Variation 1

:

CHAPTER 14.0:

VARIATION

Chapter 14.0: Variation

14.0 Variation

14.1 Introduction

14.1.1 Continuous & discontinuous variations

14.1.2 Sources of Variation

14.2 Selection

14.3 Speciation



DEFINITION OF VARIATION a change or slight difference in

characteristics/morphology/traits between individuals of the same species or natural

population

Learning Outcomes : 14.1 a) Explain Variation and its importance b) Describe types of variation: Continuous (quantitative) and discontinuous (qualitative) variations.



The importance of variations:-

Allow a species to inhabit a wider range of habitats. Increase the ability of a species to survive in a changing environment. Can survive and reproduce to pass their genes to their offspring. Natural selection increase the allele frequency of the favoured traits.



The importance of variations:-

Changing the genetic composition of the population over time which leads to evolution. May lead to the formation of a new species. Population with little variation has lower chance to survive/ adapt to changing environment. May lead to extinction of the population/ the whole species.


Two types of variation:

1. Continuous

2. Discontinuous



Variation shown by members of a species may due to: 1. Differences in genetic constitution 2. Differences in environmental conditions 3. Effects of interactions between genetics and environmental influences


VARIATION

TYPES SOURCES

DISCONTINUOUS

(qualitative)

GENETIC

CONTINUOUS

(quantitative) ENVIRONMENTAL



CONTINUOUS & DISCONTINUOUS VARIATIONS

Continuous Variation Discontinuous Variation

Individuals cannot be

grouped into distinct &

discrete phenotypes

Individuals can be grouped

into distinct & discrete

phenotypes

Characteristics vary

continuously from one

extreme to other with

intermediate phenotypes

Characteristics are distinct

with no extreme or

intermediate phenotypes





Quantitative character, can

be measured or graded on a

scale

Qualitative character, cannot

be measured or graded

Character is controlled by

two or more

genes/polygenes

Character is usually

controlled by a single gene

with clear effect

(Determined by different

alleles in a single locus)





Normal distribution curve

Discrete distribution curve





Phenotype expression of

characteristic influenced by

genetic & the environment

Phenotype expression of

characteristic influenced by

genetic only

Eg: height in humans,

skin colour of humans,

weight in humans

IQ

Eg: colour blindness,

free/attached earlobes ,

human blood group,

can/cannot roll tongue,

straight/curly hair,

wrinkled/smooth garden

peas, ability to taste PTC



TYPES OF VARIATION - CONTINUOUS

Height in humans

Handspan

Learning Outcomes : 14.1 a) Explain Variation and its importance b) Describe types of variation: Continuous (quantitatuve) and discontinuous (qualitative) variations.


TYPES OF VARIATION - DISCONTINUOUS

Cases of sickle-cell anaemia



TONGUE ROLLING

CANNOT ROLE

ABILITY TO ROLE TONGUE HAIRSTYLE

STRAIGHT HAIR

CURLY HAIR

ATTACHED OR DETACHED EAR-LOBE

Examples of Discontinuos Variation


Learning Outcomes : 14.1 a) Explain Variation in population b) State types of variation: continuous (quantitative) and discontinuous (qualitative) variations.

VARIATION

TYPES SOURCES

DISCONTINUOUS

(qualitative)

GENETIC

CONTINUOUS

(quantitative) ENVIRONMENTAL


Two main sources: 1. Genetic

2. Environmental

- Variation shown may also due to the interactions between genetic and environmental influences

Genetic variation (changes in genetic material) may involve:

1. Mutation

a) gene mutation

-changes in the sequence of nucleotide bases in a single gene may produce new / different phenotype

b) chromosomal mutation

-changes in in the number/amount or structure/ arrangement of chromosomes which can happen during mitosis and meiosis



2. genetic recombination

a) crossing over

-during prophase I of meiosis, non-sister chromatids of homologous chromosomes exchange segments;

-this produces chromosomes with new combinations of maternal & paternal genes

b) independent assortment of chromosomes during metaphase I of meiosis

c) random fertilization of gametes may produce zygote which is genetically different from others

Causes continuous and discontinuous variations, inheritable.



Gene mutation produce seedless orange

Gene mutation produce more meat

GENE MUTATION



CHROMOSOMAL MUTATION



Occur during meiosis forming recombinant variability.

CROSSING OVER




SOURCES OF VARIATION (environment)

Environmental variation involves environmental factors that act to produce phenotypic differences between individuals

Environmental variation causes continuous variation

Examples of environmental factors:

food supply (which affects growth)

Climate (eg: animals which live in cold climates grow thicker fur)

Culture (sikhs, buddist monks)


For example Sikhs grow their hair very long and never cut it, but Buddhist monks shave their heads.


Variation 1

Documents

Transcript of Variation 1