Patterns of Inheritance Flashcards
What is an allele?
alternative forms of a gene, which give rise to different characteristics
What is a dominant allele?
allele which is always expressed, even if only one copy is present
What is a recessive allele?
allele which is only expressed when two copies are present
What is a homozygous genotype?
Both alleles in a diploid cell are the same
What is a heterozygous genotype?
The two alleles in a diploid cell are different
What is a codominant allele?
Alleles which are both expressed in a heterozygote
What is a genotype?
The combination of alleles in an individual (diploid cell)
What is a phenotype?
The physical or observable trait
Most phenotypes are due to polygenic inheritance. What does this mean?
They are controlled by two or more genes
Look at the family pedigree diagram.
What do circles, squares and shading mean?
Circle = female.
Square = male.
Shaded = has the trait of interest (often a genetic disorder).
Look at the family pedigree diagram for cystic fibrosis.
How can you tell that this condition is caused by a recessive allele?
Does not occur in every generation.
A child can have the trait even if neither parent is affected.
Look at the family pedigree diagram for cystic fibrosis.
What are the genotypes of II-3 and II-4?
How do you know?
Ff (heterozygous).
Both must have one recessive allele, in order to have a child (III-1) with the homozygous recessive trait, but are not affected themselves, so must also have a dominant allele.
Look at the family pedigree diagram for polydactyly.
How can you tell that this condition is caused by a dominant allele?
If an individual has the trait, at least one parent also has the trait.
Occurs in every generation.
Look at the family pedigree diagram for polydactyly, a condition caused by a dominant allele.
Explain how III-6 is not affected, when his mother is.
Mother (II-5) is heterozygous, as inherited a non-affected allele from her father (I-1).
III-6 inherited the non-affected allele from his mother, along with a non-affected allele from his father (II-6)
What combination of sex chromosomes do females have?
XX
What combination of sex chromosomes do males have?
XY
What is the probability of having a son?
Use a genetic diagram to explain your answer.
50% chance of a son.
All children inherit an X chromosome from mother; equal chance of second X or Y chromosome from father.
Which parent controls the gender of a child? Explain your answer.
Father - sperm provides either second X or Y chromosome; egg cell always provides a X chromosome
Pure breeding brown furred mice are crossed with pure breeding black furred mice.
All the offspring are black.
What is the dominant allele?
Black
Two tall pea plants, both heterozygous for the height allele, are bred together.
What proportion of the offspring plants will be dwarf?
Use a genetic cross diagram to support your answer.
25% dwarf
A black furred mouse, heterozygous for the colour allele, is crossed with a homozygous recessive brown furred mouse.
What proportion of the offspring will be brown furred?
Use a genetic cross diagram to support your answer.
50% brown furred
Cystic fibrosis is caused by a recessive alelle.
Explain how two parents who are not sufferers can have a child with cystic fibrosis.
Both parents are heterozygotes - they have one allele for cystic fibrosis, but are not sufferers.
If the child inherits the cf allele from both parents they will be sufferers
Polydactyly is caused by a dominant allele.
Explain why a child cannot have polydactyly unless one of the parents also has the condition.
If a parent is a heterozygote they will have polydactyly - at least one parent needs to be a heterozygote in order for a child to inherit a single polydactyly allele
Hair colour in horses is controlled by a single gene, with two codominant alleles - red and white. A roan horse has a mixture of red and white hairs (heterozygous).
What offspring may occur when two roan horses interbreed?
Use a genetic cross diagram to support your answer.
25% red haired, 50% roan, 25% white haired
Hair colour in horses is controlled by a single gene, with two codominant alleles - red and white.
What offspring may occur when a roan horse (heterozygote) breeds with a white horse?
Use a genetic cross diagram to support your answer.
50% roan, 50% white haired
Two heterozygous black furred mice interbreed.
What is the probability of their offspring being brown (recessive trait)?
25% chance of brown fur
A pure breeding (homozygous) tall pea plant is crossed with a heterozygous tall pea plant.
What is the probability of an offspring plant being dwarf?
0% chance of dwarf plant
