1. Human inheritance

2. Which human characteristics show a simple pattern of inheritance? Human inheritance

3. Click here to go directly to DNA Click here to go directly to chromosomes Click here to go directly to boy or girl Click here to go directly to inheritance

4. DNA, genes and chromosomes Cell Nucleus Chromosomes (tightly packed with DNA) Gene (section of DNA)

5. DNA (deoxyribonucleic acid) What is DNA? –DNA is a long string of molecules. What does a DNA molecule look like? –a DNA molecule is like a twisted ladder. –the rungs of the ladder are made up of four different compounds called bases, which come together in pairs: Cytosine pairs with Guanine. Adenine pairs with Thymine. Why is DNA special? –the DNA molecule (ladder) can pull itself apart and make an exact copy of itself.

6. Deoxyribonucleic acid (DNA) double helix (twisted ladder) bases (rungs)

7. Deoxyribonucleic acid (DNA) Cytosine (C) Guanine (G) Thymine (T) Adenine (A) pairs with

8. DNA (deoxyribonucleic acid) What does DNA do? –DNA carries a coded messages that enables cells to build up the enzymes (proteins) that control the cell. How does DNA enable proteins to be made? –three pairs of bases (three rungs of the ladder) is the code for one amino acid. –so the sequence of bases in DNA controls the sequence of amino acids that the cell joins together to make proteins. –there can be 250 million bases in a DNA molecule.

9. Base pair amino acid codes Amino acid The order of the base pairs along the DNA molecule is also the code to decide the order in which the amino acids join to make protein molecules. Three base pairs on the DNA molecule is the code for one particular amino acid

10. Homologous chromosome pairs Chromosomes in cells are found as homologous pairs: –homologous means the same. –one of each pair comes from mum, the other from dad. –homologous chromosomes contain the same kind of gene in the same places along their length. –there can be two forms of the same gene. –each form of the same gene is called an allele.

11. Locus: position on the chromosome where the gene is located. Homologous chromosome pairs Alleles: this pair controls melanin production by skin cells. M m M = dominant allele - allows melanin production. m = recessive allele - does not allow melanin production.

12. Loci Homologous chromosome pair Tt Aa BB Cc dd Alleles of the same gene Different genes Homozygous dominant alleles Homozygous recessive alleles Heterozygous alleles Diagram of a homologous chromosome pair They come together during fertilisation. One comes from the sperm cell, the other from the egg cell. Loci indicate the position of a gene on a chromosome.

13. Male and female human chromosomes X X X Y Chromatids only appear as chromosome starts to copy itself. Ordinary human body cells each contain 46 chromosomes. Chromosomes can be sorted into homologous pairs, one of each pair from mum the other from dad. Male has one X chromosomes from his mum and one Y chromosome from his dad. Female has one X chromosomes from her mum and one X chromosome from her dad.

14. Boy or girl? 44+ 22+ 44+ 22+ 44+ 22+ 44+ Male body cells Female body cells Body cell mitosis Baby Girl Boy 22+ Sperm cells Egg cells meiosis during meiosis cell chromosome number is reduced by half fertilisation results in random recombination of X and Y chromosomes

15. Huntington’s disease A disorder of the nervous system affecting 1 in 20,000. Caused by the dominant allele of a gene. Only one allele is necessary to give the disease. So all heterozygous people could be sufferers. It shows up only when a patient is about 30 to 40 years old. Many couples will have already produced a family by this time.

16. Cross between a heterozygous person (with Huntington’s disease) and a normal homozygous recessive person: Inheritance of Huntington’s disease H h h h HhHh hh h HhHh Dominant allele = H Recessive allele = h There is a 50% chance of a baby suffing from Huntington’s disease.

17. Huntington’s disease GenotypePhenotype Hh HH hh Has Huntington’s disease because dominant allele causes the disorder. Normal. Has Huntington’s disease because dominant allele causes the disorder

18. Cystic fibrosis Cystic fibrosis is a disorder of cell membranes. Affects 1 in 2,000 children. Causes the lungs to produce a sticky mucus that makes breathing difficult. It also affects the digestive system. making the absorption of food difficult. It is caused by the recessive allele of a gene. It must be inherited from both parents Both parents may be carriers of the disorder without actually having the disorder themselves.

19. Cystic fibrosis GenotypePhenotype CcCc CC cc Normal Normal but carrying the recessive cystic fibrosis allele Cystic fibrosis sufferer

20. Cross between a homozygous dominant female and a homozygous recessive male: Inheritance of cystic fibrosis C C c c CcCc CcCc CcCc CcCc Dominant allele = C Recessive allele = c None of their babies will suffer from cystic fibrosis but they will all carry the recessive cystic fibrosis gene.

21. Cross between a heterozygous (carrier) female and a heterozygous (carrier) male: Inheritance of cystic fibrosis C c C c CC CcCc cc CcCc Dominant allele = C Recessive allele = c There is a one in four chance of a baby suffering from cystic fibrosis.

22. Cross between a heterozygous(carrier) female and a homozygous recessive male: Inheritance of cystic fibrosis C c c c CcCc cc CcCc Dominant allele = C Recessive allele = c There is a 50% chance of their babies suffering from cystic fibrosis any other babies will be carriers.

23. Cross between a homozygous dominant female and a heterozygous (carrier) male: Inheritance of cystic fibrosis C C C c CC CcCc CcCc Dominant allele = C Recessive allele = c None of their babies will suffer from cystic fibrosis but there is a 50% chance of a baby being a carrier.

24. Sickle-cell anaemia The dominant allele cannot completely ‘switch off’ the recessive allele, so both alleles influence the phenotype. Sickle-cell anaemia Red blood cells are sickle-shaped because they contain an abnormal type of haemoglobin. Common in Africa.

25. Sickle-cell anaemia GenotypePhenotype SsSs SS ss Normal Sickle cell trait – slight form of the disease. Some resistance to malaria. Sickle-cell anaemia (die young)

26. Sex linkage Inherited characteristics associated with alleles carried on the sex chromosomes: –eg: Haemophilia blood does not clot because of lack of factor 8 in the blood. Factor 8 helps to form blood clots at the site of injury. factor 8 manufacture is controlled by alleles carried on the X chromosome: allele X H causes Factor 8 formation. allele X h does not cause factor 8 formation.

27. Haemophilia Genotype / Phenotype FemalesMales GenotypeX H X H Y Phenotype GenotypeX H X h X h Y Phenotype GenotypeXhXhXhXh PhenotypeFoetus does not usually develop Normal Haemophilia

28. Inheritance of hair colour dd DD or Dd dd Dd DD or Dd Dd Alleles: D = dark hair d = red hair

29. Inheritance of ear lobes Alleles: L = free lobes l= attached lobes ll Ll ll Ll LL or Ll