Genetics Flashcards
genetic gambling
- For every gene that you have you inherit 2 allelses
* Assortment of each parents’ chromosomes into gametes is random
Chromosomes and alleles
• When sperm+egg make a fertilized egg each gamete contributes 1 of each of our chromosomes, so the new individual has 2 copies of each chromosome aka homologous chromosomes
recessive vs dominant
- Dominant: protein will be made (gene will be expressed)
* Recessive: protein will only be made if there is no dominant allele
Haploid/diploid
• We have 46 chromosomes (diploid) 2 copies of each of 23 unique chromosomes (haploid)
Homozygous
• If you have the same allele on both chromosomes
heterozygous
• If you have different alleles on the two chromosomes
3 ideas of Gregor Mendel
o rather than passing on the trait itself each parent passes on instructions for building the trait
o offspring receive 2 copies of the instructions for every trait
o the trait observed depends on the 2 sets of instructions
3 Big ideas of Mendel
o recessive/dominance o law of segregation • homologous chromosomes split apart o law of independent assortment • alleles that make it into the gamete do randomly
mendel’s law of segregation
• Each gamete gets 1 copy of each gene from the parent
Phenotype and Genotype
• Can be difficult to tell a genotype from the phenotype alone
punnett squares
• Way of mapping out the possible offspring resulting from a match
Autosomal-recessive traits
• Albinism, cystic fibrosis, hairline shape, tay sachs, Rh factor on RBCs
Pedigree
• You can use a pedigree to follow a trait through a family
Sex lnked traits
• Any traits inherited on either the X or Y chromosome
X chromosome sex linked traits
o Interesting pattern
o Two X chromosomes for females so it could be expressed in a heterozygous way
o One X chromosome for men so it must be expressed
o X linked traits: traits that are on the X chromosome
• Males are more likely to display traits inherited on their 1 X chromosome, than females on their 2 X chromosomes
What causes a phenotype
• Take single-gene trait like ear wax type/underarm odor (Gene: ABCC11)
• What could be the molecular mechanisms behind this difference in phenotype?
o Single transporter molecule that will affect secretion
Wild type
prevalent allele in a population
o Usually protein in proper amount that functions normally
mutant
rare in natural populations
o Often recessive
epigenetic
something not coded for in the genome that controls expression of the gene
Cystic fibrosis
- Mutation in a single gene for a single protein
- Protein is called cystic fibrosis transmembrane conductance regulator (CFTR), moves Cl- ions across cell membranes
- Movement of CL- affects water transport
- Effects: overly salty sweat, improper male gonadal development, thick mucus in lungs
Pleitropy
- One gene-many traits
- One gene contributing to many traits
- Ex: SRY gene. One gene on Y chromosome codes for conversion of estrogen to testosterone, controls all male characteristics
Independent assortment
- By tracking 2 traits at a time, Mendel discovered that the inheritance of each trait did not affect the inheritance of the other
- Thus, he hypothesized that traits were sorted into the gametes independently
- Mendel said: each gene is inherited separately, and inheritance of one does not influence inheritance of another
- Only part true: chromosomes sort independently, but each chromosome carries more than one gene
- Since genes are carried on chromosomes, and chromosomes are inherited as 1 unit, often these are often inherited together
- The closer genes are together on the chromosome, the MORE likely they are to be inherited together, because they don’t tend to get separated during crossing over
linked genes
• Genes that are located on the same chromosome are more likely to be inherited together
• Due to corssing over during meiosis, homologous chromosomes can exchange pieces of chromosomes and create new combinations of alleles
• The likelihood of crossing over depends on the distance between two genes
• Genes located VERY close together are unlikely to be separated by crossing over
• Called linked genes
• Certain alleles are usually inherited together
o Red hair and freckles
Linkage maps
• By charting how often two alleles were inherited together, scientists were able to map genes onto chromosomes in order!
Incomplete dominance
- Heterozygote appears as an intermediate btw the two homozygotes
- In this example, the amount of protein produced is coded for by the gene
- Red flowers have A LOT of pigment
- White flowers have no pigment
- Red and white reprocude and get pink flowers
multiple allelism
- Some traits are controlled by genes which have more than 2 alleles
- Gene that determines blood type
- ABO: codominance and multiple allelism
codominance
• The heterozygote displays characteristics of BOTH homozygotes
• Red blood cells
o Type AB
environmental effects
• The environment can affect the expression of genes, mostly through epigenetics
o Ex: skin color and identical twins
Gene interaction
• Most traits are influenced by more than one gene
• Variations
o One allele of one gene could prevent expression of an allele of a different gene
o Multiple genes have additive effects on a single character
Polygenic Trait Example: skin color
- More than one gene contributing to a single trait
- Controlled by 3 genes, each with 2 alleles
- Dark allele=more melanin production
- Light allele= less melanin production
- A^D or A^L, B^D or B^L, C^D or C^L
- Then, add in environmental effects
