PoB Week2 Genes in families & linkage mapping

Sex generates new genetic combinations

Independent segregation of 2 pairs of homologous chromosomes:

gametes of different types fuse

Isogamysame-sized gametes

Anisogamy: different-sized gametes

C. elegans and a perfect flower are

Individual organisms can make multiple gamete types

Sex determination

Some cue: temperature; presence of an individual making one class of gamete; genes; haplo-diploid polygenicsex chromosomes

Crepidula fornicata: newly-born => male; old ones => female; they are constantly mating

haplo-diploid polygenicsex chromosomes

Copidosoma floridanum polyembryonic wasps

if fertilized => females;

if not fertilized => males;

third sex: nonreproductives can be haploid or diploid

Sex chromosomes

ananema rhodensis

if XX crowded => hermaphrodite

if not =>

chromosomal sex determination systems

Y chromosomes => developmental biology => testes(gonadal sex) => male characteristics(phenotypic sex)

No Y =>

Y chromosomes => SRY gene => SRY proteins => lots of other genes and proteins => los of cellular phenotypes => testes => lots of hormonal stuff => lots of other genes and proteins => lots of cellular phenotypes => male characteristics

No Y, but with SRY gene => also male;

With Y, but lacking SRY gene => also female;

pathway change can cause different sex determination results

Linkage mapping

use crossover frequency to position loci along a chromosome

Morgan's Genetic Notation:

+: wild type, the form typical in nature genes are named for the mutant phenotype

Calculate the recombination frequency

recombination frequency =

number of recombinant offspring number of total offspring

= 151+154/2839 =0.11=11%=11cM

if genes are right next to each other

the recombination frequency is low(close to 0);

very far apart => 50%:50%

The recombination frequency is the distance between the loci. We measure these units of distance in Morgans.

1% recombination frequency is one centiMorgan, 1cM.

loci can be incorporated into a genetic map

position these things all the way along the chromosome and to end up with a linear representation of the chromosome where the distances are not base pairs or microns, but recombination frequencies.

Figure 15.12

Autopolyploid

Having more than two sets of chromosomes from a single species.

Requirements for chromosomes in sexually reproducing species:

1. Ability to pair and segregate in meiosis

2. Provide each gene in a dosage compatible with cellular processes

Ploidy

the number of sets of chromosomes Haploid, Diploid, Triploid, Tetraploid, etc

Polyploid: n > 2

allopolyploid

A fertile individual that has more than two chromosome sets as a result of two different species interbreeding and combining their chromosomes.

Aneuploidy

Abnormal number of chromosomes.

not good ploidy, too many or too few individual chromosomes

Aneuploidy is incredibly common in humans!

monosomy: one copy instead of two

trisomy: three copies instead of two

euploid

good ploidy, n chromosomes per set

cause of aneuploidy

non-disjunction in meiosis I or meiosis II: chromosomes fail to separate appropriately at anaphase

Autosomal non-disjunction most often occurs during maternal meiosis I

Sex-chromosome aneuploidy

Trisomy X

Turner Syndrome

Klinefelter Syndrome

XXY

dosage compensation

Mechanism in which X chromosome inactivation/over-activation equalize gene expression between males and females.

Why some female mammals are mosaic in color

Cells of the Inner Cell Mass inactivate one X at random.

=> duplicated through the process

=> Inactive-X-state is inherited at mitosis throughout development.

how to determine mutation on a small loci

1. senger sqeucning

2. PCR and see the gel difference

3. use restriction enzyme

Heterogametic

sex chromosomes are of different types(XY, ZW, X0)

Y-linkage

Genes for about 25 distinct proteins on the human Y; Includes:

SRY = proteins required for sperm development components of seminal fluid

Only one known Y-linked condition not related to male fertility(because mutation on the Y will result in sterility

Hemizygous

the presence of only one allele for a characteristic, as in X-linkage; hemizygosity makes descriptions of dominance and recessiveness irrelevant(no X-R to conceal the X-r)*

The son cannot get the X chromosome from his father

consanguineous mating

mating between relatives(double lines)

bacteria-like circular genome different genetic code

mitochondria chloroplasts apicoplasts

Maternal Inheritance

The mitochondrial genome is passed only along the maternal lineage

The Y chromosome is passed only along the paternal lineage

(in most species)

There are exceptions to everything! Mussels have double-uniparental mitochondrial inheritance

Heteroplasmy

: multiple mitochondrial genotypes within a single cell

polymorphism

The coexistence of two or more distinct forms(of neuocleotide) in the same population.

SNPs

single nucleotide polymorphisms