Topic 7A: Genetics Flashcards
What is monohybrid inheritance?
Inheritance of of a characteristic controlled by a single gene
What is a gene?
a Sequence of bases on a DNA molecule that codes for a protein which results in a characteristic
What is an allele?
Different versions of the same gene.
What is a genotype?
The genetic constitution of an organism eg BB or Bb
What is a phenotype
THe expression of the genetic constitution and its interaction with the environment
What does dominant mean?
An allele whose characteristics appears in the phenotype even when there’s only one copy
What does recessive mean?
An allele whose characteristic only appears in the phenotype of two copies are present
What is codominance?
When both alleles are expressed
What is locus?
A position of a gene on a chromosome.
Give and example of codominance?
sickle cell anaemia
What is sickle cell anaemia?
If the person has heterozygous phenotype its mean they have both normal Hb and some sickle Hb too. They are both equally expressed
Name a gene that has multiple alleles
Your blood can be AA/AB/OO/OA/OB/BB
What is the predicted phenotype ratio for monohybrid cross?
3:1
What is the predicted phenotype ratio for dihybrid cross?
9:3:3:1
What is the predicted phenotype ratio for codominance cross?
1:2:1
Sometimes you wont get the expected phenotype ratios. Why?
due to
sex linkage
autosomal linkage or
epistatisis
What does sex linked means?
when a characteristic’s allele is on a sex chromosome
Which sex chromosome is smaller
Y
Which sex chromosome carriers fewer genes
Y
What is X linked?
When the allele is carried on the X chromosome
Why are males more likely to show recessive phenotypes for genes that are sex linked?
Because males only have on X chromosome. The allele on that chromosome is therefore expressed even if it is recessive
Name genetic disorders that are caused my faulty alleles on the sex chromosomes
Colour blindness (recessive)
haemophilia
(x-linked disorders)
What are autosomes?
Chromosomes that are not sex chromosomes
Autosomes are said to be linked…
if the genes are on the same chromosome
What happens to autosomal chromosomes that are linked in meiosis?
They stay together during independent segregation
Their alleles are passed down to offspring
Why might autosomal linked allele might not be passed down to offspring?
They might be separated by crossing over
The closer together two genes are on the autosome…..
the more closely they are said to be linked
-This is because crossing over is less likely to split them
