Genetics and Inheritance
Introduction
● This topic helps to understand genetic characteristics like, physical structure passed down
generations
● Genetics = the study of heredity - how genetic characteristics are passed from parents 2 child
● Everyone inherits a set of genes in chromosomes from father + mother = unique to individual
but enough to identify the individual’s species
Key terminology:
Hereditary ● Passing of hereditary characteristics from parent - offspring
Filial generation (F1) ● Offspring from parent organisms
Locus ● Exact position of a gene on a chromosome
Genetic engineering ● Techniques to change genetic material of a cell/living organism - a
form of biotechnology
Concepts in inheritance
Gene Segment of DNA in a chromosome
= contains code 4 a characteristic
Alleles Different forms of a gene at same Dominant allele (T) - tall plant
locus on homologous chromosomes Recessive allele (t) - short plant
,Genotype Genetic composition of an organism
Phenotype Physical appearance of an organism
based on genotype eg. tall/short
Dominant allele Allele that’s expressed in phenotype
when found in heterozygous (Tt) +
homozygous (TT) condition
Recessive allele Allele that’s masked in phenotype
when found in heterozygous (Tt)
condition; only expressed in
homozygous (tt) condition
Heterozygous 2 different alleles 4 a certain
characteristic eg. Tt
homozygous 2 identical alleles 4 a certain
characteristic eg. TT/tt
Monohybrid cross 1 characteristic/trait shown in Flower colour only, eg.
genetic cross yellow/white flower OR shape
of seeds only, eg.
round/wrinkled seeds
Dihybrid cross 2 different characteristics in genetic Example: flower colour, eg.
cross yellow/white flower AND
shape of seeds, eg.
round/wrinkled seeds
Complete dominance Genetic cross where dominant allele The allele for tall (T) =
masks the expression of a recessive dominant over allele for short
allele in heterozygous condition (t)
Offspring will be tall because
dominant allele (T) masks
, expression of recessive allele
(t)
Incomplete dominance Cross between 2 phenotypically A red-flowered plant = crossed
different parents produce offspring with white-flowered plant -
different from both parents but with with incomplete dominance,
intermediate phenotype offspring will have pink
flowers (intermediate colour)
Co-dominance Cross where both alleles = expressed Red-flowered plant = crossed
equally in phenotype with white-flowered plant -
with co-dominance, offspring
has flowers with red + white
patches
Multiple alleles 2+ alternative forms of a gene at Blood groups = controlled by 3
same locus alleles, I^A, I^B and i
All 3 alleles = present in a
population but an individual
can only have 2 alleles
Sex-linked characteristics Traits that = carried in sex Examples: haemophilia +
chromosomes colour-blindness - alleles 4
haemophilia/colour-blindness =
indicated as superscripts on sex
chromosomes, eg. X^HX^H
(normal female), X^HX^h
(normal female), X^hX^h
(female with haemophilia),
X^HY (normal male), X^hY
(male with haemophilia)
Introduction
● This topic helps to understand genetic characteristics like, physical structure passed down
generations
● Genetics = the study of heredity - how genetic characteristics are passed from parents 2 child
● Everyone inherits a set of genes in chromosomes from father + mother = unique to individual
but enough to identify the individual’s species
Key terminology:
Hereditary ● Passing of hereditary characteristics from parent - offspring
Filial generation (F1) ● Offspring from parent organisms
Locus ● Exact position of a gene on a chromosome
Genetic engineering ● Techniques to change genetic material of a cell/living organism - a
form of biotechnology
Concepts in inheritance
Gene Segment of DNA in a chromosome
= contains code 4 a characteristic
Alleles Different forms of a gene at same Dominant allele (T) - tall plant
locus on homologous chromosomes Recessive allele (t) - short plant
,Genotype Genetic composition of an organism
Phenotype Physical appearance of an organism
based on genotype eg. tall/short
Dominant allele Allele that’s expressed in phenotype
when found in heterozygous (Tt) +
homozygous (TT) condition
Recessive allele Allele that’s masked in phenotype
when found in heterozygous (Tt)
condition; only expressed in
homozygous (tt) condition
Heterozygous 2 different alleles 4 a certain
characteristic eg. Tt
homozygous 2 identical alleles 4 a certain
characteristic eg. TT/tt
Monohybrid cross 1 characteristic/trait shown in Flower colour only, eg.
genetic cross yellow/white flower OR shape
of seeds only, eg.
round/wrinkled seeds
Dihybrid cross 2 different characteristics in genetic Example: flower colour, eg.
cross yellow/white flower AND
shape of seeds, eg.
round/wrinkled seeds
Complete dominance Genetic cross where dominant allele The allele for tall (T) =
masks the expression of a recessive dominant over allele for short
allele in heterozygous condition (t)
Offspring will be tall because
dominant allele (T) masks
, expression of recessive allele
(t)
Incomplete dominance Cross between 2 phenotypically A red-flowered plant = crossed
different parents produce offspring with white-flowered plant -
different from both parents but with with incomplete dominance,
intermediate phenotype offspring will have pink
flowers (intermediate colour)
Co-dominance Cross where both alleles = expressed Red-flowered plant = crossed
equally in phenotype with white-flowered plant -
with co-dominance, offspring
has flowers with red + white
patches
Multiple alleles 2+ alternative forms of a gene at Blood groups = controlled by 3
same locus alleles, I^A, I^B and i
All 3 alleles = present in a
population but an individual
can only have 2 alleles
Sex-linked characteristics Traits that = carried in sex Examples: haemophilia +
chromosomes colour-blindness - alleles 4
haemophilia/colour-blindness =
indicated as superscripts on sex
chromosomes, eg. X^HX^H
(normal female), X^HX^h
(normal female), X^hX^h
(female with haemophilia),
X^HY (normal male), X^hY
(male with haemophilia)
