Medelian genetics

Question 1

Define Phenotype & Genotype

Answer 1

Phe: physical appearance/expression of organism
Gen: the gene & alleles organism has

Question 2

Define Gene, Allele & Locus

Answer 2

Gene: Genetic code for a protein. > control physical charact.
Allele: An alternative form of gene (unit factor). E or e
Locus: location gene on chromosome

Question 3

Define Heterozygous & Homozygous

Answer 3

Heter: 2 diff alleles @ gene locus (Ee)
Homo: 2 alleles of a gene the same (EE or ee)

Question 4

What is P/ F1/ F2?

Answer 4

generations. Parent / Children / Grandchildren

Question 5

Define Dominant & recessive (in terms of single genes in 2 alleles)

Answer 5

Dom: trait always expressed bc mask recessive allele (EE or Ea).
Rec: trait only expressed if homozygous (ee)

Question 6

What is independent assortment of chromosomes?

Answer 6

The allele a child inherits from parents is random. (How homologous chromo. pair in metaphase)

Question 7

What is a Punnett square & when can it be used?

Answer 7

Aka test crosses that helps determine the possible genotype of offspring/s of 2 individuals. It can also discover the mode of inheritance of 1+ characteristic.

Question 8

When is a branched diagram used?

Answer 8

Branched diagrams are used with 2< genes. Ratio of each characteristic can be shown (phenotype)

Question 9

When are pedigrees used?

Answer 9

analyse the flow of genes in a particular specie

Question 10

What’s Mendel’s 3 principles of inheritance?

Answer 10

• Genetically controlled factors are controlled by UNIT FACTORS that exist in pairs (alleles)
• One unit factor is DOMINANT even when heterozygous (2 unlike unit factors) =to give one charact.
• During formation of gametes paired unit factors randomly segregate => each gamete equally receives likelihood of getting one of the other

Question 11

What is ascertainment bias?

Answer 11

limited pedigree data: small sample (include only fam) vs large random sample from population

Question 12

Differences between locus and allelic heterogeneity

Answer 12

• Allelic: diff. mutations @ 1x gene/locus => same phenotype

- Locus: diff. mutations @ 2+ gene/loci produce identical phenotypes

Question 13

which type of DNA is maternally inherited

Answer 13

mtDNA (only inherited from females = maternal)

Question 14

differentiate b/w Partial/Incomplete dominance, Co-dominance and Pseudodominance

Answer 14

• Incomplete: When one allele doesn’t mask the other = both expressed = mix phenotype. Pheno. is an intermediate to parents (e.g. red + white = pink)
• Co-dominance: both alleles expressed. Neither dominant or recessive e.g. ABO blood groups
• Pseudodominance: non-dominant mutation to appear dominant = recessive phenot. expressed bc mutation in dominant genot.- responsible for masking recessive

Question 15

Differentiate between penetrance and variable expression

Answer 15

• Penetrance: phenotype NOT EXPRESS genotype e.g. brown -> white
• Variable: a variably expressed trait will ALWAYS be expressed but the extent/intensity it is expressed will vary e.g. brown -> brown / cream / yellow

Question 16

What is epistasis & Mendelian ratio? Provide an example

Answer 16

• one gene/allele inhibits (or alter) expression of another
• 1x epistatic gene (like dominant) + 1x hypostatic gene (recessive) => alters expected Mendelian ratio E.g. MC1R has dominant & recessive epistatic alleles - control yellow or black pigment is produced

Question 17

How can sex affect expression of a trait?

Answer 17

Sex limited/influenced: expression of a trait depends on sex bc these traits are controlled by genes on autosomes. Condition where it only happens to male or female

Question 18

What is complementation?

Answer 18

Locus heterogeneity: phenotype caused by mutations in diff. genes (one mutation on one allele on gene 1 and same for gene 2). (Note: mutations are like recessive)

Question 19

What does partially sex linked mean?

Answer 19

Genes present in homologous region of X & Y chromosomes. Inheritance pattern is like normal genes

Question 20

Differentiate b/w epistatic & hypostatic (in terms of 2 genes interacting)

Answer 20

Epi: Gene that’s masking the expression of the other
Hypo: Gene that is being masked

Question 21

What is gene interaction?

Answer 21

2 genes involved;
1x responsible for the phenotype (e.g. colour: brown & black)
1x responsible for whether the phenotype will be expressed (e.g. can cause no colour = albino)
NEW PHENOTYPE PRODUCED

Question 22

What would a Y linked codition mean?

Answer 22

All males have the condition/disease

Question 23

What does haplosufficient mean?

Answer 23

an allele can fully express it’s phenotype (e.g. dominant, codominant)