Adaptations Isolation(s) Sickle Cell & Malaria GET YOUR JOURNALS!!!

What are adaptations? Adaptations – an inherited characteristic that helps an organism to survive long enough to reproduce more successfully in its changing environment and can either be structural or behavioral

Section 15.2 Summary– pages Some speciation occurs while the organisms still exist in the same area… Reproductive Isolation –Behavioral, Temporal, –Mechanical, Geographic SPECIATION without a physical barrier

Reproductive Isolation Two way reproductive isolation occur:  Prezygotic mechanisms  Postzygotic mechanisms

 Temporal Isolation: Species reproduce in different seasons or at different times of the day.  Geographical Isolation: Physical barriers (e.g., rivers, oceans, mountains) prevent the mixing of populations.  Behavioral Isolation: Species differ in their mating rituals (e.g., differing bird songs, mating colors, dances, pheromones).  Mechanical Isolation: Body structure prevents mating. Prezygotic Mechanisms

 Hybrid inviability: Embryological Arrest: Hybrid embryos often do not develop properly; no viable offspring is created.  Hybrid Sterility: Infertility: Hybrid offspring might grow to viable adults, but these are infertile and cannot produce further offspring  This shuffling, along with sexual reproduction, leads to variation within populations. This variation leads to selection, which ultimately leads to evolution. – (Donkey + Horse = Mule; Mule is sterile.) Postzygotic Mechanisms

Speciation…and so much more…

Allopatric Speciation Occurs when a population is divided by a geographic barrier – Barriers: mountains, rivers, regions excluding vital resources (water, food) areas covered with volcanic lava Interbreeding between populations not possible (reproductive isolation) Gene frequencies can diverge due to natural selection, mutation, and genetic drift

Allopatric Speciation

Section 15.2 Summary– pages Divergent evolution is when species that are similar and closely related become increasingly different from each other. THEY DIVERGE This is also called Adaptive Radiation….because it has to do with ADAPTING to different environments and RADIATING out into different species. Types of Change

Adaptive Radiation Relatively rapid evolution of many species from a single ancestor.

Section 15.2 Summary– pages When distantly-related organisms evolve to become more similar, it is called convergent evolution. Convergent evolution occurs when unrelated species occupy similar environments in different parts of the world. Types of Change Also: Co-Evolution & Parallel Evolution

Rate of Speciation Current debate: Does speciation happen gradually or rapidly? Or both? – Gradualism – Punctuated equilibrium

Gradualism  Gradual change over long spans of time  assume that big changes occur as the accumulation of many small ones develop over time.

Punctuated Equilibrium Rate of speciation is not constant – rapid bursts of change – long periods of no change – species undergo rapid change when they 1 st bud from parent population Time

Sickle Cell & Malaria (HHMI) Please watch the video on the following slide to answer the questions on your quiz.

Sickle Cell & Malaria (HHMI)

Sickle Cell & Malaria (cont.) The following video is a shorter and simpler explanation of the sickle cell gene and malaria. This video is very poor quality and does not go into as much detail…but will provide the basic information required.

Sickle Cell & Malaria

Example of Natural Selection – “survival of the fittest” Reference: Protective Effects of the Sickle Cell Gene Against Malaria Morbidity and Mortality. Aidoo M, Terlouw DJ, Kolczak MS, McElroy PD, ter Kuile FO, Kariuki S, Nahlen BL, Lal AA, Udhayakumar V. Lancet 2002; 359: Graph of survival curves ("survival function estimates") of children without any sickle cell genes (HbAA), children with sickle cell trait (HbAS), and children with sickle cell disease (HbSS). Those who had the sickle cell trait (HbAS) had a slight survival advantage over those without any sickle cell genes (HbAA), with children with sickle cell disease (HbSS) faring the worst.