Inheritance Flashcards
Define the term ‘genotype’
The genetic constitution of an organism
Define the term ‘phenotype’
The expression of genes and its interaction with the environment
Define the term ‘dominant allele’
The allele that is always expressed in the phenotype
Define the term ‘recessive allele’
An allele that is only expressed if no dominant allele is present
Define the term ‘codominant allele’
Both alleles are equally dominant and both are expressed in the phenotype
Define the term ‘multiple alleles’?
When genes can have more than two alleles for example blood groups
State an example of multiple alleles
-Blood groups
-Three alleles are associated with the immunoglobulin gene (gene 1)
-Gene 1 results in the presence of certain antigens on the cell surface of red blood cells
State the genetic diagram coding for monohybrid inheritance and state an example
-A single letter, Capital (dominant allele) or lower case (recessive allele)
-Example: A (dominant) or a (recessive)
State the genetic diagram coding for codominant inheritance and state an example
-Gene^allele
-Base letter= gene, superscript= allele
-Example: L^A L^B (the alleles are both equally dominant)
State the genetic diagram coding for autosomal linkage and state an example
-A single letter, Capital (dominant allele) or lower case (recessive allele)
-Example: Aa Bb
State the genetic diagram coding for multiple alleles and state an example
-Gene^allele
-Base letter= gene, superscript= allele
-Example: L^A L^B (the alleles are both equally dominant)
State the genetic diagram coding for epistasis and state an example
-A single letter, Capital (dominant allele) or lower case (recessive allele)
-Example: AA Bb
What is monohybrid inheritance?
Inheritance that only involves one gene
State two examples of monohybrid inheritance
Cystic fibrosis
Eye colour
Caused by a recessive allele of one gene
Explain why the results of genetic crosses often differ from the predicted results
-The probability of having a boy or a girl is always 50%
-If the probability of having a characteristic is 50%, you half this
-There is a 25% chance of having a girl with the characteristic
State three examples of monohybrid crosses
-Can predict offsprings chance of carrying a genetic disorder
-Can produce crops with desirable characteristics
-Can produce crops adapted to specific environments (drought)
State two disadvantages of monohybrid crosses
-Could result in monoculture (habitats + food sources)
-Many characteristics are polygenetic and can be influenced by the environment
What is dihybrid inheritance?
-The inheritance of two characteristics determined by two different genes at the same time
-Due to gametes and inheritance being independent
-For example shape and
If two heterozygous parents for both genes are crossed what is the ratio of phenotypes in a dihybrid cross?
9:3:3:1
What is the law of independent assortment?
-During meiosis, the chromosomes can arrange randomly
-This means either allele of gene 1 can combine with either allele of gene 2
Example question: Parents with blood group AB and blood group O reproduce. I^A and I^B are codominant and I^O is recessive. What is the probability that they will have an offspring with blood group A?
Multiple alleles
Parental genotypes= I^A I^B x I^O I^O
I^B I^O , I^B I^O , I^A I^O , I^A I^O
50% probability of blood group A
Example question: Cows can be red, white or roan. Red and white are both dominant. If two roan cows reproduce, what is the probability they will produce red offspring?
Codominance
Parental genotypes= C^R C^W x C^R C^W
C^R C^W , C^R C^R, C^W C^W , C^R C^W
25% probability of red offspring
Example question: Cystic fibrosis is caused by a recessive allele. If two carriers reproduce, what is the probability they will have a child with cystic fibrosis? What is the probability they will have a girl with cystic fibrosis? (F= dominant allele, f= recessive allele)
Monohybrid inheritance
Parental genotypes= Ff x Ff
FF, Ff, Ff, ff
25% probability of a child having cystic fibrosis
25% x 50% probability of it being a girl = 12.5%
Define the term ‘karyotype’?
The number and appearance of chromosomes in the nucleus of a eukaryotic cell
Define the term ‘
A gene whose locus is on the X chromosome
What is and why is it important?
-Genes found on either X or Y
-Can have unequal probability of being passed on
-Can be more common in one than the other
-Some genes on X have no homologous equivalent copy on Y
-Recessive characteristics found on this section of the chromosome will never be more frequent in
-They have no homologous section on Y that could carry the dominant allele
Example question: Colour blindness is caused by a recessive allele found only on the X chromosome. If a non-colour blind male reproduces with a female carrier of the allele, what is the probability their children will be colour blind?
Parental genotypes= X^R X^r x X^R Y
X^R X^r , X^R X^R , X^r Y , X^R Y
X^r Y (25% probability of child being colour blind)
Define the term ‘autosomal linkage’
Genes that are located on the same chromosome
What is autosomal linkage?
- The alleles for each gene that are linked on the same chromosome will be inherited together
-This impacts the predicted phenotypes of the gametes
Explain how autosomal linkage affects the combinations of alleles in gametes
-Crossing over in meiosis results in new combinations of alleles in gametes
-This means that the predicted gametes in the punnet square may be different
-Crossing over during meiosis can make new combinations of gametes
Define the term ‘epistasis’
This is when one gene influences (affects or masks) the expression of another gene
What is epistasis?
-This is when one gene influences (affects or masks) the expression of another gene
-One gene can control the expression of another gene
-It occurs in non-linked genes
