Lab 1: Genetics and Microevolution

genotype

The genetic composition of alleles at a gene. Notation for lists the alleles by name or letter. For example AA or Aa or A1A2

phenotype

The physical expression of the genetic makeup or genotype. For example, brown hair or black hair.

gene

The portion of a chromosome that carries the genetic information for a character. For example, a gene for flower color or a gene for pea shape.

homologous chromosomes

Chromosomes that have the same genes in the same locations in an individual. You inherited one set of homologous chromosome from your mom and one set from your dad.

locus

The physical place of a gene on the chromosome. Genes on homologous chromosomes are at the same locus.

diploid

Having two sets of homologous chromosomes. Humans are diploid.

haploid

Having a single set of chromosomes.

How many pairs of homologous chromosomes does a triploid individual have?

Tri means 3, so the individual has 3 sets of chromosomes. "Ploid" refers to sets of chromosomes.

allele

A form of a gene. For example, the gene for pea color has two alleles, yellow and green.

genotype

The genetic notation for the alleles at a gene. For example, AA or Aa,

heterozygote

Has two different alleles at a gene. For example Aa

homozygote

An individual that has two identical alleles at a gene. For example, AA and aa

dominant

The allele that is expressed in the heterozygote.

recessive

The allele that is not expressed in the heterozygote.

cross

A mating of two individuals usually written by genotypes. For example: AA x aa

true breeding

The offspring show the same phenotype through all generations. In order for this to happen the genotype must be homozygous.

carrier

An individual that has an allele for the trait, but the trait is not observed in the individual. The can carry it to the next generation without be affected themselves.

P generation

Parental generation; the parents in a cross.

F1 generation

First filial generation; the first generation of offspring in a cross.

F2 generation

Second filial generation; the second generation of offspring in a cross.

monohybrid cross

A cross of a single gene. For example AA x Ah

Gregor Mendel

The father of modern genetics. He identified patterns in the way phenotypes are inherited through monohybrid and dihybrid crosses.

Punnett square

A square diagram used to predict the genotype frequencies of offspring in a cross from the genotypes of the haploid gametes of both parents. It predicts the probabilities of all possible outcomes.

frequency

A proportion of the whole. Calculated by dividing the part by the whole.

allele frequency

The proportion on an allele in a population. Calculate by dividing the number of that allele divided by the total number of alleles in a population (two alleles per individual). Measure the genetic variation in a population.

genotype frequency

The proportion of genotypes in a population. Calculate by dividing the number of identical genotypes by the total number of genotypes (number of individuals). Show how variation is distributed among members of the population.

hypothesis

The best guess that is testable. The starting point for an investigation.

law

The result of testing a hypothesis many times and always getting the same result. Examples are the Mendel's laws of inheritance or Newton's law of gravity.

theory

An explanation of a pattern that has been so thoroughly tested that scientists agree on it and consider it to be true and correct. Theories explain the presence of laws.

theory of evolution

A scientific theory that has been so thoroughly tested that scientists agree on it and consider it true and correct. It explains the diversity in life we see around us.

microevolution

Change of allele frequencies within and among populations; evolutionary changes below the species level.

population

A group of interbreeding organisms.

gene pool

All of the genetic information of a population; all of the genes, genotypes and alleles in a population.

What is the smallest biological unit that evolves?

The population evolves. Individuals do not evolve, although individuals may acclimate.

How many alleles does every diploid individual have for one gene?

Two. The alleles may be the same (homozygous) or different (heterozygous).

How many chromosomes do humans have in each somatic cell?

46

How many pairs of homologous chromosomes do humans have in each somatic cell?

23

How many chromosomes do humans have in each sex cell (gametes)?

23

If a diploid fruit fly has 8 chromosomes, how many homologous pairs does it have?

4

If a puffer fish has 22 homologous pairs of chromosomes, how many chromosomes does it have in all

44

somatic cell

Any cell except sperm and egg. Somatic cells are diploid in humans.

sex cell

Cells that are gametes, the sperm and the egg. Sex cells are haploid.

mutation

A change in the genetic makeup. Mutation creates new alleles in a population.

natural selection

A change in allele frequencies in a population due to some alleles having an advantage in a specific environment. Alleles that have an advantage will increase in frequency, those that are disadvantageous will decrease in frequency.

drift

Change of allele frequencies due to random events. The chance appearance or disappearance of alleles.

non-random mating

Occurs when mates specifically choose each other, or avoid each other, rather than mating with each other randomly.

gene flow

The movement of alleles into or out of a population typically due to migration.

What evolutionary forces can change the allele frequencies of a population?

mutation, natural selection, drift, non-random mating, gene flow

immigration

Individuals arriving into a population; the movement of new individuals into a population.

emigration

Individuals leaving a population; the movement of individuals out of a population

sexual selection

A kind of natural selection when mates specifically choose or avoid one another. For example, female peacocks may chose males with the largest colorful tail feathers.

Which two forces in evolution are based on highly random events?

Mutation, drift are random events.

Which two forces in evolution are NOT based on highly random events?

Natural selection, non-random mating are non-random events.

Charles Darwin

Described natural selection in great detail in his book "On the Origin of Species" in 1859.

Is evolution considered a hypothesis, a law, or a theory?

Evolution is a scientific theory, it that has been so thoroughly tested that scientists agree on it and consider it true and correct. It explains the diversity in life we see around us.

Red color is true breeding in a population of peas. Does this line have alleles for white peas?

No, true breeding means that the trait will stay the same and the genotype is homozygous.

Punnett squares can accurately predict the phenotypes that will occur.

No, Punnett squares predict the probability that a phenotype will occur.

Populations can gain new alleles from immigration.

Correct. Immigrants are individuals moving into a population and if they have new alleles they add them to the gene pool of the population.

Hitchhiker's thumb is recessive. Will it be expressed in the heterozygote?

No, recessive traits are not expressed in the heterozygote.

Brown coat is dominant in prairie dogs. Will brown coat be expressed in the heterozygote?

Yes, the dominant trait is expressed in the heterozygote.

adaptation

A phenotype that has a positive effect on the survival or reproduction of an individual.

dihybrid

Genetic notation where there are two different alleles at two genes (AaDd). "Di" refers to two genes (A and D genes), hybrid means the alleles are heterozygous at both genes (Aa and Dd).

dihybrid cross

A mating where the alleles for two genes are considered and both are heterozygous. For example AaDd x AaDd

Mendel's first law of segregation

In a single gene, each allele in a pair are inherited independently. For example in the character of pea color, the alleles for yellow peas are independent of green peas. This happens because the alleles in a pair segregate into different gametes during gamete formation.

Mendel's second law of independent assortment

The two alleles from one gene separate independently from the two alleles of a second gene. For example, the character of pea shape is inherited independently of pea color.