7. Mendel & The Gene Idea Flashcards
Why did Mendel choose to use Peas?
(5)
because:
– They have a short generation time
– They have different traits that can be observed
– He could strictly control which pea plants
mated with which
– They are cheap & readily available
– They can grow fast
How did Mandel Control Mating?
(6)
Peas normally self-fertilize (self-pollinate)
– Male organs (stamens) produce pollen grains, which make sperm
– Female organs (carpels) produce eggs
– A flower’s pollen falls on the female organ of that same flower
- Mendel could prevent self-pollination by removing male organs from a flower
- He used pollen from one flower
to fertilize another
– Called a cross, or cross-pollination
What 4 Concepts did Mendel come up with?
1st concept:
Alternative versions of genes account for variations in inherited characters
2nd concept:
For each character an organism inherits two alleles, one from each parent
3rd concept:
If two alleles at a locus differ, then the dominant allele determines the organism’s appearance and the recessive allele has no
noticeable effect on appearance
4th concept:
The two alleles for a heritable character
separate (segregate) during gamete formation and end up in different gametes
What is the Law of Segregation?
(4th Concept)
This concept is known as the law of segregation!!
- Thus, an egg or a sperm gets only one of the two alleles that are present in the somatic cells
of an organism - This segregation of alleles corresponds to the distribution of homologous chromosomes
to different gametes in meiosis
What is a Punnett Square?
The possible combinations of sperm and egg can be shown using a Punnett square, a diagram for predicting the results of a genetic cross between individuals of known genetic makeup
- A capital letter represents a dominant allele, and a lower case letter represents a recessive allele
Homozygous
An organism with two identical alleles for a character is said to be homozygous for the gene controlling that character
Heterozygous
An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that character
Heterozygous
An organism that has two different alleles for a gene is said to be heterozygous for the gene controlling that character
Phenotype and Genotype
Phenotype
(physical appearance, internal anatomy, physiology, behaviour)
Genotype
(genetic makeup)
- In the example of flower colour in pea plants, PP and Pp plants have the same phenotype (purple) but different genotypes
9:3:3:1 Ratio if both parents are both heterozygous for both traits
ans
What is a Monohybrid Cross
Monohybrid cross – a genetic cross between parents that are both heterozygous for ONE trait
– For example = Rr x Rr
- The result of a monohybrid cross would be 1RR : 2Rr: 1rr
genotypic ratio, which translates to a
3 dominant trait: 1 recessive trait
phenotypic ratio
What is a Dihybrid Cross?
Dihybrid cross –
a genetic cross between parents that
are both heterozygous for TWO traits
– For example = RrYy x RrYy
– The result of a dihybrid cross would be a 9:3:3:1 phenotypic ratio
What is Complete Dominance?
Complete dominance occurs when phenotypes of the heterozygote and dominant homozygote are identical
The flower will be either red or white
What is Incomplete Dominance?
In incomplete dominance, the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties
– When two traits are not completely dominant over each other (instead there is a blending of traits) (red pink or white)
What is Co-Dominance?
In co-dominance, two X dominant alleles affect the phenotype in separate, distinguishable ways
– When two traits are BOTH equally dominant
(so both traits are present at the same time…NO blending)
(red flower with white spots)
quick summary
