Inheritance

Question 1

What is co-dominance?

Answer 1

Pairs of alleles which are both expressed when present

Question 2

What are Mendel’s (5) principals of inheritance?

Answer 2

• Organisms have discrete factors (genes)
• Organisms possess two versions of each factor
• Each gamete contains one version of each factor
• Parents contribute equally to inheritance as a result of random fusion between randomly selected egg and sperm
• Common ratio when crossing heterozygous individuals is 3:1

Question 3

What is the law of segregation?

Answer 3

When gametes form, alleles are separated so that each gamete carries only one allele for each gene

Question 4

What is the law of independent assortment?

Answer 4

The segregation of alleles for one gene occurs independently to that of any other gene

Question 5

What is the principle of dominance?

Answer 5

Recessive alleles will be masked by dominant alleles

Question 6

Define homozygous.

Answer 6

If the maternal and paternal alleles are the same, the
offspring is said to be homozygous for that gene
AA- homozygous dominant
aa- homozygous recessive

Question 7

Define heterozygous.

Answer 7

If the maternal and paternal alleles are different, the
offspring is said to be heterozygous for that gene
Aa- heterozygous

Question 8

What is a test cross?

Answer 8

Testing a suspected heterozygous by crossing it with a known homozygous recessive

Question 9

What is a dominant allele?

Answer 9

Always show their encoded trait, when

present in an organism (masks the recessive trait)

Question 10

What is a recessive allele?

Answer 10

Only express their encoded traits when no other alleles are present

Question 11

What are the different ABO blood types?

Answer 11

A- IAIA or IAi
B- IBIB or IBi
AB- IAIB
O- ii

Question 12

What is a genetic disease?

Answer 12

A disorder caused by a gene, a mutated allele rather than microbes

Question 13

What is an autosomal recessive genetic disease?

Answer 13

• Both alleles are faulty (aa)
• Aa: heterozygous, possess one copy of the faulty allele but do not develop symptoms
• Cystic fibrosis, PKU

Question 14

What is an autosomal dominant genetic disease?

Answer 14

• You either have the disease or you don’t, you can’t be a carrier
• Huntington’s

Question 15

What is sex linkage?

Answer 15

• When a gene controlling a characteristic is located on a sex chromosome (X or Y)
• Only females can be carriers of X linked conditions
• Males will always inherit an X linked traits from their mother
• Females can not inherit an X linked recessive condition from an unaffected father
• E.g. haemophilia, colour blindness, male pattern baldness