Chapter 3 Heredity and Variation

SPM: Science Form 4 2015, Hin Hua High School Klang 4A5

Human Cells Chromosomes

DNAGenes

Characteristics

/ traits

Built up of containing

determiningcontaining

containing

3.1 CELL DIVISION

Chromosomes, genes and DNA

Life cycle and cell division

Mitosis : growth

Meiosis : sexual reproduction

NUCLEUS

CHROMOSOMES-threadlike structure

-human beings have 46 (23 pairs-contain protein and DNA

DNA-Double helix structure

--Made up of series of genes

GENE-Segment of DNA

-Genetic codes which determine an organism

characteristics

Definition:

A cell division process in which a parent cell (original cell) divides into two identical daughter cells (new cells)

Occurs in:

Human and animal : somatic cells

Plants: tips of roots and shoots

Chromosomes in the nucleus shorten, thicken and more visible.

Replication of chromosomes occur.Each strand of chromosome is called

chromatid.

chromatid

centromere

nucleus membrane

The nucleus membrane forms again.Two daughter cells are formed.

Each daughter cell has the same number of the chromosomes as the parent cell.

Spindle fibres emerge.Chromosomes align themselves in the centre

of the cell.The nucleus membrane disappears.

Chromatids divide and separate to the opposite ends of the cell.

At the same time the cell starts to divide.

spindle fibres

Produce new cells for growth unicellular zygote

to multicellular organism

Asexual reproduction for simple organism like amoeba

Regenerate body parts such as lizard grows a

new tail

Vegetative reproduction such as rhizomes, tubers,

leaves

Produce new cells for replacing dead

cells/repairing tissues

Definition: A process in which a nucleus of a parent cell divides into four daughter cells through two divisions.

The daughter cells will have half the number of chromosomes in parent cell.

Occurs in reproductive organs to produce gametes (ovum and sperms ): Human and animals: testes (male) and ovary (female) Plants : anthers and ovaries

Chromosomes in the nucleus shorten, thicken and more visible.

Crossing over and replication process occur on chromatids.

Meosis 1

Chromosomes align themselves in the centre of the cell.

The nucleus membrane disappears.

Chromatids separate and move to the opposite ends of the cell.

The cell begins to divide into two.

Two daughter cells are produced.The nucleus membrane reforms.

The nucleus membrane is formed again.Four daughter cells are formed.Each daughter cell has half of the

number of chromosomes in the parent cell.

Spindle fibres emerge.Chromosomes align themselves in the

centre of the cell.The nucleus membrane disappears.

Chromatids divide and separate to the opposite ends of the cell.The cell starts to divide.

Meosis 2

Crossing over process

Independent assortment of chromosomes

(characteristics are separated during formation of gamete and randomly

combined during fertilization)

1. To produce gametes

2. To allow variation

through :

Meiosis

Fertilisation

Mitosis

Male (46 chromosomes)

Female (46 chromosomes)

Sperm (23 chromosomes)

Ovum (23 chromosomes)

Zygote(46 chromosomes)

Baby(46 chromosomes)

http://youtube.co/watch?v=Ba9LXKH2ztU

SIMILARITIES

Replication of DNA

takes place

Involves division of

nucleus and cytoplasm

Cell division occurs

DIFFERENCESMITOSIS MEIOSIS

Replication process

Number of division

Number of daughter

cells produced

Number of

chromosomes in

daughter cell

Combination of gene

Occur

One only

Four

Same as in parent cell

Same as parent cell

Occur in the first

division

Two times

Two

Half of parent cell

Different from parent cell

Crossing over processDoes not occur Occur

3.2 THE PRINCIPLES AND MECHANISM OF INHERITANCE

Gene

Exist in pair

Dominant gene

-A gene which expresses the trait when paired with a dominant or

recessive gene

-Denote as capital letter, eg

T (tall)

Dominant trait

Characteristics controlled by dominant genes

Recessive gene

-A gene which expresses the trait when paired with a recessive gene only (in the absence of a dominant

gene)

-Denote as small letter, eg t (short)

Recessive trait

Characteristics controlled by recessive genes

Chromosomes are in pair. One from the father while the other one from the mother.

Same genes:Dominant gene and recessive gene are placedopposite to each other

Homologous chromosomes

t T

Trait Dominant Recessive

Earlobes Free earlobes Attached earlobes

Tounge Ability to roll Inability to roll

Dimples Presence Absence

Hair Curly Straight

Iris colour Brown Blue

Height Tall Dwarf

Gregory Mendel was the first person who discovered the principles of heredity.

Genotype

Phenotype

The genetic information of an organism

The physical characteristics of an organism

TT tt

Tall (pure breed) Dwarf (pure breed)

T T tt

T t tT

Tall Tall Tall Tall

Tall Tall Tall Dwarf

Phenotype :

Genotype :

Phenotype :

Genotype :

Phenotype :

Genotype :

F2 Generation

F1 Generation

Gametes

Gametes

Tt Tt Tt Tt

TtTtTT t t

Key: Homozygous: both genes are

sameEg: TT, tt

Heterozygous: genes are differentEg: Tt

In the pea plant, the gene for round seed(R) is dominant to the gene for wrinkled seed(r).

a) If a homozygous round-seeded pea plant is crossed with a homozygous wrinkled-seeded plant, what will be the phenotype of F1 plants?

b) If the F1 plants are self-pollinated, what will be the genotype and phenotype ratios of the F2 plants?

RR rrRound seed Wrinkled seed

R R rr

Round Round Round Round

Parental Phenotype :Parental Genotype :

F1 Generation

Gametes

Rr Rr Rr Rr

Hence all the F1 plants have round seeds.

a) Key: R: round seededr : wrinkled seeded

b)

R r rR

Round Round Round WrinkledF2 Phenotype :

F2 Genotype :

F1 Generation

Gametes

Rr Rr

RrRrRR r r

Genotype ratio is 1 RR:2 Rr: 1rr

Phenotype ratio is 3 plants with round seeds : 1 plant with wrinkled seed

B represents the dominant gene for black cat, and b represents the recessive gene for a white cat.

What is the phenotype ratio of the number of black cats to the number of white cats if black fur cat (Bb) is crossed with another black fur cat (Bb)?

B b bB

Black Black Black White F1 Phenotype :

F1 Genotype :

Parents

Gametes

Bb Rb

BbBbBB bb

Phenotype ratio is 3 black fur cats: 1 white fur cat

Key: R: black catr: white cat

Answer:

In the pea plant, the gene for purple flowers (P) is dominant to the gene for white flowers (p). A cross between a heterozygous pea plant with purple flowers and a homozygous pea plant with white flowers is done.

What are the genotypes of the offsprings?

P p pp

Purple White Purple White F1 Phenotype :

F1 Genotype :

Parents

Gametes

Pp pp

ppPpPp pp

Genotype ratio is 2 Pp : 2 pp

Key: Pp: heterozygous , purple flowerpp: homozygous , white flower

Answer:

3.3 SEX DETERMINATION AND THE OCCURRENCE OF TWINS IN HUMAN BEINGS

Sex chromosomes: the last pair in human chromosomes

Male: 22 pairs of autosomes and a pair of sex chromosomes XY.

Female: 22 pairs of autosomes and a pair of sex chromosomes XX.

Sex determination : the sex of baby is determined by the fathers sperm (XY)

44 + XY 44 + XX

Y XGamete cells: orX

Fertilisation

Baby girl 44+XXBaby boy44+ XY

44 + XX 44 + XY

22 + X 22 + X

44 + XX 44 + XY

22 + Y22 + X

44 + XX 44 + XY

Mother Father

Gametes :

Parents :

Offsprings:

Ratio of daughter : son is 1:1

Therefore , the chance to get daughter or son is 50:50.

Daughter Daughter Son Son

An ovum is fertilised by a sperm to form a zygote.

Zygote undergoes mitosis and separates into two to develop into two embryos.

Genetically identical.

Share the same placenta.

Same sex.

IDENTICAL TWINS

Two different ova fertilisedby two different sperms at the same time.

Two different zygotes are formed and develop into two embryos.

Genetically different.

Each has own placenta.

Same sex or different sex.

Known as fraternal twins.

NON-IDENTICAL TWINS

IDENTICAL TWINSNON-IDENTICAL

TWINS

Zygote undergoes mitosis

Two embryos

Foetusshare the same placenta

Two ova are fertilised

Two different zygotes are formed

Two separate embryos

Each foetushas his own placenta

Siamese twins

Identical twins that are joined at some parts of the bodies.

Formed when zygote fails to divide completely in the course of formation.

IDENTICAL TWINSNON-IDENTICAL

TWINS

Similarities:The twins are formed in the uterus.

Two babies are formed.

One

One

Same sex

Yes

Same / identical

Yes / sharing placenta

Two

Two

Same or different sex

No

Different

No / separate placenta

Number of sperms

Fertilised ovum splits into two

Genetic make up

Sharing of placenta

Sex

Number of ova

Differences

Why do these happen to them?

3.4 MUTATION

Mutation: the spontaneous change to the structure of genes or chromosomes

Occurs in

Somatic/body cells

(can be passed down through mitosis)

Gametes/reproductive cells

(inherited)

TYPES OF MUTATION

Gene mutation

Change in the structure of DNA

Chromosome mutation

A change in the number of chromosomes or in

the structure

Downs syndrome: an extra chromosome in autosome 21 (47 chromosomes)

Klinefelters syndrome: a male with extra X chromosome (XXY)

Turners syndrome: a female with one less X chromosome (XO)

Polyploidy: having one or more chromosomes in a set of chromosome

Colour blindness: a mutated gene in the X chromosome

Sickle cell anemia: mutation in gene that produces haemoglobin; inefficient in transporting oxygen in the blood

Albinism: the gene for skin colour is mutated; unable to produce black pigment (melanin)

Haemophilia: mutation in gene that is important for blood-clotting

Downs syndrome

Additional chromosome at autosome 21.

Physical retardationThick neckSlanted eyesProtuding toungeReduced resistance to diseases

Klinefelters syndrome

A male with extra X chromosomes (having XXY)

InfertileUnderdeveloped testesNarrow shoulder Enlarged breasts

Turners syndromeA female having one less X chromosome (XO)

InfertileShortMentally retardedHas no ovariesSmall breastsFolded skin on neckNo menstrual cycle

Polyploidy

The number of chromosomes is increased by one or more sets.

More common in plants.

Colour blindnessMutant gene (recessive gene) on the X chromosome.

Not able to differentiate coloursespecially green and redMore common in males because male has only one X chromosome

Albinism

The gene for skin colour is mutated (recessive gene)

Unable to produce melanin (black pigment)White hairPink eyes and pinkish skinSkin is sensitive to sunlight

Sickle-cell anemia

Mutation in gene that produce haemoglobin

Sickle-cell shaped of red blood cellsNot efficient in transporting oxygenFacing painful crises such as chest pain, fatigue, bone pain,

Yellowing of eyes Inherited from both parents

Haemophilia

Mutation in chromosome X (for blood clotting)

Have problem in blood clotting May bleed continuously or for a longer period

A woman carrier may inherit the disease to a son

Spontaneous changes during cell division

Exposure to physical mutagens: UV radiation,

X-rays, radioactive radiation

Environmental change: the change of temperature for a long period causes genetic

evolution in organism

Exposure to chemical mutagens: Benzene,

formaldehyde, nicotine, sodium nitrite, pesticides

Give rise to variation which leads to differences in traits

Better chance of survival when new species are more resistant to diseases

Advantages

Cause physical defects

Causes genetic diseases

Some chromosome mutations and gene mutation are lethal (fatal)

Causes mental defects

Disadvantages

3.5 THE EFFECTS OF GENETIC RESEARCH ON HUMAN LIFE

Gene therapy: to replace damaged/faulty genes during

the foetal stage

Genetic screening: to predict diseases likely to develop

Gene test: to screen unborn children for diseases

Genetic engineering: to transfer DNA from one

organism to anotherHuman genome project: maps all human genes to determine genes which

causes diseases

Field of Medicine

To produce plants which are resistant to diseases and

infections

To produce engineered plants which are able to live in unfavourable conditions

To produce plants which grow and mature fast

To produce higher yields

To produce high quality of crops and livestock

Field of Agriculture

A process which involves cross breeding and cloning of plants or

animals

Advantages New varieties with

desired characteristics can be produced

To produce new and high quality crops

More resistant to diseases

Disadvantages May produce new

varieties with undesirable

characteristics

Example 1: Cow

is cross bredwith

Friesian Cow Sahiwal Cow

Mafriwal Cow

-Grow faster -Bigger in size-More milk -High resistant to disease

Example 2: Palm oil

is cross bredwith

Dura Pisifera

Tenera

-Thick mesocarp and large kennel :much oil-Thin shell: easier to extract

Thinmesocarp

Large kennel

Thickmesocarp

Smallkennel

A process of cloning a plant by using a plant part or single cell in a test tube

under a controlled condition

AdvantagesTo produce many

copies of the same plants in a short time

To produce plants anytime we want

Shorter maturation time

No variation

Disadvantages

Complete wipe-out of crops if there is spread

of diseases

a) Explant:

b) Multiplication:

c) Transplanting:

The process of producing an organism that is an exact genetic copy of

anotherProcess:

Animation For Cloning

1. Natural and artificial twinning

http://learn.genetics.utah.edu/content/tech/cloning/whatiscloning/twinning.html

2. Somatic cell nuclear transfer (as in Dolly)

http://learn.genetics.utah.edu/content/tech/cloning/whatiscloning/scnt.html

Foods from plants and animals which have had their genetic information

changed by adding genes from another organisms

Advantages:

For crops: enhanced taste and quality, increased yields,

matures faster, better resistance to diseases,

remain fresh longer

For livestock: increased resistance

to infections and diseases, higher yield

of milk, meat and eggs

Cause allergies and side effects to human beings

Milk of genetically modified animals may be unsafe

Antibiotic-resistant genes in GM organisms may be pass on to bacteria;

difficult to kill them

Genetic research is expensive, poor farmers cannot afford

3.6 VARIATION AMONG LIVING THINGS

Variation: The differences among individuals

of the same species

Continuous variation

Discontinuous variation

-Characteristics among individuals which do not show distinct differences

-Quantitative and can be measured

-Determined by genes and can be influenced by environmental factors

-Characteristics among individuals which show distinct differences

-Qualitative and cannot be measured

-Determined by a single gene and is not influenced by environmental factors

Continuous variation

Discontinuous variation

Height

Skin colour

Length of foot

Intelligence

Weight

Earlobes

Iris colourColour

blindness

Tongue rolling

Blood group

Genetic factors

Crossing over during meiosis: genetic material is exchanged

Random fusion of male and female gametes during fertilisations

Chromosome and gene mutation: creates new phenotypes

Independent assortment of chromosomes: different gametes

Environmental factors

Sunlight exposure: will have darker complexion

Water climate, temperature

pH: the Hydrangea flower is blue in acidic soil and pink in alkaline soil

Diet: a person who eats a lot will be fatter

IMPORTANCE

Ensures the survival of a species under changing

environment

Enable any species to occupy a wider range of habitat

Enable natural selection: species with favourablecharacteristics will be

selected by nature

Enable us to distinguish

individuals of the same species

Discuss the similarities and differences between continuous variation and discontinuous variation.

CONTINUOUS VARIATION

DISCONTINUOUS VARIATION

Similarity:Show differences in characteristics among

individuals of the same species

Yes

Not distinct

If it is influenced by environmental factors

cannot be inherited

Two or more genes for the same character

Quantitative/ can be measured

No

Distinct

Can be inherited

Single gene

Qualitative/ cannot be measured

Influenced by environmental factors?

Inheritance

No of gene

Type of data

Characteristic

Differences

Similarities And Differences Between Continuous And Discontinuous Variation

3.7 THE NEED TO ADHERE TO A CODE OF ETHICS IN GENETIC RESEARCH

Discuss the effects of misusing the knowledge of genetics research.

We need code of ethics!!

The produce of biological weapon: anthrax bacteria

GMF may have side effects and endanger human health,

should be labelled

Human cloning: against religion

Manipulation of human genes when

carrying out research on human being