Download LB 144: Organismal Biology

LB 144: Organismal Biology Class 8 02/04/2016 Learning objec<ves 1.  Explain Mendel’s laws with rela<on to gamete forma<on and inheritance of traits. 2.  Model and diagramma<cally explain how meiosis accounts for Mendel’s observa<ons. 3.  Apply the principles of simple Mendelian inheritance to predict paLerns of inheritance. 2 How does alignment for chromosomes affect gamete formation?
OR
- In meiosis 1, the arrangement of homologous
chromosomes on either side of the equatorial plane is
random.
-  Alleles on different chromosomes separate
independently - Principle of Independent Assortment
Mendel’s Laws 1. Principle of Segregation
-  Diploid organisms have pairs of alleles
-  Individual alleles in the pair separate during meiosis
-  Meiosis I- separation of homologous chromosomes
2. Principle of Independent Assortment
-  Different pairs of alleles on different chromosomes
separate independently of each other during meiosis.
-  Meiosis I- alignment of chromosomes
4 Viola/on of Independent Assortment: Linked Genes •  genes that occur on the
same chromosome
•  In the figure to the right,
the SCA1, IDDM1, and
EPM2A genes are
linked because they all
occur on Chromosome 6
5 Linked Genes Genes that occur on the same chromosome will not assort independently Independent assortment applies to whole chromosomes q
q Q
Q
R
R R
R
T
T t
F
F f
t
f
6 Prophase I of meiosis Pair of homologs Nonsister chroma/ds held together during synapsis Does this mean genes on the same chromosome can never be separated? 7 Prophase I of meiosis Pair of homologs Nonsister chroma/ds held together during synapsis Chiasma Centromere TEM Anaphase I Anaphase II Daughter cells Recombinant chromosomes 8 Larger the distance between genes, more likely to have cross-over
Gene 1
Gene 2
Crossing
over is rare
between
genes that
are close
together
Gene 2
Crossing
over occurs
frequently
between
genes that
are far apart
Gene 3
?
Pedigree = family tree with relatedness, sex and phenotype Many human gene/c disorders are known to be inherited as dominant or recessive traits controlled by 1 gene locus Autosomal Recessive Traits
•  Males and females are equally likely
to be affected
•  Affected offspring often have
unaffected parents
•  Trait often skips generations
•  Unaffected parents of affected
offspring are heterozygous (carriers)
•  Affected offspring are homozygous
Unaffected male
Unaffected female
Affected male
Affected female