Basics of Genetic Inheritance (Embryology) Flashcards
Describe the human karyotype:
23 pairs of chromosome:
- 22 autosomal pairs
- 1 Sex pair
- XY = Female
- XY = Male
Define ‘gene’
Section of DNA that codes for characteristic
Define ‘allele’
Versions of a gene
Define ‘genotype’
Actual state of genes in an organism (e.g. AA, aa or Aa)
Define ‘phenotype’
Physical manifestation of the genes
List the two principles of Mendelian Inheritance
- Law of segregation
- Law of independent assortment
Define ‘law of segregation’
Alleles that are together in one generation, will be separated in next.
Define ‘law of independent assortment
Alleles will mix independently in the offspring.
List the exceptions of Mendelian Inheritance
- Incomplete dominance
- Quantitative inheritance
- Co-dominant expression
- Gene linkage
- Sex chromosome
Define ‘incomplete dominance’
Heterogenous alleles lead to intermediate characteristic (e.g. Red rose + white rose -> Pink rose)
Define ‘Quantitative inheritance’
Multiple genes have minor effects on trait, with sum of gene leading to phenotype (e.g. Skin colour is reguulated by >4 genes)
Define ‘co-dominant expression’
Each allele is fully expressed (e.g. Blood type)
Define ‘gene linkage’
Genes located closely on the same chromosome are often inherited together (i.e. linked gene)
Define ‘sex chromosome’
Females get XX with 50% inactivated; Males get XY
List the patterns of genetic inheritance
- Autosomal dominant
- Autosomal recessive
- X-linked recessive
- X-linked dominant
- Maternal inheritance
Describe ‘autosomal dominant’
Need only one copy of gene for phenotype:
- Male and female equally probable
- If parents don’t have phenotype, 0% of offspring having phenotype
- If one parent has phenotype, 50-100% of offspring will (statistically)
Describe ‘autosomal recessive’
Need two copies of gene for phenotype
- Male or female equally probable
- Two/both parents need to be at least carriers
Describe ‘X-linked recessive’
Only manifests in men, unless females get two copies of gene.
No father to son transmission.
Describe ‘X-linked Dominant’
Only one copy needed in females and males.
- Passed from mothers to sons and daughters
- No father to son transmission
- Fathers always pass to daughters.
Describe ‘Maternal inheritance’
Mitochondrial genes are only passed from mother.
- Passed from mother only to sons and daughter equally
- No transmission from father
Describe gene imprinting
- One allele has an epigenetic mark that makes it silent, but it reappears in next generation
- All offspring inherit a silent gene for one generation
- Paternal imprinting = Through fathers
- Maternal Imprinting - through mothers
