Bio Unit 5 Variation and Selection Chp 1 Chromosomes, Genes, DNA Chp 2 Cell Division Chp3 Genes and Inheritance Chp 4 Natural selection and evolution Chp 5 Selective Breeding

OBJQ

What are the names of sex cell chromosomes for males and females, and what are the 22 pairs of chromosomes called?

Male sex cell chromosomes: XY

Female sex cell chromosomes: XX

22 pairs of chromosomes: Autosomes

OBJQ

Explain the terms gene and DNA

Gene: Small section of DNA that determines the particular feature inside the nucleus of a cell.

Or section of DNA that codes for a specific protein inside the nucleus of a cell.

DNA: Chemical that is the basis of inheritance of nearly all organisms.

OBJQ

Explain DNA in terms of structure and nucleotide

Structure: Double helix 

Made up of nucleotides: Sugar called deoxyribose (pentose sugar), phosphate and nitrogenous bases (Adenine, Thymine, Guanine and Cytosine)

Name 3 types of DNA replication.

Conservative, semi-conservative and dispersive

OBJR
Explain DNA replication

• The polynucleotide strands of DNA separate, carried by the helicase enzyme.

• Each strand acts as a template for the formation of a new strand of DNA. 

• DNA polymerase assembles nucleotides into 2 new strands according to base pairing rules. 

• Two identical DNA molecules are formed (semi-conservative)

Define template strand

Only 1 strand of DNA that codes for a specific protein in the cell.

Name 2 types of protein and an example.

Structural protein (Fibrous) → insoluble 

EXAMPLES: Keratin in skin, myosin in muscle

Functional protein (Globular) → soluble 

EXAMPLES: Haemoglobin, other hormones

Define codon/triplet code/amino acid coding

Sequence of three bases in the template strand of DNA codes for 1 amino acid.

What is the first step before protein synthesis?

Replication of the DNA

What are 4 differences between DNA and RNA?

DNA: Double helix 

          A-T, C-G 

          Longer and larger 

          Deoxyribose sugar 

RNA: Single-stranded

          A-U, C-G 

          Shorter and smaller

          Ribose sugar

What are 2 types of RNA and their functions?

mRNA → messenger RNA 

Function: Replication of DNA 

tRNA → transfer RNA 

Function: carries amino acids to ribosomes to make protein

OBJQ

Explain transcription of protein synthesis/central dogma

• Site: DNA 

• Part of the DNA unwinds and unzips, exposing the bases along the template strand. 

• The template strand of DNA forms a framework from which the mRNA molecule is formed

• RNA nucleotides line up alongside the template strand according to base pairing rule. 

• RNA nucleotides link up to form mRNA molecules. 

• It forms bonds between the ribose and phosphate groups (sugar-phosphate backbone) 

• RNA molecules leave DNA through the nuclear pore of the nucleus to the ribosome.

OBJQ

Explain the translation of protein synthesis/central dogma

• Site: Ribosome 

• The first tRNA to bind to the mRNA does so at the 'start codon', which

always has the base sequence AUG. This codes for the amino acid

methionine.

• Another tRNA brings along a second amino acid. The anticodon of the

second tRNA binds to the next codon on the mRNA.

• A bond forms between the methionine and the second amino acid.

• The first tRNA molecule is released and goes off to collect another amino acid.

• More tRNA molecules arrive at the mRNA and add their amino acids to the growing chain, forming a protein.

• At the end of the chain, a 'stop codon' tells the translation machinery that the protein is complete, and it is released.

OBJR

What is mutation?

Random changes in the DNA of a cell.

OBJR

Explain 4 types of DNA (Use “THE CAT HAS EYE AND EAR” to explain)

Duplication: Frameshift mutation 

Deletion: Frameshift mutation 

Substitution: Replacement 

Inversion

OBJR

State 2 ways of mutation

Body cell mutation (done after person dies)

Sex cell mutation (passed to offspring)

OBJR

What are mutation-causing agents and their examples?

Mutation-causing agents: mutagens 

EXAMPLES: Ultraviolet light, X-ray, Gamma ray, mustard gas, nitrous oxide, chemicals in cigarette smoke and tar.

 Name the protein that coils around DNA.

Histone

Explain chromosomes in male, female, sperm, egg and ribosomes.

Male: 22 pairs + XY

Female: 22 pairs + XX

Sperm: 22 pairs + X or 22 pairs + Y

Egg: 22 pairs + X 

RBC: 0 (as there is no nucleus)

What is the picture of all chromosomes called?

Karyotype

Define homologous pair and function.

Explain the number of chromosomes in diploid and haploid as well.

Homologous pair: a pair of matching chromosomes

Function: Carry genes for the same feature and are arranged in the same position along chromosomes (loci/locus)

Diploid: 46 chromosomes 

Haploid: 23 chromosomes

OBJQ

What is meant by the entire DNA of an organism?

Genome

OBJQ

What is meant by alleles?

Different forms of a gene

OBJQ 

What are the differences between mitosis and meiosis?

• Produce 2 daughter cells vs produce 4 daughter cells 

• For somatic (body) cells vs for gametes (sex cells) 

• Diploid→diploid vs Diploid→haploid

• For growth, repair and replacement of damaged cells (asexual) vs for sexual reproduction 

• Genetically identical vs genetic variation

Name stages in the cell cycle.

Interphase, nuclear division and cytokinesis (cell division)

Name stages involved in interphase and nuclear division

Interphase

-G1, S (replication), G2

Nuclear division 

-P (prophase)

-M (metaphase) 

-A (anaphase)

-T (telophase)

From the graph, how can we determine whether cytokinesis is mitosis or meiosis?

Original/initial chromosome numbers after cytokinesis → mitosis 

Half of the orginial/inital chromosome numbers after cytokinesis → meiosi

What are 2 things that dividing cells must do?

1. Copy each chromosome before dividing.

2. Must divide in a way that daughter cells also receive one extra pair of each chromosome.

OBJR

Explain briefly about PMAT?

Prophase: Duplication

Metaphase: Line up at the equator of the cell (in the equator plate) 

Anaphase: Chromosomes and their duplicates split toward opposite ends of the cell

Telophase: Cell divides into two.

How to calculate mitotic index?

Number of dividing cells/total number of cells

OBJQ

Explain meiosis in 3 steps.

• Provide genetic variations due to crossing over and independent assortment. 

There are 2 main events 

• First division (Meiosis I): One chromosome of each homologous pair goes to each daughter cell. 

• Second division (Meiosis II): Chromosomes separate into 2 parts, and one part goes to each daughter cell.

What are 2 types of variations?

Continuous variations (have a range from minimum, maximum and intermediate) are affected by both genetics and the environment. Display with a line graph.

Discontinuous variations (have separate categories) are affected by genetics only. Display with a bar graph.

Define phenotype, genotype, dominant, recessive, homozygous and heterozygous.

Phenotypes→physical features

Genotypes→genetic features

Dominant→expressed genes 

Recessive→not expressed genes 

Homozygous→homozygous dominant/recessive (TT, tt)

Hetrozygous→(Tt)

What is meant by codominance?

Codominance→when both alleles are expressed in their phenotypes

FAQ

What is meant by a dominant allele and a recessive allele?

Dominant allele→An allele that is always expressed in the phenotype of an organism.

Recessive allele→ An allele that is not always expressed in the phenotype of an organism

Name the blood type alleles for each blood type.

Type A→ IA IA, IA IO

Type B→IB IB, IB IO

Type O→IO IO

Type AB→IA IB

OBJQ

State the sex determination for males and females.

Male→44 autosomes + XY

Female→44 autosomes + XX

OBJQ + FAQ 

What is meant by polygenic inheritance?

Characteristic controlled by 2 or more genes working together.

Unit 5 Chp.4 Natural selection and Evolution

Explain how natural selection works (structure)

1. Variation within species is due to mutation 

2. Selection pressure favours the particular form of a species which has a selective advantage. 

3. Frequency of favoured form increases and reproduces to pass their genes to the next generation. (Selected for)

4. Frequency of less well-adapted species decreases and they die. (Selected against)

OBJQ + FAQ

What is meant by the term “struggle of the fittest”?

How well adapted an organisms to its environment, so that it is successful in reproduction.

What is natural selection in wasps and hoverflies?

Warning coloration

What are the adaptations of the polar bear?

• Thick fur (reduces heat loss) and white (camouflage in the snow)

• Wide, large paws (help with walking in snow and swimming) 

• Strong, muscular legs (swim continuously in the cold Arctic water for days)

OBJR

What is the term for antibodies?

Chemicals that kill or reduce the growth of microorganisms

What does natural selection lead to?

Evolution

OBJR

What is pesticide resistance in insects and an example.

When an insect has grown resistant and is no longer affected by the pesticide. EXAMPLE: DDT for mosquitoes

FAQ

What is another term for selective breeding and its defination?

Artificial selection. Breeding of only those individuals with desirable features.

Why do farmers use traditional selective breeding?

To increase crop yield

What is the earliest example of traditional selective breeding?

Cross-breeding of strains of wild wheat.

OBJR

What are the pros and cons of selective breeding?

Pros 

• Higher yields

• Resistant to certain diseases 

• Resistant to certain insect pest damage. 

• Hardier (survive in harsher climates or productive for long periods of years)

• Have a better balance of nutrients in crops 

Cons 

• Less genetically varied 

• Inbreeding 

• Slower than genetic engineering

What is the traditional cloning method for plants?

Taking cuttings

FAQ + OBJQ

Explain micropropagation in 4 steps.

• Tips of stems or side shoots are taken from parent plants (explants). 

• The explants are trimmed and surface-sterilised with ethanol or a bleach solution to kill microorganisms. Then, explants are transferred to sterilised agar medium containing nutrients and plant hormones for growth. 

• Then, explants are transferred to different agar medium with different balances of growth hormones to induce root formation. 

• Explants are transferred to a greenhouse and transplanted in compost

OBJR

Explain 5 advantages of propagating plants.

1. Produce any time of year

2. Genetically identical plants can be produced rapidly. 

3. Species that are difficult to grow can be propagated. 

4. Large numbers of plants can be stored easily.

5. Introduced into thousands of plants quickly after modifying a few plants.

FAQ + OBJQ

Explain the cloning process of Dolly the sheep in 4 steps and why biologists think there were unsuccessful attempts.

1. An unfertilised ovum from female sheep 1 is taken, and the nucleus is removed (enucleated). 

2. Mammary gland cells (udder cells) are removed from sheep 2 and cultured. 

3. One mammary gland cell is placed next to the enucleated cell, and the two cells are fused together using an electric current.

4. When it started to divide, they transferred the embryo into the uterus of a surrogate mother to complete its development. 

Biologists believe there are some problems because the genes transferred to the eggs are old genes.