Inheritance, Variation and Evolution AQA GCSE

Asexual reproduction

when there is only one parent. there's no fusion of gametes, no mixing of chromosomes, no genetic variation.

the offspring are genetically identical to the parents (clones)

bacteria, some plants and some animals are produced

asexually

is mitosis asexual or sexual reproduction?

asexual reproduction

Mitosis steps

1- duplicates the amount of DNA , each arm is an exact duplicate of the other

2- the chromosomes line up at the centre of the cell and cell fibres pull them apart, 2 arms of each chromosome go to opposite ends of the cell

3- membranes form around each sets of the chromosomes, becoming the nuclei of the 2 new cells

4- lastly, the cytoplasm + cell membrane divide

mitosis

normal body cells with chromosomes (46)

chromosomes duplicate (92)

chromosomes pulled to opposite sides poles of cell

chromosomes split to form 2 identical daughter cells (diploids)

diploid

46 chromosomes

mitosis is used in

growth, repair, development of cell, heal cuts, heal bones, embryo to adult

Sexual Reproduction

involves the fusion of male and female gametes. Because there are TWO parents, the offspring contain a mixture of their parents' genes.

sexual reproduction involves the fusion of

egg cells and sperm cells

Gamete

A specialised sex cell formed by meiosis

Runners

Long shoots from plants, such as strawberries, that are used for asexual reproduction

Meiosis is sexual or asexual reproduction?

Sexual Reproduction

Meiosis steps

1- before division, genetic information is duplicated, forming 2 armed chromosomes. After replication, the chromosomes arrange themselves into pairs

2- first division; the pairs line up in the centre of the cell

3- pairs then pulled apart, each cell has 1 copy of each chromosome (some mums, some dads)

4- second division; chromosomes line up again and the arms of the chromosomes are pulled apart

meiosis

normal cell (from testes or ovaries) with 46 chromosomes

number of chromosomes double (92)

chromosomes pulled to opposite poles of cell

chromosomes splits

chromosomes split AGAIN to produce 4, non-identical daughter cells

what does meiosis produce?

4 chromosomes, all genetically different

how many chromosomes does a gamete have?

23 chromosomes (haploid)

gametes are produced by

meiosis

mitosis VS mieosis

mitosis;

2 identical daughter cells (both with 46 chromosomes - diploids)

asexual reproduction

normal body cells

used for growth + repair

1 division

mieosis;

4 unidentical daughter cells (with 23 chromosomes - haploids)

sexual reproduction

gametes (sperm / eggs produced in testes / ovaries)

2 divisions

fertilised cells divide by

mitosis many times to form an embryo

sex cells in animals/humans

male = sperm

female = egg

sex cells in plants

male = pollen

female = egg

DNA

Nucleic acid molecules that contain genetic information and make up chromosomes

It contains coded information

DNA is a

POLYMER made up of 2 strands coiled into a double helix

what shape is DNA

double helix (twisted ladder)

What does DNA stand for?

DeoxyriboNucleic Acid

Chromosomes

long molecules of DNA that normally come in pairs

how many pairs of chromosomes do humans have?

23 pairs

XY

male sex chromosomes

XX

female sex chromosomes

the ___ pair of chromosomes carries genes which decides a persons ____

23rd, sex

Gene

Part of a chromosome, made of DNA, which codes for a specific protein

>tell us what order to put the amino acids together

there are 20 different amino acids but

1000s of possible proteins

Genome

an organisms entire set of genetic material

why is it important for scientists to understand the human genome?

- allows to identify genes in the genome that are linked to specific inherited diseases

- tiny differences' in people's genomes can be studied to help figure out migration patterns of past human populations + used to discover ancestors

Polymer

A large molecule that is made up of many repeating units

(DNA is a polymer)

Nucleotide

A molecule made of a phosphate group, a sugar and an organic base

Collagen

A protein found in connective tissue under the skin and in tendons

Mutation

A spontaneous change in the genetic material of a cell

Allele

An alternative form of a particular gene

Genotype

The combination of alleles an individual has for a particular gene, e.g., BB, Bb or bb

Phenotype

The physical expression of the genotype, i.e. the characteristic shown

Dominant

An allele that only needs to be present once in order to be expressed; represented by a capital letter

Recessive

An allele that will only be expressed if there are two present; represented by a lower case letter

Homozygous

When an individual carries two copies of the same allele for a gene, e.g., BB or bb

Heterozygous

When an individual carries two different alleles for a gene, e.g. Bb

Monohybrid inheritance

The pattern of inheritance shown when a characteristic is controlled by a single gene

Punnett square

A type of diagram used to work out the outcome of genetic crosses

Genetic cross diagram

Diagram showing how the alleles in two parents may form different combinations in the offspring when the parents reproduce.

family tree

Diagram that shows the inheritance of a genetic condition in a family.

Polydactyly

A genetic disorder caused by a dominant allele, where affected people have extra fingers or toes

polydactyly is caused by

dominant allele

For a child to have polydactyly, what must a parent have?

only one parent needs the defective allele "D"

Cystic Fibrosis

A genetic condition that causes a build-up of mucus in the lungs

cystic fibrosis is caused by

recessive allele

For a child to have cystic fibrosis, what must both parents have?

to be either carries or have the disease themselves "ff"

embryo screening

you can remove a cell from the embryo to analyse its genes

many genetic disorders can be detected this way

Against embryonic screening

1) Implies that people with genetic problems are 'undesirable' - this could increase prejudice

2) There may come a point where everyone wants to screen their embryos so they can pick the most 'desirable' one

3) Screening is expensive

4) 'Bad' alleles are destroyed after screening - unethical

Advantages of embryonic screening

1) It will help to stop people suffering

2) Treating disorders costs the government a lot of money

3) There are laws to stop it going too far e.g. parents cannot select the sex of their baby (unless for health reason)

Sex chromosomes

The pair of chromosomes that determine the sex of organisms

Variation

Differences in the characteristics of organisms

what causes differences in genes?

mutations - they occur occasionally

genetic variation

differences in the genes individuals inherit cause variation within a population

environmental variation

differences in the conditions in which an organism develops cause variation

most variation in phenotype is caused by

both genetic and environmental factors

Mutations are

change to the genome

they are random and occur due to errors during DNA replication

Evolution

A gradual change in a group of organisms over a long period of time

theory of evolution

All of today's species have evolved from simple life forms that first started to develop over three billion years ago

Who came up with the theory of evolution?

Charles Darwin

what animal does Charles Darwin use as evidence of his theory

finches

Speciation

the development of new species

Natural selection

The survival of individual organisms that are best adapted to their environment

How does natural selection work?

species show wide variation BUT limited resources mean organisms are in competition >

organisms with the most suitable characteristics for the environment are most likely to survive >

these organisms are more likely to breed >

the beneficial characteristics are passed on and gradually become more common in the population

if different species breed, they produce

infertile offspring

reasons species become extinct;

1) the environment changes to quick (e.g. destruction of habitat)

2) new predator kills them all (e.g. hunting)

3) new disease kills them all

4) they can't compete with another (new) species for food

5) a catastrophic event happens that kills them all (e.g. volcanic eruption or asteroid collision)

Fossil

The remains of animals/plants preserved in rock

3 main places fossils are found

1- sedimentary rocks

2- ice

3- amber

(4- no oxygen areas / low temps

Why is the fossil record incomplete?

- fossils that formed millions of years ago may have been destroyed by geological activity

- many early organisms were soft bodied, and soft tissue tends to decay away completely. so no traces were left behind

- we haven't found all the fossils yet

Selective breeding

The breeding process used by scientists and farmers to produce organisms that show the characteristics that are considered useful

reasons to selective breed

animals produce more meat /milk/ eggs

crops with disease resistance

animals to have a good/ gentle temperament

decorative plants / patterns on pets

steps of selective breeding

from existing stock, select the ones with the characteristics you are after

breed them with each other

select best of the offspring and breed them together

continue process over several generations , and the desirable trait gets more desirable

eventually, all offspring have the desired characteristics

selective breeding is / isn't new

it is nothing new

drawbacks of selective breeding

gene pool is reduced (reduction in number of different alleles)

which means there is less of a chance of a resistant gene against a disease

it can cause health problems (like dogs struggle to breathe)

Genetic engineering

The process of moving a gene from one organism to another

steps of genetic engineering

1. useful gene is isolated (cut) from one organism genome using an enzyme

2. It is inserted into a vector (usually a virus or bacteria plasmid)

3. Vector is introduced to the target organism and the useful gene is inserted into its cells

4. Vector 'infects' organism to help the useful gene spread

Bacteria have been genetically modified to produce

human insulin that can be used to treat diabetes

Why are crops genetically modified?

- They are engineered to be resistant to insects and to herbicides

- This will result in increased yields as less crops will die

- To be bigger

why do they genetically modify animals (e.g. sheep)

so they are bigger and produce more food

so they produce substances (like drugs) in their milk to treat human disease's

Pros and Cons of GM crops

Pros:

Increase yield,

contain nutrients for less developed nations,

grown worldwide with no problem

Cons: Affect weeds/plants/insects affecting and possibly reducing biodiversity,

not sure if its safe,

transplanted genes may get out in environment and create 'superweed'

gene therapy

The insertion of working copies of a gene into the cells of a person with a genetic disorder in an attempt to correct the disorder

Genetically modified (GM)

organisms that have had specific areas of their genetic material changes using genetic engineering techniques

Clone

An offspring that is genetically indetical ot the parent organism

Cuttings

A method of asexually reproducing plants, used by gardeners, by planting small lengths of plant shoots

Tissue Culture

A method of producing large numbers of plants asexually by growing small pats of plants in a nutrient jelly

Surrogate

A female that gestates and gives birth to an organism that has not been produce from on of her own egg cells

Binomial system

The method of naming organisms by using their genus and species

Genus

A group of closely related species

Species

A group of organisms that can reproduce with each other to produce fertile offspring

Three-domain system

A new classification system that divides organisms into three domains rather than five kingdoms

Extinct

A species that has died out

Speciation definition

Where populations have become so different that successful interbreeding is no longer possible