Block 8.3

What is a mutation?

A source of new variation

What is crossing over?

sections of DNA are exchanged between homologous chromosomes

What does crossing over allow?

New combinations of alleles- recombination

What is independent assortment?

The different possible combinations of maternal and paternal chromosomes

What does random fertilisation do?

Introduces variation because the combination of gametes that fuse to form a zygote is random

What is a genotype?

The alleles present in a cell

What is a phenotype?

The observable characteristics of an organism

What is a homozygote?

An individual with two identical alleles for a characteristic

What is a heterozygote?

The two alleles in an individual are different for a characteristic

What is a dominant characteristic?

A characteristic that always shows an effect in the phenotype

What is a recessive characteristic?

A characteristic that is only expressed if the gene is homozygous

What is codominance?

The alleles are equally dominant

What are multiple alleles?

When there are more than two possible alleles for a gene

What is a point mutation?

Only one or a small number of nucleotides are inserted, substituted or deleted.

What is a chromosomal mutation?

A change in position of genes on a chromosome

What is a whole chromosome mutation?

An entire chromosome is lost or duplicated during meiosis

What does polygenic mean?

Phenotype is determined by several genes

What is a genetic cross?

What is a pedigree diagram?

What are some sampling errors of a genetic cross?

-Chance plays a big role in reproduction -Some offspring die before they are sampled -Some offspring may escape before they are sampled

How are the different parts in a pedigree diagram represented?

-A female is represented by a circle and a male by a square -A horizontal line between a male and female links two parents -A vertical line leads down to offspring -A code can be used to show phenotype

What is autosomal linkage?

Two genes are located on the same autosome

How are Drosophila flies' characteristics linked?

Four pairs of chromosomes: one pair of sex chromosomes, three pairs of autosomes.

They can have: dominant grey body (G) or recessive black body (g) and dominant long wings (L) or recessive short wings (l)

Crossing over occurs to link the genes for colour and length

What is the expected ratio from a dihybrid cross?

9:3:3:1

If parental genotypes are LlGg x LlGg, what are the expected gametes?

LG Lg lG lg x LG Lg lG lg

What is sex linkage?

When a gene is carried on the X chromosome

What is an example of an illness caused by a sex linked characteristic?

Haemophilia- a protein needed to clot blood is missing; a recessive allele

What is chromosome mapping?

In genes that are close together (closely linked), the chance of recombination is low

If genes are further apart on a chromosome, recombination is more likely to occur

crossover value= number of recombinant offspring/total offspring X100

What is recombination?

A process by which pieces of DNA are broken off a chromosome and joined elsewhere to produce new combinations of alleles. This creates genetic diversity

What is the Chi-squared equation?

What is a Chi-squared test used for?

To establish whether the difference between observed and expected results is significant

What are the rules of a Chi-squared test?

-Sample size must be large (>20) -Data must be discontinuous -Null hypothesis must be that there is no difference between the observed and expected -Degrees of freedom=(x-1) where x is the number of expected values -If the value is greater than the critical value the null hypothesis is rejected

What is a gene pool?

All alleles of all the genes present in a population

Why does allele frequency change?

Due to natural selection leading to evolution via selection pressures

What is stabilising selection?

When the environment favours those with the most common characteristic - those on the extreme dies out and the common characteristic increases and variation decreases. Often used to conserve phenotypes present and maintain continuity

What is directional selection?

When the environment favours those individuals with characteristics on one of the extremes over the other, over time this will become the most common characteristic

What is disruptive selection?

Diversity increases as the conditions are more diverse and subpopulations form. Often leads to speciation

What is genetic drift?

Changes in allele frequency that occur by chance in small populations

What is a population bottleneck?

The severe loss in gene diversity from a catastrophic event that dramatically reduces the population and decreases the gene pool. This causes a change in allele frequencies.

What is the Founder Effect?

Loss of genetic variation that occurs when a small number of a population becomes isolated, forming a new population with allele frequencies not representative of the original population. Known as a voluntary bottleneck

What does the Hardy-Weinberg Equation allow you to do?

Use observations of phenotype frequencies to calculate associated allele frequencies in a population

What is the Hardy-Weinberg equation?

p=frequency of dominant allele q=frequency of recessive allele p^2= frequency of homozygous dominant q^2=frequency of homozygous recessive 2pq= frequency of heterozygous

What are the conditions of the Hardy-Weinberg equation?

No mutations

Random mating

Large population

Isolated population

No selection pressure