9. genetic diversity and adaptation Flashcards
what is a gene
length of DNA that codes for a polypeptides
what is the locus
the position of a gene on the chromosomes
what is a homologous chromosome
a pair of chromosomes that have the same gene at the same loci
(Different alleles)
allele
a different form of a particular gene
Describe frame shift. When does this happens
When triplets in a sequence of bases shifts to the left or right because of:
- addition of base
- deletion of base
- duplication of base
NOT substitution
How does gene mutation effect an organism
If sequence of bases is changed than a different sequence of amino acids are put together, creating a protein with a different shape.
As proteins shape determines its function, a change in shape effects it’s ability to carry out its function.
Describe what has happened when a directional selection is observed
Change in environment causes modal trait to change in response
What are the two types of selection
- Directional
- Stabilising
How do mitosis and meiosis differ
Meiosis
- TWO divisions
- HAPLOID cells are made
- introduced genetic VARIATION
mitosis
- ONE division
- DIPLOID cells are made
- create genetically IDENTICAL cells
What is the diploid number in human?
what is the haploid number in humans
46
23
Describe INDEPENDENT SEGREGATION
Two homologous chromosomes line up at equator
Which side each chromosomes are on are random
Pairs are separated
Large number of possible combinations in each daughter cell
Describe CROSSING-OVER of chromosomes
Homologous pairs line up and become tangled and twisted around each-over
This causes part of the chromaTIDS to break off and attach to opposite chromosome
Resulting in a new combinations of alleles
What three ways is variation introduced by meiosis
- Independent segregation
- Crossing over
- fertilisation is random (random sperm to egg)
What is the formula for the possible chromosome combinations (involving meiosis)
(2n)^2
N = number of homologous pairs
What two forms can chromosome mutations take?
- changes in the whole SETS of chromosomes. (polyploidy)
- changes in the number of individual chromosomes. (aneuploidy)
What is meant by ‘non-disjunction’
homologous chromosomes fails to separate during meiosis. All are pulled to same side of cell.
What is a mutagenic agent?
chemicals or radiation that increases likelihood of gene mutation by interfering with DNA replication
What is polyploidy?
changes in whole sets of chromosomes, three or more sets rather than two. - common in plants, fatal for humans
What is aneuploidy?
individual homologous pairs of chromosomes fail to separate during meiosis, resulting in more or fewer chromosomes
When does independent segregation and crossing over take place?
- homologous pairs of chromosomes line up opposite each other at the equator.
- Distribution of paternal and maternal sides at the equator are random.
- results in many possible combinations of chromosomes in daughter cells
occurs during meiosis 1
What is a diploid cell?
What is a haploid cell?
diploid, two full sets of chromosomes
haploid, one set of chromosomes
What is a homologous chromosome?
a pair of chromosomes, one maternal and one paternal. - same gene loci
Explain the process of meiosis
- first division (m1), = one chromosome from each pair into one of two daughter cells
- Second division (m2), chromatids move apart = 4 haploid cells.
What is a zygote?
fertilized egg cell, fusion of sperm cell and ovum
- mitosis
What is genetic diversity?
number of different alleles of genes in a population
What does a population need for there to be natural selection?
genetic diversity
Natural selection leads to…
evolution
What is evolution
change in allele frequency over many generations.
natural selection results in species becoming…
better adapted to their environment.
Explain the process of natural selection
- new alleles from mutations
- allele increases an individual’s chance of survival = more likely to reproduce
- advantageous alleles passed on
- advantageous allele increases in frequency (over many generations)
when modal trait changes towards one of the extremes ________ selection takes place.
directional
Identify the two types of selection.
- stabilizing
- directional
