Download GENETICS REVISION CARDs

GENETICS VOCAB CARD 1
CHROMOSOMES
Zygote- a single fertilised cell
Gene- Units of inheritance usually occurring at specific
locations, or loci, on a chromosome. (A section of DNA)
These units are responsible for hereditary characteristics
in plants and animals.
Chromatin-DNA in its normal, functional state, condenses
to form chromosomes
Chromatid-is one of the two threads of condensed
chromatin which forms one chromosome. The 2 chromatids
are connected by a centromere. They exist only during
prophase and metaphase
Haploid-a cell contains only one set of chromosomes (n)
Diploid-a cell that contains a double set of chromosomes,
one from each parent(2n)
Chromosome-each species will have a specific number of
chromosomes (e.g humans 46)
A human has 22 pairs of autosomes and one pair of sex
chromosomes.
A karyotype shows all the chromosomes
DNA
DNA- deoxyribose nucleic acid, a double stranded
helix (spiral)
The rungs of the ladder are the nitrogenous base
pairs, (A, T, C, G) which are held together by a
backbone of deoxyribose sugar (a 5 carbon sugar)and
phosphate groups.Adenine, Thymine, Cytosine,
Guanine.
A and T always pair together C and G always pair
together
DNA 2
2 complementary strands of DNA form the helix;
It is made up of-sugar-phosphate
backbone
-nitrogenous bases stacked in the
center
-antiparallel
5’ end
3’ end
-twists to right
ALLELE
Allele-an alternative form of a gene. Because they
are different, their action may result in different
expressions of a trait.
• Example: one allele may cause blonde hair,
while another causes black
• Letters are used to represent alleles
• Capital letters = dominant genes
• Lowercase letters = recessive genes
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DNA REPLICATION
(Semi-conservative replication)
DNA replication occurs prior to cell division, during
interphase. It occurs in a series of steps, each controlled
by enzymes, with energy supplied from ATP.
-parent strands separate and serve as a template for a new
strand
-enzymes break the hydrogen bonds between the bases,
unzipping the rungs of ladder.
-copied in a 5’ 3’ direction the leading strand is copied in
a straight forward manner, and the lagging strand is built
in a series of steps by Okazaki fragments.
-two new pieces of DNA result, one from the parent strand
and a newly synthesized one. Each containing half the
original DNA (hence semi (half) conservative (saved))
MITOSIS
Mitosis is the division of cells for growth and repair,
somatic cells.
It results in 2 identical cells being formed, which are
diploid (2n). Each daughter cell has the same kind and
number of chromosomes as the original parent cell.
Remember
Interphase-in the beginning, the resting stage.
Chromosomes cannot be seen theyduplicate and double in
number
Prophase- 2 p’s in prophase means stage 2. Chromosomes
become visible Each chromosome consists of two identical
chromatids.
Metaphase- Chromosomes line up at the equator (centre of
the cell) Spindles are formed to attach to the centromere
of each chromosome
Anaphase- think the godfather ‘ana then they begin to
separate. Sister chromatids separate as individual
chromosomes They move apart towards the opposite poles
Telophase-ending in 2 new cells. Chromosomes gradually
disappear. Nuclear membrane is form around each set of
chromosomes
Cytokinesis- is the division of the cytoplasm and formation
of a membrane to produce complete new cells.
LABEL THE PHASES OF MITOSIS
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1= Anaphase
2=Interphase
3=Telophase
4=metaphase
5=prophase
Each pair of chromatids is segregated, or separated,
from one another at the centromere during the
formation of gametes. This occurs at anaphase.
They separate independently of each other during
meiosis and so can form different combinations.
Leading to genetic variation.
MEIOSIS
Prophase
P2
Metaphase
M2
Anaphase
A2
Telophase
T2
SIGNIFICANCE OF MEIOSIS
PRINCIPLE OF INDEPENDENT ASSORTMENT
Producing cells with chromosome number half of the
parent cell, forming the gametes. Gametes are cells
having one chromosome from each homologous pair haploid (n)
Two nuclear divisions
l
Meiosis I and meiosis II
Four haploid cells are produced
Meiosis occurs in
§ Plants: anthers and ovules
§ Mammals: testes and ovaries
1. Leads to halving of chromosome number (haploid),
so to ensure that the diploid number of
chromosomes can be restored after fertilization
2. Produce genetic variation at
-crossing-over between homologous chromosomes
during prophase I results in recombination.
-independent assortment of chromosomes during
metaphase I
Gregor Mendel's principle of genetic inheritance stating
that different pairs of genes are passed to offspring
independently so that new combinations of genes, present
in neither parent, are possible. In other words, the
distribution of one pair of alleles does not influence the
distribution of another pair--the genes controlling
different traits are inherited independently of one
another.
The homologous chromosomes line up in random order along
the equator during metaphase, therefore the genes are
inherited independently.
For humans with 23 pairs of chromosomes there are over 8
million possible combinations of the chromosomes in the
gametes that are produced.
CROSSING OVER AND RECOMBINATION
The point of crossing over
is called a CHIASMA
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Crossing over can only occur when homologous
chromosomes come together side by side during the
early stages of meiosis.
They have to be homologous chromosomes as the
chromatids can only cross over with corresponding
gene sequences. When they become entangled they
form a chiasma. They can now pass on to the second
meiotic division to form 4 genetically different
gametes. Two of the four chromatids have
recombined genes-are recombinant, different to
that of the maternal or paternal genes. and two are
non-recombinant.
If chromatids were not involved in crossing over,
some of the gametes will have ‘original’ allele
sequences. These are non-recombinant alleles.
COMPARE AND CONTRAST MITOSIS AND MEIOSIS
MUTATIONS
It is the process of mutation
that creates the new alleles
which are the source of genetic
variation. But it is the three
processes of independent
assortment, segregation, and recombination that
shuffle the alleles creating new combinations which
produce the great variation seen within members of a
species.
TYPES OF MUTATIONS
Mitosis
Meiosis
Produces body cells(Somatic
cells)
Produces sex cells(Gametes)
Daughter cells diploid(2N)
Daughter cells haploid(N)
Two daughter cells produced
Four daughter cells produced
In metaphase chromosomes line
up singly
In metaphase I chromosomes line up as
homologous pairs(synapsis)
The two double chromosomes are called a tetrad
when they are lined up side-by-side.
Crossing over occurs during the formation of the
tetrad
One nuclear division
Two nuclear divisions
Produces cells for growth and
repair
Produces cells for sexual reproduction
Daughter cells have two sets of
chromosomes(pairs)
Daughter cells have only one member of each
pair of chromosomes
Daughter cells are genetically
identical to the parent cell
Daughter cells have one-half of the genes from
the parent cell
Insures that all daughter cells
are genetically identical
Generates genetic diversity through crossing
over and random separation of homologous pairs
of chromosomes
A mutation is the change in genetic material of an
organism. Mutations are spontaneous and random, and
typically are rare. However, their rate may be
increased by exposure to environmental factors such
as ionising radiation and mutagens. (Mutation inducing
chemicals such as benzene and formaldehyde)
While most mutations are harmful or neutral,
sometimes the altered function will be beneficial to
the individual. If the mutations occur in the gametes,
then the mutations will enter the gene pool of the
population and become subject to natural selection.
BLOCK OR CHROMOSOMAL MUTATIONS
-duplication, inversion, translocation, deletion
Mutation involving whole genes. This occurs when
parts of chromosomes are deleted, repeated, or
translocated to other chromosomes. They may
remove alleles from the gene pool (through deletion)
or produce different combinations of alleles (through
translocation).
POINT MUTATIONS
These are changes in the bases in DNA, so occur
within a gene. Bases maybe deleted, inserted or
substituted during DNA replication. This results in a
change in the base sequence of DNA that codes for a
gene, so producing a new allele.
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GENETICS VOCAB CARD 2
(INHERITANCE)
MONOHYBRID CROSSES
What proportion of the
offspring (out of 4) will be:
Recessive allele-The general term for an allele that is
masked in the phenotype by the presence of another allele.
Dominant allele-The general term for an allele that masks
the presence of another allele in the phenotype.
Genotype-The genetic makeup of an individual for a trait or
for all of his/her inherited traits-not the observable or
detectable characteristics.
Phenotype- The observable or detectable characteristics
of an individual organism; the detectable expression of a
genotype.
Heterozygous genotype- A genotype consisting of two
different alleles of a gene for a particular trait.
Homozygous genotype-A genotype consisting of two
identical alleles of a gene for a particular trait.
True/Pure breeding-An organism, which when bred with
genetically alike organisms. All the offspring are the same
as the parents. They have a homozygous genotype.
Sexed link genes- Genes that are located on the sex
chromosome, usually the X
Punnett squares - can be used to work out the probability
of a characteristic being passed on to the next generation.
A cross between a single characteristic governed by two
alleles is called a monohybrid cross.
Short Toe______
Long Toe ______
*These are your predicted
ratios.
TEST CROSS or BACKCROSS
An individual that displays a dominant trait can either be
homozygous dominant or heterozygous. To discover which we
must do a test cross.
Mating involving an unknown genotype with the homozygous
recessive eg hh to determine the genotype of the unknown
by the offspring produced.
Question
Corn seed colour is determined by a single gene. Purple
seed (P) is dominant over yellow seed (p). Max buys some
purple corn seeds from the local seed merchant. Explain
what he could do to determine whether the corn seed was
homozygous or heterozygous.
To be sure of the genotype of the individual being tested, it
must be:
-crossed with a large number of recessive individuals.
Or
-bred a number of times; this is to ensure that the masked
recessive allele will show in the offspring if present.
If no recessive features occur after multiple matings, the
tested individual can safely be assumed to be homozygous and
so can be used for breeding.
PEDIGREE CHARTS
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- Pedigree Test - Test in which you look at the
offspring of parents to determine the
genotypes of the parents.
- The squares are for males and the circles are
for females.
-If the symbol has been darkened it says the
person carries the trait.
DIHYBRID CROSSES
Is the inheritance of 2 genes controlling 2 different
features.
If two heterozygous dihybrids with complete
dominance are crossed (TtYy x TtYy). The 9:3:3:1
ratio is always the probability of getting each
phenotype.
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