genetics, populations, evolutions and ecosystems 7

#biology

allele

alternative form of a gene

heterozygous

a genotype with 2 different alleles

homozygous

a genotype with 2 of the same alleles

dominant

an allele that is always expressed in the phenotype in heterozygous organisms

recessive

an allele that does not express itself in the phenotype in heterozygous organism

genotype

the combination of alleles present within the cells of an organism

phenotype

the observable characteristics of an organism which occur as a result of genotype and the environment

what did gregor mendel investigate

genetics at the organismsl level

what does mendels law of segregation state

each individual has 2 factors (called genes now) for each characteristics

what type of cells are human cells

diploid

human cells are diploid, what does this mean

they have two copies of each chromosome (one from each parent)

what’s a locus / loci

the fixed location of the gene on each chromosome

dominant is what letter

capital

recessive is what letter

lowercase

what type of cells are gamete’s

haploids

why are gametes haploids

homologous pairs separate during meiosis so they only have one allele for each gene

when are children monohybrids

when they are heterozygous for one pair of alleles

what is mono hybrid inheritance

the simplest as it involves characteristics which are controlled by a single gene

parental generation

when performing crosses, this is what the original parents are called

filial generation

the first set of offspring of 2 parents, F1 generation

what is F1 generation

filial generation

why are expected ratios not always doing what is observed

• fertilisation is random

• samples have been taken from small populations

• co dominance

• sex linkage

what is codominance

both alleles are expressed in the phenotype

what is multiple alleles

where there are more than 2 alleles, of which only 2 may be present at the loci of an individuals homologous chromosomes

when does co dominance occur

where instead of one allele being dominant and the other recessive, both alleles are dominant

what is a gene

codes for a specific protein

dihybrid

when 2 characteristics are inherited from 2 different genes which have different alleles. these can show the probability of inheriting certain combination of 2 different character characteristics from their parents

monohybrid

predicting outcomes of crossing one characteristic (2 different alleles of the same gene)

features of a monohybrid

• inheritance of one gene

• 2 alleles, 1 from each parent

• one pair of homologous chromosomes

features of a dihybrid

• inheritance of 2 genes

• 4 different alleles

• 2 pairs of homologous chromosomes

what is it when 2 characteristics are inherited from 2 different genes which have different alleles. these can show the probability of inheriting certain combinations of 2 different characteristics from their parents

dihybrid

what is predicting outcomes of crossing one characteristic

monohybrid

epistasis

when the expression of a gene is modified by the expression of one or more other genes

what is it called when the expression of a gene is modified by tge expression of one or more other genes

epistasis

patterns of inheritence

• the Y chromosome is smaller than the X chromosome and carry fewer genes

• Males only have one copy of the X chromosome

• all Y chromosomes are inherited from fathers

• females have 2 copies of the X chromosome

definition of sex linked

a trait which is coded for by a gene on a sex chromosome

Impact of Y chromosome being smaller than the X

• carries fewer genes

• it means that most of the sex linked genes are found on the X chromosome and are called X linked

an example of a X linked gene

colour blindness and haemophillia

impact of males only having one X chromosome

means that they only have one allele of each sex linked gene, meaning they express the characterisrtic of this allele even if it is recessive. also means that males cannot be carried of X linked genes

impact of all Y chromosomes being inherited from the father

this means that males most always inherit their X chromosome from the mother. so any sex linked genes will have been passed on from female parents

impact of females having 2 copies of the X chromosome

means that females will always have 2 alleles of every X linked gene, this means that unless they have 2 copies of a recessive allele they will always have a domanint allele which will be expressed

autosomal linkage

• genes on autosomes can also be linked

• if two genes are found close together on the same chromosome, they are more likely to be inherited together as they will stay together during independent segregation of chromosomes in meiosis I and enter the gametes of the same chromosomes. this will produce an unexpected ratio

what is an autosome

one of the homologous chromosomes

what does autosomal linkage result in

an unexpected ratio as there are only two outcomes instead of the usual 4 or 16

do more genes contain linked genes or separated genes

linked

recombinant gametes

only be formed through crossing over meiosis I

what does having recombinant gametes with linked gene evidently show

crossing over had occured

what does crossing over of alleles do

crossing over puts new alleles together in combination on the same chromosome

what happens when the genes are far apart in terms of crossing over

crossing over happens more often

are crossovers between two genes that are close together common

not very common

why is crossing over between two genes that are close together uncommon

because when there is a very short distance between genes the target for the crossover is very small meaning that few such events will take place

the closer together the loci are on the chromosome the ____ the chances of the chiasma forming between them to separate them

lower

if the loci on the chromosome are very close together, what are the chance of a chiasma forming between them to separate then

very low

why is the observed ratio different to the expected

certain alleles are linked, so these are produced more . crossing over produces some other alleles too, so fewer individuals are the other alleles

define species

a group of organisms that can be interbreed to produce fertile offspring, a species exists as one or more populations

define populations

a group of organisms of the same species that occupies a particular space of a particular time and that can potentially interbreed

define gene pool

all the alleles of all the genes of all the individuals in a population at a given time

define allele frequency

how frequently a particular allele appeals in a population

equation for the frequency of alleles

number of copies of allele A in a population / total number of A/a gene copies in a population

what did the hardy weinberg principle state

the frequency’s of alleles and genotypes in a population will remain constant from generation to generation, provided that only medndelian segregation and recombination of alleles is at work, meaning that allele frequency in a population will not change from one generation to the next

no change in allele frequency relies on the following 5 assumptions being true

• no mutations occur

• no movement of alleles due to migration

• population is large

• no selection occurring

• mating is random

what is the hardy weinberg principle equation

• p+q= 1

• p(2) + 2pq + q(2) = 1

• (2) = squared

the p of the hardy weinberg principle equation represents

dominant allele

the q of the hardy weinberg principle equation represents

recessive allele

when is p+q=1 used

allele frequency

when is p(2) + 2pq + q(2) used

frequency of phenotype or genotype

define variation

difference between organisms

define intraspecific variation

differences between organism of the same species

define interspecific variation

differences between organisms that are different species

define genetic

different members of the population will have different alleles

define environment

factors in the environment affect the way genes are expressed

equation for variation, involving genetic and environment

V = G x E

3 ways variation can happen through meiosis

• independent assortment of chromosomes

• homologous recombination

• random fusion of gametes

variation during meiosis: independent assortment of chromosomes

happens through random alignment of homologous pairs

variation during meiosis: homologous recombination

crossing point - chiasma → new combination of alleles on chromosomes → homologous recombination

define mutation

changes in the base sequence in the coding part of DNA

causes of mutation

• chemicals

• ionising radiation

• happens mostly during DNA replicaiton

when does mutation mostly occur

during DNA replication, S phase

environmental variation

the environment affects the way genes are expressed

categorical data: variations of phenotypes

• genetic factors

• represented with bar chart or pie chart

• environmental factors have little influence of this

continuous data: variation of phenotypes

• environmental factors

• shown on graphs and form normal distribution curves

what is selection pressures

some individuals will die or fail to reproduce due to predation, disease, or competition for resources

selective advantage

organisms with variations that make them more likely to survive are said to have a selective advantage, allele frequencies will change as natural selection and evolution occur

speciation

new species being formed through evolution

if selection pressures are different for different populations, then evolution can occur, and new species can emerge once the populations can no longer interbreed

what occurs if selection pressures are different for different populations

evolution can occur, and new species can emerge once the populations can no longer interbreed

describe the process of natural selection

• organisms in a population produce offspring

• there is competition between offspring to survive

• these members of the population will have a variety of alleles

• the members with certain alleles will be better able to survive the competition

• these members survive better, live longer, and produce more offspring

• successful individuals pass on their alleles, likely passing on the advantageous one

• over many generations there will be more individuals with advantageous alleles

• so the frequency of the advantageous alleles will increase

what may organisms fight each other for

food, water, space, mates, light

what are the three types of adaptations

• anatomical

• physiological

• behavioural

types of adaptations: anatomical

observable structures when an animal is dissected

types of adaptations: physiological

internal workings within the organism which helps it to survive or reproduce

types of adaptations: behavioural

actions by the organism which help them to survive or reproduce

what are the three types of natural selection

• stabilising

• directional

• diversifying

types of natural selection: stabilising

acts upon extremes and favours the intermediate (middle) eg birth weights in the UK

an example of stabilising selection

UK birth rate

types of natural selection: directional

favours variants of one extreme, shifts to right or left, eg hedgehogs

an example of directional selection

hedgehogs

types of natural selection: diversifying

favours variants of opposite extremes, a dip in the middle, eg bird beaks

an example of diversifying selection

bird beaks

what is speciation

the formation of a new species by natural selection

what are the two speciation types

allopatric and sympatric