Lecture 13 - Chromosomal Basis Inheritance

Hereditary Factors

Another name for Genes

Chromosome Theory of Inheritance

Genes occupy specific loci on chromosomes

Chromosomes undergo segregation and independent assortment during meiosis

Mendel’s Laws of inheritance

 The behavior of non-homologous chromosomes can account for the independent assortment of alleles for two or more genes located on different chromosomes.— law of independent assortment
law of segregation — Two alleles for the same gene are separated randomly during meiosis, this id due to the separation of homologous chromosomes in meiosis I

Sex Chromosomes

X and Y

Autosomal Chromosomes

Non-sex chromosomes (22 of them)

X-linked Genes

around 1,100 on found on the X chromosome

If an X-linked trait is due to a recessive allele, a female will express the phenotype only if she is homozgyous for that alelle

Heterozygous females are carrier for recessive trait

Female phenotypes between heterozygous and homozygous X-linked genes

Hemizygous

Refers to a male only needing one recessive X-linked gene in order to exhibit that phenotype

Males are more likely to exhibit X-linked recessive disorders

males are hemizygous so.

X-linked disorders

• color blindness

  • muscular dystrophy

  • Hemophilia

Barr Body

Genes on ___ X-chromosome are not expressed. One X-chromosome is condensed into a compact _____.

Linked Genes

Genes that tend to be inherited together because they are located near each other on the same chromosome — crossing over is unlikely to happen, no independent assortment

Wild Type

Generally the dominant trait, but more specifically the more common trait found in nature. (Not on a sex chromosome)

Mutant Allele

Typically the recessive trait, less commonly found in nature (not on a sex chromosome)

Parental Phenotype

The phenotype of offpsirng match that of the parent

Non-parental phenotypes

Phenotype of offspirng is different than parent, this is due to genetic recombination

Crossing over

accounts for the recombination of linked genes — these recombination of genes provides new variation for natural selection

 This genetic variation provides the “raw material” on which natural selection works.

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If the traits conferred by particular combinations of alleles are better suited for a given environment, organisms possessing those genotypes will leave more offspring, and thereby pass the better suited genes on in greater quantities (percentages)

Genetic map

Ordered list of the genetic loci along a particular chromosome

Recombination Frequency

percentage of a recombinant offpspring, ______, depends on the distance between genes on a chromosome

the farther apart two genes are, the higher the probability that a crossover will occur between them and, therefore, the higher the recombination frequency.

Linkage Map

Genetic map based on the recombination frequencies

dsistance between genes are map units

Nondisjunction

Leads to abnormal chromosme number — occurs when members of a homologous chromosome do not separate properly during meiosis I or sisster chromatids fail to separate during meiosis II. — results in aneuploidy

Trisomic vs Monosomic

Cell thats have three copies of a particular chromosome type… vs cells that have only one type of a particular chromosome

Deletion

Occurs when a chromosome segment is lost - missing a certain gene

Duplication

When a segment becomes repeated within a chromosome

producti of an unequal crossover are one chromosome with a deletion and one with a ____.

Inversion

Chromosomal fragments reattaches to the original chromosome but in the reverse orientation

Translocation

Chromosomal fragment joins a non-homologous chromsome

Down Syndrome

Three copies of chromosome 21 result in…

Klinefelter Syndrome

XXY male