Biology B1, B2, B3

Variation

• What is variation?

•  What can it be due to? Give two factors and some examples.

Variation

• The difference between individuals of the same species.

• -> environmental factors (tatoos, scars, weight)

          -> genetic factors (eye colour, hair colour, weight)

Genetic Information

• What do genes do? Give two things.

• Give two facts about genes.

• What are chromosones made of?

• What are DNA molecules made up of?

• How do genes control development?

Genetic Information

• Carry information needed to develop.
• Different genes control different characteristics.

Genes...

• Occur in long strings called CHROMOSONES.
• Are located in the nuclei of each cell.

Chromosones are made of DNA. DNA molecules are...

• Made up of two strands coiled to form a DOUBLE HELIX.

• They control the development  of different characteristics by issuing instructions to the cell.
• The cell carries out these instructions by producing proteins.

Chromosones

• What is special about chromosones?

• How many chromosones do humans have?

• What is the exception?

• GIve some facts about human sex cells.

Chromosones

• Both chromosones in a pair have the same sequence of genes i.e. the same genes the same place. Different  species have different numbers of pairs

• Human cells contain 23 pairs of chromosones- 46 in total.

• Sex cells contain single chromosones.

• In humans the sex cells have a total of 23 chromosones; half the number of a normal body cell. So that when the sex cells come together and fertilise, there is a full set of 46 chromosones.

Alleles

• What are alleles?

• How many alleles does eye colour have?

• How do you inherit genes?

• What are dominant alleles?

• What are recessive alleles?

• What is a punnet diagram?

• Complete a punnett diagram where both the mother and father carry one recessive eye colour and one dominant.

Alleles

• Alleles are alternative forms of a particular gene.
• Eye colour has TWO alleles. Blue and brown for example.
• For each gene, you inherit one allele from your father and one from your mother. This is why you have similarities to both your parents. 
• Dominant alleles - control the development of a characteristic even if its present on only one chromosone in a pair.
• Recessive alleles - controls the development of a characteristic only if a dominant allele isn't present, ie. if the recessive alleles is present on both chromsones in a pair. 
• Punnett diagrams are used to show all the possible combinations of alleles and outcomes for a particular gene. They use capital letters for dominant alleles and lower case letters for recessive alleles
• 

Sex Chromosones

• What is the difference between female and male sex chromosones?

• How is the sex of an individual determined?

• What will happen if the gene isn't present?

• What happens after six weeks?

Sex Chromosones

• -> In females the sex chromosones are identical; they are both X chromosones.                                                                                                -> In males they are different; there is an X and a Y chromosone. The Y chromsone is much smaller than the X chromosone.

• It is determined by a gene on the Y chromosone called the SEX-DETERMINING REGION Y (SRY) gene.

• If there are two X chromosones present, the embryo will develop into a female. If the gene isn't present testes will begin to develop.

• The testes start producing a hormone called androgen. Specialised receptors in the developing embryo detect the androgen and male reproductive organs begin to grow.

Huntington's disorder

• Is Huntington's disorder a recessive or dominant disease?

• What is Huntington's disorder?    
  

• What does this punnet diagram tell us about Huntington's disorder?
  

Huntington's disorder

• It is a dominant disease, and so only one faulty allele is needed to cause it. 

Huntington's disorder...

• -is a gentic disorder affecting the central nervous system. It's caused by a faulty gene on the fourth pair of chromosones,
• -damages the brain's nerve cells,
• -causes gradual changes, which develop into symptons including involuntary movement and dementia,
• -is incurable, leading to a premature death.

• This tells us that only the father has the disorder,. There is a 50/50 chance that the child will get HD. Only one parent is needed to pass on the gene for the child to inherit it. The child will develop HD, for sure, since it is a dominant disorder- there are NO carriers.

Cystic Fibrosis

• Is Cystic Fibrosis a recessive or dominant disease?

• What is Cystic Fibrosis?    
  

• What does this punnet diagram tell us about Cystic Fibrosis?

Cystic Fibrosis

• It is a recessive disorder, and so two faulty alleles need to be present to cause it.

 Cystic FIbrosis...

• -affects the cell membranes, producng a thick, sticky mucus especially in the lungs, gut and pancreas. As well as the reproductive organs, the mucus blocks the sperm ducts.
• -causes weight loss, coughs, repeated chest infections, salty sweat and abnormal faeces.
• -is incurable but durable. Can be helped with physio-therapy and combinations of medicine.

• This tells us that the mother has the disorder, but the father is a carrier of the faulty allele. There is a 50/50 chance that the child will either have cystic fibrosis or or be a carrier.