Variasi 6z6b2l

Variasi

6.1: Jenis-jenis Variasi

Variasi

Selanjar

Tidak selanjar

Tiada perbezaan ketara

Perbezaan ketara dan jelas

Bersifat kuantitatif kerana boleh

diukur

Kualitatif kerana cirinya sama ada hadir atau tidak

Dikawal oleh bilangan gen yang besar

Dikawal oleh bilangan gen yang sedikit

Dipengaruhi persekitaran.

Tidak dipengaruhi persekitaran

Discontinous Variation • Differences are discrete and clear-cut • Example: A. Blood group- A,B, O and AB B. Gender- male and female C. Tongue rolling- can or not D. Ear lobe- attached or unattached E. Widow’s peak or not F. Dimple

Discontinous Variation

Continuous Variation • Differences are slight • Example: A. Height B. Weight C. Foot length

Variation

6.1: Causes of Variation.

Phenotype= genetic factor + enviromental factor • Differences are discrete and clear-cut • Example: A. Blood group- A,B, O and AB B. Gender- male and female C. Tongue rolling- can or not D. Ear lobe- attached or unattached

Causes

Independent Assortment

Genetic factors

Enviromental factors

Sexual Reproduction

Mutation

Crossing Over

Random

Gene

Chromosomal

Fertilisation

Mutation

Mutation

Crossing Over • Is exchange of portions of chromatids between homologous chromosomes. • Happens during prophase I. • In a bivalent,portions of 1 chromosome exchange places (crossed over) with corresponding portion of the other chromosome. • Points of cross over called chiasmata. • Enables maternal and paternal allele mix. • NEW combinations of genes are produced on these chromatids.

Crossing Over

INDEPENDENT ASSORTMENT • Occurs in metaphase I. • Homologous pair of chromosomes are arranged at equator/metaphase plate at random. • Each homologous pair of chromosomes is positioned relative to the poles of the independent of the other pair. • Results in variety in gametes where each with different combination of paternal and maternal chromosome.

INDEPENDENT ASSORTMENT

INDEPENDENT ASSORTMENT

RANDOM FERTILISATION • Occurs when GAMETES with diverse combination of homologous chromosomes are fused together. • Forming a zygote with an even greater variety of gene combination. • Every zygote is genetically unique.

Mutation • Is a sudden random change in the genetic composition (DNA) of a cell. • Can happen to particular genes or chromosome. • Can occur in somatic cell or gametes. • Mutation in gametes can be inherited from generation to generation.

Types of Mutation

Chromosomal

Gene

Involves change in structure of chromosomes or number of chromosomes during meiosis.

Involves chemical changes in the structure of the gene

Changes in structure can be due to deletion, duplication,inversion and translocation.

Alteration in base sequence of DNA, hence changing the GENETIC CODE AND ORDER OF ACID AMINO for protein synthesis.

Types of Chromosomal Mutation That Changes Chromosome Structure

Types of Chromosomal Mutation That Changes Chromosome Structure

• Deletion A fragment of chromosome breaks off and is lost.

Types of Chromosomal Mutation • Duplication A fragment of chromosome is doubled/repeated. The new chromosome has extra genetic material.

Types of Chromosomal Mutation • Duplication

Types of Chromosomal Mutation • INVERSION

Types of Chromosomal Mutation • INVERSION A fragment of chromosome is removed. The fragment rotates through 180° and is inserted back at same location.

Types of Chromosomal Mutation • Translocation  A fragment of chromosome breaks off and then attaches to another chromosome.

Types of Chromosomal Mutation

Types of Chromosomal Mutation That Changes Number of Chromosome

Types of Chromosomal Mutation  Change in no of chromosomes Occur when homologous chromosome fail to separate during meiosis. Causes addition or loss of chromosomes in the gametes. Also known as : Non-disjunction Non disjunction of sex chromosome can re

Types of Chromosomal Mutation Non-disjunction Non disjunction of sex chromosome can cause a sperm cell either having both X and Y chromosomes or no sex chromosome. Or can cause an ovum either having two X chromosome or having no chromosomes.

Types of Chromosomal Mutation Non-disjunction .

Types of Chromosomal Mutation Non-disjunction .

Types of Chromosomal Mutation Non-disjunction

Types of Chromosomal Mutation Effect of Non-disjunction Disease

No of Chromosome involved chromoso me

characteristic

Down’s Syndrome

47 (45+ XX or 45+XY)

Extra chromosome on chromosome 21 (trisomy 21)

Can be female or male. Learning disabilities, heart defects, susceptible to infection, short, broad face and slanted eyes.

Turner Syndrome

45 (44+ XO)

Absence of one sex chromosome

Female. Sterile and lack of secondary sexual characteristics.

Klinefelter’s Syndrome

47 ( 44+ XXY)

An extra X chromosome

Male. Low fertility, smaller testes and some breast enlargement

Types of Chromosomal Mutation Effect of Non-disjunction Disease

No of Chromosome involved chromoso me

characteristic

Patau Syndrome

47,13

Extra chromosome on chromosome 13 (trisomy 13)

Small eyes, malformed nose, cleft lip or cleft palate, extra fingers or toes, mentally retarded and deaf, heart and kidney failure

Edward Syndrome

47,18

Absence of one sex chromosome

Mental retardation,severe growth retardation, malformed digestive tract, urinary tracts and genitals.

GENE MUTATION

Gene Mutation • Is a change in the base of sequence of DNA. • Five different types: a) Duplication- portion of nucleotide chain is repeated. b) Addition- extra nucleotide sequence is inserted into the chain c) Inversion- a nucleotide separates from chain, inverse and re at its original place.

Gene Mutation d) Deletion – portion of nucleotidechain is totally removed from the chain e) substitution- one of the nucleotide is replaced by another nucleotide with different nitrogenous base.

Deletion

Example of gene mutation  sickle cell anemia  Caused by substitution of one nucleotide for another in DNA  results in incorrect amino acid in hemoglobin  alter properties of hemoglobin abnormal hemoglobin causes RBC become sickle-shaped and low binding capacity of oxygen may dies.

Example of gene mutation  cystic fibrosis Body produce excessively thick and sticky mucus that closes lungs and pancreas-impair breathing and digestion Produce extremely salty sweat loses lot of salt imbalance in mineral

Mutagens  agent that causes mutation Examples: a) X rays b) Uv light c) Gamma rays. d) Chemical such as formaldehyde, pesticide, drugs and components of tobacco smoke.

Effects of Enviromental Factors  can change in phenotypes. Influenced continous variation greatly Nutrients,light, temperature,pH Example: Hydrangea flowers are blue in acidic soil and pink in alkaline flower