wghs 11SCM GEN
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What is Genetic variation?
- Genetic variation is the variation between individuals
- in their genotype and physical phenotype. Genetic variation is essential for
- survival. For example if the environment changes (becomes an ice age) those
- individuals that have more feathers/fur will survive and reproduce, while the
- others will not. This ensures survival of the species (survival of the fittest
- – Darwin). Genetic variation can come from mate selection, mutation (gene or
- chromosomal), meiosis (crossing over, independent segregation, independent
- assortment). There are 2 main types of variation: continuous plotted on a
- histogram eg: height, or discrete (discontinuous) plotted on a bar graph eg:
- sex male or female.
What is Asexual Reproduction?
- Asexual reproduction reproduction of an organism without
- the mixing/combining of genetic material from 2 parents. Offspring all share
- the same genetic material as parents
- ie paramecium, bacteria
What is Sexual Reproduction?
- Sexual reproduction reproduction of an organism that
- involves the combination of genetic material from two parents eg Sperm &
- egg, Pollen & egg
What does the word inherited mean?
- Inherited means that a characteristic can be
- passed from one generation to the next via sex cells.
What is Genetics?
- Genetics is the study of inherited
- characteristics, organisms differences resulting from the interaction of their
- genes and it’s environment
What is a Gene?
- Gene is a unit of inheritance which is a
- section of DNA that codes for a protein
What is an Allele?
- Allele is an alternative form of a gene eg:
- yellow (Y) or green (y) peas
What are Chromosomes?
- Chromosomes are seen during cell division, found
- in the nucleus and are made up of the DNA helix. Chromosomes carry your genes, humans
- have 46 chromosomes or 23 pairs.
What is DNA?
- DNA Deoxyribonucleic Acid is a large stable double helix
- (twisted ladder) found in the nucleus of cells. DNA is made up of a backbone of
- repeating phosphate and sugar (deoxyribose). Its rungs
- are made up of 4 bases
- (cytosine matches with guanine by 3 hydrogen bonds, while adenine matches with
- thymine by 2 hydrogen bonds). DNA carries the genetic code.
What are the bases of DNA?
Cytosine which matches with Guanine and Adenine which matches with Thymine
What is the Dominant allele?
Dominant allele is always expressed and hides the recessive allele. It is given a capital letter.
What is the Recessive allele?
- Recessive allele is usually not expressed unless it
- is combined with another recessive allele. It is given a lower case letter.
What is a Genotype?
- Genotype is the pair of alleles possessed for
- a certain trait (characteristic) and is represented by letters eg: Tt, TT, tt
What is a Phenotype?
- Phenotype is the physical expression of the
- genotype which is seen on the organism eg: tall or short
What is Homozygous?
- Homozygous (purebreeding) is when an organism has 2 of the
- same alleles. The organism can carry 2 dominant alleles and is then called homozygous dominant eg: AA. The
- organism can carry 2 recessive alleles and is then called homozygous recessive eg: aa
What is Heterozygous?
- Heterozygous (hybrid) is when an organism has 2 different
- alleles for the same trait. It has a dominant and a recessive allele eg: Ff
What are homologous pairs?
- homologous pairs/
- chromosome is a set of one maternal chromosome and one paternal chromosome that pair up with each other
- inside a cell during meiosis. So you get 2 of the same chromosome, two copies of each gene (needed to
- code for the trait)
What is a Pedigree Tree?
- Pedigree (family tree) displays generations of individuals
- and their phenotypes
What is a Nucleotide?
- Nucleotide is the repeating unit that makes up
- the DNA double helix. It is composed of a sugar, phosphate and a base. There
- are 4 different nucleotides for DNA as there are 4 different bases.
What is a Mutation?
- Mutation is a change in the DNA sequence that
- is not repaired and becomes permanent. If mutation occurs in somatic (body)
- cells then the cell dies or becomes cancerous, but it cannot be passed to
- offspring. If a mutation occurs in a gametic (sex) cell then it can be passed
- to future offspring. There are 2 types of mutations: point (gene) or block
- (chromosome) mutations. Mutations are usually recessive and can be neutral,
- beneficial or negative on the organism.
What are mutagens?
- Mutagens are agents that cause genes to
- mutate. They can include: radiation, UV light, Xrays, chemicals and some
What is independent assortment?
- Independent Assortment occurs when homologous pairs of
- chromosomes line up randomly and then
- separate randomly to opposite poles of the cell in Meiosis division one.
- This leads to different combinations of genes/alleles in the daughter cells or
What is Independent Segregation?
- Independent Segregation is when chromosomes separate into
- their chromatids and randomly move to
- different poles of the cell for formation into the gametes / daughter cells in
- Meiosis division two. This produces gametes with different allele combinations
- in the gametes which are all different.
What is Crossing Over?
- Crossing Over occurs during metaphase in division
- one. This is where homologous pairs of chromosomes line up at the equator and
- form tetrads. They join at interlocking points called chiasmata and exchange
- segments of chromosome randomly. They make hybrid chromosomes which have a mix
- of paternal and maternal origin. This increases genetic diversity because
- chromosomes will have a mix of genes with different combinations.
What is Fertilisation?
- Fertilisation in sexual reproduction - the process
- where the egg meets the sperm (pollen), where the maternal and paternal
- chromosomes combine to form homologous pairs (a zygote is formed)
What is a Zygote?
- Zygote the first cell of a new organism
- containing a full set of chromosomes – one from the mother and one from the
What is a test cross?
- Test Cross (Back Cross)is used when an organism is
- displaying a dominant phenotype and you are unsure whether it could be
- homozygous dominant eg: YY or heterozygous eg: Yy. This is when you cross/mate
- that individual with a homozygous recessive eg: yy. If you get the appearance
- of recessive traits in the offspring you know the organism is heterozygous. If
- you do not get any recessive traits in the offspring it could be homozygous
- dominant, to ensure you are sure you need to do repeat crossings/matings to
- ensure that no recessive traits occur.
What is a Punnet Square?
- Punnet Square is a diagram that shows possible
- offspring of matings/crosses, can be either a monohybrid (one characteristic)
- or dihybrid (two characteristics)
What is a genotype ratio?
- Genotype ratio the ratio of the genes that results after a punnet square is completed.
- This is the ratio of the alleles present ie 1 RR: 2 Rr: 1 rr note: this ratio may not be
- the same as the phenotype ratio
What is the Phenotype ratio?
- Phenotype ratio the ratio of the physical appearance that results after a punnet
- square is completed.
- This is the ratio of what the off spring look like ie 3 Round : 1 wrinkled note: this ratio may not be the same as the genotype ratio
What is Incomplete dominance?
Incomplete dominance is where one allele is not completely dominant over the other, and the heterozygote is a mixture of the two alleles. Eg: a cross between a purebreeding red and white snap dragons has the following offspring - RR red, Rr pink, rr white
What are sex-linked genes?
- Sex-linked genes are when genes are located on one sex chromosome but not on the other. Usually traits are carried on the X
- chromosome. This is because the Y chromosome is short and does not carry these genes, they will always be expressed even if they are recessive. Eg: colour
- blindness and haemophilia in men
What is Natural selection?
- Natural selection is when individuals most fitted to their environment survive to pass on their characteristics to their offspring.
- The environment acts on an organisms phenotype, the individuals with the best
- phenotypes for the environment will survive, reproduce, pass on their advantageous phenotypes. The ones with unsuited phenotypes will be unlikely to survive, reproduce and pass on their phenotypes. In this way a species can change over time.
What is the Gene pool?
- Gene pool is all the available genes for a
- species. Eg: Some of the genes for birds are – wings, feathers, claws, beaks…
- whereas humans do not have these genes
What is the definition of haploid?
- Haploid is having a cell with only one set
- of chromosomes (n)
What is the definition of Diploid?
- Diploid is having a cell with a double set
- of chromosomes (a full set), one from each parent (2n)
What is the definition of Somatic?
- Somatic is a body cell. All cells of the
- body except for the sex cells
What is a Gamete?
- Gamete is a sex cell with half the number
- of chromosomes (eg: sperm and egg). The gametes, one from each parent combine
- at fertilisation to form the first cell of life with a full number of chromosomes called the zygote
What is a Karyotype?
- Karyotype is when chromosomes from one
- individual are organised into matching chromosomes and are arranged from
- largest to smallest
What is a Genome?
- Genome is a set of chromosomes in the
- nucleus of an organism, which is the total of an individual’s genetic material
What are Adaptations?
Adaptations features of an organism that aid in its survival in the environment it is in (may not be adaptations in different environments/ habitats) structural, functional, behavioural, life history
What are Structural Adaptations?
- Structural adaptations - Physical features of the organism that aid in its survival ie Long beak
- to dig worms out of the ground
What are Functional Adaptations?
- Functional adaptations – metabolic process/ internal processes of the organism that aid in its survival ie Well developed sense of
- smell to find food underground and in dark, Good hearing to hear prey, Produce pigment to camouflage feather
What are Behavioural Adaptations?
Behavioural adaptations – behaviours an organism displays inresponse to a stimulus (how an animal responds to things) that will aid in its survival ie Run fast, often zig-zagging, leaping and rolling when alarmed, feeding at night to avoid day time predators
What are Environmental factors?
- Environmental factors factors in the environment
- surrounding the organism that will impact on its ability to survive, do well,
- reproduce, includes both abiotic and biotic factors.
What are abiotic environmental factors?
- Abiotic environmental factors non-living factors in an organisms environment
- that impact on its ability to survive and do well, specific to the exact habitat of the organism, where it currently lives eg temperature, moisture, salinity, wind strength, current strength, pH, altitude, light availability/ intensity, substrate (soil, rock),
What are Biotic environmental factors?
- Biotic environmental factors living factors in an organism’s environment that impact on its ability to survive and do well, specific to the
- exact habitat of the organism, where it currently lives eg pathogens – diseases, bacteria; inter-relationships – predators, prey, competition – mates, resources, nests, food
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