid gametes - This allows sexual reproduction to take place.
Creates genetic variation - This increases diversity, allowing natural selection to take place.

Question 19

What are the two events within mitosis that lead to genetic variation?

Answer 19

Crossing over (or recombination)
Independent segregation (or random assortment)

Question 20

Independent segregation occurs During metaphase I
What is it ?
How does it increase genetic variation?

Answer 20

It occurs when homologous pairs of chromosomes line up randomly
whether the paternal or maternal chromosomes appears on the left or right is completely random. As a result, which chromosomes end up in each daughter cell is also random.
Independent segregation increases genetic variation by producing gametes with different combinations of alleles

Question 21

Relationship between pairs of homologous chromosomes and possible chromosome combinations
Formula for possible chromosome combinations?

Answer 21

As pairs of homologous chromosomes increases, the possible chromosome combinations increases too
2^n where n is the number of pairs of homologous chromosomes
So an organism with 4 homologous pairs can produce 2^4 or 16 possible diff combinations of chromosomes in its daughter cells as a result of meiosis

Question 22

Crossing over when does it occur?
What is genetic recombination by crossing over?
How does this increase genetic variation?

Answer 22

Occurs during prophase one when each chromosome lines up with its homologousnpartner
chromatids from homologous chromosomes twist around each other. during this twisting, tensions are created and portions of the chromatids break off and these broken portions of each chromatid are exchanged - rejoin with the chromatids of its homologous partner
It is this way that new genetic combinations of maternal and paternal alleles are produced (this produces a new combination of alleles in each chromosome. )

Question 23

Random fertilisation occurs after meiosis
What is it?
How does it increase genetic variation?

Answer 23

As each gamete contains half the normal number of chromosomes (n), the resulting zygote cell contains the diploid number of chromosomes (2n).
Half of these chromosomes are from the father’s sperm cell and half are from the mother’s egg cell.
Gametes from male and female pair at random, combines different alleles and so provides even more variety.

Question 24

Formula for the different combinations of chromosomes in thee offspring procued as the result of sexual reproduction
(possible chromosome combinations after random fertilisation)

Answer 24

(2^n)^2 where n is the number of pairs of homologous chromosomes
squared to account for the combination of two gametes.
2^n x 2^n

Question 25

Genetic diversity and adaptation Define genetic diversity

Answer 25

The total number of different alleles in a population

Question 26

What is a population?

Answer 26

All of the organisms of a particular species that live in the same place and can interbreed

Question 27

What is a gene pool?

Answer 27

The total number of alleles in a particular population at a particular time

Question 27

How does higher genetic diversity affect natural selection?

Answer 27

The greater the genetic diversity, the more likely that some individuals within a population will survive an environmental change - as organisms with advantageous traits are more likely to survive, reproduce, and pass on their alleles, influencing the gene pool. The more successful an organism is at reproducing, the more likely its alleles will be passed on to the next generation, increasing the allele frequency.

Question 28

Define allele frequency

Answer 28

The number of times an allele occurs within the gene pool

Question 29

Describe the process of natural selection

Answer 29

-There is variation in characteristics within a species. -More genetic variation emerges within a population due to random mutations. -Individuals with alleles that code for traits that are advantageous for survival are more likely to reproduce. -These advantageous alleles are passed down to offspring. -Over time, these beneficial alleles become more common in the population. -This mechanism leads to populations becoming more adapted to their environment over generations.

Question 30

What are the 3 types of selection? (only first 2 are needed )

Answer 30

Directional selection Stablising selection (Disruptive selection) not required

Question 31

Directional selection - What is it and how does the graph shift

Answer 31

Favours extreme phenotypes, favours individuals that vary in one direction from the mean of the population - changes the characteristics of a population Shifts curve in the direction of the favoured extreme

Question 32

Define phenotype

Answer 32

A phenotype is the expression of the genotype and its interaction with the environment.

Question 33

What is stabilising selection? How does it shift the graph?

Answer 33

Stabilising selection is a type of natural selection in which the intermediate phenotype is favoured. - preserves characteristics of a population Narrows the curve

Question 34

Example of directional selection

Answer 34

Antibiotic resistance in bacteria - where the resistant bacteria survive and reproduce. -Some bacteria develop random mutations that provide resistance to antibiotics. -When antibiotics are used, only the resistant bacteria survive, while the others die off. -The resistant bacteria reproduce, passing on resistant alleles to their offspring. -Over time, the proportion of resistant alleles increases, leading to mostly resistant bacteria.

Question 35

Example of stabilising selection

Answer 35

Human birth weight, where infants of average weight have higher survival rates

Question 36

What is an adaptation?

Answer 36

Adaptations are inherited characteristics that enhance an organism's ability to survive and reproduce in its specific environment.

Question 36

What are 3 types of adaptations

Answer 36

Anatomical - changes to body structure- Physical structures, both internal and external. Behavioural - changes to actions- Activities and responses, whether inherited or learned. Physiological - changes to bodily processes- Internal biological functions.

Question 37

Examples of anatomical adaptations Anatomical adaptations are the physical attributes that aid an organism's survival.

Answer 37

- Shorter ears, thicker fur in arctic foxes compared to foxes in warmer climates Body coverings - Fur, feathers, scales protect organisms and support their survival. Camouflage - Organisms with colouration that blends into their environment are less likely to be detected. Mimicry - Some species imitate the appearance of more dangerous ones for protection. Teeth - The shape of an animal's teeth are adapted to its diet.

Question 37

Examples of behavioural adaptations Behavioural adaptations are actions that increase an organism's chances of survival and reproduction.

Answer 37

Hibernation or migration Defensive responses - For example, opossums play dead and rabbits freeze to avoid detection by predators. Courtship displays - For example, male scorpions dance to attract mates. Seasonal actions - For example, migration helps birds access resources year-round and hibernation helps bears conserve energy when food is scarce.

Question 38

Examples of physiological adaptations Physiological adaptations are internal processes that give organisms an edge in survival.

Answer 38

venom production Venom - Used by snakes to immobilise prey and by plants to deter herbivores. Antibiotics - Produced by bacteria to outcompete rival species. Water storage - Desert frogs can survive for over a year without a water source by storing water in their bodies.

Answer 39

In the lumen, lipids are broken down into glycerol, fatty acids and monoglycerides. Fatty acids and monoglycerides associate with bile salts, forming micelles. This makes them more soluble in water and they’re transported to the epithelial cell. There, they enter the cell by diffusion. Inside the epithelial cell, the products of lipid digestion are converted back into triglycerides by the endoplasmic reticulum. The endoplasmic reticulum and Golgi apparatus then combine the triglycerides with proteins and cholesterol to form chylomicrons. The chylomicrons are then packaged into vesicles and released into the lymphatic system via exocytosis.