Population Genetics, Pedigrees And Mendelain Inheritance

Question 1

What is population genetics?

Answer 1

Study of allele and genotype frequency distribution change

Question 2

List the 4 evolutionary processes that influxes population genetics

Answer 2

Natural selection
Genetic drift
Mutation
Gene flow

Question 3

Define population

Answer 3

Every member with a selected characteristic

Question 4

Define sample

Answer 4

Subset of given sample which represents the population

Question 5

Define locus

Answer 5

A specific position of a specific chromosome

Question 6

Define allele

Answer 6

Alternative form of a gene/ DNA marker that is located at a specific locus

Question 7

Define genotype

Answer 7

Genetic makeup of an individual at a specific gene of DNA marker

Question 8

Define phenotype

Answer 8

Observable characteristics due to genetic makeup

Question 9

List and define the 3 genotypes

Answer 9

Homozygote- Possesses the same alleles at a specific locus
Heterozygote- Possesses different alleles at a specific locus
Polymorphism- Multiple forms of a gene in a population

Question 10

Define and explain the Hardy-Weinberg principle

Answer 10

If a population is in genetic equilibrium then:
1. The frequencies of the alleles will not change from one generation to the next
2. Genotype frequencies can be predicted from allele
frequencies

Question 11

Give the 2 equations used to calculate allele and genotype frequency

Answer 11

P + Q= 1
P^2 + Q^2 + 2PQ=1
Where p= dominant allele and q= recessive allele

Question 12

On what conditions is a population is genetic equilibrium?

Answer 12

1. The population is infinitely large
2. Random mating occurs
3. No migration occurs
4. No natural selection occurs
5. No mutations arise

Question 13

How can you estimate the carrier frequency of an autosomal recessive disorder?

Answer 13

Frequency of disease causing allele (q) is derived from the incidence (=I)
Often the incidence is known and you the allele and genotype frequencies have to be calculated

Question 14

How do you use the HW equation for X-linked conditions like haemophilia?

Answer 14

In females the carrier incidence is 2pq
For males the frequency of q= frequency of disease
Frequency in males can be used to estimate carrier frequency
For example:
Carrier frequency is 2pq= 2 x p x 1/5000

Question 15

How do you estimate allele frequency of Autosomal dominant disorders?

Answer 15

AD disorders are manifested in heterozygotes
Therefore People affected = 2pq + q^2
However q^2 i usually negligible, aprox 0
Therefore people affected=
Q= 1/2 x I

Question 16

List some commonly used shapes on a pedigree tree

Answer 16

Filled shape= clinically affected
Empty shape= unaffected
Male= square
Female= circle
Dead= diagonal line through shape
Pregnant= P inside shape
Miscarriage= Triangle
TOP= Lin through triangle

Question 17

List common lines seen on a pedigree tree

Answer 17

Generation (parents and siblings, biological)= straight line from line connecting parents to their children
Former relationship= dashed line breaking relationship line
Consanguinity= two lines connecting related individuals in a relationship
Identical twins= Line between individuals
Non- identical twins= Twins come from same descendant line of parents

Question 18

How can you tell a genetic disorder is autosomal recessive?

Answer 18

Both sexes are affected (dot inside squares and circles)
Unaffected parents have affected offspring
Condition can ‘skip’ generations

Question 19

How can you tell if a genetic disorder is autosomal dominant?

Answer 19

Vertical mode of transmission
Those who are carriers are affected by symptoms
Both sexes are affected

Question 20

How can you tell if a disorder is sex linked (X-linked)

Answer 20

Only males are affected
Females are carriers only and unaffected by symptomatic

Question 21

Define Mendelian genetics

Answer 21

The basic patterns (or laws) of inheritance that were discovered and described by Gregor Mendel

Question 22

List the basic patterns discovered by Mendel

Answer 22

Dominance and recessiveness
Laws of segregation
Law of independent assortment

Question 23

Describe the law of segregation

Answer 23

Offspring require one allele from each parent
For each trait there are 2 copies off each ‘unit of hereditary’
Each alternative form determines the appearance of specific characteristic
One alternative from is maternally inherited, one is paternal

Question 24

Describe the law of dominance

Answer 24

Hybrid offspring inherit the dominant phenotype

Question 25

Describe the law of independent assortment

Answer 25

Traits segregate independently, different traits have equal opportunity to occur together

Question 26

What is a test cross and how does it work?

Answer 26

Designed to reveal the genes type of an organism that exhibits a dominant trait
Genotypes of a test organism can be deduced by observing phenotypes of the offspring

Question 27

What is a dihybrid cross?

Answer 27

Typical breeding experiment carried out by Mendal
He cross pollinated true breeding pea varieties differing by 2 different characteristics
E.g seed colour and seed shape

Question 28

Give 3 reasons why the relationship between genotype and phenotype is rarely simple

Answer 28

Incomplete dominance
Co-dominance
Multiple alleles

Question 29

Describe incomplete dominance

Answer 29

Characterised by heterozygotes giving an intermediate phenotype
Gives 3 possible phenotypes
Appearance of the heterozygote is in between the phenotypes of the 2 parents

Question 30

Describe co-dominance

Answer 30

Characterised by 2 alleles which are both expressed in he phenotype
3 possible phenotypes: 2 parental homozygous and 1 heterozygous
Heterozygote, phenotype is not intermediate, it is distinct

Question 31

Describe multiple alleles

Answer 31

Characterised by a gene that exists in more than 2 allelic forms (most human genes)