Genetics
Summary
Presented by Kesler Science
PART 1
CHROMOSOMES AND DNA
Cell
• Smallest structural,
functional, and biological
unit of all living organism
• Often called the “building
blocks of life”
• Nucleus – organelle present
in most eukaryotic cells –
contains genetic material
All the cells in your body have chromosomes in the nucleus
Every somatic (body) cell has the same
chromosomes.
Chromosomes
• Thread-like molecules that
carry heredity information
• Made of protein and one long
molecule of DNA
• Most have arranged pairs
within the nucleus of the cell
DNA
• Deoxyribonucleic Acid or DNA
• Contains the instructions an
organism needs to develop,
live, and reproduce
• Found inside every cell
• Passed down from parents to
children (offspring)
Gene
• Basic physical and functional
unit of heredity
• Made up of DNA
• Each person has 2 copies of
each gene, one inherited
from each parent see next
slide to see the 2 copies
Chromosomes are DNA molecules carrying genetic information in the form of genes
• Each cell has 46 chromosomes
(except red blood cells and sex cells)
• Chromosomes are made of DNA
• DNA has sections called genes that
code for a trait
• GENES: The basic unit of heredity
passed from parent to child. Genes
are made up of sequences of DNA
Basic Chromosome
X/Y Chromosomes (sex chromosomes)
• Each person has one pair of
sex chromosomes in each cell.
• Females have two X
chromosomes.
• Males have an X and Y
chromosome.
• The Y chromosome contains a
gene, which triggers
embryonic development to
become a male.
Non test material – just for understanding
Mitosis
• Type of cell division
• Results in two daughter cells
having the same number and
kind of chromosomes as the
parent cell
• Cell goes through different
phases before becoming
clones of parent
Non testable – how do we get n and 2n
Mitosis vs Meiosis
• Mitosis produces 2 diploid
cells, which are identical to
the parents. (uniform)
• Meiosis produces 4 haploid
cells, which contain some
characteristics of the parent
cell but are not identical.
(diverse)
Sexual and Asexual Reproduction
Sexual Reproduction
• A sperm enters an ova
during fertilization.
• In humans, each gamete
contains 23 chromosomes.
• The two fuse to form a
zygote with 23 pairs of
chromosomes, for a total of
46.
• Offspring appearance vary
due to new combinations of
genes.
PART 2
DNA and Replication
REPLICATION
DNA
• DNA is like a blueprint for every
structure in every organism
• It has a code that can be passed onto
offspring
• Each and every cell has the same DNA
in your body, but it is slightly different to
your relatives and a little more different
to your friends
• DNA has complimentary base pairs
which makes this process easy
• DNA stays in the nucleus of the cell
• DNA is made of repeating
nucleotides of
• a sugar molecule (deoxyribose)
• Phosphate
• nitrogen bases Pair A adenine– Tthymine
Gguanine--Ccytosine
• DNA has a sugar phosphate
backbone and the rungs are the
bases
DNA Replication - The process by which a copy of
the DNA in a cell is made before the cell divides.
If you fill in the complimentary base pairs
you will see that you get 2 identical DNA
molecules
DNA Replication – Semi conservative model
1 DNA strands separate at the replication
fork separating into 2 strands
DNA Replication – Semi conservative model
1 DNA strands separate at the replication
fork separating into 2 strands
2. Both strands are copied and 2 daughter
strands are produced
DNA Replication – Semi conservative model
1 DNA strands separate at the
replication fork separating into 2
strands
2. Both strands are copied and 2
daughter strands are produced
3. Each strand is one old and
one new – identical to the
original
PART 3
DNA and RNA
HOW DOES DNA ‘ CODE’ FOR GENES?
TRANSCRIPTION
TRANSLATION
• DNA can copy itself, but it can also carry the coding system for making proteins . The
order of nitrogen bases in each gene contains information for one characteristic or
trait.
Relationship • These proteins (also called POLYPEPTIDES) are coded for by the genes.
between DNA, • These genes code for a protein or polypeptide that has an end result you can see –
the phenotype.
chromosomes • An example would be different eye colour, different hair colours or even if your blood
can clot or not. Some disease that are coded for are coeliac and cystic fibrosis.
and genes
TRANSCRIPTION
DNA to RNA
• DNA molecule you can see a gene is
highlighted
• DNA stays in the nucleus
• The mRNA messenger RNA is coded for by
the template strand of DNA
• Remember A from DNA goes with U in RNA
and T from DNA goes with A in RNA. C
goes with G.
• The process of making the mRNA strand
from the DNA template is called
Transcription
• mRNA can leave the nucleus to find a
ribosome in the cell cytoplasm (see next
slide)
Test yourself? Drag and drop the following
words – solutions next slide
Polypeptide or protein
Translation
Transcription
Nucleus
Ribosome
Amino Acid
DNA
mRNA
tRNA
TRANSLATION
Key components for translation to occur
1.
2.
3.
4.
mRNA (goes to the)
Ribosome
tRNA (brings the)
Amino Acids to the ribosome
How do we know which amino acid
1. You will have a
• GCA GGC TAC ACT
section of DNA template
strand
• CGU CCG AUG UGA
2. Find the
complimentary mRNA
3. Use your codon chart
to find the amino acids
from the original
template DNA strand
USE THE DNA TRIPLETS
• ARG
How do we know which amino acid
1. You will have a
• GCA GGC TAG ACT
section of DNA template
strand
• CGU CCG AUC UGA
2. Find the
complimentary mRNA
3. Use your codon chart
to find the amino acids
from the original
template DNA strand
USE THE DNA TRIPLETS
• ARG PRO LIE STOP
• You have just built a
protein !!!
PART 4
Punnet Squares
PROBABILITY
Vocabulary
• Genotype - the
genetic makeup of an
organism.
• Use symbols BB, Bb, bb
• Phenotype – the
appearance of an
organism based on its
genotype, plus
environmental factors
Genetics
Alleles
• Variants (differences) in a
gene - versions
• Occurs on a fixed spot on a
chromosome
• In humans an allele might
indicate blood type,
colorblindness, or many
other traits.
What does the allele indicate
in this pair of homologous
chromosome?
Dominant/Recessive
• Describes how likely it is for
certain phenotype traits to
pass from parent to
offspring
• Dominant Alleles – show
their effect with only one
copy of the allele – masks
a recessive (Bb or BB)
• Recessive Alleles – show
their effect with two copies
of the allele (bb)
Blue Eyes –
Recessive-b
Brown Eyes –
Dominant - B
Vocabulary
• Homozygous Dominant –
carries two copies of the
same dominant allele (BB)
• Homozygous Recessive –
carries two copies of the
same recessive allele (bb)
• Heterozygous – carries
two different alleles (Bb)
Punnet squares
Genotypes
¼ BB
½ Bb ¼ bb
Phenotypes
¾ Brown and ¼ Blue
Phenotypic Ratio
3 Brown : 1 Blue
Quick Action – Genetics
Choose a letter to represent your genes, one capital and
one lower case. In this example we’re using
T = tall (dominant)
t = short (recessive)
•
•
When we ask for gamete possibilities you need to mention
what the genotype possibilities are for that parent.
•
What are the gametes possible for the mother?
T and t
t
T
The only gamete possible for the dad as he is recessive is t
t
t
Quick Action – Genetics
What are the genotype
possibilities? ½ Tt and ½ tt
Phenotypes
50% tall and 50% short
Ratio
1 Tall : 1 short
Note: We didn’t use T for tall and s for short because
that would show two different genes which code for
two different traits. A genotype contains two codes
for the same trait, so we use two forms of the same
letter.
T
t
t
Tt
Tt
25%
t
tt
25%
25%
tt
25%
Female with 1 recessive allele
Male with 1 recessive
allele
Xn
Y
N
N
n
X X
X Y
n
n
n
n
X
X
X X
N
X Y
X linked crosses
• Alleles on the sex chromosomes produce sexlinked traits
• X linked dominant XN Xn ,
XN Y,
• X linked recessive Xn Y, Xn Xn
We now know about:
• AUSTOSOMAL RECESSIVE
gg
• AUTOSOMAL DOMINANT
Gg, GG
X N XN
PART 5
Pedigrees
Patterns of inheritance
• Males are represented by squares and females by
circles.
Generation numbers are represented by Roman numerals
and individuals are represented by Arabic numerals.
• The characteristic being studied is shown by
shading is shown by a horizontal line; a vertical
A marriage
line leads to the offspring.
Number the following
Page 57 booklet
Pedigree HINTS
• When analysing a pedigree to determine whether a trait is
dominant or recessive, thefollowing rules apply.
• If neither parent has a characteristic and none of their
offspring have it, then the characteristic is recessive
• If both parents have a characteristic and some of their
children have it, then the characteristic is dominant (i.e.
both parentsare heterozygous).
• If both parents have a characteristic and none of their
children have it, then the characteristic is dominant
(because, if both parents have a characteristic and it is
recessive, then all their children will have that
characteristic).
• See Figure 1.37, red hair is recessive because individual
II2 and his partner do not have red hair but some of their
hildren have it. They are both carrying the allele for red
hair, but not expressing it. They both contribute their allele
for red hair to some of their offspring.