Dr Pusey

www.puseyscience.com

Genetics & DNA

The nucleus of living cells contain chromosomes which are made up of a string of genes.

Different genes control the development of different characteristics by issuing instructions to the cell.

Stated Clearly - What exactly is a Gene

Recap Genes

Section of Chromosomes

Code for the production of Proteins (functions and structure of cell)

How are these related to inheritance?

Sperm and Egg contain 23 chromosomes each. When they form YOU, they combine into 23 homologous pairs. The genes in these are inherited, but not all are expressed (shown), since you have two sets of everything

Fancy words to know Allele: Variation of a gene

E.g Hair colour gene. blue allele, brown allele, ginger allele

Genotype: The Gene combination you have

E.g You might have a brown hair allele and ginger hair allele. This is known as your Genotype.

Phenotype: The Physical expression from your Genotype

E.g If you have the above genotype, your phenotype will be brown hair

Fancy words to know Homozygous: When your alleles are the same (e.g two

brown hair alleles) A ginger-haired person has two ginger alleles

Heterozygous: Two different alleles The guy with a brown and ginger hair colour allele.

Dominant allele: If it’s present, it’ll be the one expressed e.g. Brown hair

Recessive allele: It will only be expressed if both of the alleles are the same, otherwise the dominant guy will prevail. e.g. Ginger hair

Punnet Squares – WOOHOO! We use punnet squares as a quick and easy way to see

what the Genotype of the offspring could look like.

We can then use this Genotype to determine the characteristics of the spawn!

If Dr Pusey has blue eyes and his wife has brown eyes, what are the chances their baby will have blue eyes?

Punnet Squares – WOOHOO! Dr Pusey’s wife has brown eyes, Dr Pusey has blue eyes

Brown eye alleles are given the letter capital B

Blue eye alleles are given the letter b

The reason Brown has a capital letter, is because it is DOMINANT.

Dr Pusey’s wife can either have the genotype Bb or BB

Dr Pusey can only have the genotype bb, since it’s recessive

Note: Eye colour is slightly more complicated in reality, but this method is suitable for many inherited traits that rely on a single gene

Punnet Squares – WOOHOO! Let’s assume that Dr Pusey’s wife’s genotype is BB

We know that Dr Pusey’s genotype is bb

Now we can do our punnet square!

b b

B

B

Dr Pusey

Wif

ey

Punnet Squares – WOOHOO! Let’s assume that Dr Pusey’s wife’s genotype is BB

We know that Dr Pusey’s genotype is bb

Now we can do our punnet square!

b b

B Bb Bb

B Bb Bb

Dr Pusey

Wif

ey

Every possibility involves the Bb genotype being given to the baby. The corresponding phenotype is BROWN hair. There is no chance the baby will have blue eyes.

Punnet Squares – WOOHOO! Let’s assume that Dr Pusey’s wife’s genotype is Bb

We know that Dr Pusey’s genotype is bb

Now we can do our punnet square!

b b

B Bb Bb

b bb bb

Dr Pusey

Wif

ey

Now, there is a 50% chance of the baby having blue eyes, and a 50% chance of the baby having brown eyes.