11 - Single Gene Inheritance Flashcards
What is Mendelian Inheritance?
- each parent has 2 alleles for each character
- There are dominant and recessive alleles
- combination of dominant and recessive alleles makes the phenotype
Explain Mendel’s pea experiment
- crossed pure yellow and pure green peas
- the crossed the F1 generation
- F2 generation 3/4 yellow, 1/4 green - 1:2:1ratio
- yellow is dominant
How would you determine an unknown genotype?
test cross
How would you carry out a test cross?
- unknown genotype crossed with a homozygous recessive genotype
- if F1 is 1:1 then unknown must be heterozygous
- if F1 is all one trait, unknown must be homozygous dominant
what organisms can mendelian inheritance occur in?
diploid organisms with 2 copies of a gene
Name 4 different modes of single gene inheritance
- autosomal dominant
- autosomal recessive
- sex-linked dominant
- sex-linked recessive
What are pedigrees?
family trees that have information about disease
How do you identify a male on a pedigree?
a square
How do you identify a female on a pedigree?
a circle
How do you determine affected individuals in a pedigree?
filled in shapes
how do you determine individuals heterozygous in autosomal recessive?
half filled in
How do you determine a carrier of sex linked recessive?
a dot in the shape
How can you tell if someone is dead in a pedigree?
line through the shape
What are signs of autosomal dominant?
- all generations affected
- both sexes affected
Give an example of an autosomal dominant condition
Marfan syndrome
- issue with all fibrous connective tissue
- Caused by defects in fibrin gene in chromosome 15
are mendelian ratios observed in families?
No
Give an example of an autosomal recessive condition
Phenylketonuria (PKU)
- can’t metabolise phenylalanine
- caused by a defect in the phenylalanine hydroxylate gene on chromosome 12
What are signs of an autosomal recessive condition?
- most generations unaffected
- affects siblings of both sexes
- parents must be heterozygous and unaffected
What are signs of an X-linked dominant condition?
- disease in all generations
- affected fathers would pass it on to daughters only
- affected mothers would pass it onto both daughters and sons
What is an example of an X-linked recessive condition?
Heamophilia A
- difficulty forming blood clots
- defect in factor VIII gene on X chromosome
What are signs of an X-linked recessive condition?
- jumps a generation
- mostly males affected
- females can be heterozygous carriers
How do you determine the probabilities of an offspring genotype?
- find probability of gamete
- if single gene that will be 1/2
- multiply the probabilities of gametes to get probabilities of offspring
How would you write that two genes are linked?
by using a slash:
ex AB/ab
How would you write that two genes are unlinked?
using a semi-colon:
ex A/a ; B/b
