Upload
deirdra-lombard
View
24
Download
0
Tags:
Embed Size (px)
DESCRIPTION
Demonstrate understanding of biological ideas relating to genetic variation. Science 1.9 (AS90948). Role of DNA in carrying instructions Explain DNA structure and label a diagram Include: Nucleotide, Triplet, Sugar, Phosphate, Base, Base pair, - PowerPoint PPT Presentation
Citation preview
Specific Learning Outcomes
Role of DNA in carrying instructions◦Explain DNA structure and
label a diagram Include:
◦Nucleotide, Triplet, Sugar, Phosphate, Base, Base pair,
◦Explain why DNA is important in making each organism unique Include
◦Gene, Allele, Cell, Organism, Characteristic, Genetic code
◦Explain DNA replication◦Explain mitosis
Specific Learning Outcome
Role of DNA in determining phenotype◦Explain how sex is determined◦Explain meiosis◦Explain how chromosomes and
genes are inherited◦Explain how the genetic code
determines our characteristics ◦Use a punnett square/pedigree
tree to predict genotype and phenotype
◦Use a punnett square/pedigree tree to help explain how you test for a pure bred organism
Specific Learning Outcomes
Link between phenotype, variation and species survivalExplain the ways
inheritable and non-inheritable variation occurs
Discuss how phenotypes related to survival value
Discuss advantages and disadvantages of sexual and asexual reproduction
DNA
DNA (deoxyribonucleic acid) has 2 functions◦To control cell activities◦To pass genetic information from generation to
generationDNA is made up of small units called
nucleotides
DNA Structure
All living things have the same basic DNA structure◦2 chains made up of
nucleotides that looks like a ladder
◦Each chain is joined at the bases (A,T,G,C)
◦The bases, paired A-T and C-G, are called base pairs
◦This ladder exists in a helix shape to save room
Importance of DNA
DNA provides the information for all cellsThe sequence of bases on each strand
forms the genetic codeEach organism has its own unique code
because its order of bases is uniqueSections of the code are called genes and
code for certain characteristics (traits)The particular trait we display is called our
phenotype
DNA, Alleles, Genes, Chromosomes and Characteristics
Our DNA is wound up into chromosomes
We have 2 copies of each chromosome (1 from our Mum and 1 from our Dad)
Each of the chromosomes could have a different version of the same trait (alleles) The particular combination of alleles is called our genotype
Gene 4
Tour
Alleles
A genotype can be either:◦Homozygous (2 alleles that are the same)◦Heterozygous (2 alleles that are different)
As well as◦Dominant (always shows up)◦Recessive (only shows up if homozygous)
BB = black coat because dominant B allele is present
Bb = black coat because dominant B allele is present
bb = white coat because dominant B allele is not present
DNA replication
When an organism grows, repairs itself, reproduces or replaces old cells, new cells need to be made
Every new cell needs its own copy of the DNA so it is replicated
The double
strands of DNA
coil up into a
helix
Each of the two
newly formed DNA
double helix
molecules will
become a chromatid
Cell Division - Mitosis
Mitosis is the process of cell division for growth and repair
It makes an exact copy of the original cell to produce 2 identical daughter cells
2 daughter cells identical to original
Chromosomes line up to so that one copy can go to each cell
Chromosomes now split
Parent cell
Cell Division - Meiosis
Meiosis is the process to produce sex cells
It produces 4 daughter cells each with half the number of chromosomes
Due to crossing over and independent assortment, these cells produce inheritable variation
Replicated chromosomes separate
Homologous pairs separate into 2 cells
4 non-identical daughter cells produced
Sexual v Asexual Reproduction
Sexual reproduction involves 2 parents and produces offspring that are genetically different to the parent
Asexual reproduction involves 1 parent and produces offspring that are identical to that parent (clones)
Asexual Reproduction
Sexual Reproduction
Name of an example
Are gametes involved Is fertilisation involved
Is mitosis involved
Is meiosis involved Are the offspring genetically identical Can it be done by only one parent
Strawberry runner Puppy
No
No
Yes
No
Yes
Yes
Yes
Yes
Yes
Yes
No
No
Sex determination
Our sex is determined by either an X or a Y chromosome
Females are homozygous males are heterozygous
During sexual reproduction an egg and a sperm come together. Every egg has an X but the sperm has a 50/50 chance of being an X or a Y due to its formation in meiosis
XY XX
All genes are inherited through sexual reproduction
We can use a punnett square to determine what the chance of offspring having certain traits is going to be
Inheritance and Punnett Squares
X
X
X
Y
Sex determination
b
B
b b
A man who is heterozygous for eye colour and a woman who has blue eyes (bb)
Bb
Bb bb
bbXX XY
XYXX
Pure Breeding
A pure bred organism is one that is homozygous for the trait concerned (AA or aa)
A pure bred organism always breeds pure and has no hidden genetic characteriestic
Test Cross
A test cross is used to determine whether an individual with the dominant phenotype pure bred or not
You cross your individual with one that is homozygous recessive When you complete the cross, if any offspring have the
recessive trait the individual must have been heterozygous Eg In mice, grey coat is dominant (G) over white. A breeder
wants to know if his grey male is homozygous for colour
G G
g
g
Homozygous – no white offspring
Gg
Gg
Gg
Gg
Gg gg
ggGgg
g
gG
Heterozygous ½ grey offspring, ½ white
Pedigrees
Pedigree trees show inheritance patternsThey show the phenotypes over various
generations and can be used to determine most genotypes
Variation
Variation is the differences in a population that can come from inherited genes and the influence of the environment
Variation in inherited genes can come during sexual reproduction (crossing over and independent assortment) or from mutations
Variation is important for the survival of a species because if the environment changes, some of the population should be able to survive and continue to reproduce if the traits that they have are favourable
Evolution
Evolution is a result of this variationNatural selection is the fact that the traits
that are favourable are “selected for” in an environment
Eventually these traits will become the norm, this is how evolution occurs