Level 2 Bio: Genetic Variation Flashcards
Allele
Different form of a gene
What is allele frequency
A measure of the relative frequency of an allele in a population
Asexual reproduction
Reproduction only involving one parent, creates genetically identical offspring (no genetic variation)
Chiasma
The point on a chromosome where crossing over takes place
Homologous pair
A pair of matching chromosomes, containing the same genes, one from each parent
Gamete
Sex cell (sperm or egg)
Recessive allele
An allele only expressed when there is no dominant allele present
Homozygous
The genotype has 2 alleles the same (e.g BB)
Mutation
A sudden permanent change in the DNA base sequence
Mitosis
Cell division, producing 2 genetically identical daughter cells, occurs in body. Purpose is growth & repair. Full number of chromosomes
Meiosis
Cell division producing 4 genetically different daughter cells, creates gametes, occurs in sex organs, half number of daughter cells.
Sexual Reproduction
Type of reproduction, 2 parents, uses gametes, producing genetic variation in the offspring
Zygote
Cell formed when a sperm cell fuses with an egg cell.
Fertilisation
The process when the sperm cell fuses with the egg cell to form a zygote.
Dominant allele
An allele which will be expressed even if only one is present in genotype (e.g Bb)
Gene
A section of DNA that codes for a set protein and therefore a trait
Chromosome
A strand of DNA, which contains genes
Phenotype
The expression of the genotype as a visible trait
Heterozygous
The genotype with 2 different alleles (e.g Bb)
Semi-conservative
Each double DNA strand is composed of one new and one old strand
Carrier
An individual that has inherited a gene but does not display the trait
Genotype
The 2 alleles, the alleles you carry
Trait
A characteristic that is inherited (e.g eye colour)
Variation
Survival of a species through meiosis, a difference in base sequence between individuals
Haploid
A cell with half the number of chromosomes (n)
Nucleotide
A unit made up of a base, a sugar and a phosphate (base block of DNA)
DNA
A double helix shaped chemical which carries genetic information (instruction to build an organism)
Diploid
A cell with a full set of chromosomes (2n)
What is a source of variation
Meiosis
What are 4 ways of variation through Meiosis
1) Segregation
2) Independent assortment (influence on dihybrid inheritance)
3) Crossing over (recombination of alleles)
4) Linkage (Influence on dihybrid inheritance)
Homologous chromosome
Two matching chromosomes with same genes found in same loci (locus/location)
Sister chromatid
1 half of a replicated chromosome
Centromere
The area when the sister chromosomes are linked
How many rounds of cell division are there (meiosis)
2
What happens in meiosis 1 & how many chromosomes are there
Meiosis 1 separates the homologous pairs. The cell has 46 chromosomes
What happens in meiosis 2 & how many chromosomes are there
Meiosis 2 separates the chromatids. The cells now have 23 chromosomes. (4 daughter cells now have 23 chromosomes)
What does the DNA do when the cell is not dividing
The DNA is unwound & forms chromatin (unwound DNA)
What is recombinant chromosomes
Chromosomes that have exchanged sections of genes resulting in genetic variation.
What are the key points of crossing over
It can occur during Meiosis 1 when the two homologous chromosomes are lined up.
Some genetic info can be swapped from one chromosome to the other.
This breaks up the gene combinations that used to be inherited together.
Gametic variation increases due to new mixes of genes.
What does crossing over occur between and what does this mean
Crossing over occurs between “non sister” chromatids. This means that one chromatid must be on one of the homologous chromosomes and the other chromatid must be on the other chromosomes in the homologous pair.
Chiasma
Chiasma is the point on the chromosome where crossing over takes place
Recombinant Chromatid
Chromatids that have swapped some genes.
What is a summary of crossing over
It is where homologous chromosomes swap some genes.
It creates new combinations of alleles that are not seen in either parent.
Genes closer to the tips of the chromosomes are more likely to undergo crossing over.
What is Independent assortment & segregation and what does it mean
When homologous pairs line up in the middle of the cell, they line up randomly. It means that if you get your mum’s or dad’s chromosome from the homologous pair, it is completely random.
What is independent assortment a source of and what does it mean
Independent assortment is a source of variation as each gamete can have any combination of chromosomes. Meaning each gamete is unique & contains a different set of alleles to other gametes produced. This means every offspring will also be unique.
Genome
The total collection of genes possessed by an organism
What are the advantages of A-sexual reproduction?
Population can increase rapidly, only one parent needed, it is more time and energy efficient and it is faster than sexual reproduction.
What are the disadvantages of A-sexual reproduction?
No genetic variation, species only suited to one habitat and disease may effect the whole population
What are the advantages of sexual reproduction?
It produces genetic variation, the species can adapt to new environments, a disease is less likely to affect the whole population
What are the disadvantages of sexual reproduction?
It takes longer because a mate must be found, then the egg must be fertilised and then the offspring has to develop.
If the 2 alleles are dominant the GENOTYPE is:
HOMOZYGOUS DOMINANT
If the 2 alleles are RECESSIVE the GENOTYPE IS:
HOMOZYGOUS RECESSIVE
If the 2 alleles are different the GENOTYPE is:
HETEROZYGOUS
How do you answer questions in the exam?
-Define (terms)
-Explain
What is natality
The ratio of the number of births to the size of the population; birth rate.