SB3- Genetics Flashcards
What reproduction do do invertebrates do
Asexual reproduction is more common eg aphids produce offspring from cells formed in mitosis
How to plants usually reproduce
Asexually
What does sexual reproduction do
Combines characteristics from both parents and so produces offspring different from eachother
Why are different characteristics an advantage
If the environment changes, variation means that there is a greater chance that some offspring will be better suited to new conditions and so will me more likely to survive and reproduce
Why is asexual reproduction faster
There is no need to find a mate
What’s a zygote
When 2 gametes fuse during fertilisation
The zygote forms a ball of cells using a type of cell division called mitosis
What is DNA
It’s instructions for an organism found as code in a molecule called DNA
THE DNA of an organism is its genome
What’s the human genome like
46 very long molecules of DNA and each molecule is inside a chromosome
What are genes
Along the length of a DNA molecule are sections that each contain a code for making protein
How are proteins made
They are polymers made by linking different amino acids together in a chain
The order of amino acids is controlled by the gene
What kind of cell does mitosis produce
Diploid cells
What process is used to produce gametes
Meiosis
Tell me about meiosis
Each chromosome replicates, the 2 copies remain making each chromosome look like an X, the 2 sets of chromosomes pair up forming 23 pairs then seperate into 2 new cells, next the 2 copies of a chromosome in each x shape split into 2 more new cells therefore produces 4 haploid daughter cells
How does meiosis create genetic variation
Each chromosome in each pair contains different versions of the same genes so they are genetically
Different chromosomes so explains why brothers and sister look similar but not identical
Tell me the order of meiosis
Interphase Prophase Anaphase Telophase Interphase Metaphase Anaphase Telophase Cytokinesis
Where is DNA stored
In the nuclei of a cell - each molecule of DNA is tightly coiled and packaged up with proteins to from chromosomes
What shape is DNA
A double helix
What are the 4 bases of DNA
Adenine, thymine, cytosine and guanine
Make them simple often call them A, T, C and G
How are the bases arranged
In complementary base pairs
A and T always pair
C and G always pair
What’s a nucleotide
Each base is attached to a super and each sugar is attached to a phosphate group
The sugars and phosphate groups form the backbone of the DNA strands
How are bases joined together
Hydrogen bonds
How many bonds are between the bases
Cytosine and guanine form 3 hydrogen bonds between them
Thymine and adenine only form 2 bonds
What makes our DNA different
The order of the bases
What did Erwin Chargaff
He did chromatography experiments which showed the amount of A and T in an organisms DNA were the same, as were the amount of G AND C
What did Rosalind Franklin do
Took an X-ray photograph suggesting that DNA was a helix
What did Jerry Donohue do
Who showed them how DNA based could form hydrogen bonds
What’s the genetic code
How the order of the DNA bases caused amino acids to be joined in a certain order on a protein
What’s transcription
DNA bases are used to make a strand of RNA (ribonucleic acid)
An enzyme called RNA POLYMERASE attached up the DNA IN front of a gene in a non-coding region (so called because it does not contain code for a protein) the enzyme separates the 2 DNA strands.
The enzyme then moves along one DNA strand (the TEMPLATE strand) adding complementary RNA nucleotides. These contain the same bases as DNA except uracil (U) is used instead of thymine (T) the nucleotides link link to form a strand of RNA (mRNA)
What’s translation
The mRNA strands travel out of the nucleus through nuclear pores, in the cytoplasm the mRNA strands attach to ribosomes
A ribosome moves along the an mRNA strand three bases at a time (a codon) at each mRNA codon a molecule of transfer RNA (tRNA) with complementary bases line up- each tRNA molecule carries a specific amino acid, as the ribosomes moves along, it joins the amino acids from the tRNA molecules together, forming a polypeptide
What happens after translation
The polypeptide chain folds up to form a protein with a specific shape. Some proteins contain more that one polypeptide chain
What creates a mutation
A change In bases of a gene creates a genetic variant or mutation
How can a mutation be caused
When DNA is not copied properly in cell division. Environmental factors can also cause mutations
Some mutations change an organisms phenotype (visible characteristics)
What are alleles - what do they mean
Mutations are the reason alleles exist - one gene can have many alleles, caused by different mutations. Your characteristics are shaped by the alleles you Inherit
What’s haemoglobin like
It can 4 polypeptides of two kinds a and b (in those funny Greek letters) the polypeptides fold and join up to form a globular protein which carried oxygen.
What are mutations in non coding DNA like
RNA polymerase attaches to DNA bases in front of a gene, a mutation in this non-coding region may result in RNA polymerase not binding well - reducing transcription
Other non coding mutations can result In RNA polymerase binding better and producing more mRNA
What are the 3 laws of inheritance according to Mendel
1) each gamete receives only one factor for a characteristic
2) the version of a factor that a gamete receives is random and does not depend on the other factors in the gamete
3) some versions of a factor are more powerful than others and always have an effect In the offspring
Why was mendels work largely ignored
Did not see how ‘factors’ could explain the many variations in characteristics such as human eye colour - couldn’t see mendels ideas could explain evolution
Argued that if the factors could boy change then a species would not evolve
What are alleles
Genes for the same characteristics but contain slightly different instructions that create variations eg brown and blue eyes
How is their genetic variation
There are 2 copies of every gene in each body cell - each copy of a gene may be a different allele, the different combinations of Alleles in different people gives us slightly different characteristics
What’s homozygous
If both alleles for one gene are the same
What’s heterozygous
if the alleles are different
What is dominat
It is the allele that has an effect
What’s recessive
When an allele is in the genotype but not the phenotype
When is a recessive gene seen In phenotype
If both alleles are recessive, the recessive characteristics are seen
How is a dominant allele shown
With a capital letter
Recessive with a lower case
The dominant allele letter is always written before the recessive one
The alleles in an organism are its genotype
What the organism looks like is its phenotype
What do we use to explain the inheritance of one gene (monohybrid inheritance)
Diagrams, they predict the ratios of the phenotype
What are the sex chromosomes
They determined your sex
Two types: X AND Y makes a male
X and X makes a female
What chromosomes do gametes contain
Egg cells all contain X sex chromosomes and Sperms contain either X or Y
What are Punnett squares used for
They can demonstrate inheritance, they show possible genotypes
They calculate the theoretical probability of offspring inheriting certain genotypes / used to calculate probabilities of different phenotypes caused by alleles
Probabilities can be shown as a decimal or percentage
What does a family pedigree chart show
Shows how genotypes and their resulting phenotypes are inherited in families
What will happen if someone is given the wrong blood
The red blood cells in it will clump together which can kill
How do we classify blood
ABO blood group system
In this system everyone’s blood is one of 4 groups: A, B, AB, O
How is your blood group determined
By wether you have certain marker molecules on the outside of your red blood cells
Three main types A, B and O
Tell me s let the genes in the ABO system
The gene that is responsible for the markers in the ABO system has 3 alleles, written as I (with a little letter (A,B, or O) above small like a power would be
Everyone has 2 copies of the gene so may be homozygous for Any of the 3 alleles or heterozygous for any 2 of the three alleles I(with an O) is recessive to both I^A and I^B. However a person with genotype I^a I^b shows the effect of both alleles and has the blood group AB
What is codominance
When both alleles for a gene affect the phenotype eg blood group AB
What are sex linked genetic disorders
The Y chromosomes are missing some of genes in X chromosomes, so a man may only have 1 allele for some genes on the X chromosome, if the allele for one of these X chromosomes genes causes genetic disorder, then a man will develop that disorder
Whereas if a women has a recessive allele for a disorder she won’t get it as she still has a healthy allele with will be dominant
So probability of a man developing it will be more than a women
Tell me some examples of a sex linked disorder
Red-green colour blindness - 8% men have it only 0.5% of women have jt
A mother can be a carrier for the disorder which means she has one faulty allele and one normal allele
What is a mutation
A change in a gene that creates a new allele, often occur during cell division
Happen Becuase there is a mistake in copying DNA during cell division
More likely if there is damage to the DNA caused by radiation or certain substances
Many mutations will not change a protein at all and so have no effect on phenotype
What can mapping a persons genome do
Indicate their risk of developing diseases caused by different alleles of genes, also help identify best medicines to treat a persons illness
Becuase alleles we have can affect how medicines work in the body
How is genetic variation caused
By the different alleles inherited during sexual reproduction
Different alleles are produced by mutations, some of which cause changes in the phenotype
What’s environmental variation
Many characteristics also show environmental variation Becuase they are affected by their surroundings
Eg a plant grows according to how much light, water and nutrients it gets
What are acquired characteristics
Characteristics that are changed by the environment during the life of the individual eg loss of limb
What’s discontinuous variation
Is where the data can only take a limited set of values eg number of whole leaves a plant has
What’s continuous variation
Where data can be any value in any range eg the leaf length in a plant
What does a bar chart look like for discontinuous variation
The bars have gaps, you can only have whole numbers
What’s a bar chart like for continuous data
There are no gaps with bars
Values are grouped to make it easier to see patterns In data
What’s normal distribution for variation
Often forms a bell shaped curve (goes up and then down)
Called normal distribution Becuase it’s what’s expected for a large amount of data for a characteristic where:
The most common value is the middle value in the whole range
The further a value is from the median, the fewer individuals have that value
