23) Patterns of inheritance

Question 1

Define genotype

Answer 1

the genetic composition of an organism, which describes all the alleles it contains

Question 2

Define phenotype

Answer 2

an organism’s observable characteristics, resulting from the interaction of genotype + environment

Question 3

Define gene

Answer 3

length / section of DNA that codes for the production of a particular polypeptide

Question 4

Define locus

Answer 4

the position on a chromosome of a particular gene

Question 5

Define allele

Answer 5

a gene variant

Question 6

Describe a dominant allele

Answer 6

expressed and affects the phenotype even with a recessive allele
represented by UPPER CASE LETTERS

Question 7

Describe a recessive allele

Answer 7

only expressed when dominant allele is absent

Question 8

Describe a codominant alleles

Answer 8

2 alleles that both contribute to the organism’s phenotype to an equal extent

Question 9

Define heterozygous

Answer 9

having 2 different alleles of a gene

Question 10

Define homozygous

Answer 10

having 2 identical alleles of a gene

Question 11

Define monogenetic trait

Answer 11

a characteristic controlled by a single gene

Question 12

What do gene mutations do?

Answer 12

alter nucleotide sequences in DNA

Question 13

What is significant about genetic mutations in somatic cells?

Answer 13

they are not inherited but may result in cancer

Question 14

Give 3 types of gene mutation

Answer 14

substitution
insertion
deletion

Question 15

What happens in a substitution (point) mutation?

Answer 15

nucleotide exchanged

Question 16

What happens in an insertion mutation?

Answer 16

extra nucleotide/s

Question 17

What happens in a deletion mutation?

Answer 17

nucleotide/s removed

Question 18

What is significant about insertion and deletion mutations?

Answer 18

alter all subsequent triplet codes (frameshift) so are more likely to result in major changes to translated polypeptide (non-function polypeptide)

Question 19

Give 3 types of substitution mutation

Answer 19

silent
missense
nonsense

Question 20

What happens in a silent mutation?

Answer 20

same amino acid appear in the sequence after translation due to the degeneracy of the genetic code

Question 21

What happens in a missense mutation?

Answer 21

alters one amino acid in the primary structure of the polypeptide and is therefore, likely to disrupt tertiary structure and function

Question 22

What happens in a nonsense mutation?

Answer 22

lead to stop codons in the mRNA, resulting in the length of the final polypeptide being shorter

Question 23

What happens when a mutation benefits an organism?

Answer 23

natural selection acts to maintain the new gene variant in a population

Question 24

Give 4 examples of genetic diseases

Answer 24

cystic fibrosis
phenylketonuria (PKU)
sickle cell anaemia
Huntington’s disease

Question 25

Describe cystic fibrosis (5)

Answer 25

deletion mutation
CFTR protein is non-function leading to production of thick sticky mucus
infections, scarring in lungs
faulty recessive allele
locus = chromosome 7

Question 26

Describe phenylketonuria (PKU) (4)

Answer 26

faulty recessive allele
locus = chromosome 12
prevents enzyme that breaks down phenylalanine from being made
those born with PKU often suffer from brain damage

Question 27

Describe sickle cell anaemia (3)

Answer 27

substitution mutation in gene coding for beta-polypeptides in haemoglobin
locus = chromosome 11
amino acid valine added instead of glutamic acid

Question 28

Describe Huntington’s disease (4)

Answer 28

insertion mutation on chromosome 4
dominant allele
>40 CAG triplets (greater number -> earlier symptoms begin, 30 years)
accumulation of protein fragments in the brain, reducing ability to talk, think and more