Punnet Squares and pedigrees

Question 1

What does Homozygous mean?

Answer 1

Term used to refer to an organism that have two identical alleles for a particular trait.
o Homozygous Dominant – both chromosomes contain capital alleles

o Homozygous Recessive- both chromosomes contain lower case alleles.

Question 2

What does heterozygous mean?

Answer 2

Heterozygous- Term used to refer to an organism that has two different alleles for the same trait.

Question 3

What is a pedigree?

Answer 3

A pedigree is a genetic representation of al family tree that diagrams the inheritance of a trait or disease through several generations. The pedigree shows the relationships between family members and indicates which individuals express or silently carry a particular trait.

Silent carrier = heterozygous

Question 4

What is the purpose of a pedigree?

Answer 4

Determine the mode of inheritance of one trait – Dominant or recessive

Determine the probability of giving birth to an affected offspring for potential parents.

Potential parents should be warned of the risks of their children suffering significant disorders.

This is the role of genetic counsellors.

Question 5

What is the step to a pedigree analysis?

Answer 5

Identify if the trait is dominant or recessive so we can work out (hopefully) everyone’s genotype

Question 6

What is autosomal dominant inheritance?

Answer 6

Only one faulty copy of a gene is needed to show the condition.

Assume that affected outsiders are heterozygous.

Unaffected individuals are homozygous for the recessive allele.

Features:

Males & females affected in roughly equal portions.

Both men & women can pass the condition to sons and daughters.

Does not skip generations where individuals are affected.

Question 7

What is autosomal recessive inheritance?

Answer 7

Two copies of the mutant gene required for the condition to show.

All affected individuals are homozygous. (rr or tt)

Unaffected outsiders are assumed to be homozygous normal.

Features:

It can skip generations (unaffected parents can have a child)

Question 8

Is it a dominant or recessive pedigree?

Answer 8

If two affected people have an unaffected child, it must be a dominant pedigree.

If two unaffected people have an affected child, it must be a recessive pedigree.

If every affected person has an affected parent it is a dominant pedigree.