Genetics - Week 3 Flashcards
Are genes that are physically linked and close together likely to undergo recombination?
unlikely to undergo recombination because there are few opportunities to cross over
Are genes that are physically linked and far apart likely to undergo recombination?
more likely to undergo recombination because there are more opportunities to cross over
What are methods of fertilization?
- crossing over
- independent assortment
What is self-fertilization?
combination of one’s own gametes to produce offspring by crossing over or independent assortment
- no resulting offspring will be genetically identical to the parent
Why is self-fertilization not asexual reproduction?
gametes with half the ploidy level of the parental cell are produced
What is asexual reproduction?
offspring arise from a single parent (ie. not via fusion of gametes)
What are the pros of sexual reproduction?
more genetic variation, easier to adapt to environment
What are the cons of sexual reproduction?
- have to actually find a mate
- requires more energy and time
- takes longer to produce offspring
What are the pros of asexual reproduction?
faster to produce offspring
What are the cons of asexual reproduction?
less genetically variable offspring
What is a genotype?
genetic make-up (or set of genes, combination of alleles) of an organism/individual
What is a phenotype?
any observable characteristics (traits) of an organism/individual as a result of its genotype and interaction with the environment
What are homozygotes?
(in diploid organisms) carry two copies of same allele for a particular gene
What are heterozygotes?
(in diploid organisms) carry different alleles
What is a test cross?
crossing of an individual with an unknown genotype with an individual with a homozygous recessive genotype
What are true breeding organisms (purebreds)?
homozygotes
What are non-true breeding organisms?
heterozygotes
What is incomplete dominance?
traits blend together
What is co-dominance?
both traits appear
What is a wild type?
refers to the most common form of the allele or phenotype, or the original allele/phenotype that was observed in
What is a mutant?
refers to the less common and/or newer version of a gene/trait, that has arisen through mutation
Describe the chromosomes in humans.
humans have 46 chromosomes in each diploid cell:
- 44 autosomes (22 pairs)
- 2 sex chromosomes (X and Y)
- X (female) is bigger than Y (male)
What are physically linked genes?
genes are on the same chromosome
What are sex linked genes?
genes are on one of the sex chromosomes (either X-linked or Y-linked)
What are X-linked genes?
X chromosomes in a female act like homologous autosomes (homozygous/heterozygous)
- males only have one X chromosome (neither homozygous nor heterozygotes)
What is a carrier?
heterozygotes which have a copy of the allele responsible for the gene of interest
What are the 4 modes of inheritance?
- autosomal dominant
- autosomal recessive
- X-linked dominant
- X-linked recessive
What may indicate sex-linkage of a trait?
if you see that the distribution of a trait varies between the male & female parents/offspring
What are Punnett Squares used for?
to determine what the possible phenotypes and genotypes from fusing of gametes (crosses)
How do you approach cross questions?
- clearly state the symbols for each allele
- look at the offspring data (F1 & F2) for hints regarding modes of inheritance (ie. are there differences between the sexes?)
- provide a prediction for your hypothesis using Punnett Squares (or comparable methods using frequencies)
- provide evidence to support your prediction using the frequencies (actual numbers) provided for the resulting F1 or F2 progeny that is provided
How do you solve pedigree questions?
have a hypothesis, then, usually:
- if a trait skips no generations: DOMINANT
- unequal sex ratio: SEX-LINKED (on X chromosome)
- if more males than females affected: X-LINKED RECESSIVE
- if more females than males affected: X-LINKED DOMINANT
- if the trait is not seen in parents, but is seen in their children (at least one): RECESSIVE
- if a certain cross is not possible (due to genotypes): eliminates a mode of inheritance
