Genetics Flashcards
the basic unit of heredity is the ___
gene
genes are composed of ___ and are located on ____
composed of DNA and are located on chromosomes
when a gene exists in more than one form the alternative forms are called ___
alleles
physical manifestation of the geneti makeup is the individuals ____
phenotype
what are the 4 princples in medels 1st law of segregation
- Genes exist in alternative forms (alleles). A gene controls a specific trait in an organism
- An organism has teo allels for each inherited trait, one inherited from each parent
- the two alleles segregate during meiosis, resulting in gametes that carry only 1 allele for any given inherited trait
- if two alleles are different, only one is fully expressed (the dominant one) and silent one is recessive
Monohybrid cross
- only looking at 1 trait
- individuals being crossed = parental or P generation
- progeny are the filial or F generation (numbered sequentially F1, F2 …)
- Pp x P produces a (1:2:1) genotypic ratio but a 3:1 phenotypic ratio
what is a test cross
- used to determine genotype of an organism
- need a recessive phenotype x dominant phenotype (either homozyoug dominant or heterozygous dominant)
explain mendel’s second law: independent assortment
- dihybrid cross, parents differ in two traits as long as genes are on separate chromosomes and assort independently during meiosis
- inheritance of one trait is completely independent of inheritance of the other
*the closer genes are on a chromosome the more liekly they are to be inherited together though
Dihybrid cross
what is incomplete dominance? what is codominant
- blends of parental phenotypes
incomplete: ie if dom = red and rec = white, heterozygous = pink
codominance: hetero = red and white spickled or blood type AB is codominant - both alleles in genotype are expressed at same time without bledning of phenotype
explain sex determination
- all humans ahve 22 pairs of autosomes (pair of chromosomes), additionally women have a pair of homologous X chromosomes and men have heterologous chromosomes XY
- sex chromosomes pair during meiosis and segregate during the first meiotic division,
female can donate only X but males can donate X or Y determining the sex
- if sperm carries X or Y determines the sex, 50-50% chance
- genes located on X or Y chromosomes are sex linked, in humans most sex linked genes are located on the X
explain sex linkage
- women have 2 X and men only 1, as a result recessive genes carried on X will produce recessive phenotypes whenever they occur in men bc no other dominant allele to mask
- recessive phenotypes more common in men
- men cannot pass trait to male offspring since pass on Y not the X (only female children can eb affected by the dad), but will not show trait unless get recessive gene from mother
- if this child has sons 50% will be affected (if mother is Xx sons either XY or xY)
*NOTE sex linked recessives generally affect only men, and cannot be passed from father to son but can be passed from grandfather to grandson via daughter who was a carrier
**look for skipping generation
how to enivornmental factors effect genetics
- interaction between environment and genotype produces the phenotype
- temp can affect wings in drosophilia or hair type in rabbit
what is cytoplasmic inheritance
- DNA also found in mitochondria and other cytoplasmic bodies
- these cytoplasmic genes may interact with nuclear genes and are important in determining characteristics of organelles
- drug resistance in mnay microorganisms is regulated by cytoplasmic DNA known as plasmids that contain one or more genes
- plasmids can be passed from one bacerial call to another via transformation
what is nondisjunction
- failure of homologous chromosomes to separate proerly during meitosis I or failure of sister chromatids to separate proerly during meiosis II
- resulting zygote may have either 3 copies of that chromosome (trisomy, 2N+1) or single copy (monosomy 2N-1)
ex: trisomy on chrom 21 = down syndrome - most trisomies and monosomies are lethal cauing the embryo to spontaniously abort in early pregnancy
- can also have nondisjuction of sex chromosomes