Environmental Biology & Genetics Genotype & Phenotype M r G R D a v i d s o n

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 20152Mr G Davidson Alleles Genes control the characteristics of an organism, e.g. flower colour in peas. Alleles are different forms of the same gene. –An allele is a different form of that gene, e.g. red flower or white flower.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 20153Mr G Davidson Examples of alleles OrganismGene Different Alleles Pea plantHeightTall or dwarf HumansBlood typeA or B or O Fruit flyWing typeNormal or vestigial MaizeSeed colourPurple or yellow

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 20154Mr G Davidson Alleles Most genes normally have at least 2 forms. (Some have more than 2) Each body cell contains 2 alleles for every characteristic. This is because the cell contains 2 of each type of chromosome and the alleles are found at the same place on each of the two chromosomes.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 20155Mr G Davidson Alleles Pair of identical chromosomes Allele of a particular gene Second allele of this particular gene, which may be the same or it may be different

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 20156Mr G Davidson Alleles When gametes (sex cells) are being formed, the pair of chromosomes will be split up, each gamete only getting one chromosome. E.g. This chromosome would go to one gamete This chromosome would go to the other gamete

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 20157Mr G Davidson Alleles This means that when one gamete fertilises another, the resulting zygote will have 2 alleles, one from each gamete. The appearance of the organism depends on which of the alleles is dominant or recessive.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 20158Mr G Davidson Alleles A dominant allele will always show up in the appearance of an organism. A recessive allele will only show up if it is paired with another recessive allele. When describing an allele, for convenience, we usually give it a symbol, generally the first letter of the dominant allele.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 20159Mr G Davidson Alleles If it is dominant it gets the capital letter and if it is recessive it gets the lower case of the same letter. E.g. in pea plants tall is dominant over dwarf, and so the tall allele is given the letter T, and the dwarf allele the letter t. The genotype of the organism is the alleles it carries for that particular characteristic.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Alleles TT is a genotype and the plant will be tall. Tt is a genotype and the plant will be tall, because the T is dominant over the t. tt is a genotype and the plant will be dwarf. What the plant actually looks like (how the genes are expressed) is called its phenotype.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Genotypes & Phenotypes If both alleles are the same in the genotype of an organism, it is said to be true-breeding or homozygous, i.e. TT or tt. If the alleles are different in the genotype of the organism, it is said to be heterozygous, i.e. Tt.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Genotypes & Phenotypes GenotypePhenotypeDescription TTTallHomozygous TtTallHeterozygous ttDwarfHomozygous

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Monohybrid Inheritance In pea plants, red flower colour (R) is dominant to white flower colour (r). If we were to cross a homozygous red plant with a white plant, we would set the cross out as follows:

Monohybrid Inheritance To find out which characteristic is dominant we carry out a test cross. We cross true breeding (homozygous) strains of the two alleles. We refer to the first generation as the P (parent) generation and the resulting generations as F 1 and F 2 (first and second filial generations) Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Mr G Davidson14

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Monohybrid Inheritance RedxWhiteParent Phenotype Parent GenotypeRRx rr Gametes RRrr F1 GenotypeRr F1 Phenotypes Red All the offspring are red & heterozygous.

Monohybrid Inheritance To complete the test cross the F 1 generation are allowed to breed together producing a ratio of 3 dominant : 1 recessive trait This is split up into: 1 dominant homozygous:2 dominant heterozygous :1 recessive homozygous. Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Mr G Davidson16

Monohybrid Inheritance Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Mr G Davidson17 RedxRedF1 Phenotype F1 GenotypeRrx Rr Gametes RrRr F2 GenotypeRR RrrRrr F2 Phenotypes Red White ¾ of the offspring are red & ¼ are white.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Monohybrid Inheritance This type of inheritance was first studied in the 19 th Century by an Austrian monk called Gregor Mendel. He only studied one clear characteristic at a time in breeding experiments which we call crosses. The crosses are worked out using a Punnett square. E.g. in mice black coat colour is dominant over albino.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Monohybrid Crosses We always set out a cross the same way: Parents (P)BlackxAlbino BBbb Gametes B b The gametes for one parent go along the top. B B The gametes for the other parent go down the side. b b We can then complete the square. Bb The results of this cross are that all the F1 are black. B b

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Monohybrid Crosses If we now cross 2 of the F1 generation: F1BlackxBlack Bb Gametes B B The gametes for one parent go along the top. B b The gametes for the other parent go down the side. B b We can then complete the square. BBBb bb The results of this cross are that 3 of the F2 are black and 1 is albino. b b

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Monohybrid Inheritance We can then identify the genotype of individuals who have black fur by back- crossing them with albino mice. This is called a test backcross and would look like the following.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Monohybrid Crosses Parents (P)BlackxAlbino Bbbb Gametes Bb The gametes for one parent go along the top. B b The gametes for the other parent go down the side. b b We can then complete the square. Bbbb Bbbb The results of this cross are that half of the F1 are black and half are albino. bb

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Monohybrid Crosses Your answer should always have the parental genotypes. Your answer should always have the parental gametes. Your answer should always have a completed punnett square. Your answer should always have the F1 phenotypes and the ratio they occur in.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Family Trees Family tree diagrams can be used to show the transmission of alleles over a number of generations. The following family tree shows how the “ability to roll the tongue” allele is transmitted through 3 generations.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Family Trees = male = female = ability to roll tongue = inability to roll tongue Granny Grandad DadAuntMumUncle Brother Sister Since each organism receives 2 pieces of information for this characteristic, we now need to work out the GENOTYPE.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Family Trees RRrr Rr

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Co-Dominance It is possible for 2 alleles to have the same level of dominance, and in this case they are said to be co-dominant. In this case the offspring usually have a phenotype consisting the characteristics of both parents. E.g. If red and a white short horn cattle are crossed, the offspring has red and white hairs, resulting in a roan cow (looks pinkish).

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Co-Dominance Parents (P)RedxWhite RRWW Gametes R W R R W W RW In this case all of the offspring are “roan”. R W

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Variation There are 2 types of variation shown in organisms: –Discontinuous variation –Continuous variation

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Variation Discontinuous variation shows distinct clear-cut differences, and is controlled by only one gene. Discontinuous variation is usually displayed in a bar chart.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Discontinuous Variation e.g. eye colour

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Discontinuous Variation e.g. blood type

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Discontinuous Variation e.g. ear lobes Attached lobeUnattached lobe

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Variation Continuous variation shows a range of differences, and is controlled by more than one gene. These differences can usually be measured. Continuous variation is usually displayed in a histogram.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Continuous Variation e.g. Shell diameter in limpets.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Continuous Variation e.g. human hand span

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Continuous Variation e.g. Height

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Environmental Impact The final phenotype of an organism is influenced by variation in the environment in which the organism lives. Identical twins have the same genotype but may differ because of: –Diet (eating different food) –Activities (if one exercises a lot) –Climate (if one moves to another climate) GENOTYPE + ENVIRONMENTPHENOTYPE

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Natural Selection Most organisms produce far more offspring than are able to survive. This leads to a struggle for survival and many offspring will die before reaching an age where they can reproduce.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Natural Selection There are several reasons why offspring do not survive. –Starvation –Eaten by predators –Disease –Exposure

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Natural Selection The ones which survive often have a better phenotype, suited to the environment, and they can pass on their genes. This is called “survival of the fittest”.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Natural Selection Examples of genes which can be advantageous include: –Speed –Aggression –Resistance to disease –Coat thickness –Coat colour (better camouflage) –Quicker reactions

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Natural Selection Only the organisms better adapted to survive in their environment go on to reproduce. This can lead to the appearance of a new species. This is called evolution.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Peppered Moth The peppered moth is an excellent example of natural selection. It has a lightly speckled body colour which provides camouflage against lichens which grow on tree barks. This means the birds can’t see them.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Peppered Moth There is also a black variety of the peppered moth. (MELANIC) The black moths are easily seen and eaten by the birds. However, during the industrial revolution, the burning of coal produced a lot of black sooty smoke.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Peppered Moth This killed the lichens on the trees and turned them black. This allowed the black moths to be easily camouflaged, and so they survived to reproduce more black moths, and so the population of black moths increased rapidly. However, the speckled moth became easier for the birds to see, and so their numbers were quickly reduced.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Peppered Moth This only happened in industrial areas where the pollution was at its highest. Today both types of moth survive in different areas and they can still interbreed. –In large industrial areas the black (melanic) moth is more common. –In rural areas the light speckled moth is more common.

Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, 2015Tuesday, May 12, Mr G Davidson Peppered Moth Evolution has not yet caused these moths to become different species. Today, the Clean Air Act is reducing pollution, and this will reduce the numbers of the melanic moth. Natural selection allows the moths to survive where they are. Natural selection leads to Biodiversity.