Inheritance

Question 1

Definition of an allele

Answer 1

Alternate forms of a gene

Definition of a gene: unit of inheritance
Also sequence of nucleotides where its sequence of bases contains the information that controls the synthesis of a polypeptide

Question 2

Definition of dominant

Answer 2

Allele trait that is fully expressed in phenotype under both homozygous and heterozygous type conditions

Question 3

Definition of recessive

Answer 3

Allele trait that is only expressed in phenotype under homozygous genotype conditions

Question 4

Definition of codominant

Answer 4

Allele that contributes equally to the phenotype (red and white, not pink in Camellia flowers, C^w C^r)

Question 5

Definition of homozygous

Answer 5

Both alleles are identical for the trait

Question 6

Definition of heterozygous

Answer 6

Two different alleles for one trait (one dominant one recessive, or two codominant)

Question 7

Definition of phenotype

Answer 7

Physical/observable characteristics of an organism (descriptors)

Question 8

Definition of genotype

Answer 8

Genetic makeup of an organism (letters)

Question 9

List the components of a genetic diagram

Answer 9

Key
Parent phenotype
Parent genotype
Gamates
Random fertilisation
Offspring genotype
Offspring phenotype
Phenotypic ratio

Question 10

Why is the observed and expected ratio different

Answer 10

Small sample size and random fertilisation causes differences between the expected ratios

Question 11

How to use a test cross and interpret its results

Answer 11

Crossing target organism with a homozygous recessive organism
Homozygous: always dominant offspring, dominant homozygous. Always recessive offspring, recessive homozygous.
Heterozygous: sometimes dominant sometimes not

Question 12

What does autosomal mean

Answer 12

Chromosomes that do not determine one’s sex (not the 23rd pair)

Question 13

List sex determination contents

Answer 13

Key (let x represent the X chromosome, let y represent the Y chromosome)
Parent phenotype
Parent genotype
Gamates
Random fertilisation
Offspring genotype
Offspring phenotype
Phenotypic ratio

Question 14

What are X-linked disorders

Answer 14

Found in the X sex chromosome. Since females have 2, disorder must be dominant/homozygous recessive to show. For males with 1, no carriers: yes or no.

Question 15

Examples of X-linked disorders

Answer 15

Red-green colour blindness, Duchenne muscle dystrophy (progressive muscle weakening, loss of coordination, absence of key muscle protein dystrophin), haemophilia (blood clotting absent)
^^ all are recessive

Question 16

Definition of mutation and their causes

Answer 16

Changes in gene sequence or chromosomal structure of a gene
Caused by chemicals or radiation
Increases genetic variation by increasing number of alleles per gene

Question 17

Sickle cell anemia and Down syndrome

Answer 17

Mutation in the haemoglobin gene’s base sequence, cause mutant haemoglobin protein synthesis, lower o2 carrying capacity, forms sickle-shaped cells
Mutation during meiosis, zygote inherited 3 copies (trisomy) of chromosome 21 instead of 2 (mental retardation, heart and respiratory defects)

Question 18

Definition of variation

Answer 18

Differences in physical traits in individuals of the same species. Genetic variation inheritable, environmental conditions affect but not hereditary

Question 19

Continuous and discontinuous variation

Answer 19

Continuous: no distinct groups (height, weight), controlled by environment, histogram used
Discontinuous: distinct groups (hair and eye colour), controlled by a few genes, uninfluenced by environment

Question 20

Definitions of: allele, dominant, recessive, codominant, homozygous, heterozygous, phenotype, genotype

Answer 20

Allele: alternate forms of a gene
Dominant: allele trait fully expressed under both homozygous and heterozygous type conditions
Recessive: allele trait only expressed under homozygous conditions
Codominant: allele that contributes equally to the phenotype
Homozygous: both alleles are identical for the trait
Heterozygous: two alleles for one trait
Phenotype: physical/observable characteristics of an organism (adjectives)
Genotype: genetic makeup of an organism (letters)