Mendelian Genetics Flashcards
(41 cards)
Describe the overview of Mendels Pea plant experiment
Strict control over which plants mated with which
Each plant has both male (stamens) and female (pistil) reproductive organs
Medel looked at 7 characteristics of pea plants with contrasting traits
What is the difference between a characteristic and a trait
Characteristic - heritable feature (physical feature)
Trait - each variant of a character
Describe the first step of Mendel’s pea plant experiment
Mendel grew true breeding plants – plants that always produce offspring with the same traits
Flower Colour:
True-bred plants with purple flowers will always produce plants with purple flowers
True-bred white will only produce white.
Mendel called this the P generation (parent generation)
Describe step 2 of Mendel’s pea plant experiment
Mendel set up monohybrid crosses
True bred plant with purple flower crossed with true bred plant with white flowers
Produced F1 generation
All F1 generation plants had purple flowers
With blending, inheritance would expect plants to be intermediate in colour
Mendel hypothesised that when the purple factor was present the recessive factor (white colour) did not show
Mendel called the purple flower colour the dominant factor
What was step 3 of Mendel’s Pea plant experiment
F1 generation self fertilized
Plants with white flowers reappeared in the F2 generation
Mendel recorded 705 plants with purple flowers and 224 with white flowers
Approximately 3:1 ratio
Medel found similar findings with other traits
What did Medel conclude from his pea plant experiments
An organism inherits 2 factors (we now know as alleles) for a characteristic
- Hereditary Particles - Genes
- Alternative Forms - Alleles
When the plant reproduces these 2 characters separate (segregate during gamete formation and end up in different gametes)
What is Medel’s law of segregation
Each gamete (sex cell) gives one factor (allele)
Each offspring gets one factor (allele) from each parent
Random fusion during fertilisation
What is a dominant trait
The observed trait
What is the recessive trait
The masked trait
If the organism has two dominant alleles then
the dominant trait will be expressed (PP)
If the organism has one dominant and one recessive allele
the dominant trait will be expressed (Pp)
If the organism has 2 recessive alleles
the recessive trait will be expressed (pp)
From Mendel’s Pea plant experiment, which trait was dominant and which one was reccessive
Purple was the dominant allele
White was the recessive allele
What are alleles
Different versions of a gene
E.g. the purple flower allele and the white flower allele are different versions of a gene at the same location on homologous chromosomes
Mendel also conducted experiments on more than one trait, setting up dihybrid crosses
What did he observe
That one trait did not affect another trait
So different factors (genes) segregate independently from one another during the formation of gametes
Mendel’s law of independent assortment: genes get shuffled - these many combinations are one of the advantages of sexual reproduction
Example: Dihybrid cross: cross true-breeding yellow round pea with true breeding green wrinkled peas
What are some recessively inherited disorders
Cystic fibrosis, Tay Sachs disease, Sickle cell anemia
The disease only shows in homozygous recessive individuals - inherit recessive allele from both parents
Heterozygotes are phenotypically unaffected but act as carriers of this disorder
Vast majority of diseases are recessive
What are some examples of dominantly inherited disorders
Achondroplasia (dwarfism), Huntington’s disease
Most harmful alleles are recessive but some disorders due to dominant alleles
How many human chromosomes are there
How many pairs of human chromosomes are there
46 chromosomes - 23 pairs of homologous chromosomes (maternal set and a paternal set)
22 pairs of autosomes, 1 pair of sex chromosomes
What is a diploid cell
diploid number of chromosomes 2n=46
2 sets of chromosomes
What is a haploid cell
Haploid number of chromosomes n=23
1 set of chromosomes
What is mitosis
What is meiosis
Mitosis: process by which cells are replicated for growth, repair etc
Meiosis: process by which gametes are produced. Produces 4 daughter cells, each haploid (n) containing a single set of chromosomes
Meiosis 1 has reductional division, meaning what
homologous pairs are separated reducing chromosome number by half
Meiosis 2 has equational division, meaning what
sister chromatids are separated producing 4 haploid gametes
