i spelt this page ‘inheritence’ too many times to even say it

Gregor Mendel (1830s - 1860s)

• Experimented with pea plants; he used them to study genetics
• Determined that traits depend on separate factors from parents to offspring; and the modes of inheritence
• He looked at characteristics such as colours, shapes of ods, seeds etc. to conclude his results

He used a monohybrid cross

• This is where 2 alleles contain one trait; for example, the only alleles that control pea pod surfaces are the smooth allele and wrinkled allele (smooth allele = smooth pods)

Gregor Mendel’s Laws

Laws of segregation

• Inherits 2 alleles from both parents (1 allele from each parent)
• Dominant allele overrides recessive alleles
• Two factors separate during meiosis
• Alternative variations cause different characteristics

Laws of independent assortment

• The obtainment of an allele is afftected by nothing else; just up to chance

Laws of Dominance and Recessiveness

• Dominant > recessive basically

Pedigrees

Pedigrees are a sort of diagram used to show a family history of a trait.

Squares represent males; circles represent females

Shaded means affected by condition; unshaded means unaffected by condition

If half shaded, it means it could be a carrier (has the allele but doesn’t express it: for recessive traits)

Ways of Inheritence

Autosomal

• Dominant: expressed over recessive (only 1 dominant needed)
• Recessive: only expressed if 2 recessive traits

Sex Linked

• Means that it is carried along the X chromosome
• Girl sex chromosome is XX and boy chromosomes are XY
• Boys will show traits if their X chromosome is affected, so X(c) Y - c means affected - this is because they inherit a Y from the father which means if the X is bad, they instantly show it
• Girls will show traits if both X chromosomes are affected, X(c)X(c)
• Sex linked conditions are passed on the 23rd chromosome (the sex chromosome)

  Examples: Haemophilia (excessive bleeding), Red-green colourblindness

Notations

X - dominant normal, X(c) - recessive affected

so Boys would be either XY or X(c)Y

Girls can be XX, X(c)X, X(c)X(c); note you need to be X(c)X(c) to be affected by X linked, if it is sex linked recessive

Co-dominance and Incomplete

Co-dominance

• Make extra phenotype; 3 phenotypes
• For example, there are 3 types of blood cells, A, B and O
• A and B are dominant while O is recessive
• AB is co-dominant; it is when both A and B are expressed (because they are both dominant and are expressed)

Incomplete

• Neither are fully dominant over the other
• A and B are neither dominant nor recessive
• Blend together into a mix; combine for a new outcome

Comparing the two:

Here is an example… with my favourite animal, a kitten!

Co-dominant: White cat and black cat produce a cat with black and white patches

Incomplete: white cat and black cat blend together and form a gray cat