Codominance/ Multiple Alleles/ Sex linkage Flashcards
Define Codominance
Both alleles are expressed in the phenotype
Define multiple alleles
Where there are more than 2 alleles of which only two are present @ loci of individual homologous chromosome
How do we write the alleles to show they are codominant?
In superscript
eg w
C
r r w w r w
C C = Red C C = White C C = Roan
Cross a homozygous red-coated cow with a homozygous white-coated cow?
What is the offspring phenotype?
100% Roan
r w
C C = Roan
Cross two Roan cows together . The alleles are co dominant. What is the gametes and offspring genotype and phenotypic ratio.
Gametes = r w
C and C
Cr | Cw |
\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_\_
Cr | Cr Cr | Cr Cw |
Cw | Cw Cr | Cw Cw |
Roan : Red : White
2:1:1
Name an example of muitple alleles in humans ?
Blood types
Define sex linked
When an gene is found of the sex chromosomes
What are the genotypes of males and females?
XX and XY
What region of the Y chromosome is the gene for the testes forming ?
SRY
Sex determining region
The gene for haemophilia is sex-linked
cross a carrier female with a normal male.
What is the parental phenotype?
h H H
X X and X Y
The gene for haemophilia is sex linked
cross a carrier female with a normal male.
What are the gametes?
H h H
Female = X + X Male = X Y
What are pedigree charts used for?
To see inheritance of sex linked disease
How are males and females represented in a pedigree chart?
Males = Squares Female= Circles
A harmful recessive allels can reach a higher frequency in the population than harmful dominant allele- why?
Heterozygous can be carriers
unclear if person has recessive allele so wont be avoided
Dominant always expressed so can be less likely to reproduce and pass on to offspring
Why are observed ratios not as expected?
Fertilisation is random Linked genes Epistasis Crossing over occurs Small sample size Lethal genes
