Biology ✿ Inheritance, variation and evolution

meiosis

a type of cell division which forms gametes which are genetically different from parent cells

gametes

sex cells

sexual reproduction

mixing of genetic information (from a mother and father) which leads to variety in the offspring (meiosis)

asexual reproduction

involves only one parent and no mixing of genetic information causing them to produce to genetically identical offspring (mitosis)

what are the stages in meiosis? [3]

• DNA replicate to make copies of genenetic information

• cell divides twice to form 4 cells

• this produces gametes which are haploids and are all genetically different

why are gametes genetically different?

they receive different combinations of chromosomes

why do gametes only contain half the set of chromosomes? (23)

so that at fertilisation, when two gametes fuse they’ll have a full set of chromosomes

DNA

polymer made up of two strands forming a double helix and stores genetic code

gene

small section of DNA that codes for a protein

genome

the entire genetic code in an organism

genotype

the organisms specific genetic code

phenotype

how the genetic code is expressed in physical characteristics

state 3 advantages of understanding the human genome sequence

• can search for genes which cause diseases

• helps understanding and treatment of inherited disorders

• can trace human migration patterns from the past

chromosome

long molecule of DNA that contains genes

allele

different versions of the same gene

homozygous

2 same alleles e.g. bb or BB

heterozygous

2 different alleles e.g. Bb or bB

what is Polydactyly?

what causes this disease?

• having extra fingers/ toes

• caused by one parent passing on the dominant allele

what is Cystic fibrosis?

what causes this disease?

• a disorder of cell membranes which causes build up of mucus in the lungs

• caused by two parents (carriers) who both pass on recessive alleles

embryo screening

before an embryo is implanted in IVF, it is possible to remove cells to analyse the genes for inherited disorders

give 3 ethical reasons why embryo screen is seen as bad

• selecting embryos goes against natural life and religious beliefs

• some embryos are destroyed, which people are against as they believe is it killing a potential life

• implies people with disorders are unwanted, leading to prejudice

sex chromosome for females

XX

sex chromosome for males

XY

variation

differences in the characteristics of an organism’s population

Embryos can be screened for the alleles that cause inherited disorders.

Give two advantages of embryo screening [2]

• less people with disorders

• parents can decide if they want to continue with pregnancy

Explain the process of evolution that could cause the trend in Figure 4. [6]

• random mutations in genes causes variation of beak length

• birds with longer beaks are at advantage as they can survive easily

• they reproduce offspring

• offspring inherit and pass on longer beak allele

• allele frequency increase in each generation

mutation

changes in genes, which only very rarely will lead to a new phenotype and causes all new variants

evolution

the change of genes of a population over time which occurs through natural selection

what does the theory of evolution by natural selection state?

all species of living things have evolved from simple life forms that first developed more than 3 billion years ago

explain how evolution occurs through natural selection of variants that give rise to phenotypes best suited to their environment.

• variation in a population is caused by mutations

• there is competition between organisms to survive (food), the better adapted survive and reproduce offspring

• offspring inherit better adapted alleles

• over many generation, they cannot produce fertile offspring with other populations as a new species has been made

natural selection

the processes of organisms who are best adapted to environment survive and pass on their genes

selective breeding

the process of humans breeding plants or animals for specific genetic characteristics

give 4 examples of desired characteristics that people may want during selective breeding

• gentle nature of domestic animals

• animals which produce more milk or meat

• large/ unusual flowers

• disease resistant

Describe the steps of selective breeding [4]

• choose parents with desirable characteristics

• parents are bred

• only offspring with desirable characteristics are bred

• this is repeated over generations until the characteristic is fully developed

genetic engineering

the process of modifying an organisms genome by using another organisms genes to get a desired characteristic

Describe the steps of genetic engineering [4]

• enzymes are used to isolate required gene

• gene is inserted into a vector (e.g. plasmid) so that gene can be inserted into cell

• gene is transferred into organism at an early stage of development so they fully develop with desired characteristic

what are 3 advantages of genetical engineering

• GM usually involves transferring only one gene so it is precise

• GM crops can produce toxins to kill insects

• GM crops can be herbicide resistant making agriculture faster

what are 3 disadvantages of genetical engineering (in plants)

• GM crops which are herbicide resistant may breed with weeds

• limited research on how GM crops impact human health

• can reduce biodiversity

give 3 causes of extinction

• new predators

• new diseases

• natural disaster

how does a fossil form?

• organism dies

• layers of sediment form on top

• lack of oxygen prevents decay of bones

• eventually, the bones are mineralised

state 3 reasons why the fossil record is incomplete?

• some fossils are destroyed by earthquakes or erosion

• early forms of life were soft bodied so they decayed

• dating older fossils is hard

state 3 ways to reduce the rate of development of antibiotic resistant strains

• only prescribing antibiotics when needed

• complete full course of antibiotics so no resistant bacteria is left

• don’t prescribe antibiotics for viral infections as they only kill bacteria

Explain how the widespread use of antibiotics in farming is a threat to human life. [4]

• antibiotic is spread into the environment by faeces

• bacteria in land become antibiotic resistant

• these bacteria are human pathogens

• which cause human diseases which cannot be treated

who introduced the ‘three-domain system’?

Carl Woese

Carl Woese developed the ‘three-domain system’ of classification.

Describe the ‘three-domain system’ of classification.

• the system is based on DNA evidence

• Eukaryota → plants and animals

• Bacteria → all true bacteria

• Archaea → usually extremophiles

state the taxonomic hierarchy

Kingdom

phylum

class

order

family

genus

species

What is the naming system that Carl Linnaeus introduced?

binomial system

binomial name format

genus species

give 3 reasons why children look different

• environmental factors

• different combination of alleles

• multiple genes determine appearance

Explain why sexual reproduction could produce a new variety [3]

• fertilisation of gametes

• leads to mixing of chromosomes

• one copy of each allele is from each parent

how are new species caused by?

• isolation of population

• change of habitat

A gene codes for a particular sequence of __________ _______

amino acids