B5: Genes, inheritance and selection Flashcards
what is variation
- the difference between individuals of the same species
or - differences within species
what is variation caused by
- genetic + environmental factors
what is a phenotype
- the appearance of an organism or how the alleles are shown
> can be affected by your environment
what is genetic / inherited variation + give examples
- genetic material you inherit from your parents
- examples:
> eye colour
> hair colour
> blood group
what is environmental variation + give examples
- the environment in which you live in and how it can affect your characteristics
- examples:
> scars
> intelligence
> suntan
what is discontinuous variation + example
- when the characteristics fall into distinct / definite categories with no in-between
> examples - blood group, eye colour
what is continuous variation + example
- when the characteristic can be any value in a complete range of phenotypes from one extreme to the other
- no distinct categories
> examples - height in humans
what’s the causes of discontinuous / continuous variation
- discontinuous = genetic
- continuous = genetic + environmental
how many genes control discontinuous / continuous variation
- discontinuous = one (or few genes)
- continuous = multiple genes
what happens to offspring in asexual reproduction
- offspring get all their genes from one parent
> they are genetically identical to the parent - natural clones
what is a clone
- an organism that is genetically identical to its parent
what does asexual reproduction not require
- sex cells (gametes)
how does asexual reproduction occur
- an individual replicates their genetic material + divides in half (mitosis)
> the new organisms are clones
many ____ reproduce asexually
- plants
explain how strawberries reproduce
- reproduce asexually
- they send runners (long stems) over the ground
- the runners sprout roots at various intervals + new plants grow
- once the plants are established, the runners die and rot away
why are plants more likely to reproduce asexually
- because they retain their stem cells, whereas in animals the stem cells aren’t retained and differentiate
what happens to the offspring in sexual reproduction
- the offspring gets genes from two parents
> they will inherit a mixture of features from both parents
> offspring not genetically identical - each parent gives half of the genes to the offspring
most ____ reproduce using sexual reproduction
- animals
what are gametes
- sex cells
what are the 2 gametes
- sperm (male)
- egg (female)
how does sexual reproduction work
- organisms produce sex cells (gametes - egg + sperm) (haploid)
- the nucleus of sperm egg fuses with nucleus of egg + egg is fertilised (zygote - diploid)
- the fertilised egg divides (mitosis) + grows in the uterus + develops into the offspring
in what case would plants reproduce sexually + how
- to create a new seed, which will grow into a plant
- pollen cell (male sex cell) fuses with an egg cell (female sex cell) in the ovule
what are the gametes in plants
- pollen cell (male)
- egg (female)
what are some advantages of asexual reproduction
- is parent is well adapted to an area, the offspring will be too
- only one parent needed - animals don’t need to find partner + pollination not needed in plants
> organisms can reproduce whenever they want (or when conditions are favourable) without waiting for a partner - faster reproduction - so larger number of offspring produced quickly
what is a disadvantage of asexual reproduction
- no genetic variation
- if there’s any adverse changes to the environment, it may destroy the species + all organisms will be affected
what is an advantage of sexual reproduction
- variation in offspring leads to adaptations in species
> some organisms will have adaptations required to cope with an environmental pressure + these organisms can reproduce allowing the population to continue
what are some disadvantages to sexual reproduction
- requires 2 parent
> can be problem if organisms are isolated - slower - so resulting in fewer offspring
how many chromosomes are there in most human body cells
- 46 - diploid number
how many chromosomes do gametes contain
- 23
> haploid number
why do gametes have half the number of chromosomes
- have 23 chromosomes so that during fusion, the zygote has 46 chromosomes
what are diploid cells
- normal body cells with 48 chromosomes
or - diploid cells have a nucleus containing 2 sets of chromosomes
what are haploid cells
- gametes - they have half the number of chromosomes - only one of each
or - haploid cells have a nucleus containing a single set of unpaired chromosomes
what is mitosis
- it occurs in all living body cells + asexual reproduction
- produces 2 genetically identical daughter cells
what is a genome
- the entire genetic material of an organism
how are genomes affected by sexual reproduction
- all individuals produced by sexual reproduction have a unique genome
> except for identical twins
how are gametes made
- by a type of cell division called meiosis
> 4 haploid cells are produced from 1 diploid parent cell
describe the 2 main stages of meiosis
stage 1:
- chromosomes copied
- chromosomes line up along middle of cell in pairs (one from each parent)
- 1 member of each pair is pulled to opposite ends of the cell (when pulled apart, often sections of DNA are swapped)
- cell divides into 2
- 2 separate cells are formed
stage 2:
- chromosomes line up along the middle of each of the 2 new cells
- this time each chromosome is pulled in half - a single copy of each chromosome goes to opposite ends of the cell
- each cell then divides into 2 - resulting in 4 haploid cells
how many times does a cell divide during meiosis
- 2
what does meiosis result in
- cells that are genetically different from each other + from the parent cell
> not genetically identical - creates genetic variation
what is a chromosome
- a long strand of DNA, coiled up, carrying genetic information in the form of genes
what is a gene
- a section of DNA that codes for a specific protein
> can be copied + passed onto next generation
what is an allele
- a different version of a gene
how many copies of each gene per characteristic do you have + why
- 2 copies of every gene for each characteristic
> 1 from each of your parents
> these copies may be the same or could be different
what is a genotype
- the combination of alleles present in an organism
how are genotypes represented
- by 2 letters that are either dominant/ recessive + homozygous/heterozygous
what does it mean if a characteristic is homozygous
- you have 2 identical alleles for a characteristic
> e.g. BB or bb
what does it mean if a characteristic is heterozygous
- you have 2 different alleles for a characteristic
> e.g. Bb
what is a dominant allele
- the more stronger allele that will always show up in the phenotype
> you only need one copy of a dominant allele for the characteristic to be expressed
what is a recessive allele
- the weaker allele that only shows up if you have two copies (homozygous )
how are dominant + recessive alleles represented
- dominant = capital letter e.g. B
- recessive = lower case of the same letter e.g. b
how do you predict genetic crosses
- state phenotype of both parents
- state genotype of both parents
- state gametes of each parent - circle the letters
- use a Punnett square
how many pairs of sex chromosomes do human cells contain
- 1 pair
what do sex chromosomes control
- your sex
what is the 23rd pair of chromosomes in humans known as
- sex chromosomes
what are the chromosomes for males
XY (heterozygous)
what are the chromosomes for females
XX (homozygous)
what determines the sex of an offspring
- male gametes (sperm)
- females only produce X gametes, so its the sperm that determines the sex
draw a Punnett square for determining the sex of a human offspring
I X I Y
——————————————- 50:50 ratio
X I XX I XX of boy : girl
Y I XY I XY
when does a mutation occur
- when the sequence of DNA bases is altered
mutations occur ______
- spontaneously (randomly)
> e.g. DNA may not replicate correctly
do mutations affect phenotype
- most don’t affect phenotype
- some may influence phenotype
- a few will determine phenotype
are mutations that affect an organism’s phenotype harmful + examples
- most are harmful
> can cause: cancer, cystic fibrosis, sickle cell anaemia - some are neutral - they neither harm/benefit the individual
> freckles, tongue rolling etc. - few are beneficial
> malaria resistance, antibiotic resistance
what increases the chances of mutations
- some chemicals
> benzene + ethanol - ionising radiation
> ultraviolet from sun, x-rays
how can mutations influence an organism’s phenotype in coding DNA
- mutation alters the activity of proteins:
- if mutation occurs within a gene, DNA bases may be changed, added or deleted
- this changes the sequence of bases
- the order of mRNA bases are changed + so the order of amino acids may change
- this means that the protein produced may fold incorrectly + form a different shape
> protein structure is changed
give an example of mutations altering an organisms phenotype in coding DNA
- if protein is an enzyme, it’s active site may change shape
- substrate no longer binds + can’t catalyse a specific chemical reaction
> enzyme no longer works - can result in metabolic diseases e.g. phenylketonuria —> phenylalanine can’t be broken down by body —-> brain damage
what is a genetic variant
- a different version of a gene
what do mutations produce
- a genetic variant
what is non-coding DNA
- DNA bases that don’t code for proteins
how does mutation of non-coding DNA influence the phenotype
- it can affect how genes are expressed:
- there are specific sequences of DNA bases found before a gene which triggers the process of transcription
> they’re located within the non-coding sections of DNA - if mutation occurs within this sequence, the gene may not be transcribed into mRNA (stops transcription of mRNA)
> this means the protein the gene codes for will not be produced
what are most phenotypic features results of
- multiple genes rather than single gene inheritance
what did Gregor Mendel carry out an experiment on (1866)
- peas
what did Mendel observed in his experiment
- that characteristics such as height + colour are passed on from parents to offspring
what were the 3 big findings in Mendel’s experiment
- characteristics were determined by hereditary units (now called genes)
- genes passes on from both parents, one from each
- genes are dominant / recessive
what is classification
- the process of sorting living organisms into groups that share similar features
why do scientists classify organisms
- to identify species
- to predict characteristics
- to find or show evolutionary links
what is one of the way scientists classify organisms
- classify organisms at 7 taxonomic levels
what are the 7 taxonomic levels + the acronym for it
- King Phillip Cried Out For Good Soup
- Kingdom
- Phylum
- Class
- Order
- Family
- Genus
- Species
what happens as you go down the taxonomic levels
- the organisms share more characteristics
what are the 5 kingdoms
- plants
- animals
- fungi
- protoctista (amoeba + algae, no nucleus)
- prokaryotes (single celled, no nucleus)
what is a species
- a group of organisms that is able to reproduce to produce fertile offspring
- species is the lowest level of classification + is one type of organism
what is a Binomial nomenclature
- its a way to name species
- known as binomial as it has 2 parts:
> Genus name - capital letter
> species name - lower case
what is artificial classification
- organisms are grouped based on observable characteristics
what is the problem with artificial classification
- has caused problems in accurate classification as some species may look different but be closely related
what is natural classification
- new development have led to changes in the classification system
- DNA sequencing is used to link evolutionary relationships + identify common ancestors
> the more similar the DNA, the more closely related the species
what is phylogeny
- the study of evolutionary links
how are phylogenic links established
- by studying similarities ( + differences) in DNA between species
> the more similar the DNA, the more closely related the species are
what has led changed to the classification system
- new development
- new scientific discoveries
what is DNA sequencing used to link
- evolutionary relationships
+ identify common ancestors
what is evolution
- the gradual change in a species over time (millions of years)
or - the 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
what increases genetic variation
- mutations cause new forms of genes which adds variation
what have scientists thought to be the most common ancestor of all organisms
- unicellular aquatic organisms (similar to bacteria) that lived over 3 billion years ago
how do organisms evolve
- through the process of natural selection
how is genetic variation helpful
- the genetic variation could give an individual a competitive advantage over the other members of it species
- it’s more likely to survive + reproduce + pass on the mutated gene to the next generation
> known as survival of the fittest
give an example of evolution
- peppered moths:
- in early Britain they were pale (C19th)
> this helped camouflage them against trees + mutated moths with dark colour were easily spotted + eaten - during industrial revolution trees became covered in soot, turning bark black
> now black moths were more camouflaged + more of them survived - now dark peppered moths are more common in urban areas
describe how natural selection occurs (steps)
- individuals in species show genetic variation
- best adapted individuals are more likely to survive + reproduce (survival of the fittest)
- the ‘successful’ genes are passed to the offspring in the next generation
- offspring are more likely to have the ‘successful’ characteristic
- over time this can leas to the development of a new species
explain how antibiotic-resistant bacteria can evolve
- bacteria can reproduce rapidly
- if mutation occurs, bacterium usually dies
- sometimes it could give the bacteria resistance to antibiotics
- now the non-resistant bacteria will be killed but the antibiotic-resistant bacteria will live + reproduce passing on the antibiotic resistance
- eventually the whole species will become antibiotic resistant
what are fossils
- fossils are made when animals + plant remains are preserved in rock
what is the fossil record
- the fossil layers form a sequence showing that organisms have gradually changed over time
- top layer of rock has recent organisms
= the lower the layers, the older the organism
how do fossil records provide evidence for evolution
- oldest rocks = more simple, single-celled organisms (e.g. bacteria) + newest rocks = more complex organisms (e.g. vertebrates)
> supports theory that simple life forms gradually evolved into more complex ones - plant fossils appear before animals - they’re at the bottom of food chain as animals eat them for survival
- closely related organisms will share similarities in anatomy e.g. bone structure + scientists can show how modern day species are related to species that are now extinct
why are there gaps in the fossil record
- many organisms are soft-bodied + decompose quickly before they have a chance to fossilise
- they can easily be destroyed (e.g. volcanoes)
- most are usually found in the sea
- they are deep down in rocks
what other evidence is there for evolution
- extinction - species that don’t adapt to environmental changes die out - more than 99% of all species that have ever lived are now extinct
- molecular comparison (phylogenetics) - DNA sequence + protein structure is looked at - species that are closely related will have similarities in these molecules
- rapid change in a species - bacteria replicating rapidly allows scientists to study evolution in action - they can see how an advantageous characteristic (e.g. antibiotic resistance) becomes common in a bacterial population
what did people believe in Darwin’s time
- 1809 - that all species on Earth were created by God
where + what evidence did Charles Darwin collect about his theory
- Galapagos Islands (Spain)
- made observations on finches
- noticed that different islands had different finches
> the birds were closely related but their beaks + claws had different shapes + sizes
what conclusion did Darwin come about his observings
- that the design of the finches’ beaks was linked to food available on each island
- concluded that a bird’s beak more suitable to the food would survive longer than a bird with a less suitable
> it would have more offspring + pass on its beak characteristics
> overtime all the finches on that island would share the characteristic - Darwin called this process natural selection
what was the name of Darwin’s theory
- Evolution and natural selection
who was the other scientists that observed the theory of natural selection and evolution (not Darwin)
- Alfred Russel Wallace
what + where did Alfred Wallace carry out his observations on the theory of natural selection and evolution
- Borneo
- observed bird winged butterflies - realised all species are connected
what was the name of the book Darwin published + when
1859 - ‘Origin of species’
what book did Wallace publish
‘Darwinism’
was the work of Darwin + Wallace accepted
- scientists accepted + agreed with the work
- public didn’t - the theory conflicted with the belief that God made all things
Is Darwin’s theory of evolution accepted now + why
- yes it’s widely accepted
- because there’s an increasing amount of evidence to support his theory
> fossil record, observations of microorganisms, extinctions + recent advanced in DNA studies
did Darwin + Wallace work together
- no
- but their work was so similar they both proposed the theory of evolution through a join presentation of two scientific papers to the Linnean Society of London in 1858
