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MAKING SENSE OF
Icons CC – The Pink Group
Copyright©2017HenryExham
Icons CC – The Pink Group
Copyright©2017HenryExham
MAKING SENSE OFMAKING SENSE OF
Gene expression
Variation
Inheritance
2
Mutations
The genetic code and protein synthesis
PART1PART2
Copyright © 2017 Henry Exham
h) Define and use the terms allele, locus, phenotype, genotype,
dominant, recessive and codominant.
i) Use genetic diagrams to solve dihybrid crosses, including
those involving sex linkage, autosomal linkage, epistasis,
codominance and multiple alleles.
j) Use and interpret the chi-squared test to test the significance
of the difference between observed and expected results.
3
Copyright © 2017 Henry Exham
• So you have already studies the
structure and function of DNA, this is
called molecular genetics.
• But in this section you will study the
transmission of DNA between whole
organisms which is know as
Mendelian genetics after Gregor
Mendel (1822-1884) who was the
monk turned scientist that
pioneered this area of biology.
4
Copyright © 2017 Henry Exham
• In order to be able to explain
how genes are passed on you
need to understand all the
necessary vocabulary first.
• When answering questions its
very important to use these
terms correctly and also to
set out any genetic problems
in a very specific way which
will be explained later in this
PowerPoint.
5
Copyright © 2017 Henry Exham
6By Emw - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8025119
Your normal body cells contain 23
homologous pairs of chromosomes.
Here is one pair.
The position of each gene on a chromosome is
called its locus.
The genes at the same loci on each
chromosome will code for the same trait but
they may be different versions (alleles).
The combination of alleles for a particular trait
is called the person’s genotype.
In this case this person has one of each allele
for this gene and so they are called
heterozygous, and the genotype is Aa.
As ‘A’ is dominant over ‘a’ (shown by capital
letter) then this allele is the one expressed in
the phenotype.
A a
t t
Cw
CR
The person is homozygous recessive
for this particular trait and their
genotype will be tt
Sometimes one allele isn't dominant
over the other and they can both
contribute to the phenotype, these
alleles are codominant.
Copyright © 2017 Henry Exham
• You need to be able to understand and work out the following types of
genetic cross:
7
One gene for one characteristic (a monohybrid cross)
• Two alleles, dominant and recessive e.g. T,t
• Two alleles, codominant e.g. CR, CW.
• Multiple (more than two) alleles, e.g. IA, IB, IO
• Sex linkage: the gene is on the X chromosome so males only have a single copy e.g XHXh x XHY-
Two genes for two characteristics (a dihybrid cross)
• Two genes on different chromosomes
• Two linked genes on the same non-sex chromosome (“autosome”)
Two genes for one characteristic (epistasis / interaction)
• Epistasis: one gene masks (is “epistatic” to) another e.g. in mouse fur colour.
• Interaction: phenotype is determined by the combination of dominant and recessive alleles of two
genes.
• We will now go through these one at a time using specific examples.
Copyright © 2017 Henry Exham
• Lets start with the easiest
one, this should be revision.
• A monohybrid cross is the
inheritance pattern for a
single gene.
• Here is an example:
8
• The allele for brown is dominant and
blue is recessive.
• A man is heterozygous for brown eyes
and he mates with a woman who is
heterozygous for brown eyes, what
percentage of their children will have
blue eyes?
Parents Genotype:
Parents Phenotype:
Parents gametes:
F1 genotypes:
F1 phenotypes:
Brown Brownx
Bb x Bb
Father Mother
1 x BB, 2 x Bb, 1 x bb
¾ Brown ¼ Blue
BB Bb
Bb bb
B bB bB b B b
Copyright © 2017 Henry Exham
9
• Good examples include the genetic diseases of cystic
fibrosis and Huntington's disease.
• Cystic fibrosis is a recessive condition where as
Huntingdon's is caused by a dominant allele.
ByOpenStaxCollege-Anatomy&Physiology,ConnexionsWebsite.
http://cnx.org/content/col11496/1.6/,Jun19,2013.,CCBY3.0,
https://commons.wikimedia.org/w/index.php?curid=30148626
Copyright © 2017 Henry Exham
10
• You should know that the first level of
offspring from the parents is called
the F1 generation and the second is
called F2.
• This example shows true-breeding
(homozygous recessive) pea plants
that produce either yellow or green
seeds which are bred together.
• The F1 generation are all yellow in
phenotype but still carry the recessive
green allele.
• When these F1 offspring are bred
together with each other the green
phenotype is shown again in the F2
generation.
ByCNXOpenStax-http://cnx.org/contents/GFy_h8cu@10.53:rZudN6XP@2/Introduction,CCBY4.0,
https://commons.wikimedia.org/w/index.php?curid=49926348
Copyright © 2017 Henry Exham
11
• Geneticists use pedigree
charts to show the family
history of a genetic
condition.
• You should know how to
interpret one.
• Can you work out genotypes
of the individuals labeled 1,2
and 3?
Imagecredit“ThePunnettsquareapproachforamonohybridcross:Figure3,"byOpenStaxCollege,Biology(CCBY3.0).
Alkaptonuria is a recessive genetic disorder in
which two amino acids, phenylalanine and
tyrosine, are not properly metabolized.
Affected individuals may have darkened skin
and brown urine, and may suffer joint damage
and other complications.
Copyright © 2017 Henry Exham
12
• Where alleles show dominance it is
not always possible to to tell the
genotype of an organism.
• For example the yellow pea seed
could have either YY or Yy as its
genotype.
• In order to work out what it is, you
would do a test cross.
• This is when you cross the unknown
individual with a known genotype,
usually homozygous recessive.
• Looking at the offspring will tell you
what the genotype of the parent is.
ByKatieAnn127-Ownwork,CCBY-SA4.0,https://commons.wikimedia.org/w/index.php?curid=37309605
Copyright © 2017 Henry Exham
13
One gene for one characteristic (a monohybrid cross)
• Two alleles, dominant and recessive e.g. T,t
• Two alleles, incomplete and codominant e.g. CR, CW.
• Multiple (more than two) alleles, e.g. IA, IB, IO
• Sex linkage: the gene is on the X chromosome so males only have a single copy e.g XHXh x
XHY-
Two genes for two characteristics (a dihybrid cross)
• Two genes on different chromosomes
• Two linked genes on the same non-sex chromosome (“autosome”)
Two genes for one characteristic (epistasis / interaction)
• Epistasis: one gene masks (is “epistatic” to) another e.g. in mouse fur colour.
• Interaction: phenotype is determined by the combination of dominant and recessive
alleles of two genes
Copyright © 2017 Henry Exham
14
• So as already discussed one allele can be dominant over another. But sometimes
both alleles actually contribute to the phenotype neither one is fully dominant over
the other.
Notice carefully that in
codominance both have
alleles have capital letters
and are shown as
superscript.
Copyright © 2017 Henry Exham
To download the whole
presentation visit
www.MrExham.com
This PowerPoint is protected under copyright.
It is designed for educational use. Either personal study or to be
presented to a class. It may be edited or duplicated for these purposes
only.
It must not be shared or distributed online in any format.
Some images used are under a separate creative commons license, these
are clearly marked.
Copyright © 2017 Henry Exham
Brought to you by MrExham.com

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Cambridge Pre-U Biology - 1.6 Genes and Protein Synthesis PART 2 Sample

  • 1. MAKING SENSE OF Icons CC – The Pink Group Copyright©2017HenryExham Icons CC – The Pink Group Copyright©2017HenryExham
  • 2. MAKING SENSE OFMAKING SENSE OF Gene expression Variation Inheritance 2 Mutations The genetic code and protein synthesis PART1PART2
  • 3. Copyright © 2017 Henry Exham h) Define and use the terms allele, locus, phenotype, genotype, dominant, recessive and codominant. i) Use genetic diagrams to solve dihybrid crosses, including those involving sex linkage, autosomal linkage, epistasis, codominance and multiple alleles. j) Use and interpret the chi-squared test to test the significance of the difference between observed and expected results. 3
  • 4. Copyright © 2017 Henry Exham • So you have already studies the structure and function of DNA, this is called molecular genetics. • But in this section you will study the transmission of DNA between whole organisms which is know as Mendelian genetics after Gregor Mendel (1822-1884) who was the monk turned scientist that pioneered this area of biology. 4
  • 5. Copyright © 2017 Henry Exham • In order to be able to explain how genes are passed on you need to understand all the necessary vocabulary first. • When answering questions its very important to use these terms correctly and also to set out any genetic problems in a very specific way which will be explained later in this PowerPoint. 5
  • 6. Copyright © 2017 Henry Exham 6By Emw - Own work, CC BY-SA 3.0, https://commons.wikimedia.org/w/index.php?curid=8025119 Your normal body cells contain 23 homologous pairs of chromosomes. Here is one pair. The position of each gene on a chromosome is called its locus. The genes at the same loci on each chromosome will code for the same trait but they may be different versions (alleles). The combination of alleles for a particular trait is called the person’s genotype. In this case this person has one of each allele for this gene and so they are called heterozygous, and the genotype is Aa. As ‘A’ is dominant over ‘a’ (shown by capital letter) then this allele is the one expressed in the phenotype. A a t t Cw CR The person is homozygous recessive for this particular trait and their genotype will be tt Sometimes one allele isn't dominant over the other and they can both contribute to the phenotype, these alleles are codominant.
  • 7. Copyright © 2017 Henry Exham • You need to be able to understand and work out the following types of genetic cross: 7 One gene for one characteristic (a monohybrid cross) • Two alleles, dominant and recessive e.g. T,t • Two alleles, codominant e.g. CR, CW. • Multiple (more than two) alleles, e.g. IA, IB, IO • Sex linkage: the gene is on the X chromosome so males only have a single copy e.g XHXh x XHY- Two genes for two characteristics (a dihybrid cross) • Two genes on different chromosomes • Two linked genes on the same non-sex chromosome (“autosome”) Two genes for one characteristic (epistasis / interaction) • Epistasis: one gene masks (is “epistatic” to) another e.g. in mouse fur colour. • Interaction: phenotype is determined by the combination of dominant and recessive alleles of two genes. • We will now go through these one at a time using specific examples.
  • 8. Copyright © 2017 Henry Exham • Lets start with the easiest one, this should be revision. • A monohybrid cross is the inheritance pattern for a single gene. • Here is an example: 8 • The allele for brown is dominant and blue is recessive. • A man is heterozygous for brown eyes and he mates with a woman who is heterozygous for brown eyes, what percentage of their children will have blue eyes? Parents Genotype: Parents Phenotype: Parents gametes: F1 genotypes: F1 phenotypes: Brown Brownx Bb x Bb Father Mother 1 x BB, 2 x Bb, 1 x bb ¾ Brown ¼ Blue BB Bb Bb bb B bB bB b B b
  • 9. Copyright © 2017 Henry Exham 9 • Good examples include the genetic diseases of cystic fibrosis and Huntington's disease. • Cystic fibrosis is a recessive condition where as Huntingdon's is caused by a dominant allele. ByOpenStaxCollege-Anatomy&Physiology,ConnexionsWebsite. http://cnx.org/content/col11496/1.6/,Jun19,2013.,CCBY3.0, https://commons.wikimedia.org/w/index.php?curid=30148626
  • 10. Copyright © 2017 Henry Exham 10 • You should know that the first level of offspring from the parents is called the F1 generation and the second is called F2. • This example shows true-breeding (homozygous recessive) pea plants that produce either yellow or green seeds which are bred together. • The F1 generation are all yellow in phenotype but still carry the recessive green allele. • When these F1 offspring are bred together with each other the green phenotype is shown again in the F2 generation. ByCNXOpenStax-http://cnx.org/contents/GFy_h8cu@10.53:rZudN6XP@2/Introduction,CCBY4.0, https://commons.wikimedia.org/w/index.php?curid=49926348
  • 11. Copyright © 2017 Henry Exham 11 • Geneticists use pedigree charts to show the family history of a genetic condition. • You should know how to interpret one. • Can you work out genotypes of the individuals labeled 1,2 and 3? Imagecredit“ThePunnettsquareapproachforamonohybridcross:Figure3,"byOpenStaxCollege,Biology(CCBY3.0). Alkaptonuria is a recessive genetic disorder in which two amino acids, phenylalanine and tyrosine, are not properly metabolized. Affected individuals may have darkened skin and brown urine, and may suffer joint damage and other complications.
  • 12. Copyright © 2017 Henry Exham 12 • Where alleles show dominance it is not always possible to to tell the genotype of an organism. • For example the yellow pea seed could have either YY or Yy as its genotype. • In order to work out what it is, you would do a test cross. • This is when you cross the unknown individual with a known genotype, usually homozygous recessive. • Looking at the offspring will tell you what the genotype of the parent is. ByKatieAnn127-Ownwork,CCBY-SA4.0,https://commons.wikimedia.org/w/index.php?curid=37309605
  • 13. Copyright © 2017 Henry Exham 13 One gene for one characteristic (a monohybrid cross) • Two alleles, dominant and recessive e.g. T,t • Two alleles, incomplete and codominant e.g. CR, CW. • Multiple (more than two) alleles, e.g. IA, IB, IO • Sex linkage: the gene is on the X chromosome so males only have a single copy e.g XHXh x XHY- Two genes for two characteristics (a dihybrid cross) • Two genes on different chromosomes • Two linked genes on the same non-sex chromosome (“autosome”) Two genes for one characteristic (epistasis / interaction) • Epistasis: one gene masks (is “epistatic” to) another e.g. in mouse fur colour. • Interaction: phenotype is determined by the combination of dominant and recessive alleles of two genes
  • 14. Copyright © 2017 Henry Exham 14 • So as already discussed one allele can be dominant over another. But sometimes both alleles actually contribute to the phenotype neither one is fully dominant over the other. Notice carefully that in codominance both have alleles have capital letters and are shown as superscript.
  • 15. Copyright © 2017 Henry Exham To download the whole presentation visit www.MrExham.com
  • 16. This PowerPoint is protected under copyright. It is designed for educational use. Either personal study or to be presented to a class. It may be edited or duplicated for these purposes only. It must not be shared or distributed online in any format. Some images used are under a separate creative commons license, these are clearly marked. Copyright © 2017 Henry Exham Brought to you by MrExham.com