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? A different version of a gene
What is a genotype? The genetic constitution of an organism and its interaction with the
environment
What does the term 'dominant' mean? An allele who's characteristic appears in the
phenotype even when there's only one copy
What does the term 'recessive' mean? An allele who's characteristic only appears in the
phenotype if two copies are present
What does codominant mean? Alleles that are both expressed in the phenotype
What is the locus? The fixed position of a gene on a chromosome
Alleles of a gene are found on the same locus on each chromosome in a pair
What is a homozygote? An organism that carries 2 copies of the same allele
What is a hetrozygote? An organism that carries 2 different alleles
What is a carrier? A person carrying an allele which is not expressed in the phenotype but
that can be passed onto offspring.
How can we show the possible genotypes of offspring? By using genetic diagrams
What is monohybrid inheritance? - the inheritance of a characteristic controlled by a
single gene ( Aa )
- show the likelihood of different alleles of that gene being inherited by offspring of certain
parents
What is dihybrid inheritance? A genetic cross that examines the inheritance of 2 different
genes
( YyRr )
What is a punnett square? Another way of showing a genetic diagram
Also used to predict the genotypes of phenotypes of offspring
Can you only have 2 alleles of one gene? No you can have more than 2
It makes it more complicated
Can you use genetic diagrams to work out the chances of offspring inheritance where there is
more than one characteristic? Yes
What can be predicted? phenotype ratios
What is the expected phenotype ratio in the offspring if its a monohybrid cross between2
hetrozygous individuals? dominant : recessive
3:1
What is the expected phenotype ratio in the offspring if its a dihybrid cross between 2
homozygous parents? AA : Aa : aA : aa
9:3:3:1
What is the expected phenotype ratio in the offspring if its a codominant cross between one
homozygous parent and another?
( e.g HNHN x HSHS ) homozygous for one allele: hetrozygous for the other
1:2:1
What are the sex chromosomes for a female? XX
What are the sex chromosomes for a male? XY
When is a characteristics said to be sex-linked? When the allele that codes for it is
located on a sex chromosomes
What is the difference between the X and Y chromosome? Y chromosome is much smaller
and carries fewer genes
What does this mean? most genes on the sex chromosomes are only carried on the X
chromosome ( X linked genes )
, Why are males more likely than females to show recessive phenotypes for genes that are sex-
linked? - only have one X chromosome
- so only have one allele for sex-linked genes
- because they only have one copy they express the characteristic even if its recessive
Which genetic disorders are caused by faulty alleles on sex chromosomes? color blindness
haemophilia
What is the general term for these disorders? X linked disorders
What does the term 'autosome' mean? A chromosome that isn't sex linked
Where are autosomal genes located? on the autosomes
If 2 genes are on the same autosome, what are they? linked
How are they linked? Because they're on the same autosome they'' stay together during
independent segregation of chromosomes in meiosis I
Their alleles will be passed down onto the offspring together
For what reason may the alleles not stay together? crossing over
the closer together two genes are on an autosome... the more closely they are said to be
linked
Why are they said to be more closely linked? crossing over is less likely to split them
If 2 genes are autosomally linked , will you get the expected phenotypic ratio? no
What can show autosomal linkage? gene cross results
What is an epistatic gene? It masks the expression of another gene
Can different genes interact to form the phenotype? yes
How can many different genes control the same characteristic? the allele of one gene
masks the expression of the alleles of other genes: epistasis
If a cross involves epistatic genes, will it result in the expected phenotype ratio? No
What is the expected phenotype ratio for the offspring in a dihybrid cross involving an
epistatic allele? dominant both : dominant epistatic recessive other : recessive epistatic
9:3:4
Explain how? having 2 copies of recessive epistatic allele masks expression of the other gene
if you cross a homozygous recessive and a homozygous dominant
What is the expected phenotype ratio for a dihybrid cross involving a dominant epistatic
allele? dominant epistatic : recessive epistatic dominant : recessive both
12 : 3 : 1
What is the chi squared test? a statistical test that's used to see if the results of an experiment
support a theory
What is the null hypothesis? There is no significant difference between the observed and
expected results
How is chi squared calculated?
How do we found out if there's a significant difference? compare the chi squared test
results and the critical value
If the chi squared value is larger than the critical value... ...there is a significant difference
so the null hypothesis can be rejected
If the chi squared value is smaller than the critical value... ... there is no significant
difference so the null hypothesis can't be rejected
What level of probability do we use? 0.%
What is a species? A group of organisms that can reproduce to produce to give fertile
offspring
What is a population? A group of organisms of the same species living in a particular area at
a particular time
Can species exists as more than one populations? Yes
results in a characteristic
What is an allele? A different version of a gene
What is a genotype? The genetic constitution of an organism and its interaction with the
environment
What does the term 'dominant' mean? An allele who's characteristic appears in the
phenotype even when there's only one copy
What does the term 'recessive' mean? An allele who's characteristic only appears in the
phenotype if two copies are present
What does codominant mean? Alleles that are both expressed in the phenotype
What is the locus? The fixed position of a gene on a chromosome
Alleles of a gene are found on the same locus on each chromosome in a pair
What is a homozygote? An organism that carries 2 copies of the same allele
What is a hetrozygote? An organism that carries 2 different alleles
What is a carrier? A person carrying an allele which is not expressed in the phenotype but
that can be passed onto offspring.
How can we show the possible genotypes of offspring? By using genetic diagrams
What is monohybrid inheritance? - the inheritance of a characteristic controlled by a
single gene ( Aa )
- show the likelihood of different alleles of that gene being inherited by offspring of certain
parents
What is dihybrid inheritance? A genetic cross that examines the inheritance of 2 different
genes
( YyRr )
What is a punnett square? Another way of showing a genetic diagram
Also used to predict the genotypes of phenotypes of offspring
Can you only have 2 alleles of one gene? No you can have more than 2
It makes it more complicated
Can you use genetic diagrams to work out the chances of offspring inheritance where there is
more than one characteristic? Yes
What can be predicted? phenotype ratios
What is the expected phenotype ratio in the offspring if its a monohybrid cross between2
hetrozygous individuals? dominant : recessive
3:1
What is the expected phenotype ratio in the offspring if its a dihybrid cross between 2
homozygous parents? AA : Aa : aA : aa
9:3:3:1
What is the expected phenotype ratio in the offspring if its a codominant cross between one
homozygous parent and another?
( e.g HNHN x HSHS ) homozygous for one allele: hetrozygous for the other
1:2:1
What are the sex chromosomes for a female? XX
What are the sex chromosomes for a male? XY
When is a characteristics said to be sex-linked? When the allele that codes for it is
located on a sex chromosomes
What is the difference between the X and Y chromosome? Y chromosome is much smaller
and carries fewer genes
What does this mean? most genes on the sex chromosomes are only carried on the X
chromosome ( X linked genes )
, Why are males more likely than females to show recessive phenotypes for genes that are sex-
linked? - only have one X chromosome
- so only have one allele for sex-linked genes
- because they only have one copy they express the characteristic even if its recessive
Which genetic disorders are caused by faulty alleles on sex chromosomes? color blindness
haemophilia
What is the general term for these disorders? X linked disorders
What does the term 'autosome' mean? A chromosome that isn't sex linked
Where are autosomal genes located? on the autosomes
If 2 genes are on the same autosome, what are they? linked
How are they linked? Because they're on the same autosome they'' stay together during
independent segregation of chromosomes in meiosis I
Their alleles will be passed down onto the offspring together
For what reason may the alleles not stay together? crossing over
the closer together two genes are on an autosome... the more closely they are said to be
linked
Why are they said to be more closely linked? crossing over is less likely to split them
If 2 genes are autosomally linked , will you get the expected phenotypic ratio? no
What can show autosomal linkage? gene cross results
What is an epistatic gene? It masks the expression of another gene
Can different genes interact to form the phenotype? yes
How can many different genes control the same characteristic? the allele of one gene
masks the expression of the alleles of other genes: epistasis
If a cross involves epistatic genes, will it result in the expected phenotype ratio? No
What is the expected phenotype ratio for the offspring in a dihybrid cross involving an
epistatic allele? dominant both : dominant epistatic recessive other : recessive epistatic
9:3:4
Explain how? having 2 copies of recessive epistatic allele masks expression of the other gene
if you cross a homozygous recessive and a homozygous dominant
What is the expected phenotype ratio for a dihybrid cross involving a dominant epistatic
allele? dominant epistatic : recessive epistatic dominant : recessive both
12 : 3 : 1
What is the chi squared test? a statistical test that's used to see if the results of an experiment
support a theory
What is the null hypothesis? There is no significant difference between the observed and
expected results
How is chi squared calculated?
How do we found out if there's a significant difference? compare the chi squared test
results and the critical value
If the chi squared value is larger than the critical value... ...there is a significant difference
so the null hypothesis can be rejected
If the chi squared value is smaller than the critical value... ... there is no significant
difference so the null hypothesis can't be rejected
What level of probability do we use? 0.%
What is a species? A group of organisms that can reproduce to produce to give fertile
offspring
What is a population? A group of organisms of the same species living in a particular area at
a particular time
Can species exists as more than one populations? Yes
