Download Lesson 2- environmental inheritance and dominant recessive alleles

Lesson Starter
• How many chromosomes does almost all human cells
have?
• How many chromosomes does human sex cells have?
• What does the word allele mean?
• Give an example of variation in humans
• Give an example of variation in plants
Inheritance
Lesson 2
Learning Intention- lesson 2
•To learn about environmental variation
Environmental Variation
•Characteristics can be affected by factors other
than just genetics
Think of examples of environmental differences
between people
Environmental variation: copy
• Characteristics can be affected by factors other than just genetic
• Variation caused by surroundings is called ENVIRONMENTAL
VARIATION
Examples include: - Language spoken
- Religion
- Hair length
- Weight
- Piercings
- Tattoos
Genetic Inheritance
• Sex cells (gametes) contain only one set of chromosomes.
• After fertilisation takes place the new cell (zygote) contains two
sets of chromosomes.
• One set is from the father and the other set from the mother.
Genetic Inheritance
• Each parent contributes one piece of
information to it’s offspring for each
characteristic
• THEREFORE every inherited
characteristic is controlled by two
pieces of information
• The pieces of information can be the
same or different
Genetic Inheritance
• Pieces of information are called
genes (stored in chromosomes)
• Different versions of gene called
alleles
• You inherit one allele from your
Mum and one from your Dad
for each gene- your genotype
Task: write down 3 characteristics that
are inherited from the parents and 3 that
are environmental
Task: write down 3 characteristics that
are inherited from the parents and 3 that
are environmental
Task: write down 3 characteristics that
are inherited from the parents and 3 that
are environmental
Task: write down 3 characteristics that
are inherited from the parents and 3 that
are environmental
Video
• What does the DOMINANT gene do to the RECESSIVE
gene?
• What is the chromosome type of a girl and of a boy?
• What is haemophilia?
• What is the difference between normal RBC and RBC
affected by thalassaemia?
• Where is there a successful screening programme for
thalassaemia?
Genetic inheritance
•We receive two copies of the same gene (allele)
•Some genes are stronger than others. These genes
are dominant.
•The weaker genes are recessive.
•Dominant genes can hide (mask) other genes that
are not so strong.
Genetic Inheritance
• If an individual inherits a dominant gene for brown eyes from
one parent and a recessive gene for blue eyes from the other,
that person will have brown eyes.
• However, they would still carry a recessive gene for blue eyes
which can be passed on to their offspring.
Genetic Inheritance: copy
• We receive two copies of the same gene (allele) however some genes
are stronger than others.
• The stronger genes are called dominant and the weaker genes are
recessive.
• Dominant genes can mask the recessive genes
• Eg: If you inherit a dominant gene for brown eyes from mum and a
recessive gene for blue eyes from dad then you will have brown eyes.
• However, you would still carry a recessive gene for blue eyes which
can be passed on to their offspring.
Genetic Crosses
• Dominant genes always appear in the physical characteristics
(phenotype) of an organism- you only need one of them to
have the characteristic.
• However, a recessive gene is always hidden by a dominant
one, and if you are to have that characteristic, you need to
get two copies of the gene.​
Genetic Crosses: copy
• When carrying out genetic crosses, each gene is
represented by using a letter.
• The letter used is a capital if the characteristic is
dominant and lower case if the characteristic is
recessive.
Parents
• Phenotype
Blue eyes x Brown eyes
(recessive genes) x (dominant genes)
• Genotype
bb
BB
• Gametes passed:
All b
All B
Offspring
• Genotype:
• Phenotype:
b
B
Bb
B
Bb
b
Bb
Bb
all Bb
all Brown eyes
Examples
• Dad has brown hair (Bb) and mum has blonde hair (bb)
- What is the GENOTYPE of the offspring and what is the
PHENOTYPE?