Download 6.2 Sexual Reproduction leading to variation - science

GCSE
Biology 1b Evolution and Environment
CORE
Starter: Characteristics from sexual reproduction leading to variation
Characteristics
Meet our Mr Men
And our Little Misses
Now lets meet their children!
GCSE
Biology 1b Evolution and Environment
CORE
Starter: Characteristics from sexual reproduction leading to variation
GCSE
Biology 1b Evolution and Environment
CORE
Objective
To investigate how sexual reproduction can lead to variation within a species.
Success Criteria
By the end of the lesson I:
• can identify the two types of reproduction as sexual and asexual
reproduction.
• can explain the differences between sexual and asexual
reproduction in that sexual reproduction leads to variation
because the genes from two parents are mixed to create a new
individual whereas in asexual reproduction there is only one
parent and hence no mixing.
• can explain in detail how sexual reproduction leads to variation
within a species using the correct scientific key words.
GCSE
CORE
Biology 1b Evolution and Environment
In most cells chromosomes are matched in pairs based on their size
and shape.
Where do chromosomes come from?
Each pair of chromosomes contains one chromosome that has been
inherited from each parent.
chromosome from
female parent
GCSE
chromosome from
male parent
Biology 1b Evolution and Environment
CORE
What’s in your genes?
• Inside the NUCLEUS of every one of your cells there are CHROMOSOMES.
• CHROMOSOMES are coiled up DNA strands.
• On each CHROMOSOME there are several thousand GENES.
• GENES are shorter sections of DNA that code for particular
CHARACTERISTICS
• GENES provide instructions to make PROTEINS that control the functions of
the cell and therefore determining how the body functions (characteristics)
GCSE
Biology 1b Evolution and Environment
CORE
Asexual Reproduction
Asexual reproduction only involves 1 parent and so gives
rise to offspring known as CLONES. Why?
Daffodils can reproduce both Asexually and Sexually! Why
would this make these plants more successful? Explain the
differences between the two types of offspring?
GCSE
Biology 1b Evolution and Environment
CORE
Sexual Reproduction
• All living things can
reproduce.
• In most animals and
plants this usually
happens by sexual
reproduction.
• This is when a male and a
female mate, and produce
offspring using sex cells.
• The young plants or
animals will have similar
characteristics to their
parents but will not be
identical to them.
GCSE
Biology 1b Evolution and Environment
CORE
• Sexual reproduction involves special sex
cells called gametes.
• Male animals produce gametes called
sperm cells and female animals make
gametes called egg cells.
GCSE
Biology 1b Evolution and Environment
CORE
Draw and label sex organs in plants
• In plants, the female sex cells
are also called egg cells; the
male sex cells are found in
pollen grains in the anthers.
GCSE
Biology 1b Evolution and Environment
CORE
What is the difference between Pollination and fertilisation
Pollination is ………………..
Fertilisation is …………………..
GCSE
Biology 1b Evolution and Environment
CORE
Variation
Why is variation important ???
Increase genes in a
population
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Allow survival of
the fittest
Whole population
will not be wiped
out
Biology 1b Evolution and Environment
CORE
Sexual reproduction is VERY risky as it relies on the joining
of two sex cells. Even so, sexual reproduction is SO
important for variation amongst species and hence survival
that it can be seen in almost all types of plants and
animals
THINK
If one parent has blue eyes and
one parent has brown eyes what
colour eyes will their children
have?
Can you prove this?
GCSE
Biology 1b Evolution and Environment
CORE
GCSE
Biology 1b Evolution and Environment
CORE
Each pair of genes affects a different characteristic
Each gene can have a different form. The versions of the
same gene are called ALLELES
• Each parent will have two chromosomes that contain the gene for eye colour.
Gene
for eye
colour
How can we represent the
different eye colours?
Blue eyes
GCSE
Brown eyes
Biology 1b Evolution and Environment
CORE
I can explain how sexual reproduction leads to variation
• Different versions of the same gene are known as ALLELES.
• For example, blue and brown are two alleles for eye colour.
If we inherit one
chromosome from each
parent what ALLELES will
the offspring have?
GCSE
Biology 1b Evolution and Environment
CORE
I can explain how sexual reproduction leads to variation
The Brown
allele is
DOMINANT
over the blue
allele.
What colour
eyes will the
offspring have?
All the offspring
will have
Brown eyes
Some alleles are DOMINANT over other forms of the gene.
This means that the DOMINANT allele will always be
expressed (shown) over the RECCESSIVE allele.
GCSE
What does this
mean?
Biology 1b Evolution and Environment
CORE
I can explain how sexual reproduction leads to variation
Punnett Squares
B
Alleles
B
Brown = B
Blue
=b
b
Genotype
Homozygous Brown = BB
b
Homozygous Blue= bb
What does HOMOZYGOUS mean?
GCSE
Biology 1b Evolution and Environment
CORE
I can explain how sexual reproduction leads to variation
Can two people with brown eyes have blue eyed children?
Genotype
Brown = Bb
Brown = Bb
Homozygous
or
heterozygous?
GCSE
Biology 1b Evolution and Environment
CORE
I can explain how sexual reproduction leads to variation
PHENOTYPE means the
physical expression of the
gene.
i.e. what colour the eyes
will be
GENOTYPE is the pair of
alleles for a characteristic
i.e. BB or Bb or bb
GCSE
Biology 1b Evolution and Environment
CORE
I can explain how sexual reproduction leads to variation
GCSE
Biology 1b Evolution and Environment
CORE
INVESTIGATION
There are genes that decide whether;
• your earlobes are attached close to the side of
your head or hang freely
• your thumb is straight or curved
• you have dimples when you smile
• you have hair on the second segment of your
ring finger
You are going to complete an investigation on
HANG FREELY
babies lobes!
STRAIGHT
GCSE
ATTACHED
CURVED
Biology 1b Evolution and Environment
CORE
PLENARY
In most cells chromosomes are matched in pairs based on their size and shape.
Recap
How many chromosomes?
How many pairs?
Where are they found?
GCSE
Biology 1b Evolution and Environment
CORE
Objective
To investigate how sexual reproduction can lead to variation within a species.
Success Criteria
By the end of the lesson I:
• can identify the two types of reproduction as sexual and asexual
reproduction.
• can explain the differences between sexual and asexual
reproduction in that sexual reproduction leads to variation
because the genes from two parents are mixed to create a new
individual whereas in asexual reproduction there is only one
parent and hence no mixing.
• can explain in detail how sexual reproduction leads to variation
within a species using the correct scientific key words.
GCSE
CORE
Biology 1b Evolution and Environment