Classic Mendelian Genetics Flashcards
What were Mendel’s observations?
- a heritable factor (now called a gene)
- the heritable factor is not diluted or destroyed
- 3:1 inheritance pattern in F2 offspring
What were Mendel’s postulates? (4)
1) Units of genetic inheritance
2) Dominance/Recessiveness
3) Segregation
4) Independent assortment
MENDEL’S POSTULATES: Units of genetic inheritance
Alleles as alternate versions of genes that cause variation in inherited characters.
MENDEL’S POSTULATES: Dominance/Recessiveness
Where there are different alleles the only one is expressed so one is dominant (expressed) other is recessive.
MENDEL’S POSTULATES: Segregation
alleles are separated randomly during gamete formation
MENDEL’S POSTULATES: Independent assortment
Segregating pairs of alleles assort independently of each other.
Genetic recombination during meiosis
- During prophase 1= crossing over between homologous chromosomes
Types of genetic dominance
-COMPLETE DOMINANCE: when phenotypes of homozygote and heterozygote are identical
-INCOMPLETE DOMINANCE: when phenotype of F1 hybrids is halfway between the two parental varieties
-CODOMINANCE: when two dominant alleles affect the phenotype in separate ways.
Epistasis
When a gene at one locus influences the phenotypic expression of a gene at a second locus.
Sex determination in mammals
- the gonad has the potential to develop into either a testis or an ovary
- female has homomorphic XX male has heteromorphic XY
- X chromosome is larger than Y
- no paired genes between the chromosomes
-Sry expression; masculine phenotype
X chromosome inactivation
-occurs in female mammals
- each female carries 2 X chromosomes, one from each parent- males only have one
- in females one of each X is inactivated in each cell, dosage compensation
- inactive X chromosome is called Barr body
Autosomal Dominant Inheritance
- have at leat one affected parent
- at least a 50% chance of passing on trait
- males and females equally affected
- 2 affected individuals may have unaffected offspring
Autosomal Recessive Inheritance
- two affected individuals have an 100% chance of having an affected offspring
- males and females equally affected
- two unaffected heterozygotes resulting in one or more homozygotes
X-linked recessive inheritance
- hemizygous males and homozygous females are affected
- Daughters of affected males are heterozygous so unaffected
-Sons of affected males are unaffected - Sons of heterozygous females have 50% chance of receiving recessive gene therefore being affected
X-linked dominant inheritance
- heterozygous females are affected males are usually not viable
- because males aren’t viable homozygous females don’t exist
- affected offspring have an affected mother
Loss-of-function mutation
Inactivating mutation: the gene has reduced or lost function
Most commonly seen in recessive alleles
Gain-of-function mutation
Activating mutation: the gene product has an abnormal function
Could be positive or negative, as in dominant disease alleles
Heterosis
When two homozygous strains are crossed, offspring are generally phenotypically stronger and larger than either parent.
Overdominance
Heterozygotes in certain genes are superior to homozygotes eg. sickle cell anemia
Heterozygotes are affected to a lesser degree
Polygenic inheritance
Quantitative variation indicates polygenic inheritance, two or more genes affects a single characteristic.
Define penetrance
the proportion of individuals in a population with a given genotype that express the correct phenotype
Define expressivity
the degree to which a characteristic is expressed in a given individual
4 processes in population genetics
1) Selection
2) Mutation
3) Genetic drift
4) Gene flow
