Inheritance Fe

Question 1

Whats DNA

Answer 1

Building block of genetic material

Question 2

What is a gene

Answer 2

A segment of DNA that contains Info for the synthesis of a polypeptide that determine a particular characteristic of an organism

Question 3

What is a chromosome

Answer 3

Compacted form of DNA with proteins containing alleles

Question 4

When do the traits of dominant allele and recessive allele show

Answer 4

Trait of a dom allele will be expressed as long as one allele is present

Trait of a recessive allele will be expressed when 2 allele is present

Question 5

Traits of homo chromosomes (4)

Answer 5

Same length
Samer gene loci
Same centromere position
Same genes (can be diff alleles)

Question 6

What is genotype and phenotype

Answer 6

Genotype is genetic makeup of an organism

Pheno is the observable traits of an organism

Question 7

Describe Mendel’s 1st law of segregation

Answer 7

• The alleles of a gene exist in pairs,
each on separate members of a
homologous pair of chromosomes
• The homologous chromosomes
separate during meiosis resulting in
the alleles separating into different
gametes
• Thus, each gamete contains only
one allele of each gene#
# Allele pair (diploid condition) is
restored when ovum and sperm fuse
during fertilisation

Question 8

What is the test cross for

Answer 8

• A test cross is used to determine the
genotype of an organism with
dominant trait by crossing the
organism with a homozygous
recessive organism
• If the organism is homozygous
dominant, all the offspring should
show the dominant trait
• If the organism is heterozygous, half
the number of offspring should show
the dominant trait; The remaining
half should show the recessive trait

Question 9

What happen in complete dominance

Answer 9

• In complete dominance inheritance,
the effect of the dominant allele, in a
heterozygous genotype completely
masks the effect of the other
recessive allele

Question 10

Why would observed ratio differ slightly from expected ratio (2)

Answer 10

– The chance of each offspring receiving a certain allele from their parents is independent of other offspring (random fertilisation)

– The offspring have equal chances of survival

Question 11

How to make observed ratio nearer to expected ratio

Answer 11

increase no of offsprings

Question 12

Explain Mendel’s 2nd Law of Independent Assortment (give example)

Answer 12

Each pair of alleles segregate independently of other pairs of alleles
during gamete formation

Eg: the alleles for seed
colour and seed shape sort
into gametes independently
of each other

Question 13

Codominance

Answer 13

• Occurs when both alleles are equally expressed in the

heterozygous condition

Question 14

3 characteristics of continuous variation

Answer 14

Traits are brought about by
the combined effects of many genes

No distinct categories,
wide range of intermediates; Traits vary
gradually from one extreme to another

Greatly influenced by the environment

Question 15

3 char of discontinuous variation

Answer 15

Controlled by a single gene or a few genes

Distinct phenotypes,
no intermediate forms

Rarely/not influenced by the
environment

Question 16

3 sources of variation

Answer 16

Environment
Meiosis
Mutation

Question 17

What is Mutation

Answer 17

Refers to either a permanent change in nucleotide sequence of
DNA in the cell of an organism OR a change in the number/
structure of chromosomes

Question 18

Cause of mutation

Answer 18

result of error during the replication of the gene or

chromosome

Question 19

Chromosome mutation

Answer 19

Change in the structure or number of chromosomes

Question 20

Gene mutation and what it produces

Answer 20

Permanent change in the sequence of nucleotides in the DNA

Produces variation between individuals as it results in new alleles of genes

Question 21

Mutations can be greatly increased by _______ such as: (3)

Answer 21

mutagens

radiations
chemicals
infections agents such as viruses

Question 22

Effect of gene mutation

Answer 22

The sequence of nucleotides determines the sequence of amino
acids in a polypeptide chain
• Change in nucleotide sequence –>
Change in amino acid sequence -> Change in protein structure –> Non-functional protein

Question 23

Sickle cell anemia caused by ______

Answer 23

mutation in the gene controlling haemoglobin production

Question 24

Nondisjunction

Answer 24

• Occurs when homologous chromosomes (during meiosis I) or
sister chromatids (during meiosis II) fail to separate
• This results in some gametes having an extra chromosome
• This abnormal gamete fuses with a normal gamete,
resulting zygote will have an extra chromosome

Question 25

Evidence for common ancestry (3)

Answer 25

– Similarity of internal structures in different organisms
– Similarity of chemical processes in different organisms
- Genetic code is universal

Question 26

Principles of Natural Selection (6)

Answer 26

1. Overproduction of offspring
2. Constancy in numbers
3. Struggle for existence
4. Variation within a
   population
5. Survival of fittest
6. “Like produces like”

Question 27

Describe overproduction of offspring

Answer 27

All organisms produce large number of offspring

If all these offspring survive to maturity, it will lead to
overpopulation, as the available space and food supply will be
unable to sustain them

Question 28

Constancy in numbers

Answer 28

• In reality, most populations remain relatively constant, as most
offspring die before they reach reproductive age
• Natural checks on population growth (limited resources &
predators) controls overproduction and prevents overpopulation

Question 29

Struggle for existence

Answer 29

• Natural resources e.g. space, food supply, water, light, are limited
• Individuals compete for these natural resources with
– Members of the same species
– Members of other species
• Individuals also struggle against environmental factor

Question 30

Variation within a population

Answer 30

• Variation is the raw material for 
natural selection to act on
• Variation safeguards the species
against extinction when the 
environment change

Question 31

Which variations can be inheritable

Answer 31

variations that occur at the gene/chromosome level can be

inherited and passed on to offspring

Question 32

Survival of the fittest

Answer 32

• In the struggle for existence, individuals showing the variation
best adapted to the environment have a selective advantage
• They survive to the reproductive age where they give birth to
offspring which most likely have the same characteristic (Like
produces like

Question 33

Natural Selection Leads to Evolution

Answer 33

With each successive generation, the proportion of individuals
with the beneficial trait will increase in the population and vice
versa; This is evolution. – Favourable alleles will accumulate in the population – Unfavourable alleles will decrease or disappear from the
population

Question 34

Selection pressure

Answer 34

• Natural selection is driven by selection pressures in the
environment
• Selection pressure refers to biotic and abiotic factors that act
upon the survival and reproductive
success of individuals in a population

Question 35

Artificial Selection

Answer 35

Artificial selection is a process in which humans consciously
select for or against particular features in organisms