Topic 3.4: Inheritance

Question 1

Mendel Experiment

Answer 1

a) Crossed different varieties of purebred pea plants, collected and grew the seeds to determine their characteristics
b) Crossed the offspring with each other and grew their seeds to similarly determine their characteristics

Question 2

Results of Mendel’s experiments

Answer 2

a) Organisms have discrete factors that determine its features
b) Organisms possess two versions of each factor
c) Each gamete contains only one version of each factor
d) Parents contribute equally to the inheritance of offspring
e) For each factor, one version is dominant over another

Question 3

Principles of Inheritance

Answer 3

a) Law of Segregation
b) Law of Independent Assortment
c) Principle of Dominance

Question 4

Law of Segregation

Answer 4

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

Question 5

Law of Independent Assortment

Answer 5

a) The segregation of alleles for one gene occurs independently to that of any other gene
b) Linked genes

Question 6

Mendel’s Laws

Answer 6

a) Recessive alleles will be masked by dominant alleles

b) Co-dominance / Incomplete dominance

Question 7

Ploidity of Gametes

Answer 7

Haploid cells formed by meiosis

Question 8

What does result from the fusion of gametes?

Answer 8

Diploid zygotes with two alleles of each gene

Question 9

Genotype

Answer 9

Allele combination for a specific trait

Question 10

Types of allele combinations

Answer 10

a) Homozygous – Both alleles are the same (AA)
b) Heterozygous – Alleles are different (Aa)
c) Hemizygous – Only one allele (X/Y)

Question 11

Phenotype

Answer 11

Physical expression of a specific trait

Question 12

How is the phenotype determined?

Answer 12

It is determined by genotype and environmental factors

Question 13

Modes of Inheritance

Answer 13

a) Complete dominance

b) Codominance

Question 14

Complete dominance

Answer 14

a) One allele is expressed over another
b) Dominant allele is expressed in heterozygote or homozygous dominant
c) Recessive allele is masked in heterozygote
d) A recessive phenotype can only be expressed in homozygotes recessive

Question 15

Co-dominance

Answer 15

a) Both alleles are equally expressed in the phenotype

b) Heterozygotes have a distinct phenotype (superscript letter)

Question 16

Inheritance of ABO blood groups

Answer 16

a) The A and B alleles are co-dominant (I^A I^B)

b) The O allele is recessive (i)

Question 17

Monohybrid cross

Answer 17

It determines the allele combinations for

potential offspring for one gene only

Question 18

Steps to do a monohybrid cross

Answer 18

a) Designate letters to represent alleles (A, a)
b) Identify genotype / phenotype of parents (P generation)
c) Determine genotype of gametes (haploid)
d) Work out gamete combinations with a Punnett grid
e) Identify ratios of offspring (F1 generation)

Question 19

How are genetic diseases caused?

Answer 19

When mutations to a gene abrogate normal cellular function, leading to the development of a disease phenotype

Question 20

Causes of genetic diseases

Answer 20

a) Recessive
b) Dominant
c) Co-dominant

Question 21

Autosomal recessive + example

Answer 21

a) It require both faulty alleles (7)
b) Cystic fibrosis is caused by a mutated CFTR gene
c) Produces thick mucus that clogs airways and causes respiratory issues

Question 22

Autosomal Dominant

Answer 22

a) It requires one faulty allele
b) Huntington’s disease is caused by a mutated HTT gene (4)
c) An amplification of CAG repeats (>40) leads to neurodegeneration

Question 23

Autosomal Codominant

Answer 23

a) Sickle cell anemia is caused by a mutated HBB gene (11)

b) Sickling of blood cells leads to anemia and other complications

Question 24

Gene mutation

Answer 24

Change to the base sequence of a gene that can affect the structure and function of the protein it encodes

Question 25

Factor that increase mutation and can cause genetic diseases and cancer

Answer 25

a) Radiation | UV / X-rays
b) Chemical | Reactive oxygen species
c) Biological agents | Bacteria / Viruses

Question 26

Examples of radiation exposure

Answer 26

a) Nuclear bombing of Hiroshima (1945)

b) Accident / meltdown in Chernobyl (1986)

Question 27

Long-term consequences to radiation exposure

Answer 27

a) An increased incidence of cancer
b) Reduced immunity (- T cell count)
c) Congenital abnormalities (Chernobyl only)
d) A variety of organ-specific health effects
(e. g. liver cirrhosis, cataract induction, etc)

Question 28

Sex linkage

Answer 28

When a gene controlling a characteristic is located on a sex chromosome (X or Y)

Question 29

Sex chromosomes (Y / X)

Answer 29

a) Y chromosome is short and has few genes (<100)

b) X chromosome is large with many genes (~2000)

Question 30

Sex-linked traits

Answer 30

a) Males have a higher rate of X-linked recessive conditions as they cannot mask the recessive allele
b) Females can be carriers for X-linked recessive conditions

Question 31

X-linked conditions

a) Recessive
b) Dominant

Answer 31

a) Affected mothers must have affected sons

b) Affected fathers must have affected daughters

Question 32

Examples of X-linked recessive traits

Answer 32

a) Haemophilia (cannot clot blood properly)

b) Red-green colour blindness

Question 33

Pedigree Chart

Answer 33

Chart of genetic history over several generations

Question 34

Rules of a Pedigree Chart

Answer 34

a) Males are represented as squares, while females as circles
b) Shaded symbols denote individual has a specified condition
c) A horizontal line between man and woman represents mating
d) Offspring numbered from left to right according to age

Question 35

Autosomal Dominance

Answer 35

If both parents are affected by a trait and any offspring is not, the trait must be dominant (parents must be heterozygous)

Question 36

Autosomal Recessive

Answer 36

If neither parents is affected by a trait but any offspring is, the trait must be recessive (parents must be heterozygous)

Question 37

Sex-Linked Traits

Answer 37

No way to conclusively prove sex-linkage with a pedigree chart, but certain patterns may suggest the possibility