SESSION 7 Flashcards
Distinguish clearly between the genotype and phenotype
Genotype- the genetic make- up of an individual (either as a whole or one specific genetic locus)
E.g. Cystic fibrosis
Phenotype- all observable characteristics of an individual or the expressed trait as a result of the genetic make up one (or more) specific genetic locus (loci)
E.g. Infection
Explain how environmental factors have an influence on both phenotype and genotype
- Radiation
- Mutation
- Chemicals that affect cell growth
- Diet
- Life- style
Explain homozygous, heterozygous and hemizygous
Homozygous- two alleles of a gene are the same
Heterozygous- two alleles if a gene are different
Hemizygous- only one allele of a gene on the X chromosome (i.e. Males only)
Explain dominance, recessiveness, co- dominance and complementation
Dominance- a phenotypic trait is dominant when it occurs in both homo and heterozygous
Recessive- a phenotypic trait is recessive when it occurs only in homozygotes
Co-dominance- when both alleles are expressed in the phenotype of heterozygous,e e.g. AB blood type
Complementations- more than one gene is responsible for phenotype
- therefore a child of two recessive parents can be unaffected if parents have different defective genders, e.g. Albinism
Clearly distinguish between gene and allele
Gene- a unit of heredity; a length of DNA on a chromosome that contains the code for a protein
Allele- an alternative form of a gene; each individual has two alleles for every gene,w chin can either be the same or different
Describe pedigree analysis as a basic method in human genetics
A pedigree is a diagram showing genetic information from a family, using standardised symbols
Role:
- determine whether the trait is dominant or recessive
- discover whether the gene in question is located on the X or Y chromosome or on an autosome
- predict genetic risk in pregnancy, adult onset disorders
What are the five basic patterns of mendelian inheritance?
- autosomal recessive inheritance
- autosomal dominant inheritance
- X-linked dominant inheritance
- X- linked recessive inheritance
- Y- linked inheritance
Describe autosomal recessive traits
Recessive traits carried on autosomal have several distinguishing characteristics:
- rare traits: affected individuals parents are unaffected
- heterozygous are unaffected
- all children of two affected individuals are affected
- two heterozygous - children risk = 25%
- males and females equally affected
- disease can skip generations
Example:
- albinism
- cystic fibrosis
Explain cystic fibrosis as a autosomal recessive trait
Fatal recessive genetic disorder associated with abnormal secretions of the exocrine glands
Parents are usually phenotypically normal, but heterozygous
Affects the gene located on the long arm of chromosome 7
CFTR (cystic fibrosis transmembrane conductance regulator) protein is either absent or only partially functional
This affects the transport of chloride ions, reducing the amount of fluid added to glandular secretions, making them thicker
Results in blocked ducts and obstructed airflow of the lungs
Describe autosomal dominant traits
Dominant trait have a distinct pattern of inheritance and usually have affected family members in each generation:
- at least one affected parent
- males and females equally affected
- most children have a 50% chance of inheritance if one parent is heterozygous and the other is homozygous normal
- two affected individuals may have unaffected children
- Disease cannot skip generations
- the phenotype in homozygous dominant individuals is often more severe than the heterozygous phenotype
Example:
- Huntington disease
- Marfan’s syndrome
Explain Marfan’s syndrome as an inherited autosomal dominant trait
Dominant disorder affecting the skeletal syndrome, the eyes and the cardiovascular system
25% appear in families with no previous history - the gene has a high mutation rate
Gene responsible is called FBN1, located on chromosome 15 and encodes for protein fibrillin, a component of connective tissue
Most dangerous effect is on the aorta, it results in the weakening of the connective tissue around the base of the aorta, causing it to enlarge and eventually split open
Describe X- linked dominant traits
- hemizygous males and heterozygous females affected
- affected males transmit to all their daughters but none of their sons
- heterozygous female will transmit the trait to half of her children, sons and daughters equally affected
- on average twice as many females are affected than males
Example:
- hypophosphatemic rickets
Difference from autosomal dominant
Males pass to trait to only daughters no sons if it is X linked
Describe X- linker traits
- hemizygous males and female homozygous for the recessive allele are affected
- disease ore common in males
- affected males receive the mutant gene from their mothers
- daughters of affected males are usually heterozygous and therefore unaffected
- heterozygous female carrier has 50% chance of having affected sons
Example:
Haemophilia A
Colour blindness
Describe Y linked traits
Quite rare
The gene in question is located on the Y- chromosome and inherited directly from father to son
Define monogenetic
A characteristic that is produced by a single gene or a single allele
