Lecture 12 Flashcards
what are genes
a segment of DNA that influences the structure & function of an organism by encoding & directing the synthesis of mRNA, tRNA, rRNA & ultimately a polypeptide
allele ?
One of two or more variants of a gene pair that occur at the same locus. A diploid individual inherits two alleles for each gene, one from each parent
Alleles can be dominant, recessive, co-dominant, or show incomplete dominance.
genotype?
We call the allelic composition of an individual, the genotype
phenotype?
the appearance, or the characteristics, the phenotype.
how many gens do humans have ?
somewhere between 21,000-25,000
genome?
The complete complement of an organisms’ genes and non-gene DNA ie all the DNA in an organism.
correct order of organization of genetic material, from largest to smallest?
Genome, chromosome, DNA, gene, nucleotide
how did Mendel figure out genetics
Lots of pea plants & math
Nothing was known about meiosis
& genes weren’t even discovered yet!
how did Mendel do the crossings
P generation: were always true breeders
Parent x Parent → F1 generation
F1 x F1 → F2 generation Crossed F1 with itself to get the F2 generation
Mendel’s model of inheritance
- There are alternate versions of genes (alleles)
- For each character: an organism inherits 2 alleles, 1 from each parent
- If the 2 alleles at a locus differ: the dominant allele determines the organism’s appearance
- 2 alleles separate (segregate) during meiosis & end up in different gametes ie each parent passes on 1 copy (not 2) of each allele.
Recall the life cycle
adult → meiosis → sperm or egg → fertilization → mitosis → embryo → mitosis → fetus → mitosis → child to adult.
Character?
A feature that can be inherited. Ex hair color
Trait?
A specific version of a character. Ex RED hair
_ are to genes as traits are to alleles.
Characters
Gene locus
a specific place along the chromosome where a given gene is located. Genes are arranged in a fixed order along the chromosome
Autosomes
The chromosomes other than the sex chromosomes
Homologous chromosomes
a pair of chromosomes that carry genes for the same characters at corresponding loci. The alleles at each locus may be the same or different
Dominant allele
an allele of a gene whose expression is observable in a heterozygote. ; the phenotype of the heterozygote (ex Tt) is indistinguishable from that of the dominant homozygote (TT).
Recessive allele
an allele whose expression is observable only in the homozygous form (tt), ie when the dominant allele is absent.
Law of independent assortment
Mendel’s second law holds that during gamete formation, genes for different traits are separated from each other independently during meiosis
random line up of chromosomes during metaphase I which results in each member of a pair of homologous chromosomes separating independently of the other chromosomes during anaphase
Mendel discovered the Law of independent assortment based on the analysis of his ___.
dihybrid crosses
Law of segregation?
a diploid organism passes a randomly selected allele for a trait to its offspring, such that the offspring receives one allele from each parent.
Mendel discovered the Law of segregation based on the analysis of his __
monohybrid crosses.
Monohybrid cross
cross parents that are true-breeders (homozygous) for the character you’re studying that differ at 1 locus
ratio of Monohybrid cross?
3:1
dihybrid cross?
study of inheritance patterns for organisms differing in two traits of interest.
ratio Dihybrid cross
9:3:3:1
Punnett square?
a diagram that is used to predict the probable outcome of a particular genetic cross. The diagram is used to determine the probability of an offspring having a particular genotype.
Carrier
An individual who has a recessive, disease-causing allele at a particular locus on one chromosome of a pair and a normal allele at that locus on the other chromosome (ex if N=normal, n=disease then a carrier would be Nn) AND this individual is phenotypically normal
which one is more specific? trait or character?
trait
what % of dna is genes
les than 2%
True breeders?
Homozygous for a specific character
3 possible genotypes
Homozygous dominant: YY
Homozygous recessive: yy
Heterozygous: Yy
Monohybrids criteria
(1) One character
(2) homozygous (AA or aa)
(3) 2 parents must differ (AA x aa, not AA x AA)
Albinism: A _____ disorder
recessive
Huntington’s disease: A _____ disorder
dominant
Achondroplasia: a __trait
dominant
do one of the parents must have the disorder if it is dominant?
yes.
do one of the parents must have the disorder if it is recessive?
no, they can be heterozygote.
