Genotype, Phenotype And Inheritance Flashcards
What is a genotype?
The genes a person has on the chromosomes in their nucleus
What is a phenotype?
The proteins a person has on their cytoplasm
What can effect genotype and phenotype?
Environment Chemicals Diet Mutagens Lifestyle Radiation
What are alleles?
Different copies of the same gene
Define Homozygous
2 alleles of a gene are the same
The individual is a homozygote
Define Heterozygous
2 alleles of a gene are different
Individual is a heterozygote
Define Hemizygous
Only one allele of a gene
Eg one allele as only one X gene as male
Define dominance in inheritance
The dominant allele in a heterozygote determines the phenotype
(Only one copy is needed)
Define recessive in inheritance.
The non-dominant allele in a heterozygote is called recessive
Need 2 copies to appear in phenotype
Give an example of Co-Dominance
Human iso-glutamin gene codes for the glycoproteins on RBC surface. These are co-dominant and 2 can be present in phenotype.
A is dominant over O
B is dominant over O
A and B are co-dominant so appear together
How is a male and female represented in a pedigree chart?
Male=square
Female=circle
Unknown sex=diamond
How do you represent an effected/unaffected/carrier in a pedigree chart?
Affected=coloured in
Unaffected=not coloured
Half and half = carrier
How do we label different generations in a pedigree chart?
Label each generation with a Roman numeral
Describe the features of an autosomal recessive gene
Heterozygotes are unaffected (as recessive)
Equal in both sexes (not sex-linked)
2 heterozygote have 25% chance effected offspring
2 affected divide all can only have affected children
Give an example of an autosomal recessive genetic disease
Cystic Fibrosis
Describe the features of an Autosomal Dominant genetic disease.
Heterozygotes effected (1 copy needed)
Both sexes equally affected
Disease rarely found in homozygous state as not viable for life
If affected - 50% chance of affected offspring
Cannot skip a generation
An affected individual has at least one affected parent
Give an example of an autosomal dominant genetic condition
Huntington’s disease
Describe the features of an X-lined recessive genetic condition
Hemizygous males affected
Homozygous females affected
More common in males
Heterozygous female (carrier) has 50% chance of affected son
Affected male cant pass it on to SONS (as give them the Y gene)
Affected Male must have (at least) heterozygous carrier mother
Affected female must have affected father + carrier mother
Daughter of affected male must be carrier
Give an example of an X-linked recessive genetic condition
Haemophilia A
Describe the features of an X-Linked Dominant genetic condition
Hemizygous male affected
Heterozygous female affected
Affected male cant pass it to sons but will to ALL daughters
Give an example of X-Linked dominant genetic condition
Fragile X syndrome
Describe some feature of Y-Linked genetic diseases
Give an example
An effected mans sons will all get it
Females cant get it
Passes from father to son
Eg Y-Chromosome infertility
Describe the features of mitochondrial genetic conditions
Must be inherited from mother
Given to all of an affected woman’s children
Boys cant pass it on
What is polygenic inheritance
When the inherited disease is formed by more than one gene there are more than one possible genetic mutations
Genes on same chromosome said to be linked
Genes on diff chromomes “not linked”
Linked genes don’t show independent assortment at meiosis
Give Na example of a disease for poly genetics
Albinism
What is the effect of linked and not linked on polygenic inheritance
Not linked-can be independently assorted-4 types of gamete with 1:1:1:1 ratio
Linked-can have crossing over (if no crossing over only 2 gametes, if crossing over 4) the ratios are not 1:1 if crossing has occurred. The ratio of the last 2 depend on how much crossing over occurs.
What is recombination frequency between 2 genes dependant on
The distance between them
If close they are tightly linked (more likely to stay together)
If far apart they almost behave as unlinked genes, the further apart the more likely they are to cross over
