Bio Topic 3 - Genetics

sexual reproduction

The process involving the fusion of the nuclei of two gametes to form a zygote (fertilised egg cell) and the production of offspring that are genetically different from each other.

gamete

sex cell

How are gametes different from normal cells?

They have a haploid nucleus and contain one copy of each chromosomes compared to two copies of each chromosome in normal cells(23 chromosomes compared to 46)

Zygote

a fertilised egg cell that is diploid

disadvantage of sexual reproduction

time/effort to find a mate

difficult for isolated members to reproduce

takes longer than asexual reproduction

advantage of sexual reproduction

genetic variation

the species can adapt to new environments due to variation, giving them a survival advantage

Disease is less likely to affect population due to variation.

What is asexual reproduction?

The process resulting in genetically identical offspring being produced from one parent

Why are the offspring from asexual reproduction genetically identical?

Only 1 parent is needed, so there is no fusion of gametes and therefore no mixing of genetic information

How do bacteria reproduce?

binary fission (asexual)

What is a quick is a cycle of asexual reproduction?

Rapid reproductive cycle

Advantages of asexual reproduction

1. no need for a mate; can live isolated

2. numerous offspring quickly(much faster than sexual)

3. no energy needed for maintenance of reproductive structures

4. Energy and time efficient

4. good with stable environment as genetic variation isn't necessary if the parent cell is thriving in a certain environment.

Disadvantages of asexual reproduction

- very little genetic variation among offspring.

- Can result in extinction of species if the environment changes(massive vulnerability to change)

- Disease likely to affect the whole population due to lack of variation

Meiosis

Cell division that produces reproductive cells/gametes in reproductive organs of sexually reproducing organisms

meiosis vs mitosis differences

- meiosis has 2 cell divisions, mitosis only one

- in meiosis homologous chromosomes pair up on cell's equator, in mitosis homologous chromosomes never pair up

- after pairing in meiosits sections of dna are swapped between pairs which doesn't happen in mitosis

- After anaphase 1 of meiosis sister chromatids are still paired, in anaphase in mitosis, sister chromatids are separated

- meiosis results in 4 haploid cell, mitosis results in 2 diploid cells

- meiosis cells are genetically different but mitosis is genetically identical

In the first cell division (meiosis I),

Homologous chromosomes separate into 2 cells.The chromatids are not separated

second round of meiosis

chromatids separated , one copy of each chromosome is found in 1 in 4 genetically daughter cells

similarities of mitosis and meiosis

genetic material is duplicated

chromatid is condensed to form chromosomes , prophase

microtubules emanating from centrioles are involved in dividing the genetic material, anaphase and metaphase

What is the monomer that makes up proteins?

amino acids

Why are all siblings not identical?

Gametes of both parents have a mixture of chromosomes which combine to produce a unique combination

Codon

three-nucleotide sequence on messenger RNA that codes for a single amino acid

Anti-codon

group of three bases on opposite end of a tRNA molecule that are complementary to an mRNA codon

Polypeptide

chain of amino acids

Translation

decoding of an mRNA message into a polypeptide chain

What type of cell division occurs in the zygote as it grows?

mitosis

How is a polypeptide formed?

mRNA moves through the ribosome 3 bases at a time. Each codon codes for one amino acid.The tRNA with the anti-codon sequence matching the codon comes to the ribosome with the specific amino acid.The amino acids are added to the growing chain one by one.

Which cells undergo meiosis?

germ cells

Genome

all of an organism's genetic material

DNA double helix structure

complementary base pairs joined by hydrogen bonds

sugar phosphate backbone

gene

sequence/section of DNA that codes for a protein and thus determines a trait

What shape is a DNA molecules?

double helix

DNA sequence

order of nucleotides in a strand of DNA

Nucleotide

Building block of DNA

What makes up a nucleotide?

pentose sugar(deoxyribose/ribose), phosphate, nitrogen base

DNA is a _______ made from many ____________

polymer

monomers(nucleotides)

DNA base pairs

Adenine and Thymine, Cytosine and Guanine

Bonds that form between nucleotides/base pairs

(weak)hydrogen bonds

Why does only A bind to T and C to G?

COMPLEMENTARY BASE PAIRING(learn the phrase)

How many strands make up a DNA molecule?

2 strands

Method of DNA extraction from cells

1.Mash fruit or veg in a beaker and add 100 cm3 of water to it

2.Add salt to the 100 cm3 beaker

3.Add detergent to the solution and gently stir until salt dissolves

4.Then, filter into a test tube and then measure 10cm3 of the filtrate into a boiling tube

5. Add two drops of protease solution

6. Add ice cold ethanol by pouring it down the side of the test tube.The amount of ethanol added should not exceed volume of filtrate

7. A white precipitate has formed which can be extracted out using a glass rod

purpose of salt in extracting DNA from cells

helps clump the DNA together so it can be extracted

Why is detergent needed when extracting DNA from cells?

breaks down membrane around the cell and nucleus

Purpose of filtering the mixture (in DNA extraction)

helps isolate DNA by removing any insoluble bits from the mixture

purpose of protease in extracting DNA from cells

breaking down proteins

What is ethanol needed for when extracting DNA from cells?

Precipitating the DNA as it is insoluble in ethanol

Transcription

(genetics) the organic process whereby the DNA sequence in a gene is copied into a strand of mRNA

What enzyme makes mRNA on transcription

RNA polymerase

What might happen to a protein if there is a mutation?

Shape may change and this may affect its function

How does RNA polymerase separate DNA(transcription)?

bonds to non-coding site in front of the DNA and breaks hydrogen bonds of DNA

How is the gene transcribed to mRNA in transcription?

RNA binds to a non-coding region of DNA in front of the gene and separates the two strands of DNA by breaking the hydrogen bonds. The RNA polymerase moves along the template strand to make the mRNA strand by adding complementary RNA nucleotides.

Where does the mRNA go after transcription?

leaves the nucleus through nuclear pores, goes to the cytoplasm, binds to a ribosome to be read.

nucleotide in RNA instead of thymine

uracil which pairs with adenine

The sugar in RNA is _____, the sugar in DNA is _______

ribose and deoxyribose

ribose and deoxyribose chemical differences

ribose has one more oxygen, a hydroxide

mRNA sequence of the template strand AATCCAGTGCCA

UUAGGUCACAAU

Why must DNA be transcribed into mRNA before being translated into a protein?

DNA is too big to pass through the nuclear pores

What does mRNA stand for?

messenger ribose nucleic acid

What happens in translation, details?

mRNA enters the ribosome and the ribosome reads the mRNA one codon at a time. A tRNA molecule has an anticodon that matches the codon on mRNA. Each tRNA molecule carries a specific amino acid. The amino acids on certain tRNA molecules join together with peptide bonds in between them to make a polypeptide chain, when the tRNA molecules match to their corresponding part of the mRNA. Then, the polypeptide chain folds up to make a specific shape

Where are tRNA molecules found?

cytoplasm

Structure of a tRNA molecule

anticodon on one end which is complementary to the triplet of bases(codon) on the mRNA. On the other end is a specific amino acid

How many codons are needed to make a polypeptide with thirty amino acids?

30

A triplet of mRNA bases that code for a particular tRNA molecule is called a:

codon

Mutation

change in a sequence of bases of DNA of a gene that affects genetic information

Mutation consequences in non coding DNA of gene

RNA polymerase may not bond to dna/find it difficult to bond to translate dna into mRNA, decreasing the amount of mRNA and protein produced, or some mutations may also make binding better and increase the mRNA and protein produced

Mutation consequences in coding DNA of gene

The gene may code for a different sequence of amino acids.This would affect the (highly specific) shape and type of protein produced, which would subsequently impact its function, this could be either increasing decreasing or stopping protein activity. This in turn could also affect the phenotype of the organism

genetic code of proteins

How the order of bases results in amino acids being joined in particular order to make a protein

Genotype

the combination of alleles that control each characteristic

allele

different versions of the same gene

What are alleles caused by?

mutations

Phenotype

An organism's physical characteristics, or visible traits.

Mendel's pea experiment

First experiment:

Tall plus short pea plants made 4 tall pea plants

Second experiment:

Tall plus tall pea plants made 3 tall and 1 short pea plants.

Conclusion: the height of the offspring trees was a result of 'hereditary units' being passed down from parents. The hereditary unit for tall plants (T) was dominant over the hereditary unit for short plants (t) - the latter was recessive.

Mendel came to the conclusion that all characteristics were determined by hereditary units that were either dominant or recessive and were passed down from parent to offspring

Given that we have two copies of each chromosome, what can be said about the number of copies of genes and alleles that we have?

As we have two copies of each chromosome, we have two copies of each gene and therefore two alleles for each gene

One of the alleles is inherited from the mother and the other from the father, and these alleles do not have to correspond to the same characteristic

Alleles can either be:

dominant or recessive

dominant allele

An allele whose trait always shows up in the organism when the allele is present/only needs to be inherited from one parent in order for the characteristic to show up in the phenotype

recessive allele

An allele that is hidden whenever the dominant allele is present. A recessive allele needs to be inherited from both parents in order for the characteristic to show up in the phenotype.

How to distinguish between dominant and recessive allele on a punnett square

capital letter - dominant allele

lowercase letter - recessive allele

homozygous dominant

2 copies of the dominant allele

homozygous recessive

2 copies of the recessive allele

heterozygous

two alleles of a gene are different i.e. 1 dominant and 1 recessive

Why can't we always determine the genotype based on the phenotype

genotype could either be dominant homozygous or dominant heterozygous

How to draw punnett squares

1.Determine the parental genotypes

2.Select a letter that has a clearly different lower case, for example, Aa, Bb, Dd

3.Split the alleles for each parent and add them to the Punnett square around the outside

4.Fill in the middle four squares of the Punnett square to work out the possible genetic combinations in the offspring

female gamete chromosomes

XX

Male gamete chromosomes

XY - the Y is responsible for the sex of kid

List the possible genotypes and therefore the sex when female and male chromosomes

XX,XY,XY,XX - therefore the chances of offspring being male or female is 50 50

carrier

refers to a person that carries a recessive allele that would express a recessive trait. The person doesn't have the trait themselves(thus their genotype is heterozygous) but there is a possibility of them passing it on to offspring

What kind of inheritance do Punnett squares show?

Monohybrid inheritance

Why is monohybrid inheritance not practical?

Most characteristics are defined by the interaction of multiple genes, not just 1, for example eye colour (polygenic inheritance)

continuous variation

when there are very many small degrees of difference for a particular characteristic between individuals and they are arranged in order and can usually be measured on a scale

discontinuous variation

inheritance pattern in which traits are distinct and are transmitted independently of one another

2 ways in which phenotypic variation can be caused

Genetic

Environmental

What kind of phenotypic variation is continuous data caused by? GIve an example

a mixture of genetics and environment, i.e whilst height is genetic, poor diet can limit growth.

What kind of phenotypic variation is discontinuous data caused by? GIve an example

genetics, for example no environment will have any effect on blood type which is purely genetics

Molecule of DNA is a...

chromosome

How is the shape of a protein determined?

By the chain of specific amino acids

3 different ways a mutation can affect base sequence and its knock on effects

1. Deletion - a random base is removed from the sequence - this affects the base triplets that come after the mutation affecting the whole amino acid chain as now multiple amino acids will be altered

2. Insertion - a new base is randomly inserted into the base sequence - this impacts the base triplets later on in the sequence - having knock on effects as it affects the whole amino acid chain as now multiple amino acids will be altered

3. Substitution - a base in the sequence is randomly swapped for a different base - this only alters 1 amino acid triplet of base so it doesn't have any knock on effects

How can the frequency of mutations increase?

Although it is mostly random,it can be increased by:

1. Exposure to UV/X ray/Gamma rays

2. chemicals i.e tar in tobacco

results of mutations on enzyme activity and structural proteins

potentially decreased as shape affected thus active site shape changes thus substrate cannot fit into active site

structural proteins such as collagen can lose strength if shape changes

How can mutations be beneficial?

A mutation can lead to a new allele and thus a new phenotype.

This can provide survival advantages

How can mutations be dangerous

Can lead to harmful changes which have devastating effects on human i.e. sickle cell anaemia