3.4 Inheritance Flashcards
Phenotype
physical characteristic/expression of an organism
Genotype
the combination of alleles which an organism has
Homozygous
two copies of the same allele
Heterozygous
two different alleles (sometimes called a carrier if the recessive allele is disease-causing)
Dominant
an allele which is always expressed when it is present in both homozygous and heterozygous genotypes (uppercase)
Recessive
an allele which is only expressed when two copies are present; only in a homozygous genotype (lowercase)
Mendel’s principles of inheritance
Mendel worked with the garden pea, Pisum sativum:
Its seeds were readily available;
Pollination is relatively straight forward and controllable;
Several physical traits of the garden pea are easy to see - pea colour/shape, pod colour/shape, height, flower colour
‘Pure breeds’ created (i.e. offspring always purple-flowered)
Fast reproduction to create large sample s
Mendel Noticed…
The “short” phenotype disappeared in the F1 generation and reappeared in the F2 generation
The “short” gene must have been “hiding” → today we use the term recessive
Concluded that traits depend on two “factors” → today we call these alleles
independent assortment
means that traits are inherited independently of one another, so the inheritance of one trait doesn’t depend on the inheritance of another
I.e. certain traits are not linked or inherited together (e.g. hair colour is not connected to eye colour; if you have brown hair it doesn’t mean you will have brown eyes)
Due to the random orientation during Metaphase I & II.
complete dominance (Mendelian):
Heterozygous individuals will express a DOMINANT allele
incomplete dominance (non-Mendelian):
Heterozygous individuals will express a BLEND of alleles
Co-dominance (non-Mendelian):
heterozygous individuals will express BOTH alleles equally
Blood type O is known as…
the universal donor because they can donate to anyone.
Blood type AB is known as…
the universal acceptor because they can accept from anyone.
The ABO blood type is controlled by a single gene:
the ABO gene
alleles of ABO gene
i O allele (no antigen is produced)
IA A allele (type “A” antigen is produced)
IB B allele (type “B” antigen is produced)
dominance and codominance in blood type alleles
Dominance: IA and IB are dominant to i.
Co-dominance: IA and IB are both expressed if heterozygous
ii genotype
- no antigen production on RBC
- A and B antibody in plasma
- Blood type O
IAIA and IAi genotype
- A antigen production on RBC
- B antibody in plasma
- Blood type A
IBIB and IBi genotype
- B antigen production on RBC
- A antibody in plasma
- Blood type B
IAIB genotype
- A and B antigen production on RBC
- no antibody in plasma
- Blood type AB
X-chromosome in the non-homologous region:
Alleles in this regions are expressed whether they are dominant or recessive, as there is no alternate allele carried on the Y chromosome.
Therefore sex-linked genetic disorders are more common in males.
Examples of sex-linked genetic disorders
hemophilia
colour blindness
How is colour-blindness inherited?
The red-green gene is carried at locus Xq28.
This locus is in the non-homologous region, so there is no corresponding gene (or allele) on the Y chromosome.
Normal vision is dominant over colour-blindness.