PATTERNS OF INHERITANCE

1. PATTERNS OF INHERITANCE JANUARY 14, 2011

2. INTERESTING FACT • All the ova from which the present human poplation was derived can fit into a 5-litre bottle. • All the sperm that fertilized them could fit in a…… • THIMBLE.

3. For years similarities between children and parents  obvious. • Male + female = offspring • But how?

4. Aristotle 384-322 BC  semen + menstrual fluid  offspring X • van Leeuwenhook 1677  sperm in semen contain miniature human that implant in female to be born X • de Graaf 1670s  discovered the Graafian follicle from which came the ovum O

5. Both parents contribute hereditary characteristics and the offspring is a blend of both. • The offspring therefore has two sets of genetic information but only one of any pair of genes expresses itself.

6. MENDEL,1866 THE RUSSIAN MONK

7. Mendel performed experiments referring the process of hybridization in plants. • He focused on the different forms in which hybrid offspring appear and the statistical relationship between them.

8. HIS EXPERIMENTS • He chose the pea Pisum sativum for his research because: • Several distinct varieties existed • Easy to cultivate • Self-pollinating (pure breeding)  same characteristics gen. after gen. • Artificial cross-breeding varieties possible  fertile hybrids.

9. HIS SUCCESS • He succeeded because of careful use of the scietific method. • Familiarized self with the plants • Only one variable studied at a time’ • Meticulous methodology • Sufficient statistical data collected • Lack of genetic features such as codominance and linkage

10. DEFINITIONS • DNA- Deoxyribonucleic acid. This substance is the back-bone of all genes and therefore assists to make up chromosomes. DNA is found in the nucleus of cells. • RNA-Ribonucleic acid. This substance helps to make new DNA and hence genes and chromosomes. There are three types, one found in the nucleus and two in the cytoplasm of cells.

11. Chromosomes: material found in the nuclei of cells, are composed of DNA and protein and contain genetic information in the form of genes.

12. Genes: the basic unit of inheritance for a given characteristic or trait.

14. Alleles: contrasting forms of the same gene found occupying the same locus (position) on homologous chromosomes. They may produce the same or different qualities.

15. Homozygous: having two identical alleles in corresponding positions on homologous chromosomes.

16. Heterozygous: having two contrasting alleles in corresponding positions on homologous chromosomes.

17. Phenotype: the outward, visible expression of a gene. E.g. hair colur, eye colour, gender. • Genotype: the inward, genetic make-up of the organism, especially its alleles (contrasting genes).

18. Phenotype: the outward, visible expression of a gene. E.g. hair colour, eye colour, gender.

19. Dominant: the allele which, if present, shows its effect on the phenotype in both the homozygous and heterozygous conditions. Allele usually represented by capital letters. • Recessive: the allele which only has an effect on the phenotype of the dominant allele is absent. Allele usually represented by common letters.

21. Incomplete dominance or co-dominance: neither allele shows dominance or recessiveness. The phenotype of the heterozygote is intermediate between the two homozygous conditions.

22. MONOHYBRID INHERITANCE

23. For monohybrid inheritance Mendel stated that: • The characteristics of an organism are determined by internal factors which occur in pairs. Only on of a pair of such factors can be represented in a single gamete.

24. Monohybrid Inheritance • Inheritance is the process by which certain characteristics or traits are passed on from generation to generation. • Monohybrid inheritance is the analysis of only one of these traits at a time. • It is very simple to do.

25. A diagram called a Punnett Square is usually used in order to work out monohybrid inheritance. • We say that we perform a monohybrid cross.

26. Definitions to definitely remember when performing these crosses are: • Dominant • Recessive • Genotype • Phenotype • Co-dominance and incomplete dominance.

27. We will be using monohybrid crossing to predict the genotypic and phenotypic ratios of off-spring born with: • Different genders (male or female) • Albinism • Sickle-cell • Haemophilia • Night-blindness • Blood types

28. Finally, we will be able to trace defects, diseases or traits throughout family trees when we have mastered the monohybrid cross. • Along the way we will pay attention to ratios that are expected for certain crosses.

29. Performing Monohybrid Crosses

30. STEPS • 1). Choose letters to represent the alleles/genes. • 2). Determine the genotypes of the parents. • 3). Determine the available gametes. • 4). Draw Punnett Square. • 5). Assign gametes. • 6). Fill in Punnett Square. • 7). Analyze results for phenotypic and genotypic ratios.

32. Mating for Albinism • Albino X Albino • Albino X Homozygous black (normal) • Albino X Heterozygous black (normal) • 2 Hetero normals • Homozygous normal X Hetero normal • 2 Homozygous normals

34. Mating for Tallness • Short X Short • Short X Homozygous tall • Short X Heterozygous tall • 2 Hetero tall • Homozygous tall X Hetero tall • 2 Homozygous tall

36. Eye Colour • 2 Homozygous brown • 2 Heterozygous brown • Homo brown X Hetero brown • Homo brown X Green • Hetero brown X Green • 2 Green eyed parents

38. Inheritance of Gender • Females have 2 X chromosomes (XX). • Males have one X and one Y chromosome (XY). • Let us do a monohybrid cross to determine how sex is passed on from parents to of-spring.

40. Sex-Linked Genes • Sex-linked genes are genes that are only found on the longer region of the X chromosome and so will be absent from the Y chromosomes in males. • When performing crosses involving sex-linked genes, the letters representing the alleles are attached to larger letters that represent the chromosomes, so that we will be able to tell if we are dealing with a man or woman. • In sex-linkage, women are called carriers, but not men.

41. Mating for Haemophilia • Normal parents • Haemophiliac parents • Haem mom x Haem dad • Haem mom x normal dad • Carrier x haemophiliac • Carrier x normal

43. Mating for Colour-blindness • Normal parents • Colour-blind parents • Colour blind mom x normal dad • Colour blind dad x normal mom • Carrier mom x normal dad • Carrier mom x colour-blind dad

45. Co-dominance • A form of inheritance in which both alleles are equally shown. Blood typing is a great example. AB blood is the codominant relationship between the A protein and B protein both expressing themselves completely. AO (type O allele means there is no protein), A is dominant and you see type A phenotype. BO is the same except you see the B phenotype. Type O is recessive

46. With codominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype in which both of the parental traits appear together.

47. Mating for Sickle Cell • 2 parents with sickle cell disease • 2 parents with sickle cell trait • Sickle cell disease X Sickle cell trait • Sickle cell disease x normal • Sickle cell trait x normal

49. Incomplete dominance • A form of inheritance in which the heterozygous alleles are both expressed, resulting in a combined phenotype. The one example that most books give is seen in some flower colors. A red and a white allele gives pink. If it were codominance, you would see the red and white colors. Incomplete dominance is most commonly found in plants.

50. With incomplete dominance, a cross between organisms with two different phenotypes produces offspring with a third phenotype that is a blending of the parental traits.