BIO Flashcards
DNA
the molecule that carried the genetic instructions
Chromosome
threadlike structures that contain long lengths of DNA that hold many genes
gene
section of chromosome that codes for one trait
allele
the different forms of a gene
gamete
a sex cell
fertilisation
fusion of two gametes
zygotes
fertilised egg cell
embryo
a ball of cells formed from the zygote by cell division
homologous chromosomes
a pair of chromosomes that have the same genes in the same location, one chromosome comes from the mother and one from the father
meiosis
the type of cell division that gametes are made by
sexual reproduction
reproduction that involves two individuals contributing genetically to offspring
asexual reproduction
reproduction that involves one individual contributing genetically to offspring
genetic variation
the difference in DNA of individuals in a population/species
continuous variation
a complete range of measurements from one extreme to another
discontinuous variation
the characteristics fall into discrete categories
genotype
the alleles an individual has for a trait
phenotype
the physical expression of the gene
dominant allele
the allele that is always expressed in present
recessive allele
the allele that is only expressed in the homozygous condition
homozygous
genotype with two of the same alleles
heterozygous
genotype with one dominant and one recessive allele
punnet square
a diagram used to determine the probable outcomes of a genetic cross between two individuals
pure breeding
and organism that is homozygous for a trait
test cross
when an individual with the dominant phenotype is crossed with a homozygous recessive individual to identify if the dominant individual’s genotype is heterozygous or homozygous dominant
natural selection
a process whereby organisms better adapted to their environment tend to survive and produce more offspring
mutation
a permanent and random change in the base sequence of DNA
point mutation
a point mutation occurs when a single base or very few bases is changed which affects only a single gene
chromosomal mutation
Affects the whole or a part of a chromosome which affects multiple genes
selective breeding
the process of choosing only plants and animals with desirable characteristics to reproduce
inbreeding
the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically
DNA sequencing
the process of identifying the exact order of the bases in a DNA strand
What are the three types of point mutation
Substitution, deletion, insertion
a base/nucleotide is replaced/removed/added in the base sequence of DNA
What are the three types of chromosomal mutations
Deletion, inversion, translocation, duplication
- a part of a chromosome is lost/breaks off and flips around and attaches to the same chromosome/breaks off and attaches to a different chromosome/copied more than once resulting in extra genetic materials
What syndrome is affected by chromosomes XXY?
Klinefelters syndorme
What syndrome is affected by chromosomes XO?
Turner’s syndrome
What syndrome is affected by chromosomes 21 x 3
trisomy 21 / down syndrome
What is Haemophilia
Inherited bleeding disorder in which this blood does not clot properly. This can lead to spontaneous bleeding.
What is haemophilia caused by?
caused by a point mutation in gene that instruct protein 8 to clot blood
What is cystic fibrosis
An inherited disorder where mucus, sweat, and digestive juices are sticky and thick, leading to severe damage in the lungs and digestive system
What is cystic fibrosis cause by
a deletion point mutation of three bases
What is sickle cell anaemia
inherited disorder the affects the shape of red blood cells, which can increase lack of oxygen
What causes sickle cell anaemia
substitution point mutation in the HBB gene
Describe the DNA structure
DNA is a double stranded molecule twisted into a double helix. It is made up of repeating sub-units called nucleotides.
Explain the genetic code
The genetic code is read in triplets and these triplets code for amino acids. Amino acids are ordered according to the base sequence to form different proteins. Therefore different base sequences produce different proteins and different phenotypes.
Explain why meiosis as a reduction division is important
It reduces the number of chromosomes in the gametes it produces - from two sets in the parent cell to only one set in the gametes. Halving the number of chromosomes ensures that when gametes are joined together at fertilisation, the zygotes end up with the correct numbers of chromosomes in each cell to function correctly.
Somatic cell
A body cell that has two sets of chromosomes
Explain how meiosis produces variation
During meiosis, there is crossing over of homologous chromosomes and independent assortment of the chromosomes. This creates a new combination of alleles that are different from the parents. This increases genetic variation.
Explain how fertilisation produces variation
Fertilisation joins male and female gametes to form a zygote. It produces variation by randomly joining male and female gametes and mixing the genetic information of two parents. This increases genetic variation.
Explain how mutation produces variation
Define mutation and DNA.
In mutation, there is a random change in the base sequence of DNA. It changes how the genetic information is read and creates a new allele. A new allele codes for a different protein and changes the phenotype/trait. Therefore increases genetic variation within a species.
Describe natural selection (VARPA)
→ There is variation of phenotypes in the population and species produce more individuals than the environment can resource.
→ Individuals with the phenotype best suited to the environment have a survival advantage (camouflage from predators) so are more likely to survive to reproduce
→ and therefore pass on their alleles for the favourable/beneficial phenotype/characteristic to offspring more often,
→ which means the frequency of the favourable/beneficial allele(s) increases in the gene pool.
Implication of selective breeding - Inbreeding depression
The loss of fitness and strength of a population. Can lead to health problems in the offspring because they inherit the same harmful genes from both parents.
Implication of selective breeding - reduced genetic diversity
Only certain individuals with specific alleles are allowed to reproduce. Certain alleles are lost to the population which removes variation. Natural selection works upon variation so this may put the survival of the population at risk if a new disease or environment change occurs.
Health impacts in selective breeding
If more extreme characteristics are selected this may cause health impacts for the animal. E.g. bulldogs and cavalier king charles spaniels.
How does selective breeding lead to health impacts for bulldogs
Bulldogs are a severely flat-face breed. They are very likely to suffer from health issues due to their physical conformation including: severe breathing difficulties, skin problems, joint problems and dental issues.
How does selective breeding lead to health impacts for Cavalier King Charles Spaniels?
Syringomyelia occurs when cavities form and fill with fluid in the spinal cord due to abnormal pressure in the skull. This occurs as the brain grows but the cranium doesn’t grow at the same speed. Common signs of this include, yelping, crying and inability to move their neck.
Choose an animal and explain how to achieve selective breeding
Choose a (tree/cat or dog breed) with the (desirable characteristic)
(Cross pollinate flowers of the tree) OR (Breed the cat/dog) with the (desirable characteristic)
Collect and grow seeds OR Raise the puppy/kitten
Pick the (trees/cat/dog breed) that have the (desirable characteristic)
Continue the process until the (trees/cat/dog breed) are pure breeding for the (desirable characteristic)
(No longer showing other phenotypes)
Monohybrid inheritance
The inheritance of characteristics controlled by a single gene
Why are punnet square phenotype ratios different from the observed phenotype ratios?
- Each fertilisation event is independent and random, which is unaffected by previous outcomes so the chance of an outcome occurring remains the same for every offspring produce.
- Sample size is too small. The expected phenotype ratio may not be observed due to random chance. If more offspring are produced then you are more likely to get closer to te observing the expected phenotype ratio.
Explain DNA sequencing in the context of stomach cancer.
· Stomach cancer can be caused by a mutation in the CDH1 gene.
· Carriers of the mutated gene have a 70% higher chance of developing stomach cancer and female carriers a 30-40% higher risk of developing breast cancer. Māori have rates of stomach cancer 3x higher than Europeans due to a higher incidence of the CDH1 allele.
· A blood or saliva sample is collected and the DNA is sequenced. Normal sequence chromatograms are compared with the sample chromatogram.
· If a carrier of the gene is identified the patient can undergo regular checks for cancer or may choose to surgically remove the stomach.
Explain DNA sequencing in the context of Cystic Fibrosis
· Cystic Fibrosis can be caused by a mutation in the CFTR gene which is recessive.
· Individuals who inherit 2 copies of the mutated CF allele have a cystic fibrosis which affects the cells that produce mucus, sweat and digestive juices. These secreted fluids are normally thin and slippery but in people with CF, the defective gene causes the secretions to become sticky and thick.
Instead of acting as lubricants, the secretions block passageways, especially in the lungs and digestive system causing a higher rate of lung infection and lower nutrition absorption.
· Individuals with a family member with Cystic Fibrosis and their partner may choose to have their DNA sequenced to see if they are carriers of the mutated CFTR gene before having children.
A blood or saliva sample is collected and the DNA is sequenced. Normal sequence chromatograms are compared with the sample chromatograms.
· If a carrier of the gene is identified in both patients can undergo genetic counselling to decide whether or not to have biological children.
