Inheritance And Genetic Crosses Flashcards
In cats, males are XY and females are XX.
A gene on the X chromosome controls fur colour in cats.
The allele G codes for ginger fur and the allele B codes for black fur.
These alleles are codominant.
Heterozygous females have ginger and black patches of fur and their phenotype is described as tortoiseshell.
Explain what is meant by codominant alleles.
Codominant alleles means:
- Both alleles are expressed
Male cats with a tortoiseshell phenotype do not usually occur.
Explain why.
( In cats, males are XY and females are XX.
A gene on the X chromosome controls fur colour in cats.
The allele G codes for ginger fur and the allele B codes for black fur.
These alleles are codominant.
Heterozygous females have ginger and black patches of fur and their phenotype is described as tortoiseshell. )
Male cats with a tortoiseshell phenotype do not usually occur because:
- Male cats have a Y chromosome, which doesn’t carry that allele ( the allele that can code for tortoiseshell phenotype )
A tortoiseshell female was crossed with a black male.
Use a genetic diagram to show all the possible genotypes and the ratio of phenotypes expected in the offspring of this cross.
Use X^G to indicate the allele G on an X chromosome.
Use X^B to indicate the allele B on an X chromosome.
( In cats, males are XY and females are XX.
A gene on the X chromosome controls fur colour in cats.
The allele G codes for ginger fur and the allele B codes for black fur.
These alleles are codominant.
Heterozygous females have ginger and black patches of fur and their phenotype is described as tortoiseshell. )
Genotypes of offspring:
- X^GX^B, X^BX^B, X^GY, X^BY
Phenotypes of the offspring:
- Tortoiseshell female, black female, ginger male and black male
Ratio of phenotypes:
- 1 : 1 : 1 : 1
Polydactyly in cats is an inherited condition in which cats have extra toes.
The allele for polydactyly is dominant.
In a population, 19% of cats had extra toes.
Use the Hardy-Weinberg equation to calculate the frequency of the recessive allele for this gene in this
population.
Show your working.
( In cats, males are XY and females are XX.
A gene on the X chromosome controls fur colour in cats.
The allele G codes for ginger fur and the allele B codes for black fur.
These alleles are codominant.
Heterozygous females have ginger and black patches of fur and their phenotype is described as tortoiseshell. )
Frequency of the recessive allele:
- 0.9
Some cat breeders select for polydactyly.
Describe how this would affect the frequencies of the homozygous genotypes for this gene in their breeding
populations over time.
( In cats, males are XY and females are XX.
A gene on the X chromosome controls fur colour in cats.
The allele G codes for ginger fur and the allele B codes for black fur.
These alleles are codominant.
Heterozygous females have ginger and black patches of fur and their phenotype is described as tortoiseshell. )
( Polydactyly in cats is an inherited condition in which cats have extra toes.
The allele for polydactyly is dominant. )
The frequencies of the homozygous genotypes for this gene in their breeding
populations over time is effected in:
- Homozygous dominant will increase
- Homozygous recessive will decrease
Some populations of flies are becoming resistant to insecticides intended to kill them.
Scientists developed a method for finding out whether a fly was carrying a recessive allele, r, that gives resistance to an insecticide.
The dominant allele, R, of this gene does not give resistance.
The scientists:
• crossed flies with genotype RR with flies with genotype rr
• obtained DNA samples from the parents and offspring
• used the same restriction endonuclease enzymes on each sample, to obtain DNA fragments
Explain why the scientists used the same restriction endonuclease enzymes on
each DNA sample.
Scientists used the same restriction endonuclease enzymes on
each DNA sample because:
- It will cut DNA at the same base sequence
- So the scientist will get fragments of the required gene
The scientists added two different primers to each sample of DNA fragments for the
polymerase chain reaction ( PCR )
.
• Primer A3 only binds to a 195 base-pair fragment from allele r.
• Primer A4 only binds to a 135 base-pair fragment from allele R.
The scientists separated the DNA fragments produced by the PCR on a gel where shorter fragments move further in a given time.
Their results are shown in Figure 1.
( Figure 1 shows an image of the different positions of which the DNA fragments separated on the gel )
( The DNA fragments produce bands on the gel )
( There are three different types of DNA fragments used )
( “ L - DNA “ fragments from one of the parents )
( “ M - DNA “ fragments from the offspring )
( “ N - DNA “ fragments from the other parent )
( DNA fragments move down the gel )
( “ L - DNA “ band settles at the top of the gel )
( “ M - DNA “ produces two bands, which are in the position of “ L - DNA “ and “ N - DNA “ )
( N - DNA “ band settles quite far down the gel )
Explain why primer A3 and primer A4 only bind to specific DNA fragments.
( Some populations of flies are becoming resistant to insecticides intended to kill them.
Scientists developed a method for finding out whether a fly was carrying a recessive allele, r, that gives resistance to an insecticide.
The dominant allele, R, of this gene does not give resistance.
The scientists:
• crossed flies with genotype RR with flies with genotype rr
• obtained DNA samples from the parents and offspring
• used the same restriction endonuclease enzymes on each sample, to obtain DNA fragments )
Primer A3 and primer A4 only bind to specific DNA fragments because:
- Each primer have a specific base sequence
- That is complementary to the allele ( R or r )
Use all the information given to explain the results in Figure 1.
( The scientists added two different primers to each sample of DNA fragments for the
polymerase chain reaction ( PCR )
.
• Primer A3 only binds to a 195 base-pair fragment from allele r.
• Primer A4 only binds to a 135 base-pair fragment from allele R.
The scientists separated the DNA fragments produced by the PCR on a gel where shorter fragments move further in a given time.
Their results are shown in Figure 1.
( Figure 1 shows an image of the different positions of which the DNA fragments separated on the gel )
( The DNA fragments produce bands on the gel )
( There are three different types of DNA fragments used )
( “ L - DNA “ fragments from one of the parents )
( “ M - DNA “ fragments from the offspring )
( “ N - DNA “ fragments from the other parent )
( DNA fragments move down the gel )
( “ L - DNA “ band settles at the top of the gel )
( “ M - DNA “ produces two bands, which are in the position of “ L - DNA “ and “ N - DNA “ )
( N - DNA “ band settles quite far down the gel ) )
( Some populations of flies are becoming resistant to insecticides intended to kill them.
Scientists developed a method for finding out whether a fly was carrying a recessive allele, r, that gives resistance to an insecticide.
The dominant allele, R, of this gene does not give resistance.
The scientists:
• crossed flies with genotype RR with flies with genotype rr
• obtained DNA samples from the parents and offspring
• used the same restriction endonuclease enzymes on each sample, to obtain DNA fragments )
Figure 1 tells us that:
- Fragments L are from the parent with allele rr because they are the longer fragments ( 195 base-pair fragment )
- Fragments N are from the parent with allele RR because they are the shorter fragments ( 135 base-pair fragment )
- Fragments M are from the offspring with heterozygous ( Rr ) because there is both 195 and 135 base pair fragments present
The scientists wanted to know on which chromosome the gene with alleles R and r
was located.
From the flies with genotype RR, they obtained cells that were in mitosis and added a labelled DNA probe specific for allele R.
They then looked at the cells under an optical microscope.
Explain why they used cells that were in mitosis.
( The scientists added two different primers to each sample of DNA fragments for the
polymerase chain reaction ( PCR )
.
• Primer A3 only binds to a 195 base-pair fragment from allele r.
• Primer A4 only binds to a 135 base-pair fragment from allele R.
The scientists separated the DNA fragments produced by the PCR on a gel where shorter fragments move further in a given time.
Their results are shown in Figure 1.
( Figure 1 shows an image of the different positions of which the DNA fragments separated on the gel )
( The DNA fragments produce bands on the gel )
( There are three different types of DNA fragments used )
( “ L - DNA “ fragments from one of the parents )
( “ M - DNA “ fragments from the offspring )
( “ N - DNA “ fragments from the other parent )
( DNA fragments move down the gel )
( “ L - DNA “ band settles at the top of the gel )
( “ M - DNA “ produces two bands, which are in the position of “ L - DNA “ and “ N - DNA “ )
( N - DNA “ band settles quite far down the gel ) )
( Some populations of flies are becoming resistant to insecticides intended to kill them.
Scientists developed a method for finding out whether a fly was carrying a recessive allele, r, that gives resistance to an insecticide.
The dominant allele, R, of this gene does not give resistance.
The scientists:
• crossed flies with genotype RR with flies with genotype rr
• obtained DNA samples from the parents and offspring
• used the same restriction endonuclease enzymes on each sample, to obtain DNA fragments )
They used cells that were in mitosis because:
- Cells in mitosis have their chromosomes visible
- The scientist will be able to see which chromosome the DNA probe is attached to
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