3 Boardworks GCSE Additional Science: Biology Inheritance Uniquely you…Boardworks GCSE Additional Science: BiologyInheritanceThe population of the Earth is more than 6 billion people, and no two individuals (apart from identical twins) are genetically the same. Why?People are different because they inherit different characteristics (or traits) from their parents.Like all babies, this child carries a unique set of genes; half from his mother and half from his father.Teacher notesAsk students how many human characteristics they can identify which are open to individual variation e.g. height, weight, natural eye and hair colour etc.A person’s unique characteristics are caused by:the set of genes they inherited from their parents (nature)the environment in which they developed (nurture).
4 Inherited and acquired characteristics Boardworks GCSE Additional Science: BiologyInheritanceSome characteristics, such as eye colour and earlobe shape, are only determined by genes. These are called inherited characteristics.Other types of characteristics, such as scars and hair length, are not inherited but depend on environmental factors. These are called acquired characteristics.Differences in some characteristics are due to a combination of both inherited and environmental factors. In some cases, it can be difficult to say how much influence each factor has.
5 Boardworks GCSE Additional Science: Biology Inheritance Nature, nurture or both?Boardworks GCSE Additional Science: BiologyInheritanceTeacher notesColoured traffic light cards could be used with this activity to increase class participation, or students could work individually or in small groups, with mini-whiteboards used to convey the answers.
6 Phenotype and genotype Boardworks GCSE Additional Science: BiologyInheritanceThe overall appearance of an organism depends on two things:1. its genes (inherited characteristics)2. the effects of the environment in which it lives.All the observable characteristics of an organism are called its phenotype.The full set of genes of an organism is called its genotype.An organism’s phenotype therefore depends on its genotype plus environmental effects.phenotype = genotype + environmental effects
10 Boardworks GCSE Additional Science: Biology Inheritance What type of variation?Boardworks GCSE Additional Science: BiologyInheritanceTeacher notesAppropriately coloured voting cards could be used with this classification activity to increase class participation.
12 Observing variation in humans Boardworks GCSE Additional Science: BiologyInheritanceAs well as environmental factors such as climate and diet, humans are affected by education, culture and lifestyle.Because these factors change our phenotype, the effects of many environmental factors can be clearly seen.Scientists often use identical twins to study the effects of environmental factors. Although the twins are genetically identical, each one will have been shaped differently by their environment and experiences.Photo credit: Eyup SalmanFor example, a bad diet may cause one twin to be larger and less healthy than the other twin.
13 Genetic causes of variation Boardworks GCSE Additional Science: BiologyInheritanceSexual reproduction is the most important cause of genetic variation because it mixes up genetic material.How does it do this?During meiosis, homologous chromosomes exchange genetic material. They then line up and separate in different ways, producing a large variety of different gametes.Teacher notesSee the ‘Cell Division’ presentation for more information about chromosomes, meiosis and fertilization.At fertilization, any male gamete can combine with any female gamete.All these events occur randomly and create new combinations of genetic material.
14 Mutation and genetic variation Boardworks GCSE Additional Science: BiologyInheritanceMutation is the change in the type or amount of DNA and is therefore another cause of genetic variation.Mutations can arise spontaneously; for example, through the incorrect copying of base pairs during DNA replication, or the unequal distribution of chromosomes during cell division.Mutations can also be caused by environmental factors, such as radiation and certain chemicals. These factors are called mutagens.Teacher notesOne question for students would be to ask them about the effect of a mutation in a body cell and a mutation on a gamete. Mutations in body cells cannot be passed on to future generations, whereas a mutation in a gamete can be passed on.Some mutations may be beneficial, but many are harmful and increase the risk of diseases such as cancer.
15 Boardworks GCSE Additional Science: Biology Inheritance True or false?Boardworks GCSE Additional Science: BiologyInheritanceTeacher notesThis true-or-false activity could be used as a plenary or revision exercise on variation, or at the start of the lesson to gauge students’ existing knowledge of the subject matter. Coloured traffic light cards (red = false, yellow = don’t know, green = true) could be used to make this a whole-class exercise.
18 Different versions of genes Boardworks GCSE Additional Science: BiologyInheritanceChromosomes in a homologous pair contain the same type of genes that code for the same characteristics, such as eye colour.Each chromosome in the pair, however, may have a different version of the gene.allele for browneyesallele for blueeyesFor example, the version ofa gene on one chromosomemay code for brown eyes,whereas the version of the gene on the other chromosome may code for blue eyes.Teacher notesIt may be worth clarifying to students that, for each gene, one allele is inherited from the mother and the other allele is inherited from the father.Each different version of a gene is called an allele.
19 Boardworks GCSE Additional Science: Biology Inheritance Homozygous allelesBoardworks GCSE Additional Science: BiologyInheritanceIf the alleles for a characteristic in a homologous pair are the same, the organism is said to be homozygous for that characteristic.What colour eyes will these homozygous pairs of alleles produce?allele for brown eyesallele for brown eyesallele for blue eyesallele for blue eyes
20 Boardworks GCSE Additional Science: Biology Inheritance Heterozygous allelesBoardworks GCSE Additional Science: BiologyInheritanceIf the alleles for a characteristic in a homologous pair are different, the organism is said to be heterozygous for that characteristic.What colour eyes will this heterozygous pair of alleles produce??allele for brown eyesallele for blue eyesThe characteristic expressed by heterozygous alleles will depend on which allele is dominant and which allele is recessive.
21 Boardworks GCSE Additional Science: Biology Inheritance Dominant or recessive?Boardworks GCSE Additional Science: BiologyInheritanceThe phenotype for a particular characteristic depends on which allele is dominant and which allele is recessive.Dominant alleles are always expressed in a cell’s phenotype. Only one copy of the dominant allele needs to be inherited in order for it to be expressed. Dominant alleles (e.g. brown eyes) are represented by an upper case letter (e.g. ‘B’).Recessive alleles are only expressed in a cell’s phenotype if two copies of it are present. If only one copy is present, its effect is ‘masked’ by the dominant allele. Recessive alleles (e.g. blue eyes) are represented by a lower case letter (e.g. ‘b’).
22 Boardworks GCSE Additional Science: Biology Inheritance What eye colour?Boardworks GCSE Additional Science: BiologyInheritanceThe allele for brown eyes is dominant over the allele for blue eyes.So, what colour will the eyes be of an individual who is heterozygous for eye colour?allele for brown eyesallele for blue eyesThe individual will have brown eyes, because the allele for brown eyes masks the allele for blue eyes.
23 Boardworks GCSE Additional Science: Biology Inheritance Inheritance termsBoardworks GCSE Additional Science: BiologyInheritanceTeacher notesThis matching activity could be used as a plenary or revision exercise on terms about genes. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.
27 Boardworks GCSE Additional Science: Biology Inheritance Finding the genotypeBoardworks GCSE Additional Science: BiologyInheritanceFor some characteristics, the genotype of a homozygous recessive individual can be determined from their phenotype.For example, the allele for brown fur (B) in mice is dominant over the allele for white fur (w). This means that all white mice must therefore have the genotypewhiteBut what about individuals that have brown fur? Is their genotype BB or Bw ?A test cross can be used to determine whether an individual is homozygous or heterozygous for a dominant trait.
28 Boardworks GCSE Additional Science: Biology Inheritance What is a test cross?Boardworks GCSE Additional Science: BiologyInheritanceDuring a test cross, an individual with an unknown genotype is crossed with a homozygous recessive individual. The phenotype of the offspring will reveal the unknown genotype.If all the offspring display the dominant phenotype, then the parent of unknown genotype must be homozygous for the characteristic.If half the offspring show the dominant phenotype, and half show the recessive phenotype, then the parent must be heterozygous for the characteristic.
29 Using test crosses to find genotype Boardworks GCSE Additional Science: BiologyInheritance
30 What is incomplete dominance? Boardworks GCSE Additional Science: BiologyInheritanceSometimes two different alleles are neither fully dominant or recessive to each other.In heterozygous individuals, this creates a phenotype that is an intermediate mix of the other two. This is called incomplete dominance.For example, when a red Mirabilis jalapa plant (also called the snapdragon or ‘Four o'clock flower’) is crossed with a white Mirabilis jalapa plant, all the offspring flowers are pink because both the red and white alleles are expressed.white
32 Co-dominance in humans Boardworks GCSE Additional Science: BiologyInheritance
33 What are sex chromosomes? Boardworks GCSE Additional Science: BiologyInheritanceHumans cells contain one pair of sex chromosomes, which control gender.Y chromosomeMales have one X and one Y chromosome (XY).Females have two X chromosomes (XX).Y chromosomes are very small and contain 78 genes, whereas X chromosomes are larger and contain a 900–1,200 genes.X chromosomePhoto credit: Eye of Science / Science Photo LibraryImage shows a coloured scanning electron micrograph (SEM) of human X (centre) and Y (upper left) sex chromosomes. Each chromosome has replicated to form two identical strands (chromatids). The area linking the chromatids is the centromere. Magnification: x7150 at 6x7cm size.Because females can only produce X gametes, it is the sperm that determine the sex of the offspring at fertilization.
34 Boardworks GCSE Additional Science: Biology Inheritance Boy or girl?Boardworks GCSE Additional Science: BiologyInheritance
38 Mendel’s early experiments Boardworks GCSE Additional Science: BiologyInheritance
39 Boardworks GCSE Additional Science: Biology Inheritance Monohybrid crossesBoardworks GCSE Additional Science: BiologyInheritanceThe type of experiment that Mendel carried out, investigating just a single characteristic, is called a monohybrid cross.There are two alleles controlling pea shape. This means there are three possible genotypes that the F2 generation of plants could inherit, leading to two possible phenotypes.Genotypeheterozygoushomozygous dominanthomozygous recessivePhenotypeSSsmoothwwwrinklySwsmoothThe likelihood of a trait being produced during a monohybrid cross can be mapped out using a Punnett Square.
40 What are Punnett Squares? Boardworks GCSE Additional Science: BiologyInheritance
41 Mendel’s laws of inheritance Boardworks GCSE Additional Science: BiologyInheritanceAfter his research, Mendel proposed two laws of inheritance.Mendel’s first law: the law of segregationAlternate versions of genes (alleles) cause variation in inherited characteristics.An organism inherits two alleles for each characteristic – one from each parent.Dominant alleles will always mask recessive alleles.The two alleles for each characteristic separate during gamete production.Mendel’s second law: the law of independent assortmentGenes for different characteristics are sorted independently during gamete production.
43 Boardworks GCSE Additional Science: Biology Inheritance Glossary (1/4)Boardworks GCSE Additional Science: BiologyInheritanceacquired – A characteristic of an organism that depends on environmental factors.allele – One version of a gene, found at a specific location along a chromosome.carrier – An individual with a recessive allele, whose effect is masked by a dominant allele.characteristic – A specific feature of an organism, such as eye colour.co-dominance – A situation where two alleles are equally dominant.continuous – Variation represented by a continuous range of values and which can be measured.
44 Boardworks GCSE Additional Science: Biology Inheritance Glossary (2/4)Boardworks GCSE Additional Science: BiologyInheritancediscontinuous – Variation represented by discrete categories.dominant – An allele that is always expressed, even if the cell only contains one copy.gene – The unit of inheritance.genotype – The full set of genes of an organism.heterozygous – Having two different alleles of a specific gene.homologous chromosomes – A matched pair of chromosomes that carry genes for the same characteristics.homozygous – Having two identical alleles of a specific gene.
45 Boardworks GCSE Additional Science: Biology Inheritance Glossary (3/4)Boardworks GCSE Additional Science: BiologyInheritanceincomplete dominance – A situation where two alleles are both partially expressed, producing an intermediate phenotype.inherited – A characteristic of an organism that depends on its genes.monohybrid cross – A cross in which one pair of characteristics is studied.phenotype – All the observable characteristics of an organism.recessive – An allele that is only expressed if two versions of it are present in a cell.
46 Boardworks GCSE Additional Science: Biology Inheritance Glossary (4/4)Boardworks GCSE Additional Science: BiologyInheritancetest cross – A situation where an individual with an unknown genotype is bred with a homozygous recessive individual to reveal the unknown genotype.variation – The difference between individuals within a population.
48 Boardworks GCSE Additional Science: Biology Inheritance Multiple-choice quizBoardworks GCSE Additional Science: BiologyInheritanceTeacher notesThis multiple-choice quiz could be used as a plenary activity to assess students’ understanding of inheritance. The questions can be skipped through without answering by clicking “next”. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.