CHC Chapter 3 Study Guide
1. Describe the difference between dominant
and recessive alleles. When do you see
dominant and recessive traits in the offspring
(during which generation)?
Dominant alleles are always expressed whether
there is one or two present in the DNA.
Recessive alleles are only expressed if there are
two of them.
1. Describe the difference between dominant
and recessive alleles. When do you see
dominant and recessive traits in the offspring
(during which generation)?
Dominant trait is the trait observed in the first
generation when parents that have different
traits are bred. Appears in both generations.
Recessive trait is the trait that reappears in the
second generation after disappearing in the first
generation when parents with different traits are
bred.
2. Name and describe the three exceptions to
Mendel’s rules of heredity.
Incomplete dominance – each allele has some
influence on a trait (eg: red flower crossed with
white flower produces pink flowers)
One gene, many traits – one gene influences
more than one trait
Many genes, one trait – several genes work
together to control one trait
3. How are sex cells different from other
human body cells? Name the male and female
sex cells.
Sex cells carry ½ the number of chromosomes
as body cells
Egg - Female sex cell
Sperm - Male sex cell
4. What are homologous chromosomes?
Homologous chromosomes are a pair of
chromosomes that carry the same sets of
genes
5. Why do sex linked disorders occur more
often in males?
Y chromosome does not carry all of the genes
of the X chromosome
Females have a backup gene if one is
damaged, males do not
6. Describe the difference between genotype
and phenotype.
Genotype – inherited alleles for an organism Actual genes inherited by an organism
Phenotype – organism’s appearance - physical
appearance
7. What happens when a true-breeding plant
self pollinates?
When a true-breeding plant self-pollinates, all
of its offspring will have the same trait as the
parent
8. How do the results of mitosis and meiosis
differ?
Mitosis results in two body cells which are
genetically identical to the parent cell.
Meiosis results in four sex cells which contain
half of the chromosomes of the original cell.
Define the following words.
• probability- mathematical chance that
something will happen
• selective breeding- Organisms with
desirable characteristics are mated
• pedigree- tool for tracing a trait through
generations of a family
Define the following words.
• homozygous- organism with two dominant
or two recessive alleles
• heterozygous- organism with one
dominant & one recessive allele
• Punnett Square - shows the possible
combinations of offspring from particular
parents