1 / 23

Topic 4.3

Topic 4.3. Theoretical genetics. 4.3 Define…. Mendel’s experiments. Mendel’s experiments. Monohybrid cross: A cross that tracks the inheritance of a single character. Pea colour Mendel’s experiment. Flower colour Mendel’s experiment:. P. true-breeding purple-flower peas.

angie
Download Presentation

Topic 4.3

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Topic 4.3 Theoretical genetics

  2. 4.3 Define…

  3. Mendel’s experiments

  4. Mendel’s experiments Monohybrid cross: A cross that tracks the inheritance of a single character. Pea colour Mendel’s experiment Flower colour Mendel’s experiment: P true-breeding purple-flower peas true-breeding white-flower peas F1 100% self-pollinate F2 3:1 75% purple-flower peas 25% white-flower peas

  5. Mendel’s experiments Therefore, the Principle of Segregation indeed is a general principle of genetics.

  6. Mendel’s conclusions: • Inheritance is not blended. • The inheritable factor for white color was not lost, it was masked by the presence of purple color factor. • The hybrid plants inherit one factor from each parent and so have two different factors. • When they form male and female gametes they pass on either the dominant or the recessive factor, not both. Mendel’s Law of Segregation: Each genetic trait is produced by a pair of alleles which separate during reproduction. During meiosis, each gamete only gets one copy of the genetic trait.

  7. Mendel’s conclusions: Mendel’s Law of Segregation:

  8. 4.3.2 Punnet Squares • (1) Define symbols: • P = Purple allele • p = White allele • (2) State the cross • (3) Diagram the gametes • (4) Complete the squares • (5) Summarize the results: • Genotype • Phenotype In a Punnett square for a monohybrid cross, the Principle of Segregation is applied.

  9. Monohybrid test cross • How can you determine genotype from individual expressing dominant phenotype? - DD or Dd? Cross the individual with dominant phenotype with a homozygous recessive individual.

  10. 4.3.2 Punnet Squares

  11. Others inheritance pattern Co-dominance Multiple alleles: ABO group

  12. 4.3.5 Determination of gender in humans How many chromosomes do humans have? How many pairs of chromosomes? How many of them are autosomes? How many of them are sex chromosomes ?

  13. 4.3.5 Determination of gender in humans Some genes are present on the X chromosome and absent from the shorter Y chromosome in humans

  14. 4.3.7 Define sex linkage Genes located on a sex chromosome are called sex linked genes. In humans the term usually refers to X-linked characters: genes located only on X chromosomes. Fathers can pass X-linked alleles to their daughters, but not sons. Mothers can pass sex-linked alleles to both sons and daughters. Homozygous or Heterozygous for a sex-linked trait ♀:2 X’s Chromosomes Hemizygous for a sex-linked trait Shows a recessive trait even with only one recessive allele ♂:1 X Chromosome

  15. 4.3.8 Describe the inheritance of colour blindness The allele of color vision is carried on the part of the X chromosome that is missing from the Y chromosome. This means that a male will only have one allele for color vision. There is a defective, recessive allele of the color vision gene which can lead to color blindness, particularly of red and green light. C= allele for normal vision c= allele for color blindness

  16. 4.3.8 Describe the inheritance of colour blindness What happens if we cross a normal sighted female with a color blind male? What happens if we cross a normal sighted male with a carrier female?

  17. 4.3.8 Describe the inheritance of Haemophilia Haemophilia is a sex-linked disease, caused by a recessive allele on the X chromosome. The gene that codes for Factor VIII, an important protein involved in blood clotting, is a sex-linked gene found on the X chromosome. A defective recessive allele of the gene can lead to haemophilia. H= normal allele h= haemophiliac allele

  18. 4.3.9 Female and sex linkage  Females can be homozygous or heterozygous for the sex-linked alleles 4.3.10 Females carriers for X-linked recessive alleles. • Carrier are individuals that are heterozygous for the allele. • The have both the dominant and the recessive (disease) allele. • Carriers do not have the disease.

  19. 4.3.11 Predict genotypic and phenotypic ratios…

  20. Pedigree Charts: • Pedigree charts show a record of the family of an individual • They can be used to study the transmission of a hereditary condition • They are particularly useful when there are large families and a good family record over several generations.

  21. Generations are identified by Roman numerals Individuals in each generation are identified by Arabic numerals numbered from the left Therefore the affected individuals are II3, IV2 and IV3 I II III IV Pedigree Charts:

  22. 4.3.11 Deduce the genotypes and phenotypes … Females who have more than four sons, with none exhibiting hemophilia, are likely to have the genotype NN. If she has had four or fewer sons her genotype is less certain. In such cases her genotype is labeled N_. LABEL THE REST OF THE FEMALES AS EITHER N? OR NN. Q10 What is the probability of parents 1 and 2 having a hemophiliac child ? Q11 Is there any chance of parents 3 and 4 having a hemophiliac son ? Explain. Figure I Hemophilia Pedigree

  23. 4.3.11 Predict genotypic and phenotypic ratios…

More Related