Please enable JavaScript.
Coggle requires JavaScript to display documents.
Genes and inheritance (Alleles and genes ((Genotype: the alleles each cell…
Genes and inheritance
Alleles and genes
Each features is controlled by a gene, found on a chromosome
-
-
-
One allele is dominant over the other allele, which is recessive
When two different alleles are in the same cell, only the dominant allele is expressed
An individual can have two dominant (homozygous), two recessive (homozygous), or one of each allele in each cell (heterozygous)
-
-
Test cross
Used when you can't tell if something is heterozygous or homozygous (TT or Tt – both appear the same)
-
Every other possible variable has to be controlled including the genotype of the plant it's bred with
=> the other plant has to be homozygous recessive
- breed the two plants
- write out a genetic cross for both possibilities
- predict the outcome for each
- compare breeding experiment with predicted outcomes to see which result matches the prediction most closely
Outcomes:
–> homozygous: all offspring are dominant
–> heterozygous: half are dominant, half are recessive
-
Codominance
If two alleles are expressed in the same phenotype, they are codominant
eg. snapdragon plants have red, white, or pink flowers
–> red flowers + white flowers –––> pink flowers
–> pink flowers + pink flowers –––> 1 red : 2 pink : 1 white
-
Sex chromosome
-
Two Xs in every female cell except egg,
one X and one Y in every male cell except sperm
-
Polygenic inheritance
-
eg. skin colour – several genes where some promote melanin production and some do not
=> produces a wide range of phenotypes
-
Predicted ratio
Ratios in genetic crosses are predicted ratios – in breeding experiments they are unlikely to fit exactly
-