Transcript Slide 1
We are learning today about Why you are you! 20/07/2015 What am I looking for? •Can we all recall the terms gene, allele and characteristics?(Pass) •Can most of us use a Punnett square?(Merit). •Can some of us use Pedigree Analysis? (Distinction) word bank available 1 Kate and her sister have similar features. Baby George will inherit some of them. Biological families have characteristics in common because we inherit genes from each parent. Different forms of the same gene are called alleles. Combining the alleles gives us our characteristics. Monohybrid inheritance 2 Zag and Pod are aliens. They want to have offspring. It is important to Zag that some of their offspring have yellow antennae like her. Their antennae colour is controlled by just one gene. Passing on a characteristic controlled by one gene is called monohybrid inheritance. Monohybrid inheritance 2 The two versions of the antennae gene (the alleles) are, C – blue allele c – yellow allele Zag and Pod inherited one allele from their mother and one from their father. Zag inherited c(mother) and c(father) so she is cc Pod inherited C(mother) and C(father) so he is CC Remember last lesson? 2 Two of the same allele (version of a gene) = homozygous Zag’s genotype is cc = homozygous Her phenotype is yellow antennae Pod’s genotype is CC = homozygous His phenotype is blue antennae Quad has two different alleles = heterozygous Quad’s genotype is Cc = heterozygous Monohybrid inheritance 6 We can use a Punnett square to find out the chances of their offspring having yellow antennae. father’s genotype C C c Cc Cc c Cc Cc mother’s genotype c c C C Cc Cc Cc Cc CC = blue cc =yellow but all the offspring are 3 Cc What colour will their antennae will be? In fact they will have blue antennae. The Blue allele is described as DOMINANT. Even if the blue gene is inherited from only one parent that colour will take over. Genotype Cc gives phenotype blue antennae The yellow allele is RECESSIVE. So Pod is obviously not what Zag is looking for! 2 What about Quad? He has genotype Cc. father’s genotype mother’s genotype C c c Cc cc c Cc cc but now two offspring, (50% chance), have yellow antennae. as before two offspring ,(50% chance), have blue antennae. Lan has genotype Cc and so has blue antennae. 2 What would Quad’s offspring with Lan be? Fill in the square on your sheet and of find out 3 out 4 offspring father’s genotype mother’s genotype C c C CC Cc c Cc cc have blue antennae. -75% This relationship could produce a yellow antennae offspring, but it is less likely -25% The Punnett square only tells you the chance that each offspring will have the characteristic. If the Quad and Lan had offspring there is a 25% chance for each one that they will have yellow antennae. The square does NOT say that if they had 4 offspring 3 would definitely have blue antennae and 1 would have yellow. Summary 9 characteristics are inherited from our Some of our .............................. genes We inherit one version of the parents through our ............. one from our father. allele – from our mother and ........ gene – ............ If we inherit the same allele from both parents our homozygous genotype is ........................ If we inherit different versions of the gene our genotype heterozygous is ........................... dominant The alleles for each characteristic can be .................. recessive (lower case letter) (capital letter) or..................... dominant allele will always ‘win’. The ................... Have a go at the question on the worksheet. Get back to work!! Mutations Our genes and chromosomes are made of DNA. Sometimes the code it contains has been changed. E.g. the base pairs might be in a different order. This different code means that the gene might produce a different effect. This change in code is called a mutation. Some mutations can be useful – beneficial Some mutations dangerous - harmful http://www.bbc.co.uk/learningzone/clips/mutations-and-genetic-diseases/10653.html Sickle Cell Disease. 4 Sickle cell disease is caused by a mutation in the gene that controls making haemoglobin (the chemical that carries oxygen in your blood). Think about this couple who are thinking of starting a family. Mum: genotype - Rr phenotype unaffected carrier A carrier is someone who can pass on the disease but doesn’t have it themselves. Dad: genotype - Rr phenotype unaffected carrier On your sheet fill in the Punnett square for the couple to show their chances of having children with sickle cell disease. father’s genotype mother’s genotype R 3 r R RR Rr r Rr rr So, for this couple the chance of having a child with sickle 4 or 25%. 1 in ........ cell disease is ....... 50 The chance of being a carrier is ..............% Here is another type of genetic diagram to show this. 1 Fill in the details on your sheet. What if one of the parents has the disease and the other is a carrier? father’s genotype r r Rr Rr Fill in the punnet square on your sheet mother’s genotype R r rr rr The chances of their child having sickle cell is 50% (2 in 4 or 1in 2) What if one parent has the disease but the other isn’t even a carrier? r R r R r R r R r R R r Now all the children are carriers but none of them has sickle cell disease. 4 Pedigree Analysis. 2 The inheritance of a particular characteristic in a family can be studied using a pedigree chart. male carrier female carrier fully shaded = with disease ? half shaded = carrier carrier carrier carrier carrier Is Theo a carrier, a person who has sickle cell or an unaffected person? 20/07/2015 What am I looking for? •Can we all recall the terms gene, allele and characteristics?(Pass) •Can most of us use a Punnett square?(Merit). •Can some of us use Pedigree Analysis? (Distinction) word bank available