Genetic Diversity - Mutations And Meiosis

Question 1

What is a gene mutation

Answer 1

A change in the sequence of base pairs in DNA molecule that may result in an altered polypeptide

Question 2

Why don’t most mutations alter the polypeptide produced

Answer 2

Genetic code is degenerate

Question 3

Deletion mutation explained

Answer 3

Mutation that occurs when a nucleotide is randomly deleted
Changes the amino acid it would have coded for
Has a knock on effect by changing the triplets further on in the code

Known as a frame shift mutation
Drastically changes the polypeptide produced

Question 4

Substitution mutation explained

Answer 4

A base is randomly swapped for a different base
Only changes the amino acid coded for by the triplet

Can be:
Silent
Missense
Nonsense

Question 5

What does a substitution silent mutation do

Answer 5

Mutation does not alter the amino acid sequence of the polypeptide because certain codons may code for the same amino acid

(Degenerate)

Question 6

What does a substitution missense mutation do

Answer 6

Mutation alters a single amino acid in the polypeptide chain

Question 7

Nonsense mutation substitution what is it

Answer 7

The mutation changes a base and thus an amino acid
This amino acid then codes for a stop codon changing the final polypeptide produced

Question 8

How do mutagenic agents pose a danger for mutations

Answer 8

There are natural mechanisms in cells that ensure the accuracy of DNA replication (eg. Proofreading of DNA in DNA replication)
When mutation rate rises above a normal level they are ineffective
Mutagenic agents raise this

Question 9

Examples of mutinogens

Answer 9

High energy radiation
Ionising radiation
Toxic chemicals

Question 10

What is non disjunctioning and what does it cause

Answer 10

When chromosomes fail to separate during meiosis
Gametes end up with one extra copy of a particular chromosome

Thus gametes end up with a different number of chromosomes than normal

If the abnormal gametes take part in fertilisation then a chromosome mutation occurs resulting in an abnormal amount of chromosomes than normal eg. Down’s syndrome

Question 11

What daughter cells does meiosis produce

Answer 11

Genetically different
Due to the process of independent assortment and crossing over

Question 12

What is independent assortment

Answer 12

The alleles of two or more different genes get sorted into gametes independently of one another

The allele a gamete received for one gene does not influence the allele received for another

This is because homologous chromosomes line up in random orientations at the middle of the cell (metaphase)

Question 13

What is crossing over

Answer 13

The process where a chromatid breaks during meiosis and rejoins to the chromatid of its homologous chromosome so that its alleles are exchanged

Question 14

Prophase 1 meiosis

Answer 14

DNA condenses and becomes chromosomes
DNA replication has already occured so we have 2 sister chromatids joined at the centromere
Arranged in homologous pairs
Crossing over of non sister chromatids occurs
Centrioles migrate to opposite poles
Nuclear envelope breaks down

Question 15

Metaphase 1 meiosis

Answer 15

The homologous pairs line up along the equator of the spindle with the spindle fibres attached to the centromeres

Question 16

Anaphase 1 meiosis

Answer 16

Homologous pairs of chromosomes are separated as microtubules pull whole chromosomes to oppposite ends of the spindle
centromeres do not divide

Question 17

Telophase 1 meiosis

Answer 17

Chromosomes arrive at opposite poles
Spindle fibres start to break down
Nuclear envelopes form around the two groups of chromosomes

Question 18

Cytokenisis 1 meiosis

Answer 18

Cell organelles are distributed between the 2 developing cells
In animal cells the cell surface membrane pinches inward creating a cleavage furrow in the middle of the cell which contracts dividing the cytoplasm in 2

In plant cells vesicles gather along the equator of the spindle. The vesicles merge with each other to form the new cell surface membrane and create a middle lame lame

Question 19

Is there an interphase between meiosis 1 and 2

Answer 19

No

Question 20

Prophase 2 meiosis

Answer 20

Nuclear membrane breaks down
Chromosomes condense
Spindles form at A riGHT ANGLE to the old one

Question 21

Metaphase 2 meiosis

Answer 21

Chromosomes line up in a single file along the equator of the spindle

Question 22

Anaphase 2 meiosis

Answer 22

Centromeres divide and individual chromatids are pulled to opposite poles
Creates four groups of chromosomes that have half the number of chromosomes compared to the original parent cell

Question 23

Telophase 2 meiosis

Answer 23

Nuclear membranes form around each group of chromosomes

Question 24

Cytokenisis 2 meiosis

Answer 24

Cytoplasm divides as new cells surface membranes are formed creating four haploid cells

Question 25

2 methods for how meiosis increases the genetic diversity of gametes produced

Answer 25

Crossing over and independent assortment result in different combinations of alleles in gametes

Question 26

What is crossing over

Answer 26

The process by which non sister chromatids exchange alleles

Question 27

What is the process of crossing over

Answer 27

In meiosis 1 homologous chromosomes pair up and are in close proximity Non sister chromatids can become tangled and cross over Cross over places stress on the DNA molecules A section of chromatid may break and rejoin with the chromatid on the other chromosome

Question 28

What is chiasmata

Answer 28

The crossing over points

Question 29

Why is the swapping of alleles in crossing over important

Answer 29

Results in a new combination of alleles on the two chromosomes

Question 30

Where is crossing over more likely to occcur

Answer 30

Further down the chromosome away from the centromere

Question 31

What is independent assortment

Answer 31

The production of 2 different combinations of alleles in daughter cells due to the random alignment of homologous pairs along the equator of the spindle The increases genetic variation

Question 32

Process of independent assortment

Answer 32

In prophase 1 Homologous chromosomes pair up In metaphase 1 Pulled towards equator Each pair can be arranged with either chromosome on top this is random Homologous pairs are then separated and pulled apart to different poles Thus the combination of alleles that end up in each daughter is dependant on how the chromosomes were lined up

Question 33

Formula of the number of possible chromosomal combinations resulting from meiosis =

Answer 33

2^n N= number of chromosome pairs

Question 34

What is formed when a male gamete fuses with a female gamete

Answer 34

A zygote

Question 35

Are zygotes ever genetically identical

Answer 35

No basically a 0 percent chance

Question 36

How do optical microscopes work

Answer 36

Light is directed through a thin specimen Light is focused on several different lenses so that the image is visible through the eyepiece Magnifying power can be increased

Question 37

Limitation of optical microscopes

Answer 37

Size of cells or structures may appear inconsistent in different specimen slides Because cells structures are 3d and have all been cut at different planes so we have different orientations of organelles

Question 38

How to distinguish between meiosis 1 and 2

Answer 38

In meiosis 1 only : homologous chromosomes pair up side by side If there are 2 cells forming In meiosis 2: no pairs of chromosomes 4 cells are forming

Question 39

Distinguishing features stage of meiosis 1

Answer 39

Prophase 1 = homologous pairs line up Metaphase 1 = homologous pairs side by side on equator of spindle Anaphase 1 = whole chromosomes are pulled to opposite poles with centromeres intact Telophase 1 = 2 groups of condensed chromosomes with nuclear membranes forming around them Cytokenisis = cytoplasm is dividing and 2 calls are forming

Question 40

Distinguishing features in each stage of meiosis 2

Answer 40

Prophase 2 - single chromosomes whole are visible\ Metaphase 2 - single whole chromosomes are lined up along the equator Anaphase 2 - centromeres divide and chromatids pulled to opposite poles Telophase - nuclei are forming around the 4 groups of condensed chromosomes Cytokenisis - cytoplasm is dividing and 4 haploid cells are forming

Question 41

How many daughter cells in meiosis vs mitosis

Answer 41

Meiosis has 4 instead of 2

Question 42

Does meioisis make genetically identical cells

Answer 42

No

Question 43

Why is diploid genetically identical cells important for mitosis function

Answer 43

Th body needs growth and cell replacement to occur - these cells need to perform the same function as the old ones so be genetically identical

Question 44

Why is 4 haploid cells important for meiosis function

Answer 44

Genetic variation within families and population Reduces the risk of inheriting genetic diseases

Question 45

What does a zygote contain

Answer 45

Male chromosomes with crossed over alleles and female chromosomes Resulting in a genetically diverse cell