Inheritance

Question 1

Define genotype

Answer 1

Genetic makeup of an organism. It describes all the alleles that a organism contains

Question 2

Define mutation

Answer 2

Any changes to the base sequence in the DNA. This may be inherited if it occurs in the formation of the gametes.

Question 3

Define phenotype

Answer 3

The observable characteristics of an organism. This is the result of an interaction between expression of the genotype and the environment

Question 4

Define modification

Answer 4

Any change to phenotype that doesn’t affect the genotype and so is not inherited

Question 5

Define gene

Answer 5

A section of DNA, a sequence of nucleotide bases, that codes for a polypeptide

Question 6

Define locus

Answer 6

Position of a gene on a chromosome

Question 7

Define allele

Answer 7

One of the different forms of a gene

Question 8

Define co-dominance

Answer 8

Two alleles that both contribute to the phenotype

Question 9

Define monohybrid inheritance

Answer 9

Inheritance of a single gene

Question 10

State the law of genetics/segregation

Answer 10

In diploid organisms, characteristics are determined by alleles that occur in pairs. Only 1 pair of alleles can be present in a single gamete

Question 11

Define polymorphic loci

Answer 11

A gene that has more than 2 alleles

Question 12

Define dihybrid inheritance

Answer 12

A phenotype that is inherited as a result of two different genes

Question 13

Define crossover value and state the equation

Answer 13

Percentage of offspring with recombinant phenotypes.
=No. Of recombinants/no. Of offspring X 100

Question 14

How to find distance between linked genes

Answer 14

Crossover value in map units

Question 15

Define angiosperm

Answer 15

Flowering plant

Question 16

Define monoecious plants

Answer 16

Separate male and female flowers on the same plant (e.g. maize)

Question 17

Define dioecious plants

Answer 17

Separate male and female plants (e.g. Holly)

Question 18

Define an autosome

Answer 18

Homologous pairs that are the same size, same genes, and same order of genes

Question 19

Describe DMD

Answer 19

Duchenne Muscular Dystrophy affects the dystrophin gene that codes for the protein Dystrophin - a component of a glycoprotein that stabilises the cell membranes of muscle fibres. It starts around 2-3 years, and results in loos of muscle mass and progressive muscle weakness

Question 20

How does ionising radiation affect DNA

Answer 20

Joins adjacent pyramidines in DNA causing DNA polymerase to sometimes insert an incorrect nucleotide

Question 21

State the 4 types of mutation

Answer 21

1) gene/point mutation - change in base sequence during S phase
2) chromosome mutation - damaged chromosomes may rejoin incorrectly
3) aneuploidy - loss/gain of a single chromosome during anaphase
4) polyploidy - increase in the entire haploid set

Question 22

State the 5 types of gene/point mutations

Answer 22

1) addition/insertion (frame shift)
2) duplication (frame shift)
3) subtraction/deletion (frame shift)
4) substitution (single aa)
5) inversion (single a.a.)

Question 23

State the 3 affects gene/point mutation can have

Answer 23

1) non-sense mutation - STOP codon produced
2) mis-sense mutation - different a.a. therefore different protein
3) silent mutation - different a.a. but same protein

Question 24

Describe sickle cell anaemia

Answer 24

Substitution/mis-sense point mutation
Gene that codes for CTC (glutamate) is changed to CAC (valine)
Glutamate is large and hydrophobic, valine is small and hydrophillic
When oxygen tension is low, haemoglobin aggregates and collapses becoming sickle shaped (frail, may break)
Normal = HbA (Hb^A), mutated = HbS (Hb^S). Both codominant
High amounts of heterozygous gives selection advantage against malaria

Question 25

State the 4 types of chromosome mutations

Answer 25

1) structural changes - crossing over and change in number of gene loci
2) inversion - region breaks of and flips 180
3) translocation - region breaks off and rejoins a different end
4) deletions - loos of a region

Question 26

Describe Down’s syndrome

Answer 26

Non-disjunction causes (usually) and extra chromosome 21 in one gamete, and one too few in the other. Normally trisomy and monosomy is fatal at early stages of foetal development.
Translocation Down’s - fragment of 21 chromosome attached to another resulting in partial trisomy with 2 copies of 21 and an extra part attached to another

Question 27

Define endomitosis

Answer 27

Replication of chromosomes without the follow up cytokinesis

Question 28

Define epigenetics

Answer 28

The control of gene expression by modifying DNA or histones, but not by affecting the DNA nucleotide sequence