Biology

Topic 3

define asexual reproduction

1 parent and relies on mitosis

define sexual reproduction

2 parents, relies on meiosis

advantages of asexual reproduction

rapid and no need to find a mate

Disadvantages for asexual reproduction

no variation so if conditions change they will all die

advantages of sexual reproduction

variation so keeps the option for adaption open

disadvantages of sexual reproduction

slow and need to waste resources on finding a mate

what is a zygote

fertilised egg

genome

complete DNA of an organism

meiosis

1 diploid parent cell copies its DNA and ribosomes to then split twice. Creates 4 genetically different gametes.

mitosis

interphase-copy

prophase-nucleus

metaphase-middle

anaphase-apart

telophase-nucleus

cytokinesis-split

4 DNA bases and which one they are complementary to

A--T G---C

Why are DNA called complementary?

The weak hydrogen bonds holding them together. G has 3 so can only link up to C whereas A only has 2 so has to link to T.

The backbones of DNA are called

sugar phosphate backbone

A nucleotide is

The phosphate group connected to the sugar pentose connected to the nitrogenous base.

DNA extraction method (and why each one is important)

Crush up sample (to increase the surface area)

Add salt and detergent (to break up the cell and nucleus membrane allowing the DNA out)

Place it in a water bath ( to speed up the reaction)

Filter (to remove debris)

Add ice cold ethanol ( to precipitate the DNA making it visible)

What is 1 protein made of?

3 amino acids

Where are proteins made?

In the cells ribosomes

The function of DNA polymerase:

Copy over the DNA code

Describe transcription

Attach- RNA polymerase attaches to the non-coding site of DNA

Unzip- It unzips the DNA

Copy- mRNA goes in, copies the DNA code while replacing the T into a U

Leave- mRNA leaves via the nuclear pore

Describe Translation

Attach- in the ribosome are tRNA codons with an amino acid attached

Match-the tRNA matches to part of the RNA codon

Bond- The amino acid bonds together. The codon moves on to find another amino acid.

What is a triplet of bases called?

A triplet codon

How does mRNA differ to DNA?

mRNA is single stranded, uses U whereas DNA is double strand and uses T

Does a mutation always change the amino acid produced by it’s code?

There are multiple codes for 1 amino acid so it may not even change the end product (the protein)

What is a mutation?

A mistake when copying over code (usually happens in protein synthesis)

What happens after the mutation?

The protein it codes for may change producing the wrong one, too little or even to much of it. May affect the active site shape therefore causing the substrate not to fit so the product can not be formed.

What can happen if the mutation is in the non-coding site of the DNA?

The RNA polymerase might not be able to attach to it.

What was meant by the term blended characteristics?

A theory that an offspring’s characteristics are a definite average of it’s parent’s traits.

Who disproved the theory of blended characteristics?

Gregor Mendel

Gregor Mendel’s investigation on pea plants:

Got 1 pure bred tall pea plant and 1 pure bred short pea plant

Crossed them

1st generation was all tall hiding the recessive gene (short) behind the dominant one (tall) and had a phenotype of Pp

Crossed 2 of these

2nd generation was 75% tall and 25% short revealing the hidden characteristic.

How did Mendel control his experiment?

Paintbrush for fertilisation so he knew which plant fertilized which.

Paper bag over the top of the flower to stop further fertilization from other plants.

What does allele mean?

2 forms of the same gene

What is meant by phenotype?

Physical characteristics we inherit

Genotype

2 genes we inherit

What does homozygous mean?

having 2 of the same genes

What does heterozygous mean?

Having 2 different genes

Probability of having a boy : girl

1:1

Chromosomes a boy has

XY

Chromosomes a girl has

XX

How can 2 brown eyed parents have a blue eyed child?

If they are both carriers of the blue eyed gene (Bb genotype).

What are the 3 alleles that control blood groups?

I^a I^b I^o

4 blood groups

A . AB . B . O

How can a person get blood group O

If they inherit allele O from both parents.

What does codominant mean?

2 alleles that are both expressed in the phenotype, neither one takes presidency.

If a person has a blood type B what is their genotype?

AB or BO or BB

Why are males more affected by sex linked disorders?

They only have 1 X chromosome so whichever gene lands on it is the one that will be expressed.

What is the human genome project?

Scientists across the world decoded the full human genome → 3.3 million base pairs

What can scientists do with the information from the genome project?

Gene therapy, find things like breast cancer, tell us who the parent is, find diseases so we can take preventative action.

What are the disadvantages of the human genome project?

May cause stress/ anxiety. May make it harder to get insurance.

What is variation?

Small changes/ differences between organisms of the same species.

What are the 2 causes of variation?

Environmental and genetic

What is an example of a genetic cause and an environmental cause?

Genetic → Blood group and Environmental → Scars

Example of discontinuous variation

→ caused by genetics only →bar chart →Blood group, Tongue roller →falls into distinct groups

Continuous variation examples

→ Normal distribution curve → Range of values → Arm span, height, leaf length → Caused by both environmental and genetic