Laws of Inheritance Flashcards
Who cares about genetics and inheritance?
- dog breeders care
- owners of pedigree animals care
- farmers care
- increasing part of the conversation relating to treatment
What are the Three Laws of inheritance?
- First Law = Law of segregation
- Second Law = Law of independent Assortment
- Third Law = Law of dominance
What is the First Law - Law of segregation?
- every individual organism contains two alleles for each trait, and that these alleles segregate (separate) during meiosis such that each gamete contains inly one of the alleles
What is the Second Law - Law of independent Assortment
- Alleles for separate traits are passed independently of one another from parents to offspring
What is the Third Law - Law of dominance
- recessive alleles will always be masked by dominant alleles
Are the Three Laws always correct?
- no there are always variants
What is a locus?
- position of gene on a chromosome
- loci (plural)
What are alleles?
- alleles are varieties of the same gene
Describe the position of alleles:
- alleles are always in the same position on the chromosome (locus)
How are alleles created?
- they are created by mutations in the DNA
What can allele mutations cause?
- these mutations can give a different phenotype
What is a phenotype?
- phenotype can be both a physical appearance or the biochemical ability e.g., enzyme production
What does a diploid individual contain?
- contains two copies of each gene
- one from each parent
What does a homozygous individual contain?
- contains two identical copies
What does a heterozygous individual contain?
- contains two different copies (alleles)
A phenotype is an expression of genotype - what does this include?
- morphology
- biochemistry
- behaviour
What is a genotype?
- alleles of a particular gene or genes
- present in a particular individual
What are the exceptions to the first law?
- prokaryotes (bacteria and archaea) - binary fission instead
- clonal reproduction
- haploid organisms
- sex chromosomes
Describe a gamete:
- haploid
- contains one copy of each parent gene
determined at random
Describe a zygote?
- diploid
- formed by fusion of two gametes
- formed by fusion of two gametes
- from same or different individuals
- develops into diploid individual
Independent assortment should lead to …
- no bias
What are the exceptions to independent assortment?
- clonal reproduction - entire genome is inherited
- genes on the same chromosome - more likely to be inherited together = linkage
When does crossing over (recombination) happen?
- crossing over happens in prophase 1 of meiosis - only in the production of gametes
What happens if crossing ever happens after the gene?
- there is no recombination (not for that gene anyway)
What happens if recombination (crossing over) happens between the centromere and gene?
- there is recombination
The further the alleles are apart there is more chance of what?
- the more chance there is of recombination
In complete dominance the phenotype of recessive allele is only expressed when?
- only when homozygous for recessive
In the Law of dominance if there is complete what will happen to the recessive?
- if there is complete dominance the dominate allele will mask the recessive allele in phenotype
What happens if there is incomplete dominance?
- phenotype of heterozygote is intermediate between two homozygotes
- roan horses
What happens if there is co-dominance?
- both alleles contribute to the phenotype
- the effects of both alleles are seen to their full extent
What is a second cross?
- between two individuals from F1 generation
What is a first cross?
- between two individuals
What does autosomal mean?
- the gene is located on one of the numbered or non-sex chromosome
