genetics 7a Flashcards
What is a gene?
A sequence of DNA bases that codes for a polypeptide or functional RNA.
Where are genes located?
On chromosomes in the nucleus of eukaryotic cells.
What is a chromosome?
A long molecule of DNA wrapped around histone proteins, carrying genetic information.
What is a locus?
The fixed position of a gene on a chromosome.
What is an allele?
A different version of a gene, with a slightly different base sequence.
What is a genotype?
The genetic makeup (combination of alleles) of an organism.
What is a phenotype?
The observable characteristics of an organism, resulting from its genotype and the environment.
What does it mean if an allele is dominant?
Only one copy is needed to express the trait in the phenotype.
What does it mean if an allele is recessive?
Two copies are needed for the trait to be expressed.
What are codominant alleles?
Both alleles are expressed in the phenotype; neither is dominant over the other.
What is homozygous?
An organism with two identical alleles for a gene.
What is heterozygous?
An organism with two different alleles for a gene.
What is a carrier?
An individual who carries one recessive allele for a disorder but does not express the disorder.
What is monohybrid inheritance?
The inheritance of a single gene.
What tool is used to show possible genotypes and phenotypes of offspring?
A Punnett square or genetic diagram.
Can genes have more than two alleles?
Yes — this is called multiple alleles, although only two can be present in an individual at once.
What is an example of codominance and multiple alleles?
ABO blood group system: IA and IB are codominant, IO is recessive.
What is dihybrid inheritance?
The inheritance of two different genes at the same time.
What is the expected phenotypic ratio for a dihybrid cross of two heterozygotes (AaBb x AaBb)?
9:3:3:1
What chromosomes determine sex in humans?
Females: XX, Males: XY
Why are sex-linked traits more common in males?
Males have only one X chromosome, so recessive alleles on the X are always expressed.
What is sex linkage?
When a gene is located on a sex chromosome, usually the X chromosome.
Give an example of a sex-linked disorder.
Haemophilia – caused by a recessive allele on the X chromosome.
What are autosomes?
Chromosomes that are not sex chromosomes.
What is autosomal linkage?
When two genes are located on the same autosome and tend to be inherited together.
How can crossing over affect autosomal linkage?
It can separate linked genes, leading to recombination.
What is epistasis?
When the allele of one gene affects or masks the expression of another gene.
Give an example of epistasis.
A gene causing baldness masks the gene for widow’s peak — baldness is epistatic.
What is the phenotypic ratio for recessive epistasis?
9:3:4
What is the phenotypic ratio for dominant epistasis?
12:3:1
