genetics and meiosis Flashcards
what is a gene
a section of DNA that makes a certain protein, each gene has a locus
what is an allele
one of two or more forms of a gene, variation of traits
what is a genotype
Genotypes- which alleles are present on the chromosome, genetic makeup (EE, Ee, ee)
what is a phenotype
phenotypes - physical expression of a trait (what is physically observable)
what is a locus
Locus- specific position on a pair of homologous chromosomes
where are alleles located
locus
dominant vs. recessive
dominant-uppercase letters, only one copy of dominant allele is necessary to carry out most dominant phenotypes
recessive- lowercase letters, 2 copies of recessive alleles are necessary to carry out recessive phenotypes
homozygous vs. heterozygous
homozygous- 2 same alleles (RR, rr), heterozygous- 2 diff alleles (Rr)
law of independent assortment
the alleles that are passed down in an offspring aren’t related to each other, are passed down individually. Offspring can have diff combos of traits (alleles)
law of segregation
only one of the two alleles that an organism has will be passed to each gamete that it makes. Therefore, the alleles must separate or segregate during gamete formation
law of dominance
one allele has a greater influence than the other, resulting in the dominant phenotype
what is genotype of homozygous recessive
rr (two lowercase letters)
genotype of homozygous dominant
RR (two uppercase letters)
genotype of heterozygous
Rr (one upper one lower)
what is used to find diff combos of genes based off two parents’ genotype
Punnett squares tell us all the possible combinations of gametes and all the possible genotypes
how are phenotype/genotype frequencies calculated on monohybrid punnet squares
For monohybrid, each box=25% (¼)
Ex: What is the genotype of a parent that is homozygous dominant for hair color (h) and heterozygous for eye color (e)
HHEe
FOIL AaBb
AB, Ab, aB, ab
how are genotypes/phenotypes calculated in dihybrid punnet squares
1 box is 1/16= 6.25%
When does it happen - what process and what phase. What is necessary for it to happen (crossing over)
Occurs in prophase I in meiosis between tetrads, it is the exchangement of genetic material/segments of chromosomes between maternal and paternal chromosomes
What happens and why can it only happen in meiosis and not mitosis (crossing over)
there is no homologous chromosome pairing in mitosis, therefore the duplicated chromosomes do not exchange genetic material, also the goal of mitosis is to make genetically identical somatic cells, and the point of crossing over is to contribute to genetic variation
how does crossing over contribute to genetic variaiton
Homologous pairs are already not completely identical due to the different alleles, so crossing over makes them more genetically unique by exchanging genetic material
3 processes that increases genetic diversity
independent assortment, crossing over, random fertilization (offspring inheriting diff combos of alleles)
