Chapter 16-Mendel And Monohybrid Crosses Flashcards
Define Genetics
The study of inheritance.
What is genetics? (USE THIS AS AN EXPLAINATION)
Genetics is the study of how we inherit traits and characteristics from our parents.
What characteristics do farmers artificially select for?
Good milk production, high milk solids and good fertility in dairy cattle.
Resistance to disease and high crop yields in plants
Good conformation and fast growth rate in beef animals.
Define variations
Variations are differences that exist among individuals of the same population.
Define artificial selection
Artificial selection is a process where humans breed plants and animals for certain desirable traits.
How is artificial selection mainly carried out?
Artificial selection is mainly carried out by selective breeding.
What does polled mean?
Cattle that have the absence of horns are described as being polled.
Give an example of a naturally polled animal
Aberdeen Angus cattle are naturally polled.
What are the two forms of the gene that controls the polled trait:
One that causes the animal to be polled and
The one that is for the presence of horns
What is it called when genes exist in two different forms
Allele
What is a gene
A gene is located in a chromosome and contains information to produce a protein.
What is an allele
Alternative forms of the same gene, e.g. height in pea plants: Tall (T) and dwarf (t).
When different alleles exist for a gene, one is ___ and the other is ___
When two different forms exist for a gene, one is dominant and the other is recessive
Dominant alleles are ones that appear ___ within a population and recessive alleles only occur ___
Dominant alleles appear regularly within a population and recessive alleles only occur occasionally.
Define dominant
Expressed in the phenotype when present in the genotype, and is usually represented with a capital letter, e.g. T.
Define recessive
Expressed only when an individual has no dominant allele present, and is usually represented with a lower case letter, e.g. t.
Define genotype
The genes that are present in an organism, whether they are expressed or not, e.g. Tt
Define Phenotype
The outward appearance of the organism.
Define Monohybrid Cross
Looks at the inheritance of a characteristic that has two alleles, e.g. the study of the polled characteristic, which has a gene expressed in two different forms, one for the presence of horns and one that causes the animal to be polled.
Define Mendel’s Law of Segregation
This law states that when gametes are formed only one allele from a pair of alleles is carried in the gamete.
Why did Gregor Mendel use pea plants for his inheritance studies?
- Pea plants produce large amounts of seeds
- Peas are easy to grow
- The traits he chose has easily distinguishable alternatives (alleles)
- he concentrated on the inheritance of one characteristic at a time
- He controlled pollination in pea plants, crossing plants with alternative traits by hand.
Define Homozygous
The alleles present in the genotype are the same. e.g. PP (homozygous dominant) or pp (homozygous recessive); true breeding.
Define Heterozygous
The alleles present in the genotype are not the same, e.g. Pp. Heterozygous genotypes are often referred to as hybrids as they have one dominant and one recessive allele.
Define Hybrid Vigour
The increased productivity displayed by offspring from genetically different parents.
Give another name for Hybrid Vigour.
Heterosis
Define Gamete
Sex cell (egg and sperm); Gametes are haploid (n)
Define F1
First-generation offspring.
Define Incomplete Dominance
Neither allele present in the genotype is dominant, which results in a blend of the two alleles in the phenotype, e.g. Shorthorn cattle: red x white = roan
Define Multiple Alleles
When a characteristic is controlled by two or more alleles, e.g. blood groups in humans.
Define Continuous Variation
When a characteristic is controlled by a number of genes interacting with each other to give a range of phenotypes rather than two distinct groups.
How is separation of alleles caused?
Separation of alleles is caused by meiosis during gamete formation.
What is a back cross?
A back cross involved the mating of a hybrid with a pure-breeding recessive animal or plant. It is used to establish if the hybrid is homozygous dominant or heterozygous.
Give two examples of what demonstrates incomplete dominance.
The inheritance of roan coat colour in Shorthorn cattle and pink flowers in snapdragons demonstrates incomplete dominance.
In animals, what characteristics show continuous variation? What are these traits controlled by and what do they produce when interacting with each other?
In animals, characteristics such as milk yield, growth rate and carcase quality show continuous variation.
What dictates the phenotype of an organism?
The genotype and environmental factors dictate the phenotype of the organism.
Define Co-dominant
Both alleles of a gene are equally dominant and both are expressed equally in the phenotype when they occur together in the genotype.
