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Topic 13 Reproduction / DNA / Genes - Coggle Diagram
Topic 13 Reproduction / DNA / Genes
Reproduction
Asexual
:
reproduction with one parent with no Fusion of gametes. There is no mixing of genetic information and the offspring are genetically identical
4 advantages
:
1. only one parent needed 2. doesn't need to find a mate so more energy and time efficient 3. faster than sexual reproduction 4. when conditions are favourable many identical offspring can produced
Malarial parasites
-
reproduce asexually when in the human host
Fungi
-
reproduce asexually by producing spores
Plants
-
Reproduce asexually by producing runners (e.g. strawberry plants) or by bulb division (e.g. daffodils)
Sexual
:
reproduction with two parents with the fusion of gametes during fertilisation. Involves mixing of genetic information and the offspring are genetically varied
Gametes produced by meiosis are genetically different due to the mixing of genes/alleles from two parents during fertilisation
3 advantages
:
1. produces variation in the offspring 2. If the environment changes the variation gives a survival advantage (by natural selection)
Malarial parasites
-
reproduce sexually when in the mosquito
Fertilisation
After fertilisation
the fertilised cell egg divides by mitosis to form an embryo. Cells in the embryo (stem cells) begin to differentiate
Cell division
Meiosis
Purpose
-
to produce gametes
Happens where?
-
testes and ovaries
Divisions
-
two
Daughter cells
-
four
Number of chromosomes per daughter cell
-
23
Dip/Hap
-
Haploid
Genetically different/identical
-
different
Process
-
1. the DNA replicates 2. The cell divides twice to form four gametes with half the number of chromosomes 3. Gametes are genetically varied
It is important for the number of chromosomes to half due to the fact that when they fuse together they will have 46 and the number of chromosomes is not doubled
Mitosis
Purpose
-
growth and repair of tissues
Happens where?
-
in most tissues
Divisions
-
one
Daughter cells
-
two
Number of chromosomes per daughter cell
-
46
Dip/Hap
-
Diploid
Genetically different/identical
-
identical
(In both mitosis and meiosis DNA is replicated during inter phase)
DNA/Genes
DNA
DNA is
The genetic material found inside the nucleus of a cell. DNA structure is a polymer made up of two strands twisted into a double helix. DNA is a polymer made from four different nucleotides
A = Phosphate
B = Sugar
C = Base
The 4 DNA bases and pairing
A and T, C and G
Chromosomes
A chromosome is
a structure containing DNA
Genes
A gene is
a small section of DNA, which codes for a specific sequence of amino acids, which folds up to make a protein.
The genome is
All the genetic material (DNA) of an organism
3 benefits of studying the human genome:
1. Identifying genes linked to different types of disease 2. Treating inherited disorders 3. Tracing human migration patterns from the past
The genetic code is
A sequence of three bases codes for a specific amino acid
A mutation is
a Change in the base sequence of DNA
A mutation in a non coding region of DNA can:*
Switch a gene on (it is expressed) OR switch a gene off (it isn’t expressed.*
when mutations happen and their usual effect:*
Mutations happen continuously and most have no or little effect. Some can affect protein shape and function or the expression of genes.*
A mutation can: - cause a change in DNA base sequence - cause a Change in amino acid sequence in protein - cause a Change in protein shape
A change in shape of a working enzyme can cause:
a change in the shape of an active site, an enzymes substrate and active site no longer complementary
An allele is
a form of gene
A recessive allele
needs two copies to be expressed
A dominant allele
only needs one allele to be expressed (usually expressed with a Capital letter)
A genotype
is a combination of alleles someone has
homozygous recessive genotype
2 copies of the recessive allele (e.g. aa)
Homozygous dominant genotype
2 copies of the dominant allele (e.g. AA)
Phenotype
is characteristics that someone has
'
expressed
'
is when the allele affects the method
Two characteristics that are controlled by a single gene
are reg-green colour blindness and fur colour in mice
Determines the gender:
The genes on one of the pairs of chromosomes male (XY) female (XX)
Most characteristics are controlled by multiple genes interacting
Proteins in DNA
the process of protein synthesis
1
.
A ‘template molecule’ (mRNA) is made from a gene
2
.
The ‘template molecule’ (mRNA) leaves the nucleus (through through pores) and travels to a ribosome
3
.
Amino acid ‘carrier molecules’ (tRNA) bring particular amino acids to the ribosome
4
.
The ribosome joins the amino acids together form a amino acid chain - in the order given by the code on the template molecule (mRNA)
5
.
The amino acid chain leaves the ribosome and folds up to form a protein with a unique shape
3 types of protein found in the body:
1. enzymes 2. hormones 3. structural proteins e.g. collagen
how a change in shape could affect the working of a structural protein like collagen
May lose strength
Disorders
A inherited disorder
is Disorder caused by the inheritance of a certain allele
Cystic fibrosis
Disorder of cell membranes, caused by a recessive allele
polydactyl
Disorder of cell membranes, caused by a recessive allele
A carrier
is a individual has the allele for the disorder but isn’t affected. (Their genotype must be heterozygous for this trait).
embryo screening
is Removing a cell from an embryo (or foetus) and testing its DNA for the allele that causes an inherited disorder
Advantages
:
1
.
A couple can prepare for having a child with a disorder
2
.
A couple could choose to abort an embryo with disorder
Disadvantages
:
1
.
embryos may be harmed (e.g. abortion)
2
.
risk to mother
3
.
emotional stress for parents
4
.
expense
Mendel Mendel discovered from his plant breeding experiments
The inheritance of each characteristic is determined by ‘units’ that are passed onto their offspring unchanged
these units are now refereed to as genes
Reasons his work was not accepted: 1.
Other theories of inheritance were accepted at the time e.g. blending of characteristics
2
.
Mendel’s work was published in an obscure journal
three subsequent discoveries that helped support the work of Mendel:
1.
Late 1800s - behaviour of chromosomes during cell division was observed.
2
.
Early 1900s - it was observed that chromosomes and Mendel’s ‘units’ behaved in similar ways. This led to the idea that the ‘units’ (now called genes) were located on chromosomes.
3
.
In the mid-1900s the structure of DNA and the mechanism of gene function was worked out.
