17.3 Inheritance (Cambridge (CIE) O Level Biology): Flashcards
Exam code: 5090
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Define inheritance.
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Cards in this collection (48)
Define inheritance.
The transmission of genetic information from generation to generation.
Define allele.
A different version of a particular gene.
Define genotype.
The combination of alleles that control a characteristic.
Define phenotype.
The observable characteristics of an organism.
Define dominant allele.
An allele that is always expressed, even if only one copy is present.
Define recessive allele.
An allele that is only expressed if two copies are present.
Define homozygous.
When the two alleles of a gene are the same.
Define heterozygous.
When the two alleles of a gene are different.
A allele only needs to be inherited from one parent to show up in the phenotype.
A dominant allele only needs to be inherited from one parent to show up in the phenotype.
True or False?
A recessive allele must be inherited from both parents to be expressed.
True.
If only one recessive allele is present, the dominant characteristic will show instead.
True or False?
Homozygous means having two different alleles of a gene.
False.
Homozygous means the two alleles are the same; heterozygous means they are different.
What is meant by a 'pure-breeding' individual?
An individual that is homozygous for a characteristic and always produces offspring with the same characteristic.
Define monohybrid inheritance.
The inheritance of a characteristic controlled by a single gene.
Define Punnett square.
A genetic diagram that shows the possible combinations of alleles in the offspring of a cross.
How is a dominant allele represented in a genetic diagram?
With a capital letter.
How is a recessive allele represented in a genetic diagram?
With a lower case letter (the same letter as the dominant allele).
In a genetic diagram you should always write the allele first.
In a genetic diagram you should always write the dominant allele first.
What phenotype ratio results from crossing two heterozygous individuals (Tt × Tt)?
A 3:1 ratio (dominant : recessive).
What phenotype ratio results from crossing a heterozygous individual with a homozygous recessive (Tt × tt)?
A 1:1 ratio.
True or False?
Crossing two pure-breeding parents (TT × tt) produces all heterozygous offspring.
True.
Every offspring inherits one dominant and one recessive allele, giving the genotype Tt.
True or False?
Punnett square predictions always match real-life results exactly.
False.
Predictions are based on chance, so real results can differ, especially with small numbers of offspring.
A pure-breeding individual is for a characteristic.
A pure-breeding individual is homozygous for a characteristic.
What does completing a Punnett square allow you to predict?
The probability of different genotypes and phenotypes in the offspring.
In a Tt × Tt cross, what percentage of offspring are predicted to show the recessive phenotype?
25%.
Define codominance.
When both alleles of a gene are expressed in the phenotype, with neither being recessive to the other.
How many alleles are there for the gene controlling blood group?
Three alleles: IA, IB and IO.
Which two blood group alleles are codominant?
IA and IB.
Alleles IA and IB are both dominant to allele .
Alleles IA and IB are both dominant to allele IO.
What is the genotype of a person with blood group AB?
IAIB.
True or False?
The inheritance of blood group is an example of codominance.
True.
Alleles IA and IB are codominant, so blood group AB shows both antigens.
What blood group is produced by the genotype IOIO?
Blood group O.
What sex chromosomes do females have?
XX.
What sex chromosomes do males have?
XY.
Because only he can pass on a Y chromosome, the determines the sex of the child.
Because only he can pass on a Y chromosome, the father determines the sex of the child.
True or False?
The mother determines the sex of the child.
False.
The father determines the sex, as only he can pass on an X or a Y chromosome.
What is the chance of a child being male?
50% (there is always a 50% chance of a boy and a 50% chance of a girl).
Define mutation.
A random change in the DNA base sequence.
What effect do most mutations have on the phenotype?
No effect, as the protein may work just as well as the non-mutated version.
Give an example of a harmful mutation in humans.
Sickle cell anaemia.
Which protein is affected by the sickle cell anaemia mutation?
Haemoglobin.
A mutation is a random change in the DNA sequence.
A mutation is a random change in the DNA base sequence.
Name two factors that increase the rate of mutation.
The mutation rate is increased by:
ionising radiation
some chemicals
True or False?
Most mutations are harmful.
False.
Most mutations have no effect on the phenotype.
True or False?
Mutation is a source of new alleles.
True.
Mutation gives rise to new alleles, contributing to genetic variation.
Down's syndrome is a chromosome mutation in which a person has chromosomes instead of 46.
Down's syndrome is a chromosome mutation in which a person has 47 chromosomes instead of 46.
Give one type of ionising radiation that can increase the mutation rate.
Gamma rays (also x-rays or ultraviolet rays).
How does mutation contribute to genetic variation?
It can give rise to new alleles, which may be passed on to offspring.
Why are ionising radiation and some chemicals linked to cancer?
They increase the mutation rate, which raises the chance of cells becoming cancerous.
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