Download Chromosomes

Chromosomes
strands of DNA in pairs
Chromosomes
Vehicle of trait inheritance.
Each chromosome in a pair is from one parent.
Each pair = homologous chromosomes.
DNA
GENE: sequence of DNA on a
chromosome that codes for a
protein.
Columbia, MO?
North
America
Solar system
galaxy
Alleles and loci
ALLELES: two alternate forms of a gene on a pair of
homologous chromosomes.
LOCUS (plural ‘loci’): position of the allele on the
chromosome.
Alleles
Alleles work in pairs (each allele is in one of
two homologous chromosomes).
Dominant alleles: always expressed.
Recessive alleles: only expressed in absence
of a dominant allele.
Alleles
TT (Homozygous dominant)
tt (Homozygous recessive)
Tt (Heterozygous)
Trait expression
Genotype: genetic make-up for a trait
(eg. Tt).
Phenotype: genotype + environment,
or the expression of a trait.
(Eg. Tall plant, brown eyes etc).
A monk played with peas…
Gregor Mendel is considered the father of
modern genetics. He was an Austrian monk
who worked with pea plants.
Replaced Blending Theory with Particulate
Theory of Inheritance.
…and discovered the meaning of sex!
Genetic recombination:
process by which combination of genes in
offspring is different from that in either
parent.
Genetic recombination has two laws…
Law of Equal Segregation
Either allele from either homologous
chromosome has equal probability of
ending up in the gamete.
Law of Independent Assortment
Genes on different chromosomes assort
independently of each other.
Monhybrid Cross (one trait)
P
TT X tt
F1
Tt X Tt
F2
T
T
t
t
Can you
fill in this
Punnett
square?
PUNNETT square: table used to determine all
possible genotypes in the next generation.
Dihybrid cross (two traits)
P
F1
RRSS
RrSs
X
X
rrss
RrSs
F2
RS
RS
How
Rs
about
this one? rS
rs
Rs
rS
RrSS
rs
Polygenic traits
• Most traits not influenced by only one gene.
• Multiple genes may interact to influence a
trait.
• e.g.: Multiple genes interact to influence
human height.
Polygenic variation
Frequency
Polygenic traits tend to have normal
distributions. (This is a histogram.)