Genotype, Phenotype and Inheritance Flashcards
Define genotype.
The entire genetic makeup of an individual.
Define phenotype.
The physical characteristics that are expressed.
Define homozygous.
When an individual have two alleles of a gene that are the same.
Define heterozygous.
When an individual have two alleles of a gene that are different.
Define hemizygous.
Only one allele of a gene. This is usually on the X chromosome (Males only!)
Define dominant.
A dominant allele determines the phenotype. This means that in a heterozygote the dominant allele determines the phenotype.
Define recessive.
A recessive allele doesn’t usually determine the phenotype. In a heterozygote the recessive allele does not determine the phenotype.
Explain the difference between gene, genotype and alleles.
If a gene is ‘A’ the genotype will A1A2 or AA. The alleles will be A1 and A2.
Explain co-dominance.
For example in blood type which is determined by gene I there are three alleles: A, B and O or: IA, IB, and I0.
Both A and B are dominant over 0. However neither allele A or B are dominant over each other. This means they are co-dominant. This produces a produce a new phenotype.
What is the genotype and phenotype of blood group A?
Genotype: IAIA or IAI0
Phenotype: A
What is the genotype and phenotype of blood group B?
Genotype: IBIB or IBI0
Phenotype: B
What is the genotype and phenotype of blood group AB?
Genotype: IAIB
Phenotype: AB
What is the genotype and phenotype of blood group 0?
Genotype: I0I0
Phenotype: 0
What is a autosomal recessive disease?
A disease that is only expressed when the recessive allele can be expressed.
Will a heterozygote be affected by an autosomal recessive disease?
No heterozygotes are unaffected.
Are males and females equally affected?
Yes they are.
What is the chance of two heterozygote autosomal recessive to have affected offspring?
25%.
Give an example of an autosomal recessive disease.
Cystic fibrosis.
Can an autosomal recessive disease skip a generation?
Yes it can. It can seems to come out of no where.
What is autosomal dominant.
When heterozygotes are affected. The dominant allele determine the phenotype.
Can homozygotes have an autosomal dominant disease?
Yes in case they have both the dominant alleles that means. This is however very rare because diseases in a homozygote are usually very severe so it is not usually suitable for life.
Give an example of an autosomal dominant disease?
Huntington’s Disease.
Can an autosomal dominant disease skip a generation?
No it can’t. This is because it can’t be carried without being expressed.
What is an X-linked recessive disease?
A disease where the allele is locate on the X chromosome.
Give some features of x-linked recessive.
Disease is more common in males. This is because males only have one X chromosome whereas females have two. This mean that males cannot have a dominant allele to ‘overthrow’ the recessive allele.
What is the chance of a female carrier to have an affected son?
50%
What is the chance of an affected male to have an affected son?
0% the X-chromosome from a father to a son can’t give X-chromosome to son, only Y-chromosome.
How does mitochondrial inheritance work?
Al individuals will inherit the disease from their mother, never from father.
What does polygenic inheritance entail?
That more than one gene can be involved in producing a phenotype.
What are linked genes? (regarding polygenic inheritance)
Genes on the same chromosome.
What are non-linked genes? (regarding polygenic inheritance)
Genes that are on different chromosomes.
How do non-linked and linked genes differ more?
Linked genes do not show independent assortment at meiosis since they are on the same chromosome. However recombination can occur.
What is recombination frequency in linked genes dependent on?
The distance between the genes. Tightly linked genes are less likely to undergo recombination.
