Heterozygous: an individual inherits two different forms of the same gene
Homozygous: an individual inherits the same allele from both parents; genes are the
Dominant allele: where the phenotype is always present.
Recessive allele: can be masked but is still present
Difference between an organism’s genotype and its phenotype?
Genotype: the organism’s actual genes that you cannot completely see.
Phenotype: the physical appearance of organisms.
Single gene trait: a single gene with two alleles and each one produces a distinct
Mendel’s contribution to genetics:
-Law of segregation and law of independent assortment
Segregation: two factors/ traits from each parent separate and go to the offspring so
the offspring will carry both genes.
Law of independent assortment: Laws of chance decide which traits the offspring
Dihybrid crossing. How the law of independent assortment relates to dihybrid
-Green pod colour and yellow seed colour (dominant)
-Yellow pod colour and green seed colour (recessive)
-Offspring was heterozygous (GgYy) (green pod and yellow seed)
Chromosome theory of inheritance: explains that chromosomes carry genetic
material. Inheritance patterns may be explained by assuming that genes are located
on specific sites of the chromosomes. (e.g. Blonde hair and blue eyes usually go
together because hair and eye colour are located on the chromosome closely
Why linked genes cannot assort independently: Linked genes are on the same
chromosome so they are physically attached and cannot separate
Inheritance patters in recessive and dominant traits? – If it skips a generation; it is
recessive. If the child has the dominant trait one of the parents must also have it.
Examples of human disorders (dominant):
-Huntington Disease Examples of human disorders (recessive):
Incomplete dominance: when one allele of the same gene isn’t completely dominant
over the other (Red flower and White flower produce pink flower)
Multiple allele: there are three or more alleles for a trait. (Blood type A, B, and O)
Co-dominance: When a single gene has two dominant alleles. (Blood type AB)
Pleiotropic: one gene influencing many traits (e.g. Genes that control cats fur can
influence their brain and eye colour.)
Polygenic: many genes affecting one trait. (e.g. Skin colour. BBBBBB= very dark skin,
bbbbbb= very light skin. All other combinations are intermediates.
Sex-linked inheritance: XX= female child XY= male child.
Genes that are carried by either sex are called sex-linked inheritance.
Sex-linked diseases: diseases determined by a chromosome.
-Hemophilia: an X chromosome disease; usually affecting males.
-Chromosomal abnormalities: Any change in normal structure of chromosome;
resulting in physical or mental abnormalities.
-Turner’s Syndrome: Chromosomal disorder affecting females who have only one X
chromosome; dwarfism, heart problems, underdeveloped sex organs.
How can sickle-cell be adaptive?: It can protect against malaria.
Darwin’s Observation about natural selection:
-All species have great fertility potential
-Populations remain stable in size
-Environmental resources are limited
-Individuals of a population vary in inheritance.
-Much variation is inheritable
Why individuals cannot evolve: They cannot change their own genetics. Populations
can evolve. Not humans.
Why evolution doesn’t lead to perfectly adapted organisms---mutations and changes
happen all the time. Not all of the less adapted organisms result in killing another. How evolutionary change takes place?
Difference between natural selection and evolution?
Evolution: A change into something different or better
Natural selection: Where individuals do not survive or reproduce and do not pass on
Examples of natural selection:
-Some giraffes have long necks and some have short necks. If short tree shrub