3.7 Genetics, populations, evolution and ecosystems Flashcards
(56 cards)
Define genotype and phenotype
Genotype:
-genetic constitution of an organism
-determines the limits within characteristics may vary between individuals
Phenotype:
expression of this genetic constitution and its interaction with the environment
sme key terms
homologous pair = two copies of each chromosome, so cells have two copies of every gene
-as two copies of a gene present in an individual, possible to have different allele combinations within an individual
Genotype = alleles of a gene possessed by that individual
Homozygous = the two allele copies are identical in an individual
Heterozygous = the two allele copies are different in an individual
Genotype of an individual affects their phenotype
Phenotype = the observable characteristics of an organism
Define dominant, recessive and codominant
dominant:
-alleles that are always expressed in the phenotype, in both homozgous and heteroxygous individuals
recessive:
-only expressed in the phenotype if no dominant allele is present
-means they’re only expressed in a homozygous individual
codominant:
-both alleles are expressed in the phenotype at the same time
-seen in heterozygous individuals
-e.g. blood type
Define genes and alleles:
gene:
-sequence of DNA nucleotide bases that code for a particular protein
allele:
-different forms of a gene
difference between homozygous and heterozygous
homozygous:
-two copies of the same allele
heterozygous:
-organism has two different alleles
Define homozygous dominant and homozygous recessive
Homozygous dominant:
-organism with 2 dominant alleles
Homozygous recessive
-organism with 2 recessive alleles
Define sex-linkage
A gene whose locus is on the X chromosome
Define autosomal linkage
Genes that are located on the same chromosome, hence will be inherited together
Impacts predicted gametes
Define epistasis
What are the 2 genes involved?
What is dominant epistasis and recessive epistasis?
When one gene modifies or masks the expression of a different gene at a different locus
Epistatic gene: gene that is suppressing the other gene
Hypostatic gene: gene that is suppressed
Dominant epistasis: expression of dominant allele(s) of epistatic gene masks expression of hypostatic gene
Recessive epistasis: two copies required to mask expression of the hypostatic gene
Define monohybrid and dihybrid
Monohybrid: genetic inheritance cross of a characteristic determined by one gene
Dihybrid: genetic inheritance cross for a characteristic determined by two genes
Define the following:
gene pool
population
allele frequency
Gene pool: all the alleles of all the genes within a population at one time
Population: all the individuals of one species in one area at one time that can interbreed to make fertile offspring
Allele frequency: the proportion of an allele within the gene pool
Describe how a chi-squared test should be carried out
Species Exist in Populations
A species can be defined as a group of similar organisms that can reproduce to give fertile offspring
Organisms of the same species have the same number of chromosomes in their cells
Humans have 46 chromosomes
The reason that two organisms from a different species cannot produce fertile offspring is due to the fact that different species have a different diploid number of chromosomes in their cells
For example, a horse has 64 chromosomes in its cells while a donkey has 62. When the haploid gametes from a horse (32) and a donkey (31) combine, the resulting zygote has 63 chromosomes
Cells that have an odd number of chromosomes are not viable. The chromosomes can not form homologous pairs during meiosis to produce gametes
Members of a species do not live alone
Instead, they live in populations
Species can exist as one or more populations, for example:
The American black bear (Ursus americanus) is one species but has multiple populations in America and Canada
The Javan rhinoceros (Rhinoceros sondaicus) has only one population on the island of Java in Indonesia
Defining a species
The system used by biologists to organise living organisms into categories is based on dividing organisms into species
There are several factors that need to be taken into consideration when defining a species or determining whether two organisms belong to the same species
Similarities/differences in observable features (morphology)
Similarities/differences in DNA
Similarities/differences in RNA
Similarities/differences in proteins
The ability to interbreed and produce fertile offspring
The Definition of a Population
a group of organisms of the same species in a particular space at a particular time that can interbreed to produce fertile offspring
Why may allele frequencies or gene pool change over time
-due to processes such as natural selection
the characteristics of the species population will also change
-over time, these changes can become so great that a new species forms
Apparatus & Techniques: Collecting Data about the Frequency of a Phenotype
The frequency of a phenotype is simply the number of individuals in a population that have a specific, observable trait (a particular phenotypic characteristic)
Many organisms have traits that show more than one phenotype (e.g. shell colour in banded snails can be pink or yellow and flower colour in pea plants can be purple or white)
Phenotype frequencies can be calculated by counting the number of times a particular phenotype appears in a population (or sample of a population) and dividing this by the total number of individuals in the population (or the sample)
Phenotype frequencies are normally given as a percentage of the total population
Phenotype frequency = (total individuals with phenotype ÷ total individuals in population) × 100
Step 1: Calculate the phenotype frequency of purple flowers
Phenotype frequency = (total individuals with phenotype ÷ total individuals in population) × 100
= (7 ÷ 9) × 100
= 0.78 × 100
= 78%
Step 2: Calculate the phenotype frequency of white flowers
Phenotype frequency = (total individuals with phenotype ÷ total individuals in population) × 100
= (2 ÷ 9) × 100
= 0.22 × 100
= 22%
Step 1: Calculate the total number of snails in the sample
= 275 + 150 + 75
= 500
Step 2: Calculate the total number of pink-shelled snails (genotypes: CᴾCᴾ and CᴾCʸ)
= 275 + 150
425
Step 3: Calculate the phenotype frequency of pink-shelled snails
Phenotype frequency = (total individuals with phenotype ÷ total individuals in population) × 100
= (425 ÷ 500) × 100
= 0.85 × 100
= 85%
Step 4: Calculate the phenotype frequency of yellow-shelled snails
Phenotype frequency = (total individuals with phenotype ÷ total individuals in population) × 100
= (75 ÷ 500) × 100
= 0.15 × 100
= 15%
What is the Hardy-Weinberg Principle of natural selection?
Benefit of it?
-states that if certain conditions are met, the allele frequencies of a gene within a population will not change from one generation to the next
-allows allele and genotype frequencies within populations to be calculated
-can be used to predict how these frequencies will change in future generations
Conditions for the Hardy-Weinberg principle
-organisms are diploid
-organisms reproduce by sexual reproduction only
-there is no overlap between generations, i.e. parents do not mate with offspring
-mating is random
-population is large
-no migration, mutation, or selection (natural and artificial)
-equal allele frequencies in both sexes
-Hardy-Weinberg principle can be useful when building models and making predictions, but the assumptions listed are very rarely, if ever, all present in nature
Hardy-Weinberg equations
p + q = 1
p2 + q2 + 2pq = 1
Ecology starts
Define ecosystem
the community and the biotic and abiotic factors in its environment, which can vary in size
Define habitat
part of an ecosystem where an organism lives
Define niche
an organism’s role in an ecosystem, including its position in the food web and its habitat
each species occupies its own niche, governed by adaptation to biotic and abiotic factors
Define carrying capacity
the maximum population size an ecosystem can support
Define predation
when an organism eats another
