Unit5: Biological Inheritance
- 2. INDEX 1. Genes 2. Early Genetic Studies 3. Special cases 4. Location of Genes 5. DeterminingSex
- 3. 1. Genes Hereditary trait • characteristic which can be passed on to the offspring. Gene • Unit that transmits genetic information. It is made up of DNA. Genotipe • set of genes that an individual has Phenotype • Set of observable traits that an individual has (it can be influenced by the environment) (caracteres hereditarios/características hereditarias)
- 4. A gene can have different variants, called alleles. An individual has 2 alleles for each trait: one from the father and one from the mother If both alleles are the same for a trait (purebred) Homozygous individual If both alleles are different for this trait (hybrid) Heterozygous individual (individuo homocigoto/heterocigoto) (Línea pura)
- 5. Example 1: For the trait “hair colour in guinea pigs”: Two alleles are possible: N = black dominant allele n = white recessive allele GENOTYPE PHENOTYPE NN dominant homozygous Black nn recessive homozygous White Nn heterozygous black The dominant allele prevent the recessive allele from appearing
- 6. Example 2: For the trait “flower colour in morning glory flower” two alleles are possible: N1 (red) and N2 (white) GENOTYPE PHENOTYPE N1N1 (homozygous) Red N2N2 (homozygous) White N1N2 heterozygous Pink!! N1N1 N2N2 N1N2 N1 and N2 are equally strong, they are co-dominant alleles and cause INTERMEDIATE INHERITANCE
- 7. 2. Early Genetic Studies Gregor Mendel was an Austrian monk (2nd half of the 19th century) His discoveries form the basis of modern genetics. He worked with pea plants (easy to see traits and to handle) He did lots of crossings between pea plants with different traits probabilities Seeds Smooth Wrikled Yellow Green Flowers Red White Stems Long Short He started working with purebred individuals (homozygous individuals) (NN or nn)
- 8. 1st Mendel’s Law: Principle of Uniformity When two purebred individuals are crossed, all of their offspring (F1) will have identical phenotypes. They will also have identical genotypes: heterozygous P: parents Gametes produced F1: first filial generation Page 88 activities 1 and 2 Yellow pea Green pea Yellow peas
- 9. Principle of Segregation Gametes produced Gametes produced When two heterozygous individuals from the F1 are crossed, in the F2 appear again the two phenotypes of the Parentals Genotypes probabilities: AA 25% Aa 50% aa 25% Phenotypes probabilities: Yellow 75% Green 25%
- 10. 2nd Mendel’s law: Principle of Independant assortment When two individuals that have two or more different traits are crossed, the transmission of each trait is independent from the other traits This only works for non-linked traits!! A = yellow a = green A>a B = smooth b = wrinkled B>b Possible gametes: AB ab Possible gametes: AB Ab aB ab
- 11. Phenotypes probabilities: Yellow smooth (A_B_) Yellow wrinkled (A_bb) Green smooth (aaB_) Green wrinkled (aabb) 9/16 3/16 3/16 1/16 9:3:3:1 Page 91 activities 3, 4, 8, 9, 10 and 11
- 12. 4. Chromosomal theory of heredity Morgan (1915) developed a theory about the role of chromosomes in inheritance: Chromosomal theory of heredity (teoría cromosómica de la herencia) • Genes are located on chromosomes on a specific place (locus). • Each gene is made up of a segment of DNA. • 2 alleles which determine a specific trait are located on two homologous chromosomes. Drosophila melanogaster (1 locus/ many loci)
- 13. Some genes and their locus on chromosome 7
- 14. All the genes located on the same chromosome are linked to each other and are transmitted together, specially if they are not very far away from each other Page 95 activities 15, 16, 17, 23
- 15. 5. Determining Sex In many animals there are different chromosomes in males and females: In human being 2 sex chromosomes XY/XX 44 autosomes Common to both sexes Genes not related to sexual differences Genes that take part in the development of the male XX XY Page 95 activities 15, 16, 17, 23 Page 91 activities 5 and 7
- 16. Human female karyotype Human male karyotype Karyotype = the chromosomes of a cell, usually displayed as a systematized arrangement of chromosome pairs in descending order of size.
- 17. 6. Inheritance Linked to Sex A trait linked to the X chromosome is a trait controlled by a gene located on the X chromosome. Examples: daltonism (colour blindness) and haemophilia Individuals Female Male XX (healthy) XY (healthy) XdXd (ill) XdY (ill) XdX (carrier but healthy) Problem: A daltonic man wants to have babies with a healthy woman. What are the probabilities to get a daltonic boy?
- 18. Man with daltonism x healthy woman Xd Y X XdX XY Genotypes: XdY XX Problem 2: A healthy man wants to have babies with a carrier woman for haemophilia. What are the probabilities to get a haemophilic boy? Sol.: all boys are healthy and all girls are carrier The probability to obtain a daltonic boy is 0%. Genotypes: XY XdX X Y X XX XY Xd XhX XhY (50% of men will be haemophile) Sol.: The probability to obtain a haemophilic boy is 25%.
- 19. Family tree: Haemophilia in the Borbons http://biogeogc.wikispaces.com/Gen%C3%A9tica
- 20. 7. Mutations Mutations are unexpected and random changes in genes or DNA sequence. Mutation types Gene mutation The alteration affects the chemical structure of the DNA. Chromosome mutation The alteration affects the structure of the chromosomes. Numerical mutation The alteration affects the number of chromosomes. Chromosome mutation Gene mutation
- 21. Numerical mutations Karyotype from a male with Klinefelter syndrome
- 22. Causes of mutations Physical mutagens Radiation (X-rays, UV rays from the Sun…) Chemical mutagens Pollutants, tobacco smoke, some pestices… Biological mutagens Some viruses like Human Papilloma Virus
- 23. Page 101 activities 26, 27, 31, 32 Page 102 activities 2, 8 and 10 Development of Basic Competences page 103 (ALL) Glossary: • Purebred • Intermediate inheritance • Genotype • Phenotype • Allele • Trait