Topic 4 - Genetic variance and biodiversity Flashcards
What is a gene mutation ?
Mutations
A spontaneous change in the DNA sequence of chromosomes.
What are 4 types of mutations ?
Mutations
- Substitutions - one base is substituted with another.
- Additions - one base is added.
- deletions - one base is deletion.
- non disjunction- a chromosome does not fully divide during meiosis.
Why can substitions not always cause changes in the primary structure of a protein ?
Mutations
Beacuse the genetic code is degenerate.
Why do additions and deletions usually always cause changes in the primary sequence of a protein ?
Mutations
Because it changes the number of bases that are present therefore it causes a frameshift
What are mutagenic agents ?
Mutations
things that increase the rate of mutations, e.g. ultravoilet radiation, ionising radiation and some chemicals and viruses.
What are chromosome mutations ?
Mutations
It can arise spontaneously by chromosome non-disjunction during meiosis. Individual pairs of chromosomes fail to separate, it leads to gametes having more or less chromosomes.
What occurs during down syndrome ?
Mutations
It is caused by a person having an extra chromosome 21, or part of it. It fails to separate during meiosis and one cell gets an extra copy . When it gets fertilised it results in the zygote has 3 chromosome 21.
What is a diploid cell ?
Meiosis
- Normal body cells with cell with 2 of each chromosome, one from the male and one from the female.
- 46 chromosomes.
- 2n
What is a haploid cell ?
Meiosis
Gametes with 23 chromsomes
theres one copy of each chromosome
n
What is a zygote ?
Meosis
A zygote cell is produced when a haploid sperm cell fertilises a haploid egg cell to form a diploid cell which divides to develop into a new organism.
What does ‘fertilisation is random’ mean and what happens as a result of this ?
Meiosis
- Any sperm cell can fertilize any egg cell.
- Random fertilisation produces zygotes with different combinations of chromosomes.
- Mixing genetic material increases genetic diversity within a species
Explain the stages of meiosis
Meiosis
- Interphase: DNA unravels and replicates. ATP content increases and organelles also replicate.
*Meiosis I - Prophase I: Chromones condense, getting shorter and fatter forming homologous chromosomes. Centrioles move to opposite poles of the cell forming a network of spindle fibres. The nuclear envelope disintegrates and the nucleolus disappears. Crossing over may occur.
- Metaphase I: The homologous pairs line up along the equator of the cell, attached to the spindle fibres by their centromere. Independent segregation may occur here.
- Anaphase I: The centromeres divide, splitting the homologous pais of chromomes. Spindle fibres contract, pulling the chromosomes to opposite ends of the cell.
- Telophase I: Chromosomes reach opposite poles of the cell and uncoil, becoming long and thin . A nuclear envelope forms around the 2 sets of chromosomes, forming 2 nuclei.
- Cytokinesis I: The cytoplasm divides, forming 2 genetically different cells.
Meiosis II - Prophase II: Chromones condense, getting shorter and fatter forming pairs of sister chromatids attached at the centromere. Centrioles move to opposite poles of the cell forming a network of spindle fibres. The nuclear envelope disintegrates and the nucleolus disappears.
- Metaphase II: The chromosomes line up along the equator of the cell, attached to the spindle fibres by their centromere.
- Anaphase II: The centromeres divide, chromomes. Spindle fibres contract, pulling the sister chromatids to opposite ends of the cell.
- Telophase II: Chromosomes reach opposite poles of the cell and uncoil, becoming long and thin. A nuclear envelope forms around the 4 sets of chromosomes, forming 4 nuclei.
- Cytokinesis II: The cytoplasm divides, forming 4 genetically different halploid cells.
What is crossing over in prophase I ?
Meiosis
- Homologous pairs of chromosomes pair up, the chromatids twist around each other and some parts may swap.
- This means that each of the 4 daughter cells contains chromatids with different allleles, increasing genetic variation.
- occurs between non sister chromatids.
What is independent segregation in metaphase I ?
Meiosis
- It is completely random which of the chromosomes end up in each daughter cell.
- As a result each daughter cell has a different combination of maternal and paternal chromosomes, increasing genetic variation.
During meiosis, which things lead to increased genetic variation ?
Meiosis
Crossing over during prophase I and independent segregation during metaphase I.
What are the differences between mitosis and meisosi ?
Cell Division
- In mitosis, cell division occurs once, however in meiosis, cell division occurs twice.
- In mitosis cells that are produced are diploid and therefore have the same number of cells as there parent, however in meiosis, cells that are produced are haploid and therefore have half of the amount of cells that their parent cell had.
- In mitosis 2 daughter cells that are genetically identical are produced, however, in meiosis, 4 daughter cells that are genetically different are produced.
- Mitosis is asexual reproduction, meiosis is sexual reproduction.
What is genetic diversity ?
Genetic Diversity
The number of different alleles of genes in a specific population.
What are the sources of genetic variation ?
Genetic Diversity
- mutations
- fusion of gametes
- independent segregation
- crossing over
- gene flow
What are the three types of adaptations ?
Natural selection
Behavioural
Pysiological
Anatomical
What are behavioural adaptations ?
Natural selection
Ways and organism acts which increases its chances of survival and repproduction, e.g. possums play dead to escape from attack by their predator.
What are pysiological adaptations ?
Natural selection
Processes insdie an organisms body that gives it an increased chnace of survival and reproduction, e.g. when brown bears hibernate in winter, their rate of metabolism decreases to conserve energy.
What are anatomical adaptations ?
Natural selection
Structural features on an organsims body that give it a better chance of survival and reproduction, e.g. whales have a layer of thick blubber that keep them warm in the cold sea.
What are the 2 types of selection ?
Natural selection
Directional
Stabalising
How does natural selection and evolution work ?
Natural selection
- A random mutation occurs within an organism resulting in a new allele.
- Most mutations are harmful, however, in certain envitonments, the new allele of a gene may benefit the organism, leading to increased reproductive success.
- The advantageous gene is inheritied by members of the next generation.
- Over many generations, the new allel increases in frequency in the population (evolution).
