The origins of genetic variation Flashcards
Genotype
All the genes and alleles an organism has
Phenotype
Alleles that are expressed as a characteristic
Allele
A version of the same gene
Locus
Position of a gene
Homozygous
2 is the same alleles
Heterozygous
2 different alleles
Dominant
Alleles that are expressed
Recessive
Only expressed with 2 alleles present and without dominant present
Co dominant
2 equally dominant alleles
Multiple alleles
More than 2 alleles for the same trait
Gene
A sequence of bases on a DNA molecule coding for a sequence of amino acids on a polypeptide chain
Monohybrid inheritance
Study of the inheritance of one characteristic
Monohybrid inheritance: phenotypic ratio of F2 generation
3:1 dominant: recessive
Monohybrid with codominant alleles phenotypic ratio
1:2:1 with the 2 being both traits expressed
Law of segregation
Characteristics of a diploid organism are determined by pairs of alleles only one of which is transferred to a gamete
What is a test cross used for
Used to determine whether an organism showing the dominant characteristic is homozygous or heterozygous
How to perform a test cross
Cross with a homozygous recessive. If offspring show the recessive trait the parent must be heterozygous
Cystic fibrosis
Recessive allele of a gene on chromosome 7. Normally codes for membrane protein production- CF thick mucus is produced in lungs and pancreas
Huntington’s disease- why does this dominant allele survive in the population?
Delayed penetrance- symptoms don’t start until later in lire when person has most likely reproduced and passed on allele already
Male and female heterosomes
Female- XX male- XY
Genes located on heterosomes are
Sex linked
Y linked diseases
Rare as there is little room on the chromosome
Can males be carriers of X linked disease?
No but they can have the condition
Why is X linkage more common?
X chromosome is larger
Part of it doesn’t have a homologous section of the Y chromosome so only one allele of a gene is present- it is always expressed
Dihybrid inheritance
2 characteristics that are controlled by different genes at different loci
Dihybrid F2 generation phenotypic ratio
9:3:3:1
Genes and the environment
Genotype and environment result in phenotype
Polygenic inheritance
Phenotype trait controlled by more than one gene
Linkage
Genes that are closely located on the same chromosome tend to be inherited together unless crossing over separates them
In crosses where linkage is happening a large proportion of the offspring are..
Of the parental genotype
Could expect a 3:1 ratio if genes are linked in dihybrid because they are inherited as one
Types of selection
Distriptive
Stabilising
Directional
What is a gene pool
Total information from all the genes and alleles of the breeding individuals in a population at a particular time
What is happening if there is a constant change in allele frequency in a population
The population is evolving because the proportion of organisms in the population carrying a particular allele
Allele frequency
Number of different alleles for the same trait
Genetic drift
Random changes in allele frequency
Effect of genetic drift in a large population
Little effect and allele frequency remains stable
Effect of genetic drift on a small population
Large impact
Population bottlenecks
Occurs when a genetically diverse population is drastically reduced by a non selective event eg volcano
Total genetic diversity of survivors likely to be much lower- this will be maintained even as population re establishes
The founder effect
When a new population is founded from a subset of the original population eg migration of an island
What does the hardy Weinberg assume
The population is large
Has random mating
Is experiencing no selection
Has no mutation emigration or immigration
What are the equations for hardy Weinberg
p+q = 1 p2+2pq+q2= 1
