3. Voice of the Genome (2)

Question 1

Features of Ovum

Answer 1

Follicle Cells, Zona Pellucida, Cortical Granules, Lipid droplets, plasma membrane, haploid nucleus

Question 2

Features of Sperm cell

Answer 2

Acrosome, haploid nucleus, head, middle piece, neck, mitochondrion, flagellum

Question 3

How are eggs specialised for function?

Answer 3

cytoplasm contains nutrients and a store of energy for the dividing zygote after fertilisation. (lipid droplets)
Zona pellucida (protective coating) hardens after fertilisation to prevent the entry of other sperm cells (polyspermy)
Follicle cells: protective coating
haploid nucleus - full set of chromosomes restored.

Question 4

How are sperm cells specialised for function?

Answer 4

A lot of mitochondria provide energy for the sperm cells to move. Acrosomes contains digestive enzymes which break down the zona pellucida and allow sperm to penetrate the egg

Question 5

Process of fertilisation

Answer 5

1. sperm head meets the zona pellucida and acrosome reaction occurs. enzymes from the acrosome digest the zona pellucida
2. Sperm head plasma membrane fuses with the cell membrane of the egg allowing the sperm nucleus to enter the egg cell.
3. Cortical reaction occurs - cortical granules in the ZP release enzymes that cause the zona pellucida to harden.
4. The nuclei fuse and a full set of chromosomes is restored, forming a diploid zygote.

Question 6

Location of genes on a chromosome

Answer 6

locus / loci

Question 7

Linkage and chromosomes

Answer 7

The closer the loci of the genes on the chromosome, the more closely linked they are because they are less likely to be separated during recombination in meiosis

Question 8

recombination in meiosis

Answer 8

exchange of genetic material between paternal and maternal chromosomes which leads to genetic variation and a combination of traits found in either parent.

Question 9

Autosomal linkage

Answer 9

alleles on the same autosomal chromosome/ gene are more likely to be inherited together

Question 10

autosomal chromosome

Answer 10

non-sex chromosome

Question 11

Sex linkage/ why are men more likely to have disorders like haemophilia

Answer 11

Some genes are sex linked because they occur on the X chromosome.
Y chromosome is smaller than the X chromosome therefore they only need one copy for the allele to be expressed.

Question 12

Process of meiosis 1

Answer 12

Nucleus of original parent is diploid and contains two sets of chromosomes. Chromosomes replicate and the homologous pairs of chromosomes are split up to produce two haploid nuclei.
Each chromosome still consists of two chromatids

Question 13

Process of meiosis 2

Answer 13

chromosome separates to produce four haploid nuclei. Each chromosome consists of a single chromatid

Question 14

What does meiosis result in

Answer 14

genetic variety -> results in production of gametes

Question 15

Why is having genetically different offspring advantageous

Answer 15

natural selection - genetic variation = species can adapt to new environments due to variation which gives them a survival advantage.

Question 16

How does meiosis ensure genetic variation

Answer 16

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

Question 17

crossing over

Answer 17

sections of DNA are swapped over between non sister chromatids at the chiasma resulting in the creation of a combination of new alleles, increasing genetic variation

Question 18

when does crossing over occur

Answer 18

Meiosis 1 - homologous chromosomes pair up and are in close proximity to each other (a.k.a. bivalents) - non sister chromatids cross over and get entangled at the crossing point the chiasmata.

Section of chromatid breaks off and re-joins with the chromatid from the other chromosome

Question 19

Where is crossing over more likely to occur?

Answer 19

Further down the chromosome away from the centromere.

Question 20

independent assortment

Answer 20

various combinations of ways maternal and paternal chromosomes can be distributed between the two daughter cells

Answer 21

For two bivalents there are two possible orientations.
The pairs line up along the equator of the spindle independently of eachother

At the end of meiosis 2 each orientation gives two types of gamete - resulting in four types of gamete altogether

Question 22

mitosis

Answer 22

process of cell division resulting in two genetically identical daughter cells

Question 23

role of mitosis

Answer 23

identical daughter cells are used for growth, repair and asexual reproduction

Question 24

Mitosis stages

Answer 24

PMAT - prophase metaphase anaphase telophase

Question 25

Interphase

Answer 25

stage where the cell prepares for mitosis - growing and replicating chromosomes preparing for cell division

Question 26

G1 stage

Answer 26

cell grows in size and synthesises mrna and proteins required for DNA synthesis. DNA replicates

Question 27

S stage

Answer 27

the cell synthesises a complete copy of the dna in its nucleus

Question 28

G2 stage

Answer 28

Cell prepares to divide, replicating organelles for a full set in each new cell

Question 29

Prophase

Answer 29

chromosomes condense and nuclear envelope disintegrates

Question 30

Anaphase

Answer 30

duplicated chromosomes separate and move towards the opposite poles of the cell by spindle fibres retracting

Question 31

Metaphase

Answer 31

chromosomes align at the equator of the cell, spindle fibres attach to the chromatids

Question 32

Telophase

Answer 32

chromosomes are now on opposite sides of the cell and nucleus reforms. forming two identical nuclei.

Question 33

Cytokinesis

Answer 33

cytoplasm pinches in on itself to form two daughter cells

Question 34

stem cell

Answer 34

undifferentiated cells

Question 35

multipotency

Answer 35

cells which can differentiate into many different types of cell

Question 36

totipotency

Answer 36

cells which can differentiate into every type of specialised cells including placental cells

Question 37

pluripotency

Answer 37

cells that can differentiate into many types of specialised cells but not placental cells

Question 38

uses of stem cell therapies

Answer 38

embryonic stem cells (umbilical cord), adult stem cells (bone marrow) are used to treat Diabetes, multiple sclerosis, Parkinson's, replace damaged tissues like nerve tissue in spinal cord injuries.

Question 39

Ethics behind use of stem cells

Answer 39

For: Stem cells ca save many lives and improve the quality of life for many people. Against: Embryos are killed in the process of embryonic stem cell extraction risk of infection potential to become cancerous

Question 40

Differential gene expression step 1+2

Answer 40

1) stimulus acts on unspecialised cells 2) activator and repressor molecules bind to promoter regions on the DNA sequence, so some genes are switched on and become active, whereas other genes are switched off 3) active genes are transcribed to produce RNA

Question 41

Differential gene expression step 4+ 5

Answer 41

4) mRNA is translated on ribosomes and used to produce proteins. 5) these proteins modify the cell by determining cell structures and controlling cell processes

Question 42

Differential gene expression step 6

Answer 42

6) Changes to the cell by these proteins causes the cell to become specialised - these changes are permanent as they are difficult to reverse.

Question 43

Lac Operon (lactose absent)

Answer 43

Lac repressor protein binds to the operator region. The presence of this protein means that RNA polymerase is unable to bind to the promoter region. Transcription of the structural gene does not take place and therefore no lactase enzyme is synthesised.

Question 44

Can prokaryotes have an operon?

Answer 44

Yes - they can form an operon - a cluster of genes controlled by the same promoter and transcribed together. example: lac operon in bacteria

Question 45

Lac Operon (Lactose present)

Answer 45

Lactose binds to the binding site on the repressor protein - changing its shape, making it unable to bind to the operator site RNA polymerase is able to bind to the promoter region and transcription takes place. all 3 structural genes (lac Z, Y, A) are translated

Question 46

Why is the lac operon important

Answer 46

prevents waste of energy - molecules that are not needed are not transcribed and translated, saving energy.

Question 47

Phenotype

Answer 47

observable characteristics of an individual resulting from the interaction between the genotype and the environment

Question 48

Epigenetics

Answer 48

modifications that alter gene activity without changing the DNA sequence. can occur as a response to changes in environment

Question 49

Operon

Answer 49

cluster of structural genes that are transcribed together

Question 50

How do transcription factors control the expression of genes?

Answer 50

(1) gene expression can be controlled by altering the rate of transcription of genes. (2) This is controlled by transcription factors - proteins that bind to DNA and activate/deactivate genes by increasing/ decreasing rate of transcription

Question 51

activators

Answer 51

increase the rate of transcription

Question 52

repressors

Answer 52

decrease the rate of transcription by preventing rna polymerase from binding and stopping transcription

Question 53

Transcription factors in eukaryotes vs prokaryotes

Answer 53

Eukaryotes- transcription factors bind to specific dna sites near the start of their target genes. Prokaryotes - control of gene expression involves transcription factors binding to operons

Question 54

DNA Methylation

Answer 54

addition of a methyl group - can cause activation/ inactivation of chromatin. Represses a gene The group binds to the CpG site (between cytosine and Guanine) Increased methylation changes the DNA structure so that the proteins and enzymes needed for transcription can't bind to the gene so the gene is not expressed.

Question 55

DNA acetylation

Answer 55

addition of an acetyl (COCH3) group - activates chromatin and allows transcription acetylated - chromatin is less condensed - proteins involved in transcription can bind to the DNA, activating genes

Question 56

What happens when acetyl groups are removed?

Answer 56

acetyl groups removed from the histone = chromatin becomes highly condensed and the genes are repressed as transcription proteins can't bind to them

Question 57

Histone modification

Answer 57

DNA Acetylation - Histones are proteins that dna wraps around to form chromatin. How condensed chromatin is affects the accessibility of the DNA and whether it not the proteins and enzymes needed for transcription can bind to it.

Question 58

How are epigenetic changes passed on following cell division

Answer 58

1) Following cell replication, epigenetic changes to its gene expression is passed on to daughter cells 2) epigenetic changes passed on = genes that were activated/ deactivate in the original cell will be activated/ deactivated in the daughter cells 3) if an epigenetic change occurred in response to a change in environment, daughter cells are equipped to deal with that change in environment

Question 59

Monogenic inheritance

Answer 59

Characteristics influenced by one gene only.

Question 60

Discontinuous variation + examples

Answer 60

variation caused by monogenic inheritance. Characteristics influenced by one gene only. Example - eye colour

Question 61

Continuous variation + examples

Answer 61

Variation caused by polygenic inheritance. (multiple genes at different loci) and also environmental factors Examples: Height - also influenced by nutrition Lung cancer - presence of proto-oncogenes

Question 62

Polygenic inheritance

Answer 62

Several genes at different loci are involved in determining a characteristic

Question 63

what is fertilisation?

Answer 63

fusion of the nuclei from a male gamete and a female gamete

Question 64

sister chromatids

Answer 64

identical copies formed by the DNA replication of a chromsome. both copies are joined by a common centromere

Question 65

chromatids

Answer 65

one of the two identical halves of a chromosome that has been replicated in preparation for cell division

Question 66

chromosome

Answer 66

package of DNA containing a part of genetic material of an organism. 23 pairs of chromosomes, 46 altogether in an adult human

Question 67

homologous pair of chromosomes

Answer 67

Two chromosomes in a pair - one inherited from mother and the other one from the father