Module 6: Patterns of inheritance Flashcards
What is a gene?
Sections of DNA within the genome that contain instructions to code for proteins. Contain individual characteristics like eye colour.
What are chromosomes?
Thread-like structure in the nucleus that contains DNA and proteins. It is made by DNA tightly coiled around proteins called histones. Has a centromere that divides the chromosome into two ‘arms’.
How many chromosomes do humans have? How are they passed on?
22 pairs of numbered chromosomes (autosomes) and one pair of sex chromosomes (XX or XY).
Children inherit half from mum and half from dad.
Define phenotype.
Observable characteristics of an organism like height.
Define monogenic inheritance.
Where 1 phenotypic characteristic is controlled by a single gene.
Define dihybrid inheritance.
Where 2 phenotypic characteristics are determined by 2 different genes present on 2 different chromosomes at the same time.
What is meant by sex-linkage?
Where an allele is located on one of the sex chromosomes, meaning its expression depend son the sex of the individual.
What is meant by multiple alleles?
A gene with more than 2 alleles.
What is it meant by codominant alleles?
Two dominant alleles that both contribute to the phenotype, either showing a blend of characteristics or appearing together.
What is meant by autosomal linkage?
Where 2 gene loci are found on the same autosomal NON-sex chromosome, so they are likely to be inherited together.
What is meant by epistasis?
Where 2 non-linked genes interact, with 1 gene either masking or suppressing the other gene.
What is the chi-squared test?
Statistical test to find out whether the difference between observed and expected data is due to chance or real effect. Compares phenotypic ratio with observed ratio.
How can the number of genes coding for a characteristic influence variation?
=> Discontinuous variation where the characteristic is determined by 1 gene (monogenic inheritance)
=> Continuous variation where the characteristic is determined by more than 1 gene (polygenic inheritance).
What is stabilising selection?
Occurs when environmental conditions stay the same and favours individuals closest to the mean, and any new characteristic is selected against. Results in low diversity.
What is directional selection?
Occurs when environmental conditions change. Individuals with phenotypes suited to new conditions survive and pass on genes.
What is genetic drift?
A change in population’s allele freq that occurs due to chance rather than selective pressure.
What is the genetic bottleneck?
Where a catastrophic event dramatically reduces the size of population, decreasing the variety of alleles in the gene pool.
What is the founder effect?
Where a small number of individuals become isolated, forming a new population with a limited gene pool.
Explain what the Hardy-Weinberg principle is.
Allows us to estimate the freq of alleles in a population.
The freq of each allele must add up to 1. p + q = 1
p is the freq of dominant allele
q is the freq of recessive allele
What about the Hardy-Weinberg equation for calculating genotype frequency?
The freq of each genotype must add up to 1. p^2 + 2pq + q^2 = 1
Where p^2 is the freq of homozygous dominant.
2pq is the frequency of heterozygous dominant.
q^2 is the freq of homozygous recessive.
What is speciation?
Where a population is split and isolated with 2 different selective pressures on the 2 groups. If the genetic make up changes, the 2 groups can no longer interbreed so have become separate species.
Difference between allopatric and sympatric speciation?
Allopatric - speciation resulting from physical barrier like a river.
Sympatric - speciation resulting from a non-physical barrier like a mutation that no longer allows 2 organisms to produce fertile offspring.
What is artificial selection?
Humans choose particular organisms to breed together to produce a desired characteristic in the offspring.
E.g. plant seeds that produce larger fruit and veg, cows with higher milk yield are selectively bred.
Ethical issues to artificial selection.
=> Anatomical changes in animals e.g. respiratory issues in brachycephalic dogs.
=> Higher susceptibility to disease in both plants and animals.
