3.4 Inheritance Flashcards
Who was Gregor Mendel?
Gregor Mendel was an Austrian monk who developed the principles of inheritance by performing experiments on pea plants
What was his first experiment?
First, he crossed different varieties of purebred pea plants, then collected and grew the seeds to determine their characteristics
What did he do with the F1 generation?
Next, he crossed the offspring with each other (self-fertilization) and grew their seeds to similarly determine their characteristics
How many times did mendel perform his experiments?
These crosses were performed many times to establish reliable data trends (over 5,000 crosses were performed)
What did Mendel find out about breeding purebred varieties?
When he crossed two different purebred varieties together the results were not a blend – only one feature would be expressed
E.g. When purebred tall and short pea plants were crossed, all offspring developed into tall growing plants
What did Mendel find out regarding self-fertilisation?
When Mendel self-fertilised the offspring, the resulting progeny expressed the two different traits in a ratio of ~ 3:1
E.g. When the tall growing progeny were crossed, tall and short pea plants were produced in a ratio of ~ 3:1
What did Mendel find out about genes?
Organisms have discrete factors that determine its features (these ‘factors’ are now recognised as genes)
What did Mendel find out about alleles?
Furthermore, organisms possess two versions of each factor (these ‘versions’ are now recognised as alleles)
What did Mendel find out about gametes?
Each gamete contains only one version of each factor (sex cells are now recognised to be haploid)
What did Mendel find out about parental contribution?
Parents contribute equally to the inheritance of offspring as a result of the fusion between randomly selected egg and sperm
What did Mendel find out about dominant/recessive?
For each factor, one version is dominant over another and will be completely expressed if present
What are Mendel’s 3 rules?
- Law of Segregation
- Law of Independent Assortment
- Principle of Dominance
What is the law of segregation?
Law of Segregation: When gametes form, alleles are separated so that each gamete carries only one allele for each gene
What is the law of independent assortment?
The segregation of alleles for one gene occurs independently to that of any other gene*
The law of principle dominance?
Recessive alleles will be masked by dominant alleles†
What is the exception to the law of independent assortment?
The law of independent assortment does not hold true for genes located on the same chromosome (i.e. linked genes)
What is the exception to the principle of dominance?
Not all genes show a complete dominance hierarchy – some genes show co-dominance or incomplete dominance
What are gametes?
Gametes are haploid sex cells formed by the process of meiosis – males produce sperm and females produce ova
What happens to homologous chromosomes in meiosis I?
During meiosis I, homologous chromosomes are separated into different nuclei prior to cell division
What does the separation of homologous chromosomes also segregate?
As homologous chromosomes carry the same genes, segregation of the chromosomes also separates the allele pairs
What do gametes carry?
Consequently, as gametes contain only one copy of each chromosome they therefore carry only one allele of each gene
What are gametes categorised as?
Gametes are haploid, meaning they only possess one allele for each gene
What will occur when gametes fuse, due to them being haploid?
When male and female gametes fuse during fertilisation, the resulting zygote will contain two alleles for each gene
What is the exception for gametes fusing and producing a zygote with two alleles for EACH GENE?
Males have only one allele for each gene located on a sex chromosome, as these chromosomes aren’t paired (XY)