A-Level Biology - 3.7.1 Inheritance
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20 Terms
What is the genotype of an organism?
The genotype is the genetic constitution of an organism
What is the phenotype of an organism?
Physical characteristics of an organism due to the expression of the organisms alleles, and environmental factors
Give the three types of allele expression
dominant
recessive
codominant
What does homozygous mean?
two of the same alleles for a specific gene
What does heterozygous mean?
two different alleles for a specific gene
What is a dominant allele?
In a heterozygous individual, the allele which is expressed and determines the phenotype
What is a recessive allele?
In a heterozygous individual, the allele that will not be expressed in the presence of a dominant allele
What is a codominant allele?
Both alleles are expressed in the phenotype
What is a monohybrid cross?
a cross that involves hybrids for a single trait
only two alleles for a single gene involved
What is a dihybrid cross?
a cross that involves hybrids for two traits
four alleles for two genes involved
What is the phenotypic ratio for a dihybrid cross between heterozygous parents?
9:3:3:1
How many possible genotypes are there for a dihybrid cross between heterozygous parents?
9
What is a sex-linked allele?
An allele that is found on the X chromosome
What is autosomal linkage?
two genes are on the same chromosome
passed to gamete and inherited together
How can autosomal linked genes be separated?
through crossing over ONLY
(not separated by independent assortment as they are on the same chromosome)
What is epistasis?
genes at one locus interact with genes at another locus by masking or suppressing their expression
What is the chi-squared test (χ²) used for?
comparing expected results with observed results
eg comparing the goodness of fit of observed phenotypic ratios with expected ratios
How many degrees of freedom are there in a chi-squared test?
n-1
where n is the number of categories
What is the critical value in a chi-squared test and how is it used?
critical value is at p=0.05
if chi-squared value is *more* than critical value, then p
Why are observed phenotypic ratios obtained in the offspring often not the same as expected?
Small sample size
Fusion of gametes is random
Linked Genes (eg sex linkage)
Epistasis
Lethal genotypes