Biology: B1, B2, B3 Revision Summary

Page 1

B1 – You and Your Genes (Even

Smaller) Summary

Genes:

Genes make Proteins like Antibodies,

Keratin and Hormones.

Genes give characteristics such as Hair Colour,

Height, Weight and

Eye Colour. Environment effects

characteristics, Height depending on your Diet.

Chromosomes:

Humans have 23

pairs of chromosomes. Total = 46. Each

Chromosome Gene is in a Particular Position =

same position on Partner Chromosome ->

Also referred to as a Locus.

Alleles:

Dominant

and Recessive alleles are given as either BB,

Bb or bb. The Dominant version of the gene will mask the recessive version. ‘Aa’ the big ‘A’ would

hide the effect of the little ‘a’ so all you would see is the effect of the

dominant gene pair.

Versions of a Gene are called Alleles. 2 of the same alleles either ‘AA’ or ‘aa’ are

called Homozygous. ‘AA’

= Homozygous Dominant |

‘aa’ = Homozygous Recessive. One of each ‘Aa’ = Heterozygous.

Genotype: What Genes you have ‘Aa’.

Phenotype: What it looks

like e.g. Dimples or No Dimples.

Combining Genes:

Sperm and Egg cells have a

unique combination of Alleles.

E.g. your Brother or Sister will have some

similarities to you however, they are not identically

the same. Different Characteristics = Different combination

of alleles.

Gender is Determined on the 23rd

pair of Chromosomes. XX = Female & XY = Male.

Genetic Disorders

Huntington’s disease is

caused by inheriting a dominant allele. ‘H’ - Huntington’s disease. ‘h’ = Healthy Person. Huntington’s

disease --> ‘HH’ ‘Hh’. Healthy --> ‘hh’ Alleles. Symptoms:

Memory Loss, Confusion,

Tremors, Clumsiness

and Loss of Balance. Does not appear

until later ages --> Late 30’s 40’s and Even 50’s.

Huntington’s disease is a Faulty Dominant

Allele. Currently No Cure.

Cystic Fibrosis is caused

by inheriting a faulty recessive allele.

‘F’ = Healthy (FF

& Ff). | ‘f’ = Cystic Fibrosis (ff). The middle Healthy

Allele, ‘Ff’

is called the Carrier because the Dominant ‘F’ masks the Recessive ‘f’ Allele.

Genetic Testing

You

can be tested as an adult for Genetic Testing --> Alleles you inherited when you were conceived = have for the rest of your life.

You can test the Baby when it’s an Embryo this is called PGD (Pre-Implantation genetic diagnosis) this is where you

would take out 1 of the cells from the 8 cell stage you

could then see if it was carrying a Genetic Disease by looking at the Alleles. This method

does not harm the Baby.

Testing

a Fetus = Risks such as infection to the mother and possible Miscarriage. Ethical Decisions --> Do you keep the Baby if you know it has a Genetic Disease or have

an Abortion? In the future --> Test people using certain Drugs. Save Money + Lives.

Ethics

Some issues of

Genetic Testing --> Who has access to

this information E.g. If a Life Insurance company knows you have a Genetic Condition = increased price. If the Police arrest someone and take a sample = allowed

to keep that sample on the database? Should people be able to have access to your information without your permission?

Regulations and laws

in place that are used to determine this

kind of information like who has access this information and what they can do with it.

Stem Cells

Stem Cells --> found

in the embryo. We can remove embryonic

stem cells & use them to grow new organs for

people with damaged tissue in organs. Not yet 100% effective.

Adult Stem Cells --> found in tissues such as Bone Marrow, and Tooth

tissue therefore not many Adult Stem

Cells.

Identical twins = examples of natural clones they

are GENETICALLY identical not just similar. Some organisms

reproduce asexually --> Strawberry

plants and Potatoes.

Page 2