BIO 181- Chapter 12: Mendel's Experiments & Heredity
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50 Terms
What is a character?
A distinct heritable feature, such as flower color
What is a trait?
A specific variation of a character, such as purple or white flowers
What is a true-breeding organism?
One that produces the same trait when self-fertilized
What is hybridization?
Mating two contrasting true-breeding varieties
What is the P generation?
The parental generation in a genetic cross
What is the F1 generation?
The hyrbrid offspring of the P generation
What is the F2 generation?
Offspring produced when F1 individuals reproduce
What happened when Mendel crossed true-breeding purple and white flowers?
All F1 offspring were purple
What ration did Mendel observe in the F2 generation for flower color?
About 3 purple: 1 white
What is a dominant trait?
A trait expressed when at least one dominant allele is present
What is a recessive trait?
A trait masked when a dominant allele is present
What did Mendel call what we now call a gene?
A heritable factor
What is an allele?
An alternative version of a gene
What is a locus?
The specific location of a gene on a chromosome
How many alleles does a diploid organism usually inherit for each gene?
Two, one from each parents
What happens when two different alleles occur at one locus?
The dominant allele usually determines the phenotype in a complete dominance
What is the law of segregation?
Two alleles separate during gamete formation
Where do the separated alleles end up during segregation?
In different gametes
What biological process explains Mendel’s law of segregation?
Separation of homologous chromosomes during meiosis
What is a Punnett square?
A diagram used to predict outcomes of a genetic cross
What does a capital letter represent in a Punnett square?
A dominant allele
What does a lowercase letter represent in a Punnett square?
A recessive allele
What does homozygous mean?
Having two identical alleles for a gene
Give an example of a homozygous dominant genotype.
PP
Give an example of a homozygous recessive genotype.
pp
What does heterzygous mean?
Having two different alleles for a gene
Give an example of a heterozygous genotype.
Pp
What is a genotype?
An organisms genetic makeup
What is a phenotype?
An organisms observable trait or appearance
Why can phenotype fail to reveal genotype?
Dominant alleles can mask recessive alleles
What is a monohybrid?
An individual heterozygous for one character
What is a monohybrid cross?
A cross involving one character, often PpxPp
What is a dihybrid?
An individual heterozygous for two characters
What is a dihybrid cross?
A cross that follows inheritance of two characters
What is the law of independent assortment?
Allele pairs for different genes assort independently during gamete formation
What meiotic event produces independent assortment?
Random alignment of homologous pairs in metaphase 1
When does independent assortment apply most clearly?
To genes on different chromosomes or far apart on the same chromosome
Why may nearby genes on the same chromosome not assort independently?
They are linked and tend to be inherited together
What is complete dominance?
The heterozygote has the same phenotype as the dominant homozygote
What is incomplete dominance?
The heterozygote has an intermediate phenotype
What is co-dominance?
Both alleles are fully and distinctly expressed
What are multiple alleles?
When a gene has more than two possible alleles in a population
What is a pleiotropy?
One gene influences multiple phenotypic traits
What is epistasis?
One gene alters or masks the phenotypic expression of another gene
What is a test cross used for?
Determining the genotype of an individual with a dominant phenotype
Who is the unknown individual crossed with in a test cross?
A homozygous recessive individual
If a test cross produces recessive offspring, what is the unknown parent’s genotype?
Heterozygous
If a test cross produces only dominant offspring, what genotype is likely?
Homozygous dominant
When are recessive inherited disorders usually expressed?
When an individual is homozygous for the recessive allele
What is a carrier of a recessive disorder?
A heterozygous person who carries the allele but usually has a normal phenotype