5.5 When genes change

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5. It runs in the family

On inheritance, family trees, genetics and DNA

Draw a Punnett square showing the crossing of the F1 flowers from Mendel's pea plants.

purple x white gives purple offspring. Purple must be dominant

    P = purple

    p = white

Purple F1 crossing gives purple + white flowers

F1 must be Pp

F1: Pp x Pp

F2: PP 25% Purple

      Pp 50% Purple

      pp 25% White

	P	p
P	PP	Pp
p	Pp	pp

5.5 when genes change

    What is a mutation?

    How can a disease be inherited from one generation to the   

    next?

mutations

= change in a gene or chromosome (genotype)

This may result in no/small/large change in phenotype

mutations

= change in a gene or chromosome (genotype)

This may result in no/small/large change in phenotype

the change can be negative/neutral/beneficial

mutations 

mutations 

External caused by known mutagens 

• Radiation: (eg. UV light, X-ray, radioactive decay)
• Chemicals (eg. benzene in cigarette smoke)
• Bacteria or viruses (eg. HPV)
  

Internal

• DNA replication
  

mutations 

Gene mutations

    Defect of a gene

    eg. sickle cell disease

Chromosome mutations

    Change in a whole chromosome

     eg. extra chromosome 21 leads to Down Syndrome

Definitions

A= healthy

a = sickle cell disease

Person with AA is healthy

Person with aa has sickle cell disease

Person with Aa is a 'carrier'

Read section 5.5

Do exercises 30, 31, 32 (34, 35 and 36)

Also on SOM