Genetics Test #3 - Variation in Chromosome structure, mendelian inheritance, pedigrees/probabilities, and extensions of mendelian inheritance

Differences between members of the same species or those of different species

micrograph of metaphase chromosome

Binding Pattern, Size, and Centromere

Submetacentric, metacentric, acrocentric, and telocentric

Shorter arm → p

Longer arm → q

Look at banding patterns

• Change in total amount of genetic material

• Rearrangement of genetic material

Deletion and Duplication

Inversions and translocations

An internal deletion within and chromosome

An end deletion of a chromosome

Terminal deletion - loss of part of chromosome 5

Interstitial deletion - loss of part of chromosome 15

Interstitial deletion

inversion

Centromere is included

Inversion without centromere

A gene is repositioned in a way that alters its gene expression?

• Ex. euchromatin to heterochromatin area

Inversion Heterozygotes

The morphological characteristics of an organism

• eg. eye color is a character

describes the specific properties of a character

• eg. blue eyes is a trait

Paired factors for a given character segregate randomly so that half of the gametes receive one factor and half of the gametes receive the other

The segregation of any pair of hereditary determinants is independent of the segregation of other pairs

Monohybrid cross

Dihybrid cross.

Modern interpretation of Mendel’s Law of Segregation

Through a dihybrid test-cross

a cross with homozygous recessive for both genes

the chance that the event will occur in the future

For product rule, the order of events are specified. With binomial expansion, the order is not specified.

P = probability that the unordered outcome will occur

n = total number of events

x = number of events in one category

p = individual property of x

q = individual probability of the other category

a dominant allele does not influence the outcome of a trait in a heterozygote individual

• example: Polydactyly

How many individuals in a population carry a particular allele of a gene that also express the associated trait

Expressivity

The presence of a dominant negative allele could interfere with the wildtypes in the protein to function

• Heterozygote intermediate between the homozygotes

  • Example: Red, White, and Pink Flowers

• The heterozygote form has a biological advantage that the homozygous species don’t express

  • Example: Sickle cell

    • HH - unaffected, not malaria resistant

    • Hh - unaffected, malaria resistant

    • hh - sickle cell disease

• Environmental conditions have an impact on the phenotype of the organisms

  • Example: Fox has brown coat in the summer and white coat in the winter

• Neither trait is dominant to the other

  • Example: ABO blood group

Traits are governed by genes on the sex chromosomes

• Color blindness, hemophilia, muscular dystrophy

Different in males than females

• not on sex chromosomes

• difference in heterozygotes

• male pattern baldness, scurs in cattle

• One normal chromosome

• One chromosome with an inversion

• Two chromosomes with a deletion and a duplication

• One normal chromosome

• One chromosome with an inversion

• Two chromosomes with a deletion

  • Dicentric chromosome

  • Acentric chromosome

the requirement for two wildtype copies of a gene for a normal phenotypeS

Transfer of genetic material occurs in only one direction

Majority of chromosome 21 is attached to chromosome 14

• Example of Robertsonian translocation

A rearrangement of genetic material, but no change in the total amount of DNA

Balanced translocations

Translocation cross

Men, they are hemizygous - have one chromosome

Allele is dominant in one sex but recessive in the opposite sex

• Alleles are on autosomes not sex chromosomes

• Sex-influenced traits are visible in heterozygotes

  • Example: Scurs

    • SS - Scurs in males and females

    • ss - no scurs in males and females

    • Ss - - scurs in men and no scurs in females

  • Example: Patterned Baldness

Traits that occur in only one of the sexes

• Genes are controlled by sex hormones

  • Example:

    • Ovary development is limited to females

    • Testes growth is limited to males

    • Male plumage in birds

• Allele is one that has the potential to cause the death of an organism

  • Example:

    • Agouti Gene in Mice

      • AA - agouti coat

      • AAy - Yellow Coat

      • AyAy - dead

May kill an organism only when certain environmental conditions prevail (eg. temperature sensitive)

Same phenotype caused by mutations in different genes. Wild-type offspring are produced from a cross between parents that both display the same recessive phenotype

a gene can mask the phenotypic effects of another gene

Alleles of one gene modifies the phenotypic outcome of alleles of a different gene

• Example:

  • B dominant - Black Coat

  • b recessive - brown coat

  • D dominant - intense color

  • d recessive - diluted expression of the color

Existence of multiple genes that perform the same function

• If one gene is missing, a paralog may be able to carry out the missing function

  • Example:

    • Inheritance of capsule shape in shepherd’s purse, gene redundancy

    • 15:1 ratio

      • TTVV/TtVv vs ttvv

• Produces viable gametes

• Chromosomes diagonal to each within the translocations cross segregate into the same cell following meiosis I

• One cell receives 2 normal chromosomes and the other receives 2 translocated chromosomes

• Four genetically unbalanced gametes

• Adjacent non-homologous chromosomes segregate into the same cell after meiosis I

• Both cells have one normal and one translocated chromosome

• Four genetically unbalanced gametes

• Centromeres do not segregate properly during meiosis I

• One cell receives both copies 1 and the other copies of the centromere on chromosome 2

• Variation in the number of particular chromosomes within a set 2n-1, 2n+1

- Variation in the number of complete sets of chromosome 3n, 4n, 5n

AneuploidyWhat

The are inactivated and become bar bodies

After fertilization, the X chromosome is still expressed before being deactivated.

refers to the failure of chromosomes to segregate properly during anaphase

• Homologs do not separate

• All four gametes are abnormal

  • Two trisomic gametes

  • Two Monosomic gametes

Sister chromatids do not separate and migrate to one pole

• Two abnormal gametes

  • Trisomic

  • Monosomic

• Two normal gametes