Hi everyone, welcome to IGCSE Study Buddy where you can revise biology topics from the Cambridge IGCSE syllabus. If you are enjoying these videos so far, please don't forget to hit the like button and subscribe to our channel. In this video, you are going to learn part 1 of chapter 18, Variation and Selection. Variation is the differences between individuals of the same species.
Variation can be genetic and or phenotypic. Genetic variation is the differences in genetics among individuals within the same species. Examples of genetic variation include Blood group, eye colour, gender and the ability to roll the tongue.
Phenotypic variation is the variability of phenotypes within a population. So we know that phenotypes are the observable features of an organism. Phenotypic variation can be caused in two main ways. It can be genetic, that is controlled entirely by genes, or it can be environmental, that is caused entirely by the environment in which the organism lives. For example, factors such as climate, diet and lifestyle can cause differences in phenotypes.
An example of environmental variation is the difference in body type between an active person who exercises regularly and has a fit physique and a person who leads a less active lifestyle and may have a less muscular body type. Genetic variation in populations can be caused by various factors. Mutation, meiosis, random mating and random fertilization. Variation can be continuous or discontinuous. Continuous variation results in a range of phenotypes between two extremes.
Examples include body length and body mass. Continuous variation is caused by both genes and the environment. For example, if two siblings have the same genetic predisposition for height but one sibling has access to better nutrition and receives proper health care, they may grow taller compared to their sibling who lacks these advantages.
Discontinuous variation results in a limited number of phenotypes can be found in the following studies. with no intermediates. Examples include ABO blood groups, seed shape in peas and seed colour in peas.
Discontinuous variation is usually caused by genes only, unlike continuous variation which is caused by both genes and the environment. Let's investigate and describe examples of continuous and discontinuous variation. Continuous variation is when a trait can have many different values within a group of individuals. It's like a smooth gradual change without clear categories.
For example, when we talk about height, people can be short, tall or any height in between. It's a spectrum with no distinct groups, just a range of possibilities. They can usually be measured on a scale, for example, mass, height, etc. When graphs of these data are plotted, continuous variation gives smooth bell curves. This continuous variation is when a trait can have Only specific, distinct options without any in-between possibilities.
It's like having clear categories or groups for a particular characteristic. For example, when we consider blood group, it can be either A, B, AB or O with nothing in between. It's not a smooth spectrum but rather separate and defined options.
When graphs of these data are plotted, discontinuous variation gives a step-like shape. Let's move on to mutation. Mutation is genetic change. Gene mutation is a random change in the base sequence of DNA of an organism.
These genetic changes can occur due to a variety of factors including ionizing radiation such as X-rays and gamma rays can cause mutation by breaking DNA strands or altering the sequence. and exposure to some chemicals such as tar in tobacco. These factors increase the rate of mutation.
Mutation is the way in which new alleles are formed. If the mutation occurs at a particular allele, this allele may be altered, changing how it functions. Remember, an allele is a variation of a gene.
For example, let's say a brown-furred population of rabbits has a mutation that leads to lighter-coloured fur, which helps them blend in better with their environment and avoid predators, increasing their chances of survival. Next, let's learn about adaptive features. An adaptive feature is an inherited feature that helps an organism to survive and reproduce in its environment.
First, let's learn about the adaptive features of hydrophytes that allow them to survive in their environment. Hydrophytes are plants that are adapted to grow in or around water, such as ponds, lakes and rivers. Hydrophytes have special adaptations to survive in water. They have wide and flat leaves to increase their surface area to float near the water surface and efficiently absorb more sunlight required for photosynthesis.
Hydrophytes have small roots because they can absorb water directly through their leaves and stems. The stomata or tiny openings on their leaves are the ones that are most likely to absorb mostly found on the upper side allowing for efficient gas exchange. Next the adaptive features of xerophytes. Xerophytes are plants that are adapted to survive in dry environments with limited water. These plants have adaptive features which allow it to maximize water uptake and minimize water loss.
They have thick waxy cuticle on leaves to prevent water loss. Stomata are located in sunken pits to reduce water loss. They have small leaves, usually needle-shaped, to reduce surface area for evaporation. They have extensive roots to access water from deeper soil layers. and maximize water uptake.
They have thick stems or leaves that store water for periods of drought. You should be able to interpret images or other information about a species to describe its adaptive features. That concludes Part 1 of Chapter 18, Variation and Selection. Please visit our channel to explore the Cambridge IGCSE Biology playlist where you can find part 2 of chapter 18. Hope this video helped you. Please share your thoughts and suggestions in the comments section.
Thank you for watching and please don't forget to subscribe to IGCSE Study Buddy for more biology revision videos. Bye-bye.