Meiosis & genetics (genetics & inheritance) Part 2 - (Week 8) Flashcards
What generation are the ‘true-breeding parents’?
P generation
What is the hybrid offspring of the P generation called?
F1 generation
What do we call the offspring of the F1 generation?
F2 generation
If two contrasting ‘true-breeding’ white & purple flowered pea plants are bred together, what colour will their offspring be?
F1 hybrids (P gen offspring) will all be purple flowers
What colour will the offspring of purple flowered F1 hybrids produce?
Flowers purple & white with ratio of 3:1
What does the offspring in F1 & F2 generation of pea plants suggest?
Mendel called the purple flower the ‘dominant’ trait and the white flower the ‘recessive’ trait
What are alleles?
They are alternative versions of a gene - each gene resides at a specific locus on a specific chromosome
For ‘true-breeding’ parents, what type of alleles do they have?
They have alleles at a particular locus that are identical (e.g both dominant/both recessive)
Do alleles in F1 hybrids have alleles at identical or different loci?
The two alleles in an F1 hybrid are at loci that are different
Give the 4 main ideas that explain the 3:1 inheritance pattern observed in F2 offspring
- Alternative versions of genes account for variations in inherited characters
- For each character, an organism inherits 2 alleles, one from each parent
- If the 2 alleles at a locus differ, then one (dominant allele) determines organism’s appearance, & the other (recessive) has no noticeable effect on appearance
- The law of segregation
What is the law of segregation?
The 2 alleles for a heritable character separate (segregate) during gamete formation (meiosis) & ended up in different gametes (gametes get only one of the 2 alleles present in the organism)
What does it mean if an organism is ‘homozygous’ for a gene?
An organism with two identical alleles for a character is homozygous for the gene controlling that character
What does it mean if an organism is ‘heterozygous’ for a gene?
An organism that has two different alleles for a gene is heterozygous for the gene controlling that character
Homozygotes are not true-breeding. True or false?
False. Homozygotes are true-breeding, heterozygotes are not
What is meant by the term ‘phenotype’?
Physical appearance
What is meant by the term ‘genotype’?
Genetic makeup
How can we determine genotype?
Do a testcross
- Breed the mystery individual with a homozygous recessive individual
- If any offspring display the recessive phenotype, the mystery parent must be heterozygous
What is dihybrid inheritance?
Simultaneous inheritance of 2 characteristics
Using a dihybrid cross, Mendel developed the Law of Independent Assortment. Describe what the means
- Each pair of alleles segregates independently of each other during gamete formation
- Applies only to genes on different, non homologous chromosomes or those far apart on the same chromosome
- Genes located near each other on the same chromosome tend to be inherited together
What is the Hardy-Weinberg Principle?
It states that the frequency of dominant and recessive alleles will remain constant from generation to generation provided certain conditions exist
What are the certain conditions required for the Hardy-Weinberg Principle to be true?
- No selection is taking place (all alleles are equal)
- No mutations occurring
- Mating is random
- Population is large
- No migration
What equation must you use to calculate the frequency of a dominant or recessive allele?
p+q = 1.0
p = dominant allele
q = recessive allele
these frequencies are expressed as %, fractions or decimals
How can you calculate the frequency of a genotype?
p^2 + 2pq + q^2 = 1.0
What genotype does p^2 represent?
Frequency of the homozygous dominant
What genotype does 2pq represent?
Frequency of the heterozygous
What genotype does q^2 represent?
Frequency of the homozygous recessive
How do you calculate the chance for various genotypes in a multi character cross?
- A multi character cross is equivalent to 2+ independent crosses occurring simultaneously
- To calculate chances for various genotypes, consider each separately
- Multiply each individual probability
When does Mendelian inheritance not apply?
When:
- Alleles are not completely dominant or recessive
- A gene has more than two alleles
- A gene productes multiple phenotypes
(However the basic principles still apply)
What is complete dominance?
It occurs when phenotypes of the heterozygote & dominant homozygote are identical
What is incomplete dominance?
When the phenotype of F1 hybrids is somewhere between the phenotypes of the two parental varieties
What is codominance?
Two dominant alleles affect the phenotype in separate, distinguishable ways
Give an example of incomplete dominance
When two different coloured ‘true-breeding’ parent flowers produce a hybrid offspring with a colour inbetween the two
Give an example of codominance
Blood groups in humans. There are 3 alleles: IA, IB, i (IA & IB are dominant, i is recessive)
