Inheritance And Evolution Flashcards
Define variation
Differences in characteristics among organisms of the same natural population or species
What is continuous variation and its characteristics?
Type of variation in which individuals show a complete gradation from one extreme to the other without any break.
- Has intermediates
- Caused by both environmental conditions and genetic factors
- They are quantitative and can be measured eg height, weight
- They are polygenic (controlled by many genes)
- Gives a normal distribution curve with many organisms lying in the normal
What is discontinuous variation and its characteristics?
Type of variation in which individuals show clear-cut differences with no intermediates between them
- Has no intermediates
- Caused by genetic factors
- They are qualitative and cannot be measured
- They are controlled by a single gene
Give examples of continuous and discontinuous variation
Continuous;
- Skin color
- Height
- Intelligence
- Weight
- Length
Discontinuous;
- Blood types in humans
- Wing lengths in drosophila
- Sex in humans
What is a gene?
A basic unit of inheritance for a given characteristic
What is a phenotype?
The outward appearance of an organism
What is a genotype?
The genetic constitution of an organism with respect to the alleles
What is an allele?
One of a number of alternative forms of the same gene responsible for determining contrasting characteristics
Distinguish between homozygous and heterozygous
Homozygous is a diploid condition in which alleles at a given locus are identical while heterozygous is a diploid condition in which alleles at a given locus are different
What is the dominant allele?
An allele, which influences the appearance of the phenotype, even in the presence of an alternative allele
What is the recessive allele?
An allele, which influences the appearance of the phenotype only in the presence of another identical allele.
Give examples of characteristics that follow monohybrid inheritance
- Height in plants
- Horned and hornless condition in cattle
- Albinism
- Seed shapes
- Seed color
What are characteristics of albinos?
- Pink eyes
- White hair
- Photophobia
What risks associated with albinism?
-Skin cancer
-Sun burns
-Blindness
What is dihybrid inheritance?
Inheritance of two pairs of contrasting characteristics
State examples of the deviations from Mendelian laws
- Linkage (linked genes)
- Multiple alleles
- Incomplete dominance
- Co-dominance
- Lethal genes
- Epistasis
- Gene complex
- Pleiotropy
- Polygenes
Define linked genes
Any two genes carried on the same chromosome
What is linkage?
Linkage is a phenomenon in which genes carried on the same chromosome, fail to separate during meiosis, and are therefore inherited together as inseparable units
True or false;
Chances of crossing over increase with increasing distance of the two gene loci
True
What are recombinants?
These are new gene combinations among offspring, different from the parental genotype.
Define crossover value
This is the percentage of offspring that show recombination
What is epistasis?
This is a condition in which one gene suppresses the effect of another gene located on different loci
What name is given to the gene that suppresses the other in epistasis?
Epistatic /inhibiting gene
What name is given to the gene that is suppressed in epistasis?
The hypostatic gene
What is incomplete dominance?
This is a phenomenon, where equal expression leads to formation of a completely new phenotype.
Define co-dominance
In this case, both alleles fail to show complete dominance or recessiveness, but instead are equally expressed in the phenotype
What antigens are found on the cell surface membrane of red blood cells of blood group, A, B, AB and O respectively?
Blood group A- antigen A
Blood group B- antigen B
Blood group AB- antigen AB
Blood group O- no antigens
Which antibodies are found in each of the blood groups?
Blood group A- antibody b
Blood group B- antibody a
Blood group AB- no antibodies
Blood group O- antibody a and b
What are sex linked characteristics?
These are characteristics that are determined by genes, carried on sex chromosomes, and only limited to a given sex
Defined the term twins and explain the two types of twins
Twins are two babies born from one mother as a result of the same pregnancy
Identical twins are two babies from one egg and one sperm cell
Fraternal twins are two babies from two eggs and two sperm cells
What are sex limited characteristics?
These are characteristics that are determined by genes carried on autosomal chromosomes, not affected by sex
What is hemophilia?
This is a condition in which the blood of an affected person takes too long to clot, or has a reduced ability to clot due to lack of one of the clotting factors
What are lethal genes?
These are genes that cause lethal effects, or death of organisms, possessing such genes
Define mutation
A mutation is a change in the amount, arrangement or structure of the DNA of an organism
Explain the two types of mutation
- Chromosomal mutation (aberration)
- Change in the amount or arrangement of DNA - Gene mutation (point mutation)
- Change in structure of DNA at a single locus
What are the causes of mutation?
- High energy electromagnetic radiation
- Mutagenic high energy particles
- Chemical substances
- Drugs
- Food preservatives
- Pesticides
What are the two types of chromosomal mutations?
- Aneuploidy
- Polyploidy/ Euploidy
Define aneuploidy
This is a condition in which half the daughter cells produced have an extra chromosome while the other half have a chromosome missing
Define euploidy/ polyploidy
This is the condition in which the cells of an organism possess extra sets of chromosomes beyond the normal diploid number
What is non-disjunction?
This is the failure of a pair or pairs of homologous chromosomes to separate during anaphase one of meiosis
What is aneuploidy?
This is a condition in which half of the gametes formed during meiosis contain extra number of chromosomes while, the other half have a chromosomes missing
What is a polygenic trait?
This is a trait in which the phenotype is controlled by more than one gene.
What is pleiotropy?
This is a phenomenon in which a single gene influences (affects) two or more distinct phenotypic traits.
Or; Expression of multiple traits by a single gene
Give an example of a pleiotropic trait
-Sickle cell anemia
-Albinism
Give examples of a polygenic trait
- Human height
- Human hair color
- Human skin color
What is genetic drift?
Loss of genes from a small population or the change of gene frequency of a small population by chance alone and not natural selection which results into the change of the gene frequency of the small population.
What is gene frequency?
How common an allele is in a population
What is a gene pool?
Total variety of genes and alleles present in a sexually reproducing population.
What are the causes of variation in man?
- Independent assortment
- Crossing over
- Random fertilization
- Mutation
- Genetic drift
- Cross breeding
What is evolution?
This is a gradual process by which new species are formed from pre-existing less differentiated species over a period of time due to changes in the prevailing environmental conditions.
Or;
The change, over a long time, in the genetic composition of a population which leads to the emergence of new species.
Define natural selection
A process by which organisms that are better adapted to their environment survive while those that are less adapted are eliminated.
State Mendel’s laws of genetic inheritance
The law of segregation: The characteristics of a diploid organism are controlled by alleles that occur in pairs and of each pair of such alleles, only one can be carried in a single gamete.
The law of independent assortment: Each of a pair of contrasted characteristics may be combined with either of another pair
What is sickle cell trait?
A condition where an individual has 30-40% normal red blood cells, the rest being normal as the disease is in the heterozygous state.
In short sickle cell trait = homozygous state of the sickle cell allele
What is autopolyploidy?
The type of polyploidy whereby the increase in sets of chromosomes occurs within the same species.
The actual number of chromosomes in an autopolyploid is always an exact multiple of the haploid number
(Autopolyploidy happens when a plant or organism doubles its own chromosomes, making extra copies from the same species.)
What chemical can be used to induce autopolyploidy?
Colchicine
Inhibits spindle formation and prevents chromosomes separating during anaphase
What is allopolyploidy?
The form of polyploidy in which organism has a chromosome number which is a multiple of the original haploid number thus it is fertile
(Allopolyploidy happens when two different species combine their chromosomes to create a new plant or organism with mixed traits from both.)
