midterm 1 - genetics Flashcards
What organism did Gregor Mendel use for his experiments and why? (3 reasons)
A garden pea plant, because mating could be controlled, the generation time is short and they have easily observable characters.
By Mendel’s definitions, what is a character?
A character is a detectable, inheritable feature.
By Mendel’s definitions, what is a trait?
A trait is a variant of a character.
What is a true breeding organism?
A true breeding organism is an organism that always passes on the same traits; both copies of a gene give rise to the same trait when self fertilized.
What is an allele?
An allele is a variant of a gene.
What is a locus?
A locus is a specific location on a chromosome (genes are at specific loci). Different alleles are DNA variations at a specific genes locus.
Describe the relationship between dominant alleles and recessive alleles.
Dominant alleles mask recessive alleles. When both alleles are inherited by an organism, it is the dominant gene that will be expressed.
Do homologous chromosomes have the same gene loci?
Yes, homologous chromosomes have the same gene loci.
Do homologous chromosomes have the same alleles?
No. Homologous chromosomes do have the same genes at the same loci but not necessarily the same variants of those genes.
The monohybrid cross is used to track the inheritance of how many characters?
A monohybrid cross is used to track the inheritance of a single character.
What is a phenotype?
A phenotype is the observable traits of an organism.
What is a genotype?
A genotype describes the specific genes of an organism.
What is a homozygous genotype? What’s the difference between a homozygous dominant and homozygous recessive genotype?
A homozygous genotype means the alleles are the same. If both are dominant alleles, the organism is said to have a homozygous dominant genotype. If both alleles are recessive, the organism is said to have a homozygous recessive genotype.
What is a heterozygous genotype?
A heterozygous genotype means that the two alleles are different. In this case, the dominant allele would be expressed and the organism would have a dominant phenotype.
What is Mendel’s Law of Independent Assortment?
Characters are independently sorted from each other, they are inherited separately. Both paternal and maternal genes do not necessarily stay together. In other words, genes that were inherited together do not have to be passed on together.
What is the purpose of a dihybrid cross?
To track the inheritance of 2 characters.
What is Mendel’s Law of Segregation?
That allele pairs separate during gamete formation and unite randomly upon fertilization.
Define incomplete dominance. (3)
When a heterozygous has an INTERMEDIATE phenotype. In this case, both alleles can be represented by capital letters. Each genotype results in a different phenotype.
Define codominance. (3)
Heterozygotes fully express both alleles. Both alleles can be represented by capital letters (ex. blood type).
Which blood type is the universal recipient?
AB
Which blood type is the universal donor?
O
Describe multiple alleles.
This is when one gene has more than two possible alleles (more than 2 variants). Blood types have 3 alleles, but an individual can only carry 2 alleles for a gene.
Describe Epistasis.
Epistasis is when a gene at one locus alters the PHENOTYPIC EXPRESSION of a gene at another locus.
Describe pleiotropy.
Pleiotropy is when a single gene has multiple phenotypic effects.
Describe polygenic inheritance. (2)
Polygenic inheritance is when a single trait depends on more than one gene. Additive effect of two or more genes leads to a single phenotypic character (skin colour, height).
Explain x-inactivation. (2)
Females only have one active X chromosome. The inactive chromosomes condense into a dense object called the BARR BODY.
Why are calico cats always female?
Calico cats are female because females only have one active X chromosome in their cells. If both chromosomes carry different alleles, then the colour of the fur will depend on which chromosome is inactivated on that specific part of the cats body.
