B5.1 Inheritance Flashcards
What is variation?
Differences within species.
State four examples of variation.
- Height
- Build
- Eye colour
- Hair colour
- Blood group
- Language
Name the two causes of variation within species.
- Genetics
- Environment.
How can variation of a characteristic displayed be further categorised?
Into continuos vs. discontinuous variation.
What is discontinuous variation?
- Variation that produces distint categories
- e.g. Eye colour, blood group, gender
What is continuous variation?
- Variation that cannot be placed in distinct categories and instead produces a spectrum
- e.g. height, weight, skin colour
What type of variation will human body mass display?
Continuous.
What causes variation?
Mutations in the genetic code.
What is asexual reproduction?
- Reproduction that produces a clone that is a genetically identical to it single parent.
- There is no mixing of genetic material
Give two examples of organisms that can replicate asexually.
- Potato plants
- Stawberries
- Spider plants
- Bacteria
- Mushrooms
- Daffodils
How does asexual reproduction take place?
Mitosis.
What is sexual reproduction?
- Reproduction requiring two parents
- Genetic information is taken from both parents
- Organisms produce haploid gametes that fuse during fertilisation
- Offspring are not identical
- Results in variation
Give one advantage and one disadvantage of sexual reproduction.
- Advantage: Variation in offspring leads to adaptation in a species. This results in some organisms within a species containing adaptations that allow them to cope with an environmental pressue. These organisms can reproduce, enabling the species/population to survive.
- Disadvantage: Reproduction requires two parents. Reproduction is slowers, so few offspring are produced.
Give one advantage and one disadvantage of asexual reproduction.
Advantages
- If the parent was well adapted to an area then the offspring will share an identical set of characteristics
- Only one parent is needs - animals do not need to find a partner, plants do not require pollination.
- Faster, so large numbers of offspring are produced quickly
Disadvantage:
- Adverse changes to the biotic or abiotic factors may destroy the species, as all organisms affected due to the being no variation.
What is a gamete?
- A sex cell
- Haploid cell used in sexual reproduction
- Sperm & egg
- Pollen & ovule
What is a chromosome?
Tightly packaged DNA wrapped around histone proteins.
What is a gene?
A section of DNA that can (but not always) code for a protein.
What is an allele?
Different versions of the same gene e.g blue eyes vs. green eyes
What is a dominant allele?
A version of a gene where only one copy is required for it to be expressed in the organisms phenotype.
What is a recessive allele?
A version of a gene where two copies are required for it to be expressed in the organisms phenotype.
What is meant by the phrase ‘pure breeding’?
The organism is homozygous for a characteristic.
What is meant when an organism is homozygous?
When an organism has two copies of the same allele (either both dominant or both recessive).
What is meant when an organism is heterozygous?
When an organism has two different version of the same gene (one dominan and one recessive).
What is the genotype?
The genes present for a trait.
What is the phenotype?
The visible characteristics displayed as a result of an organisms genotype.
What is genome?
All of the genes present in an organism.
What happens during fertilisation?
The nuclei of two haploid (n) gametes fuse to produce a single diploid (2n) cell known as a zygote.
How are gametes made?
Meiosis.
What are the stages of meiosis?
Stage 1:
- The chromosomes are copied
- The chromosomes line up upon the midline of the cell in pairs (one from the father, one from the mother)
- Spindle fibres form
- Spindle fibles contract towards the oppostive poles
- One member of each pair is pulled to opposite ends of the cell - sections of DNA are often swapped at this stage (crossing over & recombination).
- The cell divides in two form two separate cells
Stage 2:
- The chromosomes line up upon the midline of each new cell
- Spindle fibres form
- Spindle fibles contract towards the oppostive poles
- The chromosomes are pulled in half - a single copy of each chromosome goes to the opposite end of the cell
- Each cell divides in two. This results in four haploid (n), genetically diffenrent cells.
Compare mitosis and meiosis.
Mitosis
- The cell divides once
- Two cells produced
- Same number of chromosomes as parent cell
- Used for growth & repair
- Happens in all parts of the body
- Daugther cells genetically identical to parent cell
Meiosis
- The cell divides twice
- Four cells produced
- Half the number of chromosomes as parent cell
- Used to produce gametes
- Happens in the gonads only (testes/ovaries)
- Daugther cells genetically unique cells to parent cell
What is the different between dipoild and haploid cells?
- Haploid cells have half the amount of genetic information as diploid cells
- Haploid cells are germ (sex) cells
- Diploid cells are somatic (body) cells
What type of cell does meiosis produce?
Haploid germ cells e.g sperm and egg
How are dominant alleles represented in a punnett square?
Uppercase letters
How are recessive alleles represented in a punnet square?
- Lowercase version of the same letter as the dominant allele
What is a mutation?
An alteration in the sequence of DNA bases.
What is a mutagen?
- Substances or conditions that increase the chance of a mutation occuruing.
- e.g. ionising radiation, benzene, ethanol, smoking
Describe how a mutation in a coding DNA sequnece could be detrimental.
- DNA bases within the coding gene may be changes, added or deleted.
- This changes the sequence of bases, therefore the order of base produced during transcription is altered.
- This then alters the amino acids coded for in translation affecting the protein produced.
- The protein produced may be the wrong protein, or fold incorectly and form a different shape
- This change may affect the protein, particularly in specific molecules like enzymes and antibodies.
Describe how a mutation in a non-coding DNA sequnece could be detrimental.
It may stop transcription and alter the expression of genes.
State three negative examples of gene mutations.
- Huntington’s disease
- Sickle cell anaemia
- Cystic fibrosis
- Cancer
- Alpha & Beta thalassemia
- Tay-sachs disease
- Phenylketonuria
- Hemochromatosis
- Marfan Syndrome
State three neutral examples of gene mutations.
- Tongue rolling
- Polydactyly
- Joined ear lobes
- Most mutations are neutral
State three examples of beneficial gene mutations.
- Antibiotic resistance in bacteria
- Colouring that aids camoflauge
- De-pigmentation in cold/dark climates
- Production of lactose post-infancy
State three important findings of Gregor Mendel.
- Characteristics are determined by hereditary units (now refered to as genes)
- Offspring recieve units from both paretns, one unit from each, so share traits with both paretns
- Hereditary units are dominanr or recessive, so traits not always visible.
What discovery lead to people accepting Mendel’s ideas?
The discovery of the gene.
Who captured the famous ‘photograph 51’?
Rosalind Franklin.
