3.4 Inheritance Understanding: -Mendel discovered the principles of inheritance with experiments in which large numbers of pea plants were crossed -Gametes are haploid so contain one allele of each gene -The two alleles of each gene separate into different haploid daughter nuclei during meiosis -Fusion of gametes results in diploid zygotes with two alleles of each gene that may be the same allele or different alleles -Dominant alleles mask the effects of recessive alleles but co-dominant alleles have joint effects -Many genetic diseases in humans are due to recessive alleles -Some genetic diseases are sex-lined -The pattern of inheritance is different with sex- linked genes due to their location on the sex chromosome -Many genetic diseases have been identified in humans but most are very rare -Radiation and mutagenic chemicals increase mutation rate and can cause genetic disease and cancer Applications: -Inheritance of ABO blood groups -Red-green colour blindness and haemophilia as examples of sex linked inheritance -Consequences of radiation after nuclear bombing of Hiroshima and Nagasaki and the nuclear accidents at Chernobyl Skills: -Construction of Punnett grids for predicting the outcomes of monohybrid genetic crosses -Comparison of predicted and actual outcomes of genetic crosses using real data -Analysis of pedigree charts to deduce the pattern of inheritance of genetic diseases Nature of science: -Making quantitative measurements with replicates to ensure reliability: Mendel’s genetic crosses with pea plants generated numerical data

Presentations Inherited diseases: Cystic fibrosis Huntingdon’s Red-green colour blindness Haemophilia

Inherited Diseases How common is the disease? Where is it most common in the world? Is it a dominant or recessive allele that causes it? Which chromosome is the gene located on? What are the symptoms? Can you die from this disease? When do the symptoms start? What age? Is it mainly in males or females or both? Is there a cure? How can the symptoms be eased? Include a punnett square to show how the disease could be inherited Is this a sex-linked disease? (on an X or Y chromosome?)

Homework Look at page 197 We will complete the experiment during our lesson on Tuesday next week Bring in: -2 plant cuttings (you choose the plant!) (One for control, one to check a variable) -2 small bottles (must be clear and same size) Write down the following ready for Tuesday 19 th May: -Hypothesis -Independent variable, dependent variable, control variable

Gregor Mendel Create a Facebook page for Gregor Mendel (a fake one – on paper!) -Profile picture -Birth date/death date -Who was he -What did he do -What did he find out -How has his work influenced us today? Why is it important -Any other interesting information about him -Relevant status updates

Mendel Genetic crossing is the name given to the process whereby genes are mixed during reproduction. Mendel was a monk with a passion for gardening. He was curious about what caused the different colours of pea plants. Worked out that genes are inherited from our ancestors and they can skip a generation. Also worked out that some characteristics are dominant over others and will always be expressed.

Dominant and Recessive? Some characteristics are dominant, some are recessive. Dominant genes will ‘beat’ recessive genes and will appear as a phenotype (feature). Dominant TraitsRecessive Traits Brown eyesBlue eyes DimplesRed hair FrecklesThin lips Dangly earlobesAttached earlobes If you have a dominant trait, you may carry the recessive gene too.

Dominant & Recessive In this example, the mother has dimples which is a dominant trait (D). The father does not have dimples so does not have the dominant gene (d). dd DDd ddd So the child has a 2 in 4 chance of having dimples inherited from the mother. homozygous heterozygous

Mendel’s Peas Mendel had observed that the seeds of his pea plants varied in several ways – whether the peas were round or wrinkled and whether they were green or yellow. He did monohybrid crosses on both characteristics, but then decided to look at how they were inherited together…. (monohybrid = looking at one gene)

There are four possible combinations of the two characteristics. Peas can be: 1) round and yellow 2) round and green 3) wrinkled and yellow 4) wrinkled and green

From his monohybrid trials, Mendel had discovered that the allele for yellow colour was dominant to that for green. He had also found that the allele for round peas was dominant to the allele for wrinkled peas. Starting with individuals that were homozygous, either for both dominant characteristics or both recessive characteristics, he set off breeding again…

PhenotypeRound, yellowWrinkled, green Genotype RRYY rryy Gametes all RY all ry F1 all RrYy All of the F1 generation would be heterozygous for both characteristics, meaning that they would all be round and yellow. As with monohybrid crosses, he then crossed two of the F1 generation together… X

PhenotypeRound, yellow Genotype RrYy Gametes RY, Ry, rY, ry F2We really need a punnet square for this… X Round, yellow RrYy RY, Ry, rY, ry

RYRy rY ry RY Ry rY ry

RY ¼ Ry ¼ rY ¼ ry ¼ RY ¼ RRYYRRYyRrYYRrYy Ry ¼ RRYyRRyyRrYyRryy rY ¼ RrYYRrYyrrYYrrYy ry ¼ RrYyRryyrrYyrryy

F ::: Round Yellow Round Green Wrinkled Yellow Wrinkled Green This is the typical ratio expected in a dihybrid cross.

Mendel Pioneer in obtaining quantitative results and having large numbers of replicates Now standard practice in science to do repeat experiments to demonstrate reliability -Comparisons -Anomalies identified and excluded -Statistical tests

Gametes

Zygotes Diploid Nucleus contains 2 chromosomes of each type Contain different alleles for genes depending on what they inherit from parents. Segregation: separation of different alleles into haploid cells during meiosis

Alleles Dominant alleles mask the effects of recessive alleles (co-dominant alleles have joint effects)

Co-dominance Some genes have pairs of alleles where both have an effect when present together: Mirabilis jalapa Red flowered plant + white flowered plant = pink flowers

Co-dominance

Blood groups (co-dominance) Which blood group is the most common? Which is the least common? Which is a universal donor? Which is a universal receiver? (Do not worry about positive/negative)

Blood group questions… Which blood group is the most common? O Which is the least common? AB Which is a universal donor? O Which is a universal receiver? AB

ABAOB There are four ABO blood groups

ABO Blood groups In 1900 Karl Landsteiner discovered that human blood differed from one individual to another. This difference is due to the presence of antigens on the membranes of red blood cells and on the antibodies in plasma.

Blood groups Person with a specific antigen on their red blood cells does not possess the corresponding antibody in their plasma. When a patient receives a blood transfusion it is vital that the blood is compatible with his own. (They cannot contain same antigen and antibody)

Blood groups The gene for blood type is represented I. Allows more than two alleles: i = Blood group O (no antigens) I A = Blood group A (Produce A antigens, B antibody in plasma) I B = Blood group B (Produce B antigens, A antibody in plasma)

Co-dominance phenotypegenotype(s) A I A I A I A i B I B I B I B i ABIAIBIAIB O i

Blood groups Are parents able to have 4 children each with a different blood group? How?

Inheritance of ABO blood groups parental genotypes I A i X I B i gametes f1 genotypes f1 phenotypes phenotypic ratio

Inheritance of ABO blood groups parental genotypes I A i X I B i gametes I A i I B i f1 genotypes f1 phenotypes phenotypic ratio

Inheritance of ABO blood groups parental genotypes I A i X I B i gametes I A i I B i f1 genotypes I A I B I A i I B i i i f1 phenotypes phenotypic ratio

Inheritance of ABO blood groups parental genotypes I A i X I B i gametes I A i I B i f1 genotypes I A I B I A i I B i i i f1 phenotypes AB A B O phenotypic ratio

Inheritance of ABO blood groups parental genotypes I A i X I B i gametes I A i I B i f1 genotypes I A I B I A i I B i i i f1 phenotypes AB A B O phenotypic ratio 1 : 1 : 1 : 1

What do you predict? CrossPredicted outcome Pure breeding parents one with dominant allele and one with recessive allele Pure breeding parents with different co-dominant alleles Two parents with one dominant and one recessive allele each A parent with one dominant and one recessive allele and a parent with 2 recessive alleles

What do you predict? CrossPredicted outcome Pure breeding parents one with 2 dominant alleles and one with 2 recessive alleles All offspring will have same character as parent with dominant allele (will carry recessive allele) Pure breeding parents with different co-dominant alleles All offspring will have the same character and the character will be different from both parents (will be a mixture of the two) Two parents with one dominant and one recessive allele each Three times as many offspring have the character of the parent with dominant alleles as the recessive A parent with one dominant and one recessive allele and a parent with 2 recessive alleles Equal proportions of offspring with the character of an individual with a dominant allele and the character of an individual with recessive alleles

Recessive Diseases (cystic fibrosis) -Most diseases caused by a recessive allele -Disease in individuals without dominant allele -Have two copies of the recessive allele If they have one dominant allele and one recessive allele they are able to pass on that disease to offspring CARRIER

Sex-linked diseases Dominant or co-dominant alleles Usually carried on the X chromosome Haemophilia Red-green colour blindness Affects more males

Co-dominant diseases Sickle cell anaemia HbA = normal haemoglobin, can get malaria, not anaemic HbS = sickle cell haemoglobin, can get malaria, anaemic HbS and HbA = normal haemoglobin, mild anaemia, increased resistance to malaria

Punnett squares look at the theoretical probability that a child will inherit a trait We use pedigrees to show inheritance of a disease/trait in a family Pedigrees

Pedigree Chart Diagrams which show biological relationships. They are used to show how a trait can pass from one generation to the next.

Pedigree Legend Male Female Horizontal line between male and female indicates a mating Shaded symbols stand for individuals with the trait being traced; they are the affected ones.

RECESSIVE DOMINANT

Pedigree I II 1.Which female(s) have inherited the disease? 2.Which male(s) have inherited the disease? 3.Is this disease dominant or recessive? III

Pedigree Challenge! D = normal d = disease Genotype A F B G C H D # E

Pedigree Challenge! D = normal d = disease Genotype A DdFdd B G Dd C ddH D Dd# E dd recessive disease

Human Genetic Diseases Most diseases have been identified (about 4000) Mostly rare recessive alleles Chance of inheriting a recessive allele and carrying it is much higher than inheriting 2 recessive alleles Able to sequence your genes to see if you or your partner are a carrier

Causes of Mutation Already know about the types of mutation that occurs in DNA

Causes of Mutation Radiation Can have enough energy to cause chemical changes in DNA Gamma rays, alpha particles, UV radiation and X-rays Chemical substances Benzopyrene and nitrosamines (tobacco smoke)

Causes of Mutation Mutations can affect the gene that controls cell division Cells divide endlessly = tumour Body cell mutations eliminated when that person dies If mutations happen in gametes they can be passed on

Causes of Mutation Hiroshima Nagasaki Chernobyl Where are these places? Why did it happen? What were people exposed to? How many people died immediately? What has happened to others since then? What other effects were there? (Environment, animals) What is the future for these places?