UNIT 3 AOS1 Flashcards
Genotype
2 letters representing a gene’s allele pair.
TT, Tt
Phenotype
An observable trait from a person’s genes.
eg. Hair, eyes.
Punnet Square
Predicts the outcome of crosses of the offspring.
Heterozygous
2 different genes, the alleles are different.
Tt
Homozygous
2 of the same genes, alleles are the same.
TT, tt.
Rules of Testcross
50% Recessive, 50% dominant phenotypes = heterozygous.
100% dominant phenotypes = homozygous.
Dominant vs recessive.
Dominant traits are always expressed and are more present then recessive traits.
Monohybrid crosses
A genetic cross is performed to observe the inheritance of alleles and phenotypes for a single gene.
Passed down from parents to children.
Autosomal Dominant
Traits are always expressed whether there are 1 or 2 copies of the allele.
H= hair, h= no hair.
HH or Hh.
Autosomal Recessive
traits are only expressed if there are 2 copies of the recessive gene.
H= hair, h = no hair.
hh
Complete dominance.
Where a dominant allele is fully expressed in the phenotype and masks the expression of a recessive allele. It can mask a recessive gene.
Codominance.
In the inheritance of co-dominant alleles, neither allele is dominant or recessive, so both alleles are shown equally.
rrxww=rw (red and white spots, so roan)
Incomplete dominance.
No allele masks the effect of the other allele, no allele is dominant in the heterozygous phenotype, the traits blend together.
r=red.
w=white.
rw=pink
rrxww=rw
Sex-Linked Inheritance.
Shows the dominant/recessive inheritance but genes are carried on the X chromosome not the autosome.
X can carry, Colourblindness and Haemophilia.
Dihybrid cross
YyRr x YyRr
Used to observe the inheritance of alleles and phenotypes for two genes.
4x4 punnet square. (16)
YR
Yr
yR
yr
Haploid
a single set of chromosomes.
Diploid
2 sets of chromosomes.
Karyotype
Visual representation of an individual’s entire genome (complete set of DNA) organised in homologous pairs.
Polygenic inheritance
Characteristic influenced by 2 or more genes.
Stages of Meiosis
Prophase 1 + 2.
Metaphase 1 + 2.
Anaphase 1 +2.
Telophase 1 + 2.
Cytokinesis.
Prophase 1
- Chromosomes condense.
- Nuclear membrane breaks down.
- Crossover can occur in a random assortment.
Crossover is the exchange of DNA, between paired homologous pairs.
Metaphase 1
- Chromosomes line up on the equator in homologous pairs.
Anaphase 1
- Spindle fibres shorten.
- Chromosome pairs separate towards the poles.
Telophase 1.
- Double-stranded chromosomes at the poles.
Then the cell splits, cytokinesis.
