Monohybrid Inheritance

Question 1

Define genotype

Answer 1

The genetic make-up of an organism (DNA, chromosomes)

Question 2

Define phenotype

Answer 2

Visible characteristics in the organism (controlled by genotype and sometimes environment)

Example - Height, Hair colour, Skin colour

Question 3

Describe homozygous

Answer 3

Having a pair of identical (homo = solo) alleles, controlling the same characteristics. The organism would be pure-breeding for that characteristic

Question 4

Describe heterozygous

Answer 4

Having a pair of different alleles for a characteristic

Question 5

Describe a dominant allele

Answer 5

A gene that always appears in the phenotype whether the organism is heterozygous of homozygous

Question 6

Describe a recessive allele

Answer 6

A gene that only shows in the phenotype when the organism is homozygous

Question 7

What is the purpose of a Punnet Square?

Answer 7

• Monohybrid inheritance is the inheritance of characteristics controlled by a single gene.
• This can be determined by using a Punnet Square
• It shows the possible Allele combinations that could be produced in the offspring.

Question 8

How do you identify an Unknown genotype?

Answer 8

• Breeders can use a test-cross to find out the genotype of an organism showing dominant phenotype.
• This involves crossing the unknown individual with the individual showing the recessive phenotype
• If the individual is showing recessive phenotype it must be a homozygous recessive
• By looking at the ratio of phenotypes in the offspring, we can tell whether the unknown individual is homozygous dominant or heterozygous

Question 9

Why do we use family pedigree diagrams?

Answer 9

To trace the pattern of inheritance through generations of a family

Question 10

What are the rules in a family pedigree diagram?

Answer 10

Males = Square
Females = circles
Affected = red
Unaffected = blue

Question 11

Describe co-dominance

Answer 11

Both alleles in heterozygous organisms are neither recessive, and they are both displayed in the phenotype

Question 12

What’s an example of co-dominance?

Answer 12

Blood groups - there are three alleles of a gene governing this instead of two

Question 13

Which blood group is co-dominant and which is recessive?

Answer 13

IA and IB - co dominant
IO - recessive

Question 14

Describe what a sex-linked characteristic is

Answer 14

When alleles that control a particular characteristic are found on the sex chromosomes - makes the characteristic more common in one sex than the other

Question 15

Are alleles more common on the X or the Y chromosome?

Answer 15

X chromosome. The Y chromosome is much smaller.

Question 16

What’s an example of sex-linked conditions?

Answer 16

Red-green colour blindness

Question 17

What is a carrier?

Answer 17

• The person with one recessive allele
• Does not have the disease but has a 50% chance of passing it to her offspring