1 / 10

Monohybrid Inheritance

Monohybrid Inheritance. Section 11. Monohybrid Inheritance. Gregor Mendel (1822-1884): - Used varieties of pea plant - Ensured large numbers were used - Studied only 1 characteristic - Observed 3:1 phenotypic ratio

sdominguez
Download Presentation

Monohybrid Inheritance

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. Monohybrid Inheritance Section 11

  2. Monohybrid Inheritance • Gregor Mendel (1822-1884): • - Used varieties of pea plant • - Ensured large numbers were used • - Studied only 1 characteristic • - Observed 3:1 phenotypic ratio • Principle of segregation: ‘ the alleles of a gene exist in pairs but when gametes are formed, the numbers of each pair pass into different gametes. Thus each gamete contains only one allele of each gene.

  3. Homozygous (TT) or (tt) – 2 of the same allele • Heterozygous (Tt) – 2 different alleles

  4. Law of probability • Most monohybrid crosses give roughly 3:1 phenotypic ratio • 1 in 4 chance of a recessive allele being expressed • 200 animals – roughly 150 have 1 phenotype, 50 will have another • Since fertilisation is random – rarely 3:1 exactly

  5. Monohybrid Inheritance in humans • Family trees used to predict genetic trends • E.g. tongue rolling • Rhesus D antigen: • D-antigen – found on some blood cells • Present = Rhesus positive blood (Rh+) • Absent = Rhesus negative (Rh-) • Rh- people produce anti-D antibodies –’sensitised’ • Antigen-D present (DD/Dd) • Antigen-D absent (dd)

  6. Monohybrid Inheritance in humans • Albinism: • Inability to make melanin – pigment for skin, eyes, hair etc. • Is a recessive trait • AA or Aa = normal • aa = albino • Other examples • - Cystic Fibrosis (mucus secretion) • - Phenylketonuria (PKU) • - both are recessive traits

  7. Monohybrid Inheritance in humans • Huntingdon’s Chorea: • Determined by a dominant allele • Only expressed after average of 38 years old • 50% chance of children of Huntingdon’s sufferer getting the disorder • 1 in 20,000 cases

  8. Incomplete dominance – sickle cell anaemia • Mutation of haemoglobin gene – haemoglobin S synthesised • Homozygous (SS) – Sickle cell anaemia • - reduced oxygen carrying capacity • - blood cells malformed (sickle-shaped) • Heterozygous – (HS) – Sickle cell trait - both types of haemoglobin present - neither H or S are dominant (incomplete dominance) - sickle cell = malaria resistance

  9. Incomplete / Co-Dominance • Incomplete – both alleles expressed in the phenotype, but unevenly • - sickle-cell: more H than S expressed • Co-Dominance - both alleles equally expressed in the phenotype • - AB blood – exactly 50:50 split • - MN blood - another blood type antigen • - no antibodies produced • - equal expression (equal dominance

  10. Multiple Alleles • 3 or more alleles for a characteristic • 3 alleles = 6 possible genotypes • No. of phenotypes depend on the type of dominance • – complete, incomplete or co-dominance • E.g ABO blood – 6 genotypes, 4 phenotypes

More Related