Mendelian Genetics

Question 0

What is an allele?

Answer 0

Variant of the same gene

Question 1

What are Mendels 2 laws?

Answer 1

1) each trait has 2 hereditary determinants
1 allele per parent. Both alleles passed in equal proportions

2) traits segregate independently of each other

Question 2

Why can you only infer a genotype from a recessive trait?

Answer 2

Recessive phenotypes can only have one genotype - homozygous recessive.

Whereas a dominant phenotype can either be homozygous or heterozygous

Question 3

What is the F2 ratio for a dihybrid cross?

Answer 3

9:3:31

Question 4

Independent assortment of two genes predicts a __:__:__:__ phenotype ratio from a __:__:__ genotype ratio

Answer 4

9: 3:3:1
1: 2:1

Question 5

Why does Mendels 2nd law only work for unlinked genes?

Answer 5

Genes very close on a chromosome tend to be inherited as a haplotype

Question 6

The trait that persists in the F1 generation is the _______ trait

Answer 6

Dominant

Question 7

What is a backcross?
What is a testcross?
What is a monohybrid cross?

Answer 7

• From a F1 hybrid to one of the homozygous parents
• from an individual to a homozygous recessive parent to determine if individual is homozygous or heterozygous
• cross between parents that differ at a single gene pair

Question 8

What is penetrance?

Answer 8

Probability that A carrier of a dominant mutation will actually show signs of the disorder
Incomplete penetrance is where a person with the mutation does not get the disease. Could be age linked. Explains skipping of generations

Question 9

What is a de novo mutation?

Are males or females more likely to pass on a de novo mutation?

Answer 9

Healthy parents have an effected child. Many are lethal. Healthy parent could be a pre mutation carrier, harbouring an unstable repeat which could cause de novo in later generations

• males more likely, due to the pathophysiology of spermatogenesis

Question 10

What is an obligate daughter? What % of her sons or daughters are affected?

Answer 10

Daughter of an x disorder male. Always a carrier.

50% of sons and 25% of daughters

Question 11

What is allelic heterogeneity

And locus heterogeneity

Answer 11

Allelic - same gene but different allele mutation= same disorder
Locus - different gene mutation = same disorder

Question 12

Monohybrid cross = W/W x __/__ = W/__

Answer 12

WW + ww = Ww

Question 13

Dihybrid cross = Wg x __\_ = __\_

Answer 13

Wg x wG = WG/gw

Question 14

What’s an easy calculation to work out the number of offspring with a trait for F2?

Answer 14

Number of Offspring/16 x selected trait (9 or 3 or 3 or 1)

Question 15

Give the stages of spermatogenesis

Answer 15

Spermatogonium
Primary spermocyte
Secondary spermatocytes
Spermatids
Spermatozoa

Question 16

Give the stages if egg gamete formation

Answer 16

Oogonium
Primary oocyte
Secondary oocyte OR polar bodies
Egg

Question 17

What are the two main reasons that linked genes may not give an expected genotype

Answer 17

• close genes inherited as a haplotype

- physically linked genes undergo independent assortment

Question 18

What are the main modes of inheritance? (Inheritance patterns)

Answer 18

Single gene/Mendelian

• autosomal dominant/recessive
• x linked dominant/ recessive

Multifactorial
Mitochondrial