Inheritence, variation and variation

how many pairs of chromosomes do humans contain

23 pairs in the nucleus

meiosis

formation of four non identical ceels from one cell

mitosis

formation of 2 identical cells from one cell

type of cell where chromosomes aren’t paired

gametes

what type of cell division produces gametes

meiosis

what are pollen and egg cells an example of

gametes

sexual reproduction

• involves fusion of male and female gametes- fertilisation

• mixing of genetic info- offspring has genetic info from both male and female offspring

• see variation in offspring as every gamete is diff

how many chromosomes do gametes have

23 chromosomes

how many chromosomes does a normal cell have

23 pairs and 46 chromosomes

asexual reproduction

• only one parent

• doesnt include gametes or fertilisation

• offspring are all genetically identical-

• only involves mitosis not meiosis

reproduction of plants

• plants reproduce by growing tiny buds

• buds drop off and grow into new plants

• offspring are genetically identical to parent

where does meiosis take place?

in reproductive organs- testes in males and ovaries in females

meiosis

• formation of four non-identical cells from one cell

• human cells contains 23 pairs of chromosomes whilst gametes contain 23 single chromosomes

• involves 2 cell divisions

process of meiosis

1. copies of the genetic information are made

2. the cell divides twice to form four gametes, each with a single set of chromosomes

3. gametes are haploid

4. all gametes are genetically different from each other

what do sexual reproduction produce?

• fusion of gametes- fertilisation

• cell now has normal no. of chromosomes- restored

• after fertilisation, the new cell divides by mitosis producing a clump of identical cells (embryo)

advantages of sexual reproduction

• produces a variation in offspring

  • means if enviroment changes species is more likely to survive

  • different characteristics (survival advantage)

  • variation decreases chance of the whole species becoming extinct

• selective breeding

  • type of reproduction mixes the genetic info from 2 organisms

  • organisms with different desirable characteristics can be bred to produce offspring with even more desirable characteristics

  • speeds up natural selection

  • e.g. to increase food production by breeding 2 animals with lots of meat

advantages of asexual reproduction

• only one parent is needed

• uses less energy and is faster as organisms don’t need to find a mate

• in favourable conditions lots of identical offspring can be produced

organisms that reproduce asexually and sexually

• malarial parasites

• some fungi

• some plants

reproduction of malarial parasites

- they cause malaria, spread by mosquitoes and transferred to humans through a bite

• reproduce sexually in the mosquito

• reproduce asexually in the human host (in liver and blood cells)

reproduction of some fungi

- many species can undergo both types pf reproduction, releasing spores which land and become fungi

• spores produce asexually are genetically identical

• spores are produces sexually when conditions change, in order to increase variation and avoid extinction

reproduction of some plants

• many plants reproduce sexually using pollen, which must reach the egg cells in female parts of another flower- pollination and forms seeds

• strawberry plants reproduce asexually as they produce runners- new identical plants grow of runners

• daffodils reproduce asexually- grow from bulbs- new bulbs can grow from the main one, producing new identical plant

- advantageous in plants as it means they can reproduce even if the flowers have been destroyed by frost or other animals

DNA

• genetic material in the nucleus of a cell- chemical

• is a polymer made up of 2 strands which wrap around each other like a rope- double helix

gene

• small section of DNA on a chromosome

• triplet of bases that codes for a specific protein

• each gene codes for a particular sequence of amino acids- together a chain of amino acids can join together to make a protein

genome

• all the genes coding for all the proteins within an organism

• entire genetic material so human genome is what makes us human

benefits of the human genome

• help us search for genes that are linked to a certain disease- increase risk

• helps us understand and to treat inherited disorders

• can use genome to trace human migration patterns from the past- ancestry

DNA structure

• polymer made from 4 different nucleotides

• each nucleotide consists of a common sugar and phosphate group with one of four different bases attached to the sugar

the bases in dna

• A, C, G, T

• 4 different nucleotides

nucleotide

• consists of a common sugar and phosphate group with one of four different bases attached to the sugar

  • the phosphate group and sugar molecule never change

dna strands

• are complementary- same bases always pair on opposite strands

what is C attached to on dna strands

linked to G

what is G attached to on dna strands

linked to C

what is T attached to on dna strands

linked to A

what is A attached to on dna strands

linked to T

what is DNA made up of?

small parts called nucleotides

chromosomes

structures made up of long molecules of DNA found in nucleus

complementary base pairing

• A only links to T

• G only links to C

code of DNA

order of different bases

how many groups of bases code for an amino acid

3

how many times of amino acids are there

20 types- so order of bases in DNA determine which proteins are produced

proteins

polymers of amino acids

what determins shape of protein

specific order of the amino acids

what determines the functions of amino acids?

specific order of amino acids

what determines the order of amino acids in a protein

sequences of bases in the gene

how does the cell read the dna sequence

as triplets of bases

protein synthesis

process of producing a protein from DNA- if a gene is coded to make a protein, it has been expressed

protein synthesis process- complicated

1. DNA contains the genetic code for making a protein, but it cannot move out of the nucleus as it is too big.

   2. The two strands pull apart from each other, and mRNA nucleotides

   (messenger RNA: a different type of nucleotide) match to their

   complementary base on the strand.

   3. The mRNA nucleotides themselves are then joined together, creating a new strand called the mRNA strand. This is a template of the original DNA.

   4. The mRNA then moves out of the nucleus to the cytoplasm and onto

   structures called ribosomes.

   5. At the ribosomes, the bases on the mRNA are read in threes to code for an amino acid (the first three bases code for one amino acid, the second three bases code for another etc).

   6. The corresponding amino acids are brought to the ribosomes by carrier molecules.

   7. These amino acids connect together to form a protein.

   8. When the chain is complete the protein folds to form a unique 3D structure.

protein synthesis process- simplifies

1. transcription- the base sequence of genes is copied into a complementary template molecule- mRNA (messenger)- single stranded molecule- passes out of molecule and into cytoplasm

2. transalation- mRNA attaches to a ribosome molecule, amino acids aew now brought to the ribosomes on carrier molecules- tRNA (transfer)- ribosomes then read triplets of bases and use it to join together the correct amino acids in the correct order- once done, protein chain folds into unique 3d structure

functions of proteins

• enzymes

• hormones

• structurla protein

functions of proteins- enzymes

biological catalysts that speed up the rate of reaction

functions of proteins- hormones

chemical messengers that send signals around the body

functions of proteins- structural proteins

strong proteins in order to form structures, such as collagen

mutations

changes to a base/genetic codes

how often do mutations occur

happens all the time- spontaneous

when do mutations have no effects

• sometimes different base triplets can encode for the same amino acids so won’t have an effect

what happens when a mutation changes shape of protein

• dramatic effects- active site of enzyme may change so won’t attach to specific substrate

• e.g. if structural protein changes shape- it may lose its strength

what do chromosomes also contain

non coding parts of DNA- regions that switch gene on or off so tell gene when to produce a protein

what can mutations lead to

• cancer- uncontrolled cell division

where is DNA found??

in chromosomes

how many chromosomes does a normal human cell contain

23 pairs of chromosomes

chromosome

A structure found in the nucleus which is made up of a long strand of DNA.

gamete

An organism’s reproductive cell (egg in female and sperm in males), which has half the number of chromosomes (23).

genes

• A short section of DNA that codes for a protein, and therefore contribute to a characteristic.

• Some characteristics are controlled by a single gene, such as fur colour in mice and red-green colour blindness in humans

• most characteristics are the result of many different genes interacting

alleles

• different forms of a gene

• humans have 2 alleles of each gene- one from each parent

genotype

tells us the alleles present e.g. Aa

homozygous

When both inherited alleles are the same (i.e. two dominant alleles or two recessive alleles).

phenotype

The physical characteristics that are observed in the individual, e.g. eye colour

heterozygous

When one of the inherited alleles is dominant and the other is recessive.

dominant allele

Only one (out of the two alleles) is needed for it to be expressed and for the corresponding phenotype to be observed- capital letter

recessive allele

Two copies are needed for it to be expressed and for the corresponding the phenotype to be observed.

what characteristics are controlled by a single gene

• fur colour in mice

• red-green colour blindness in humans

cystic fibrosis

this is a disorder of the cell membranes, resulting in thick mucus in the airways and pancreas

what two alleles does a person with cystic fibrosis have?

• both parents are carriers

• homozygous of the recessive allele

• recessive allele- defective cell membrane

how is a person with (Cc)- cystic fibrosis characterised as?

a carrier

punnet squares

• numbers are simply probabilities- not accurate at all

polydactyly

having extra fingers or toes

what type of disorder is polydactyly

inherited disorder

what allele does a person with polydactyly have

• dominant allele

• heterozygous OR homozygous- PP or Pp

• one can’t be a carrier of the polydactyly disorder

• pp doesnt have the disorder

embryonic screening

• allows scientists to observe whether the child will have a genetic condition or not.

• embryo’s that arent defective are inserted into the women- develop healthy offspring

• embryo is developed in lab or extracted DNA from the womb

arguments for embryonic screening

• Reduces the number of people suffering(ethical).

• Treating disorders is very expensive (economic).

• There are many regulations in place to stop it getting out of hand (social).

arguments against embryonic screening

• Could encourage people to pick characteristics - creating designer babies (ethical).

• It is expensive to carry out screening(economic).

• May promote prejudice as it suggests that those with genetic disorders will not live a full life or are unwanted (social).

• Decisions about terminating a pregnancy have to be made (social).

• The procedure can lead to a miscarriage(social).

gene therapy

scientists may be able to correct faulty alleles and use this to treat inherited disorders

how many genes only determine inherited characteristics

22 chromosomes

if 22 pairs of chromosomes are used to determine inherited characteristics, what is the last pair used for

determines the sex- X and Y chromosomes

what chromosomes does a male have

X and Y

what chromosomes does a female have

X and X

punnet squares shows sex of child to be

50/50

variation

all the differences in the characteristics of individuals in a population

3 main causes of variation

• genetic causes

• enviroment

• combination of genes and enviroment

variation- genetic causes

• alleles that induviduals have inherited

• The combining of genes from the mother and father creates genetic

  variation

• Only identical twins have the same genotype

variation- enviroment

• The conditions the organism grows and develops in also affects its appearance.

• Examples include scars in animals, or smaller and yellow leaves in plants.

variation- combination

e.g. height- caused by genetics but must have coorect diet

what are genetic variations caused by

• mutations- random changes in the DNA

• take place all the time- spontaneous

what is it very rare that mutation would lead to

• change in phenotype

• can be beneficial if it does occur if there is a change in enviroment it can lead to rapid changes in a species

evolution

change in the inherited characteristics of a population over time through a process of natural selection which may result in the formation of a new species

theory of evolution

All species have evolved from simple life forms (single cells) that first developed more than three billion years ago.

what does evolution occur because of???

natural slection

what happens if a mutation provides a survival advantage

• organism is more likely to survive to breeding age.

• The mutation will then be passed onto offspring.

• Over many generations, the frequency of the mutation will increase within the population.

what causes speciation

• so different in phenotype

change in species

they can’t interbreed to produce a fertile offspring