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From Mendel to DNA. Learning Objectives What did Mendel’s experiments teach us about inheritance? What are DNA fingerprints? How are specific proteins made in the body?. Carried out breeding experiments with peas. Used pure strains of: round, wrinkled, green and yellow peas .

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from mendel to dna

From Mendel to DNA

Learning Objectives

What did Mendel’s experiments teach us about inheritance?

What are DNA fingerprints?

How are specific proteins made in the body?


Carried out breeding experiments with peas.

  • Used pure strains of: round, wrinkled, green and yellow peas.
  • Cross bred the peas and counted the different offspring.
  • Found that characteristics were inherited in clear predictable patterns.

Gregor Mendel


Mendel suggested that there were separate units of inherited material. He realised some characteristics were dominant over others and that they never mixed together.


A gene is a section of DNA coding for a particular feature.

e.g. eye colour, attached/unattached ear lobes, ability to roll tongue.

so what is dna
So what is DNA....

DNA is a chemical that stores your genetic material.

sequence of bases forms the genetic code
Sequence of bases forms the genetic code

Each base is like one letter in a four-letter alphabet.

These letters make up 3 letter groups called codontriplets.

Each triplet is one piece of information.







  • How did Mendel’s experiments with peas convince him that there were distinct ‘units of inheritance’ which were not blended together in offspring?
  • Why didn’t people accept his ideas?
  • The development of the microscope played an important part in helping to convince people that Mendel was right. How?
  • Explain with reference to the structure of DNA the saying ‘One gene, one protein’.
dna fingerprinting
DNA fingerprinting

‘DNA fingerprinting’ – a technique that uses the unique patterns in your DNA to identify you.

dna fingerprinting1
DNA fingerprinting
  • Certain areas of your DNA produces very variable patterns under the microscope.
  • These patterns are more similar between people who are related than between total strangers.
  • The patterns are known as DNA fingerprints.
  • They can be produced from very tiny samples of DNA from body fluids such as blood, saliva, semen.
  • Two men claim to be the father of the same child.

Explain how DNA fingerprinting could be used to find out which one is the real father.

inheritance in action

Inheritance in Action

Learning Objectives

How is sex determined in humans?

Can you predict what features a child might inherit?


The complexity of an organism does not seem to be correlated with the number of chromosomes it has.

Fruit fly – 8

Kangaroo – 12

Human – 46

Chicken – 78

Fern - 1200


In 22 cases each chromosome in the pair is a similar shape and has genes carrying information about the same things. But one pair of chromosomes may be different – these are the sex chromosomes.


Chromosomes from a female

Chromosomes from a male


Pair 23 – the non-matching pair of chromosomes

  • Sex chromosomes
    • Two X chromosomes mean you are female
    • One X chromosome and a Y chromosome mean you are male.
  • Twins are born. Twin A is XY and twin B is XX. What sex are the two babies?
  • The chromosomes we inherit carry our genetic information in the form of genes. A gene can be pictured as a position on a chromosome.
  • Many of these genes have different forms.

Alleles – are different versions of the same gene.

    • For example the gene for dimples may have the dimple or no-dimple allele.
  • An allele can be dominant or recessive.
  • Individuals can be homozygous or heterozygous.
    • Individuals who are homozygous for a certain gene carry two copies of the same allele.
    • Individuals who are heterozygous for a certain gene carry two different alleles.

A recessive characteristic will only be shown if an individual ishomozygous for the recessive allele.

  • A dominant characteristic will be shown even if an individual is heterozygous for the dominant allele.

Genetic diagrams are used to show possible outcomes of a particular cross. Dominant allele is shown by a capital letter, and a recessive allele by a lower case letter.



Huntington’s disease





Downs syndrome

Cystic fibrosis