Genetic Inheritance Flashcards
Phenotype
physical manifestation of a genetic trait
not just what you see with your eyes, but could be something cellular as well
Genotype
the combination of genes responsible for a phenotype
Dominant Alleles
only one copy necessary for the phenotype to be expressed
represented with capital letters
How are genes inherited?
Every cell, and thus, every gene, has two copies, one copy from your mom and one from your dad - but the copies might not have the same alleles, however, have the same genes
The copies of the same chromosomes are know as homologues
each person inherits two alleles for every gene - one maternally, one paternally
except for sex chromosomes
Locus
the location of a gene on a chromosome
genes can be describes in terms of their loci
Recessive Alleles
both alleles must be recessive for it to be expressed
Gain of function mutation
the mutation makes the protein do something it couldn’t do before
tend to be dominant
Loss of function mutation
protein can’t do something it can do before as result of mutation
typically recessive
Homozygous
two copies of same allele (RR, rr)
Heterozygous
what you get when you cross a homozygous recessive and homozygous dominant
one recessive and one dominant allele
Hemizygous
only one copy of an allele is present
occurs with genes on X and Y chromosomes
also nondisjunction with organism with aneupoloidy
Self-cross Heterozygous
genotype: 1:2:1 ratio, 25% offspring homozygous dominant, 50% heterozygous, 25% homozygous recessive
phenotype: 3:1 ratio, 75% will show dominant phenotype, 25% will show recessive
Test-cross
done to distinguish if a genotype is heterozygous or homozygous
done with a homozygous recessive
RR x rr = you’ll have all Rr, or dominant phenotype expressing offspring
Rr x rr - you’ll have 50% dominant expressing and 50% recessive expressing offspring
Wild-type
default phenotype or genotype present in the most members of a species
Codominance
when two dominant alleles can be expressed at the same time
example: human blood typing ABO, or dalmations (BW alleles)
Incomplete Dominance
heterozygote displays a blended phenotype
ex: snap dragon flower, dom = red, rec = white, hetero = pink
Penetrance
likelihood that a carrier of a given genotype will manifest the corresponding phenotype
ex: BRCA1 gene - 80% risk of developing breast cancer, so 80% penetrance
Expressivity
intensity or extent of variation in phenotype
how much of an effect does that mutation have on the phenotype, vs with penetrance it is, does it effect the phenotype or not, and how ofen?
Dihybrid Cross
when you cross two heterozygotes for two different traits
offspring will have the characteristic distribution of 9/16 dual dominant, 6/16 one recessive trait (3/16 of one type of recessive allele, 3/16 with the other), 1/16 dual recessive
9:3:3:1
Law of independent assortment
the law that there is no link between inheritance with an allele of one gene and the allele of a different gene
however, this is not the case, as links that are closer together are less likely to undergo recombination that those that are further apart during prophase I of meiosis
What are the 3 components of a evolutionary system?
- variations in population
- mechanism for variations to be reproduced over time
- environmental constraints that allow favorable variations to be reproduced more than others (aka differential reproduction)
Gene pool
combined set all all genes/alleles in a population
used to describe the genetic status of a population
evolutionary success = increase representation of certain allele within the pool
Hardy-Weinberg Equilibrium
used to model stable gene pools
only applies under these criteria:
1. organisms must be diploid and reproduce sexually
2. mating is random
3. populations size is very large
4. alleles randomly distributed by sex
5. no mutations occur
6. no migration into or out of population
represent by p + q = 1
where p and q are two different alleles within an entire population (gene pool)
when we square these, we are crossing them, and are able to come up with the different possible combinations of the alleles
p^2 + 2pq + q^2 = 1
Stabilizing Selection
both extremes of a phenotype are selected against
Directional selection
one extreme phenotype selected against
Disruptive selection
median phenotype selected against
Genetic drft
role of chance, in the absence of strong selective pressures, in determining reproductive fitness of various alleles
Bottleneck effect
external event dramatically reduces size of population in a way that is random, so that the allele left over is just random in terms of survival
ex: a flood wipes out population indiscriminately
