Inheritance and Populations

Define the term genotype

all of the alleles that an organism carries on its chromosomes

Define the term phenotype

observable characteristics of an organism which the result of the genotype as well as environmental factors

Define the term gene

Section of DNA that codes for a particular protein

Define the term allele

Variant of a gene

What is a dominant allele

Always expressed in the phenotype when in the genotype

What is a recessive allele

Only shown in the phenotype when homozygous

Define the term homozygous

Two of the same alleles (AA or aa)

Define the term heterozygous

Two different alleles (Aa)

Define the term sex linkage

Gene located on X/Y/sex chromosomes

Define the term codominant

Both alleles are expressed/shown in phenotype

What are the 4 main sources of genetic variation and what are their consequences

• Independent segregation - results in different combinations of chromosomes and different allele combinations in each gamete. Causes genetic variation between gametes produced by an individual

• Crossing over - results in new combinations of alleles on chromosomes. Causes genetic variation between gametes produced by an individual

• Random fusion of gametes - results in genetic variation between zygotes

• Mutation - changes to DNA base sequences resulting in the generation of a new allele. Causes genetic variation between individuals within a species population

Define monohybrid inheritance

Monohybrid inheritance is when a phenotype or trait is controlled by a single gene.

Why are males more likely to express a recessive sex-linked allele

Most sex-linked alleles are located on the X chromosome. Therefore males will only get one copy of the allele so will express the characteristic even if it is recessive. Since females get two X chromosomes, this is less likely as two recessive alleles required

Define dihybrid inheritance

The inheritance of two different genes, that determine two phenotypes, on two different chromosomes.

What does pure breeding mean in terms of alleles

Homozygous pair of alleles

Using a pedigree chart, how can you prove an allele is sex-linked

If the only individuals expressing the allele are male

Using a pedigree chart, how can you prove an allele is recessive and not sex-linked

A father, who does not suffer from the disease has a daughter who does

What does a 9:3:3:1 ratio for offspring phenotype ratio suggest (dihybrid inheritance)

Both parents were heterozygous for both genes

Define population

All of the organisms of one species in an ecosystem

Define gene pool

All alleles of all the genes of all individual in a population at a given time

Define allele frequency

Number of times an allele occurs within the gene pool

What are the two Hardy-Weinburg equations and what does each letter reprensent

p + q = 1

p² + q² + 2pq = 1

p - frequency of dominant allele

q - frequency of recessive allele

p² - frequency of the genotype homozygous dominant

q² - frequency of the genotype homozygous recessive

2pq - frequency of the genotype heterozygous

Define autosomal linkage

two or more genes are on the same autosomal chromosome (not sex chromosomes)

Define epistasis

Gene interaction when allele of one gene affects or masks the expression of another in the phenotype