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.
Prophase 2.
- Chromosomes condense.
- Spindle fibres begin to form.
- 2 sister chromatids.
Metaphase 2.
- Chromosomes line up on the equator, (singular).
- Spindle fibres attach.
Anaphase 2.
- Chromatids separate.
- Chromosomes become single-stranded and move to poles.
Telophase 2.
- Single-stranded chromosomes are at the poles.
Then cytokinesis.
Gametogenesis
Haploid cells develop into gametes, sperm + egg.
Epigenetics.
External factors that influence how a gene is expressed.
Phenotypes are influenced by DNA interactions that modify the expression of genes.
Methylation
Methyl groups tag DNA and activate or repress genes.
Histone Modification.
Winding of DNA.
Binds Epigenetic factors to histone ‘tails’ altering the extent to which DNA is wrapped around histones and the availability of genes in the DNA to be activated.
Importance of Epigenetics.
Helps control cell differentiation.
Acts as a rapid feedback mechanism where an organism can respond to changes in the environment.
Proportionate heritability.
Not all variation in phenotypes of a population can be explained by genetic factors alone.
A person with type A blood makes -
B anit-bodies.
If a person has A blood, they won’t have anti-A antibodies, they’ll have B antibodies so they won’t have antibodies that fight against their own blood type.
If you have type A blood you have:
type A antigens on the surface of your red blood cells and B antibodies in your blood.
If you have type B blood you have:
type B antigens on the surface of your red blood cells and A antibodies in your blood.
If you have type AB blood you have:
both type A and B antigens on the surface of your red blood cells and neither anti-A or anti-B antibodies in your blood.
Explain how a type A blood transfusion could be fatal for a person with type B blood.
Type A blood will block blood vessels and they have type A antibodies.
