Nota SAINS 1511: HEREDITY AND VARIATION

HEREDITY AND VARIATION: 

HEREDITY AND VARIATION PRESENT BY : PN. LELY NORIZAWATI

Cell Division: 

Cell Division Genes are units of inheritance that determine the characteristics of an individual The characteritics of individuals that are controlled by genes include the colour and type of hair, types of ear lobes, being right handed or left handed and many more. Genes are found in long molecules called deoxyribonucleic acids (DNA)

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There are thousand of genes in a DNA molecule DNA molecules are found in chromosomes. Chromosomes are thread- like structures in the nucleus of a cell.( pg 46) Each chromosome contains a long DNA molecule enveloped by protein. Chromosomes exist in pair, so do genes. Each pair of genes control one characteristic of an individual. Organisms of the same species have the same number of chromosomes in their cells.

CELL DIVISION: 

CELL DIVISION There are two types of cell division, namely (a) mitosis (b) meiosis Mitosis is process whereby a cell divides into two identical cells, each having exactly the same number and kind of chromosomes as the parent cell. Mitosis occurs in somatic cell.

Look also text book pg 48-49: 

Look also text book pg 48-49

Continue…: 

Continue… Mitosis in animal cells is similar to that in plant cells. The only differences between the two occurs during the division of the cytoplasm. In animal cells, the cytoplasm divides when the cell membrane shrinks in the middle of the cell, whereas the division of the cytoplasm in plant cells happens by formation of a new cell wall at the cell equator.

Cytokinesis…: 

Cytokinesis …

Meiosis: 

Meiosis Meiosis is a process whereby a cell divides into four daughter cells, each containing only half the chromosome number of the parent cell. Meiosis occur in reproductive organs to produce gametes. In human beings and animals, meiosis takes place in ovaries and testes. In plants, meiosis occurs in anthers and ovaries.

Continue…: 

Continue… In meiosis, nucleus divides twice but chromosomes double only once. Thus, each daughter cell has only half the number of chromosomes compared to the parent cell Each human somatic cell contains 23 pairs (46 chromosomes). Each sperm and ovum produced through meiosis has only half the number of chromosomes compared to the somatic cells. Hence, a sperm or an ovum

Comparison Between Mitosis And Meiosis: 

Comparison Between Mitosis And Meiosis

The importance of Mitosis and Meiosis.: 

The importance of Mitosis and Meiosis. In multicelular organism, mitosis produces new cells for (a) growing purpose (b) replacing worn-out or dead cells Unicellular organism reproducee asexually by mitosis. Mitosis is important to maintain the genetic materials in daughter cells.

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In agricultural field, mitosis is used in the techniques of cloning and tissue culture. Meiosis is important to organism that reproduce sexually because gametes are produced by meiosis. During meiosis, crossing over and random distribution of chromosomes occurs. This results in differences among individuals of the same species.

The Principles and Mechanism of Inheritance. : 

The Principles and Mechanism of Inheritance. Dominant genes express their effects whenever they are present. Capital letter is used(T, M) Recessive genes only show their effects in the absence of dominant genes. Small letter is used( t, m) Genotype : The genetic composition of an organism or the type of gene. ( TT, Tt ) A cross which carried out to study the inheritance of one trait is called a monohibrid cross.

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Phenotype refers to the observable characteristics of an organism such as curly hair Homozygous : A person who has two identical genes (for example, CC or cc) Heterogygous : A person with two different genes (for example, Cc) The first generation of the cross is called the first fillial or F1 generation.

Example of Monohybrid Cross: 

Example of Monohybrid Cross Characteristic – height T – dominant, t - recessive P genotype Tt X tt Gametes T t t t Fertilization F1 generation Tt tt Tt tt Phenotype Tall short tall short Phenotype Ratio 1 Tall : 1 Short Genotype Ratio 1 Tt : 1 tt

Sex Determination and The Occurrence of Twins in Human Beings.: 

Sex Determination and The Occurrence of Twins in Human Beings. Each human cell contains 23 pairs of chromosomes. Of these, 22 pairs are autosomes which play no part in determining the sex of a person. There are two types of sex chromosomes, namely the X chromosome and the shorter Y chromosome. Females have 44 + XX and male have 44 + XY

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HUMAN KARYOTYPES ( MALE AND FEMALE ) Things to discover : Identify the male and the female karyotypes

Sex Determination: 

Sex Determination During meiosis female produce only one type of ovum, which contain 22 autosomes and an X chromosome ( 22+X) In males, testes produce two types of sperm. ( 22 +X) and ( 22+Y) 3. The sex of baby is determined by the type of sperm that fertilises the ovum.

Schematic diagram of sex determination in human: 

Schematic diagram of sex determination in human Parent Father Mother Somatic Cell 44 + XY X 44 + XX Gametes 22 + X 22 + Y 22 + X 22 + X Genotype of F1 44+XX 44+XY 44+XY 44+XX generation Phenotype female male male female

The Occurrence of Twins: 

The Occurrence of Twins Identical twins results from the fertilizationof a single ovum by a single sperm. The single zygote that is formed then undergoes mitosis and divides into two embryos.. Then two fetus which share the same placenta. Contain same genetic information.

Non-Identical Twin: 

Non-Identical Twin Are formed if the two ova are fertilised by two sperm Two zygotes will be formed which develop into two foetuses . Each foetuses has his or her own placenta. Genetically different Same or different sexes

Siamese Twins: 

Siamese Twins Developing zygote which begin to split into two identical twins may for some reason, stop splitting halfway. Joined at some parts of their body. Contain exactly the same genetic information.

Mutation: 

Mutation Is a spotaneous change in the genetic information of an organism. Down’s syndrome, klinefelter’s syndrome and turner syndrome are caused by chromosome mutation. Colour -blindness, haemophilia and albinism are caused by genes mutations

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Chromosome mutation

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Karyotype of female with Down’s Syndrome A Down’s Syndrome individual has an extra copy of chromosome number 21, giving a total of 47 chromosomes in each cell.

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DOWN SYNDROM Affected individuals show : Mental and physical retardation To being susceptible to disease such as leukimea They have short, stocky bodies,thick neck They have fold of skin above the eyes

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GENE MUTATION May occur on a recessive or a dominant gene. Occurs at a single locus or gene position on a chromosome Involves either : - deletion - insertion - substitution of a nucleotide base Types of gene mutation:

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SICKLE RED BLOOD CELL Sickle - cell anemia – Caused by a mutation on a recessive allele responsible for the production of haemoglobin. - The mutated allele causes the red blood cells become sickle shaped or S – shaped. EXAMPLES :

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They have : White hair, pinkish eyes and skin - very sensitive to sunlight. ALBANISM - ALBINO The mutated allele cannot produce an enzyme responsible for the production skin pigment ( melanin )

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DO YOU KNOW? An example of a genetic disease by deletion is ß -thalassaemia - Affected individuals suffer from aenemia because they do not produce enough haemoglobin. POLYDACTYLISM - POLYDACTYL

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Syndrome No. of chromosomes Description Symptoms Turner 45 44 autosomes and one X chromosomes 1. Female. 2. Low level of sex hormones. 3. Very little development of secondary sexual characteristics klinefelter 47 44 autosomes and XXY sex chromosomes 1. Male. 2. Undeveloped sex organs. 3. Low level of testosterone. 4. Sparse body hair. 5. Developed breasts polyploidy 3n (triploid) 4n (tetraploid) Addition of one or several whole sets of chromosomes in an organism. Common among flowering plants and food like tomato, apple and wheat – produce bigger fruit.

Genetic diseases of mutation: 

Genetic diseases of mutation Genetic diasease Types of mutation Type of chromoome involved / number of chromosome Albino Gene mutation Autosome chromosome Sickle – cell anaemia Gene mutation Autosome chromosome Haemophilia Gene mutation Sex chromosome ( X ) Colour blind Gene mutation Autosome chromosome Syndrome Down Chromosome mutation Autosome chromosome / increase one chromosome at 21 chromosome Turner Chromosome mutation Sex chromosome / decrease one X chromosome Klinefelter Chromosome mutation Sex chromosome / increase one X chromosome Jacob Chromosome mutation Sex chromosome / increase one Y chromosome

The effects of genetic research on human life.: 

The effects of genetic research on human life. Genetic research in the field of medicines has contributed to the treatment of hereditary diseases. In the field of agriculture, genetic research is used in the production of genetically-modified food and selective breeding of plants and livestock The human genom project aims at identifying all the genes in the human genome.

Examples of variation in humans: 

Examples of variation in humans Curve Whorl Loops Composite Roller Non-roller Free lobe Attached lobe FINGERPRINTS EAR LOBE SHAPE TOUNGE - ROLLING

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Examples of variation in humans Body weight

Examples of variation in animals: 

Examples of variation in animals

Types of variation: 

Types of variation Two types of variation i) continuous variation ii) discontinuous variation

Continuous variation: 

Continuous variation The characters can be measured or graded on a scale. Examples : height, body weight, skin colour. Individuals show gradual differences from one extreme to another extreme / no clearly defined or distinct differences between the traits expressed for the characteristic. Graf plotted is normal distribution curve. Controlled by the genetic factor but easily influenced by environment. The character are not inherited

Discontinuous variation: 

Discontinuous variation The characters are discrete and cannot be measured. Examples : Ability to roll the tongue, type of ear lobe, type of blood, height. No intermediate forms. Graf plotted is discrete distribution curve. Controlled by the genetic factor and cannot influenced by environment. The characters are inherited.

Comparison between continuous variations and discontinuous variations : 

Comparison between continuous variations and discontinuous variations Continuous variations Discontinuous variations 1. Individuals show gradual difference 1. No intermediate phenotypes 2. Quantitative character, can be measured or graded 2. Qualitative character, cannot be measured or ungraded 3. Normal distribution curve 3. Discrete distribution curve 4. Character easily influenced by environment 4. Character is not influenced by environment 5. The characters are not only inherited 5. The characters are inherited

CAUSES OF VARIATION: 

CAUSES OF VARIATION GENETIC FACTORS ENVIRONMENTAL FACTORS Crossing over ( prophase 1) Independent assortment ( metaphase I ) Mutation (my occurs in reproductive cells) Random fertilization ( between gametes )

Exercises.: 

Exercises. Give three factors that may caused variation by enviroment ?

THE END FOR THIS CHAPTER: 

THE END FOR THIS CHAPTER THANK YOU FOR LISTENING