This lesson introduces how genes and chromosomes contribute to inherited characteristics. It also explains how an organism’s genetic makeup differs from the traits we can observe.
Physical characteristics are influenced by genes, which are carried on chromosomes. In a diploid organism, chromosomes occur in pairs called homologous chromosomes. The two chromosomes in a homologous pair have the same genes arranged in the same order, although the versions of those genes may differ.
All flashcards
What does a monohybrid cross examine?
The inheritance of one characteristic.
How does incomplete dominance affect a heterozygote’s phenotype?
It produces a phenotype intermediate between those of the two homozygotes.
What happens to alleles in a codominant heterozygote?
Both alleles are expressed rather than blending into an intermediate phenotype.
What does hemizygous mean for an X-linked gene in an XY individual?
The individual has one allele for the gene, with no corresponding allele on the Y chromosome.
What is a recessive lethal allele?
An allele that causes death when an individual has two copies.
Quiz questions
How does a test cross help identify the genotype of an organism with a dominant phenotype?Answer: It crosses the organism with a homozygous recessive partner and examines the offspring.
How does a codominant heterozygote differ from an incompletely dominant heterozygote?Answer: In codominance, both alleles are expressed; in incomplete dominance, the phenotype is intermediate.
For an X-linked gene absent from the Y chromosome, which parent supplies a son’s X chromosome?Answer: His mother supplies his X chromosome.
Why can a dominant lethal allele with effects beginning after reproductive age be inherited?Answer: Carriers may reproduce and transmit the allele before its lethal effects appear.
What do Punnett-square proportions represent for a cross?Answer: Expected probabilities for offspring, not guaranteed outcomes in a small group.
Based on Biology 2e by Mary Ann Clark, Matthew Douglas, Jung Choi (OpenStax), licensed CC BY 4.0. Adapted into a summary, flashcards and quizzes.