B17- Inherited Change Flashcards
Monohybrid inheritance
Monohybrid inheritance overview:
- Involves inheritance of a single gene
- Pure-breeding:
- Repeated breeding for a specific trait
- Results in homozygous organisms for that gene
- Crossing pure-bred organisms:
- Produces heterozygous offspring
- Pure-bred parents: Parental (P) generation
- Heterozygous offspring: F1 (first filial) generation
Mendel Law
In diploid organisms, characteristics are determined by alleles that occur in pairs. Only one of each pair of alleles can be present in a single gamete.
Probability and the genetic crosses
Ratio: A measure of relative size between two groups, expressed as a proportion
Actual vs. Predicted Ratios:
- Actual ratios often differ from predicted ones
- Discrepancies are due to statistical error
Sample Size Impact:
- Larger samples increase likelihood of actual results matching theoretical predictions
Dihybrid Inheritance
Although we normally look at the inheritance of the single gene (monohybrid inheritance), in practice, thousands of characteristics are inherited together. We look at how 2 characters, determined by 2 different genes located on different chromosomes inherited- dihybrid inheritance.
Mendels Experiment
Mendel investigated the inheritance of 2 characters of the pea plant:
Seed shape - round is dominant over wrinkled
Seed colour - yellow is dominant over green
He crossed 2 pure breeding types:
Round with yellow seed (dominant for both characters)
Wrinkled with green seed (recessive for both characters)
Codominance
both alleles are expressed in the phenotype as they are equally dominant.
Multiple alleles
A genes has more than 2 alleles again, letter for gene is used in upper case and the alleles are shown with another letter in superscript.
Sex-linkage
22 pairs of autosomes- identical in appearance regardless of sex and 1 pair of sex chromosomes that women have XX chromosomes and males have XY.
Sex-linked Inheritance
Key points about sex-linked inheritance:
- X and Y chromosomes differ in size
- Part of the X chromosome has no homologous region on Y
- Recessive alleles on this non-homologous X region are more likely expressed in males
Autosomal Linkage
Any 2 genes that occur on the same chromosome are said to linked.
All genes on a single chromosome form a linkage group.
If there is no crossing over, all linked genes remain together during meiosis and do not segregate in accordance with Mendel’s Law of Independent Assortment.
Epistasis
the allele of one gene affects the expression of another. Epistasis reduces the number of possible phenotypes.
Population genetics
studies genes and alleles of an entire population, not just how it is passed on from one individual to another.
Population
a group of organisms of the same species that occupy a particular space at a particular time and can potentially interbreed.
Gene pool
all the alleles of all the genes of all the individuals in a population at a given time.
Allele frequency
the number of times an allele occurs within the gene pool
Species
The system used by biologists toorganise living organismsinto categories is based on dividing organisms into species.
Variation in Phenotype
- Random fertilisation: Gametes with different alleles combine randomly
- Meiosis: Random assortment of alleles during gamete formation
- Mutation: Creation of new alleles that can be inherited
- Environmental influences: Impact on phenotypic expression of traits
Variation due to environmental factors
- Characters influenced by environmental factors are often controlled by multiple genes, called polygenes.
- Environmental factors play a significant role in shaping these characteristics.
- It’s challenging to differentiate between genetic and environmental influences on these traits.
- Due to this complexity, any conclusions drawn about these characteristics should be treated with caution.
Correlation Coefficient
Correlation coefficient- when sampling collects two variables it is possible to use a calculation to determine whether the variables correlate in any way. The variables compared need to plotted on the latter graphs which will indicate possible relationships that can be tested.
