Genetics Flashcards
What does homozygous mean?
Homozygous refers to an organism that has two copies of the same allele, one from each parent.
What does heterozygous mean?
Heterozygous refers to an organism that has inherited different alleles from each parent.
What is a dominant allele?
A dominant allele is always expressed in the phenotype, even if only one copy is present. It is usually represented by a capital letter.
What is a recessive allele?
A recessive allele is only expressed if both alleles are recessive. It is usually represented by a lowercase letter.
What is co-dominance?
Co-dominance occurs when both alleles are expressed in the phenotype, often leading to a blend or a characteristic showing both alleles.
What is a monohybrid cross?
A monohybrid cross studies the inheritance of a single characteristic using a Punnett square.
What is an example of a monohybrid cross?
A cross between a tall plant (TT) and a short plant (tt) produces offspring with a genotype of Tt and a phenotype of 100% tall.
What is a dihybrid cross?
A dihybrid cross examines the inheritance of two different characteristics at the same time, assuming genes are on different chromosomes.
What is the typical phenotypic ratio for a dihybrid cross?
The phenotypic ratio is typically 9:3:3:1 (e.g., round yellow, round green, wrinkled yellow, wrinkled green).
What happens in co-dominance inheritance?
Both alleles are expressed equally in the phenotype, for example, in pink flowers resulting from red (C^R) and white (C^W) alleles.
What are sex-linked genes?
Sex-linked genes are located on the sex chromosomes (X or Y), and males are more often affected because they only have one X chromosome.
Why are men more likely to be affected by sex-linked disorders?
Men have only one X chromosome, so any recessive allele on the X chromosome will be expressed.
What is autosomal linkage?
Autosomal linkage occurs when two or more genes are located on the same autosome (non-sex chromosome) and are inherited together.
Why do linked genes not assort independently?
Linked genes stay together during meiosis unless crossing over separates them, so they pass into gametes together.
What is epistasis?
Epistasis occurs when the allele of one gene affects or masks the expression of another gene in the phenotype.
Give an example of epistasis.
For example, one gene produces an intermediate molecule, and another gene converts it into a pigment. If the first gene is non-functional, no pigment is produced.
What is the Hardy-Weinberg equation for allele frequency?
The equation for allele frequency is p + q = 1, where p and q are the frequencies of dominant and recessive alleles.
What is the Hardy-Weinberg equation for genotype frequency?
The equation for genotype frequency is p² + 2pq + q² = 1, where p² is the homozygous dominant, 2pq is heterozygous, and q² is homozygous recessive.
What assumptions does the Hardy-Weinberg principle make?
The Hardy-Weinberg principle assumes a large population, no mutations, random mating, no migration, and no natural selection.
